Systems and methods for peak current adjustments in power conversion systems

System and method for regulating an output of a power conversion system. An example system controller includes a signal generator and a modulation and drive component. The signal generator is configured to receive at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system and receive a second signal indicating a magnitude of a primary current flowing through the primary winding, and generate a third signal. The modulation and drive component is configured to receive at least the third signal, generate a drive signal based on at least information associated with the third signal, and output the drive signal to a switch to affect the primary current.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 201210529679.4, filed Dec. 10, 2012, commonly assigned, incorporated by reference herein for all purposes.

Additionally, this application is related to U.S. patent application Ser. Nos. 12/859,138, 13/052,869 and 13/215,028, incorporated by reference herein for all purposes. Moreover, this application is also related to U.S. patent application Ser. No. 13/646,268, incorporated by reference herein for all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. More particularly, the invention provides adjustments of peak current. Merely by way of example, the invention has been applied to power conversion systems. But it would be recognized that the invention has a much broader range of applicability.

Generally, a conventional power conversion system often uses a transformer to isolate the input voltage on the primary side and the output voltage on the secondary side. To regulate the output voltage, certain components, such as TL431 and an opto-coupler, can be used to transmit a feedback signal from the secondary side to a controller chip on the primary side. Alternatively, the output voltage on the secondary side can be imaged to the primary side, so the output voltage is controlled by directly adjusting some parameters on the primary side.

FIG. 1(a)is a simplified diagram showing a conventional flyback power conversion system with primary-side sensing and regulation. The power conversion system100includes a primary winding110, a secondary winding112, an auxiliary winding114, a power switch120, a current sensing resistor130, an equivalent resistor140for an output cable, resistors150and152, and a rectifying diode160. For example, the power switch120is a bipolar junction transistor. In another example, the power switch120is a MOS transistor.

To regulate the output voltage within a predetermined range, information related to the output voltage and the output loading often needs to be extracted. In the power conversion system100, such information can be extracted through the auxiliary winding114. When the power switch120is turned on, the energy is stored in the secondary winding112. Then, when the power switch120is turned off, the stored energy is released to the output terminal, and the voltage of the auxiliary winding114maps the output voltage on the secondary side as shown below.

VFB=R2R1+R2×Vaux=k×n×(Vo+VF+Io×Req)(Equation⁢⁢1)
where VFBrepresents a voltage at a node154, and Vauxrepresents the voltage of the auxiliary winding114. R1and R2represent the resistance values of the resistors150and152respectively. Additionally, n represents a turns ratio between the auxiliary winding114and the secondary winding112. Specifically, n is equal to the number of turns of the auxiliary winding114divided by the number of turns of the secondary winding112. Voand Iorepresent the output voltage and the output current respectively. Moreover, VFrepresents the forward voltage of the rectifying diode160, and Reqrepresents the resistance value of the equivalent resistor140. Also, k represents a feedback coefficient as shown below:

FIG. 1(b)is a simplified diagram showing a conventional operation mechanism for the flyback power conversion system100. As shown inFIG. 1(b), the controller chip of the conversion system100uses a sample-and-hold mechanism. When the demagnetization process on the secondary side is almost completed and the current Isecof the secondary winding112almost becomes zero, the voltage Vauxof the auxiliary winding114is sampled at, for example, point A ofFIG. 1(b). The sampled voltage value is usually held until the next voltage sampling is performed. Through a negative feedback loop, the sampled voltage value can become equal to a reference voltage Vref. Therefore,
VFB=Vref(Equation 3)

Combining Equations 1 and 3, the following can be obtained:

Based on Equation 4, the output voltage decreases with the increasing output current.

But the power conversion system100often cannot provide effective response to output loading changes. Hence it is highly desirable to improve the techniques of primary-side sensing and regulation.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. More particularly, the invention provides adjustments of peak current. Merely by way of example, the invention has been applied to power conversion systems. But it would be recognized that the invention has a much broader range of applicability.

According to one embodiment, a system controller for regulating an output of a power conversion system includes a signal generator and a modulation and drive component. The signal generator is configured to receive at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system and receive a second signal indicating a magnitude of a primary current flowing through the primary winding, and generate a third signal. The modulation and drive component is configured to receive at least the third signal, generate a drive signal based on at least information associated with the third signal, and output the drive signal to a switch to affect the primary current. The signal generator and the modulation and drive component are further configured to, if an output voltage of the power conversion system is constant and an output current of the power conversion system falls within a first predetermined range, generate a modulation signal as the drive signal based on at least information associated with the magnitude of the input voltage without taking into account the magnitude of the primary current flowing through the primary winding, and if the output voltage is constant and the output current falls within a second predetermined range, generate the modulation signal as the drive signal based on at least information associated with the magnitude of the primary current without taking into account the magnitude of the input voltage.

According to another embodiment, a system controller for regulating an output of a power conversion system includes a signal generator and a modulation and drive component. The signal generator is configured to receive at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, process information associated with the first signal, and generate a second signal based on at least information associated with the first signal. The modulation and drive component is configured to receive at least the second signal, generate a drive signal based on at least information associated with the second signal, and output the drive signal to a switch to affect a primary current flowing through the primary winding. The signal generator and the modulation and drive component are further configured to, if an output voltage of the power conversion system is constant and an output current of the power conversion system falls within a first predetermined range, generate a pulse-width-modulation signal corresponding to a pulse width and a modulation frequency as the drive signal. The pulse width decreases if the input voltage increases and if the output voltage and the output current remain constant.

According to yet another embodiment, a system controller for regulating an output of a power conversion system includes a signal generator, a first comparator, a second comparator, and a modulation and drive component. The signal generator is configured to receive at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, process information associated with the first signal, and generate a second signal based on at least information associated with the first signal. The first comparator is configured to receive the second signal and a third signal associated with a feedback signal of the power conversion system and generate a first comparison signal based on at least information associated with the second signal and the third signal. The second comparator is configured to receive the second signal and a threshold signal and generate a second comparison signal based on at least information associated with the second signal and the threshold signal. The modulation and drive component is configured to receive at least the first comparison signal and the second comparison signal, generate a drive signal based on at least information associated with the first comparison signal and the second comparison signal, and output the drive signal to a switch to affect a primary current flowing through the primary winding. The modulation and drive component is further configured to, if the third signal is larger than the threshold signal in magnitude, output the drive signal to close the switch if the second signal is smaller than the third signal, and if the threshold signal is larger than the third signal in magnitude, output the drive signal to close the switch if the second signal is smaller than the threshold signal.

In one embodiment, a method for regulating an output of a power conversion system includes receiving at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, receiving a second signal indicating a magnitude of a primary current flowing through the primary winding, and processing information associated with the first signal and the second signal. The method further includes generating a third signal, receiving at least the third signal, and processing information associated with the third signal. In addition, the method includes generating a drive signal based on at least information associated with the third signal, and outputting the drive signal to a switch to affect the primary current. The process for generating a drive signal based on at least information associated with the third signal includes, if an output voltage of the power conversion system is constant and an output current of the power conversion system falls within a first predetermined range, generating a modulation signal as the drive signal based on at least information associated with the magnitude of the input voltage without taking into account the magnitude of the primary current flowing through the primary winding, and if the output voltage is constant and the output current falls within a second predetermined range, generating the modulation signal as the drive signal based on at least information associated with the magnitude of the primary current without taking into account the magnitude of the input voltage.

In another embodiment, a method for regulating an output of a power conversion system includes receiving at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, processing information associated with the first signal, and generating a second signal based on at least information associated with the first signal. The method further includes receiving at least the second signal, processing information associated with the second signal, generating a drive signal based on at least information associated with the second signal, and outputting the drive signal to a switch to affect a primary current flowing through the primary winding. The process for generating a drive signal based on at least information associated with the second signal includes, if an output voltage of the power conversion system is constant and an output current of the power conversion system falls within a first predetermined range, generating a pulse-width-modulation signal corresponding to a pulse width and a modulation frequency as the drive signal. The pulse width decreases if the input voltage increases and if the output voltage and the output current remain constant.

In yet another embodiment, a method for regulating an output of a power conversion system includes receiving at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, processing information associated with the first signal, and generating a second signal based on at least information associated with the first signal. The method further includes receiving the second signal and a third signal associated with a feedback signal of the power conversion system, processing information associated with the second signal and the third signal, and generating a first comparison signal based on at least information associated with the second signal and the third signal. In addition, the method includes receiving the second signal and a threshold signal, processing information associated with the second signal and the threshold signal, and generating a second comparison signal based on at least information associated with the second signal and the threshold signal. Moreover, the method includes receiving at least the first comparison signal and the second comparison signal, processing information associated with the first comparison signal and the second comparison signal, generating a drive signal based on at least information associated with the first comparison signal and the second comparison signal, and outputting the drive signal to a switch to affect a primary current flowing through the primary winding. The process for outputting the drive signal to a switch to affect a primary current flowing through the primary winding includes, if the third signal is larger than the threshold signal in magnitude, outputting the drive signal to close the switch if the second signal is smaller than the third signal, and if the threshold signal is larger than the third signal in magnitude, outputting the drive signal to close the switch if the second signal is smaller than the threshold signal.

Depending upon embodiment, one or more benefits may be achieved. These benefits and various additional objects, features and advantages of the present invention can be fully appreciated with reference to the detailed description and accompanying drawings that follow.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. More particularly, the invention provides adjustments of peak current. Merely by way of example, the invention has been applied to power conversion systems. But it would be recognized that the invention has a much broader range of applicability.

Referring toFIGS. 1(a) and 1(b), information about the output voltage of the power conversion system100often is sampled only once every switching period. The switching period is inversely proportional to the switching frequency, which usually is set low at no load or light load conditions to reduce power consumption. But the low switching frequency often leads to poor dynamic response for the power conversion system100if the load changes from no load or light load to full load. For example, if the switching frequency is several hundred Hz at no load or light load conditions, information about the output voltage of the power conversion system100is sampled once every several msec. If the load changes from no load or light load to full load (e.g., the output current changing to 1 A at full load), the output voltage may drop below an acceptable level, because the controller does not respond until the next sampling is performed after, for example, several msec. One way to solve this problem is to increase the switching frequency at no load or light load conditions. But if the switching frequency is increased, the peak current of the primary winding at no load or light load conditions should be limited such that the output voltage does not exceed an acceptable level.

If the switching frequency is further increased, the peak current of the primary winding at no load or light load conditions should be further reduced to decrease the standby power consumption. In a conventional current-mode pulse-width-modulation (PWM)/pulse-frequency-modulation (PFM) flyback power conversion system (e.g., the system100), the information associated with a primary current flowing through the primary winding is often needed to generate a pulse signal (e.g., a PWM signal or a PFM signal) to close (e.g., to turn on) or open (e.g., to turn off) a power switch (e.g., the switch120) in order to affect the power delivered to the output load. A leading edge blanking (LEB) pulse is usually used to chop off on-spikes which often appear every cycle at the beginning of a current-sensing process. For example, the width of a leading edge blanking pulse is usually in the range of 250 ns to 350 ns. The blanking pulse width and the propagation delay of a controller often determine a minimum duration of an on-time period within a switching period associated with the power switch (e.g., the switch120). Usually, such a minimum duration of the on-time period is larger than what is needed to regulate the output voltage at no load or light load conditions in some applications, especially when the line input voltages are high.

FIGS. 2(a) and 2(b)are simplified diagrams showing switching frequency and peak current as functions of output current of a power conversion system according to an embodiment of the present invention. These diagrams are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The waveform202represents the switching frequency (e.g., FSW) as a function of output current (e.g., Iout), and the waveform204represents the peak current (e.g., Is_peak) for the primary winding as a function of output current (e.g., Iout). For example, if the power conversion system is at no load conditions; if Iout=I6, the power conversion system is at maximum load conditions; and if I5≦Iout<I6, the power conversion system is at full load conditions. In another example, I1≦I2≦I3≦I4≦I5≦I6. In yet another example, if I1≦Iout≦I6, the power conversion system operates in an output-voltage regulation mode, for example, a constant-voltage (CV) mode. In yet another example, if Iout>I6, as the output power remains at a maximum power, the output voltage drops with the increasing output current, and the power conversion system no longer operates in output-voltage regulation mode, e.g., the CV mode. In yet another example, if the power conversion system operates in the constant-voltage (CV) mode, the output voltage is regulated to be at a predetermined voltage value.

As shown inFIG. 2(a), the switching frequency (e.g., FSW) keeps at a minimum frequency fminand does not change with the output current (e.g., Iout) if I1≦Iout≦I2according to one embodiment. For example, the switching frequency (e.g., FSW) changes with the output current (e.g., Iout) at a slope S1fif I2≦Iout≦I3. In another example, the switching frequency (e.g., FSW) increases from the minimum frequency fmin(e.g., at I1) to a frequency f1(e.g., at I3). In yet another example, the switching frequency (e.g., FSW) changes with the output current (e.g., Iout) at a slope S2fif I3≦Iout≦I5. In yet another example, the switching frequency (e.g., FSW) increases from the frequency f1(e.g., at I3) to a frequency f2(e.g., at I5). In yet another example, the switching frequency (e.g., FSW) changes with the output current (e.g., Iout) at a slope S3fif I5≦Iout≦I6. In yet another example, the switching frequency (e.g., FSW) increases from the frequency f2(e.g., at I5) to a maximum frequency fmax(e.g., at I6). In yet another example, the switching frequency (e.g., FSW) keeps at the maximum frequency fmaxand does not change with the output current (e.g., Iout) if Iout>I6. In yet another example, each of the slopes S1f, S2fand S3fis larger than zero. In yet another example, the slope S2fis equal to the slope S3f.

As shown inFIG. 2(b), the peak current (e.g., Is_peak) for each switching period (e.g., Tsw) changes with the output current (e.g., Iout) at a slope S1Pif I1≦Iout≦I2according to another embodiment. For example, the peak current (e.g., Is_peak) for each switching period (e.g., Tsw) changes with the output current (e.g., Iout) at a slope S2pif I2≦Iout≦I4. In another example, the peak current (e.g., Is_peak) for each switching period (e.g., Tsw) changes with the output current (e.g., Iout) at a slope S3pif I4≦Iout≦I5. In yet another example, the peak current (e.g., Is_peak) for each switching period (e.g., Tsw) changes with the output current (e.g., Iout) at a slope S4pif I5≦Iout≦I6. In yet another example, the slopes S1pand S3peach are larger than zero. In yet another example, the slopes S2pand S4peach are equal to or larger than zero. In yet another example, the peak current (e.g., Ipeak) has a minimum value Is_min(e.g., at I1) and a maximum value Is_max(e.g., at I5).

According to yet another embodiment, the power conversion system operates with voltage-mode pulse-width modulation (VPWM) for I1≦Iout≦I2. For example, in the VPWM mode, the information associated with the primary current flowing through the primary winding current is not needed for generating a pulse signal (e.g., a PWM signal) to close (e.g., to turn on) or open (e.g., to turn off) a power switch. In another example, the leading edge blanking is not necessary for the VPWM mode, and thus the duration of an on-time period within a switching period associated with a power switch is not limited by a blanking time duration. In some embodiments, the power conversion system changes to current-mode modulation (e.g., pulse-width modulation or pulse-frequency modulation) for I2≦Iout≦I6. For example, the power conversion system operates with pulse-frequency modulation (PFM) for I2≦Iout≦I4. In another example, the power conversion system operates with both pulse-frequency modulation and pulse-width modulation for I4≦Iout≦I5. In yet another example, the power conversion system operates with pulse-frequency modulation for I5≦Iout≦I6.

As shown above and further emphasized here,FIGS. 2(a) and 2(b)are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the switching frequency (e.g., FSW) changes with the output current (e.g., Iout) at a slope S4fif I5≦Iout≦Im, and changes with the output current (e.g., Iout) at a slope S5fif Im≦Iout≦I6, where I5≦Im≦I6, and S4fand S5fare different.

FIG. 3is a simplified diagram showing a power conversion system that adjusts switching frequency and peak current in response to output current according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The power conversion system300includes a system controller302, a primary winding360, a secondary winding362, an auxiliary winding364, a switch366, a current sensing resistor368, an equivalent resistor374for an output cable, resistors370and372, rectifying diodes376and382, and capacitors378and380. The system controller302includes a voltage-mode component304, a mode controller306, a frequency component308, a sampling switch310, an error amplifier320, a capacitor322, a sampling controller324, a demagnetization detector326, an oscillator328, a line sensing component330, resistors332and334, a signal conditioning component336, a modulation component338, a logic component340, a driving component342, comparators344,346and348, and a LEB component350. In addition, the system controller302includes terminals311,312,314,316and318. For example, the switch366is a transistor. In certain embodiments, the signal conditioning component336is omitted. In some embodiments, the LEB component350is omitted.

According to one embodiment, information about an output voltage402is extracted through the auxiliary winding364. For example, the auxiliary winding364, together with the resistors370and372, generates a feedback signal404. In another example, the system controller302receives the feedback signal404at the terminal311(e.g., terminal FB). When the switch366is opened (e.g., being turned off), the energy stored in the transformer including the primary winding360and the secondary winding362is released to the output terminal in certain embodiments. For example, the demagnetization process associated with the transformer starts, and a secondary current494flowing through the secondary winding362decreases in magnitude (e.g., linearly). In another example, when the demagnetization process almost ends and the secondary current494flowing through the secondary winding362approaches zero, the sampling controller324outputs a sampling signal498to close (e.g., to turn on) the sampling switch310to sample the feedback signal404. In yet another example, after the sampling process is completed, the sampling controller324changes the sampling signal498to open (e.g., to turn off) the switch310. In yet another example, the sampled signal is held on the capacitor322. In yet another example, a sampled and held signal420is generated at the capacitor322and received by the error amplifier320(e.g., at an inverting terminal). In yet another example, the error amplifier320also receives a reference signal406(e.g., Vref) and generates an amplified signal408which is associated with a difference between the signal420and the reference signal406.

The amplified signal408is used for selecting an operation mode (e.g., by the mode controller306), for adjusting switching frequency (e.g., by the frequency component308), and for affecting peak values of a primary current422that flows through the primary winding360so as to affect the power delivered to the output, in some embodiments. For example, the amplified signal408is received by the mode controller306which generates a signal428. In another example, the frequency component308receives the signal428and outputs a signal430to the logic component340which generates a signal432. In yet another example, the driving component receives the signal432and generates a driving signal499to affect the status of the switch314. In yet another example, the amplified signal408indicates the output load conditions in closed loop regulation. In yet another example, the waveform of the driving signal499is substantially the same as the waveform of the signal432.

According to another embodiment, the primary current422that flows through the primary winding360is sensed by the current sensing resistor368, which in response outputs a current sensing signal410to the comparators344,346and348(e.g., through the LEB component350). For example, if the switch366is closed (e.g., being turned on), the transformer stores energy and the primary current422increases in magnitude (e.g., linearly), causing the current sensing signal410(e.g., Vcs) to also increase in magnitude (e.g., linearly). In another example, the comparator346also receives a signal412which is generated by the signal conditioning component336and associated with the amplified signal408, and outputs a comparison signal436to the modulation component338. In yet another example, the comparator344also receives a threshold signal416(e.g., Vth_max) and outputs a comparison signal438to the modulation component338. In yet another example, the comparator348also receives another threshold signal418(e.g., Vth_minwhich is smaller than Vth_maxin magnitude) and outputs a comparison signal440to the modulation component338.

According to yet another embodiment, the feedback signal404is received by at least the demagnetization detector326and the oscillator328. For example, the demagnetization detector326outputs a detection signal423, and the oscillator328also outputs a clock signal424. In another example, the line sensing component330outputs a signal426which is associated with an input signal442(e.g., Vin). In yet another example, the voltage-mode component304receives the signals412,426and432and outputs a signal444which is received by the modulation component338. In yet another example, the modulation component338outputs a modulation signal446to the logic component340which outputs the signal432to close (e.g., to turn on) or to open (e.g., to turn off) the switch366in order to affect the primary current422. In yet another example, the signal426is proportional to the signal442in magnitude, as follows.
IfI_vin≧0,I_vin=α×Vin−β  (Equation 5)
where I_vin represents the signal426, Vinrepresents the signal442, and α and β represent constants respectively.

As discussed above and further emphasized here,FIG. 3is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the switch366is a bipolar junction transistor (BJT), and the driving component342generates a current signal (e.g., the signal499) to drive the switch366. In another example, the switch366is a metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated-gate bipolar transistor (IGBT), and the driving component342generates a voltage signal (e.g., the signal499) to drive the switch366.

FIG. 4(a)is a simplified diagram showing a power conversion system that adjusts switching frequency and peak current in response to output current according to another embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The power conversion system500includes a system controller502, a primary winding560, a secondary winding562, an auxiliary winding564, a switch566, a current sensing resistor568, an equivalent resistor574for an output cable, resistors570and572, rectifying diodes576and582, and capacitors578and580. The system controller502includes a voltage-mode component504, comparators506,544,546and548, a exponential generator508, a sampling switch510, an error amplifier520, a capacitor522, a sampling controller524, a demagnetization detector526, an oscillator528, a line sensing component530, resistors532and534, a signal conditioning component536, a modulation component538, a logic component540, a driving component542, and a LEB component550. In addition, the system controller502includes terminals511,512,514,516and518. For example, the switch566is a transistor (e.g., a bipolar junction transistor). In certain embodiments, the signal conditioning component536is omitted. In some embodiments, the LEB component550is omitted if the power conversion system500operates with a voltage-mode control mode.

For example, the power conversion system500is the same as the power conversion system300. In another example, the system controller502is the same as the system controller302. In yet another example, the primary winding560, the secondary winding562, the auxiliary winding564, the switch566, the current sensing resistor568, the equivalent resistor574, the resistors570and572, the rectifying diodes576and582, the capacitors578and580, the voltage-mode component504, the comparators544,546and548, the sampling switch510, the error amplifier520, the capacitor522, the sampling controller524, the demagnetization detector526, the oscillator528, the line sensing component530, the resistors532and534, the signal conditioning component536, the modulation component538, the logic component540, the driving component542, and the LEB component550are the same as the primary winding360, the secondary winding362, the auxiliary winding364, the switch366, the current sensing resistor368, the equivalent resistor374, the resistors370and372, the rectifying diodes376and382, the capacitors378and380, the voltage-mode component304, the comparators344,346and348, the sampling switch310, the error amplifier320, the capacitor322, the sampling controller324, the demagnetization detector326, the oscillator328, the line sensing component330, the resistors332and334, the signal conditioning component336, the modulation component338, the logic component340, the driving component342, and the LEB component350, respectively. In yet another example, the terminals311,312,314,316and318are the same as the terminals511,512,514,516and518, respectively. In yet another example, the exponential generator508and the comparator506are part of the mode controller306and the frequency component308as shown inFIG. 3, and the mode controller306and the frequency component308include one or more additional components.

According to one embodiment, information about an output voltage602is extracted through the auxiliary winding564. For example, the auxiliary winding564, together with the resistors570and572, generates a feedback signal604. In another example, the system controller502receives the feedback signal604at the terminal511(e.g., terminal FB). When the switch566is opened (e.g., being turned off), the energy stored in the transformer including the primary winding560and the secondary winding562is released to the output terminal in certain embodiments. For example, the demagnetization process associated with the transformer starts, and a secondary current694flowing through the secondary winding562decreases in magnitude (e.g., linearly). In another example, when the demagnetization process almost ends and the secondary current694flowing through the secondary winding562approaches zero, the sampling controller524outputs a sampling signal698to close (e.g., to turn on) the sampling switch510to sample the feedback signal604. In yet another example, after the sampling process is completed, the sampling controller524changes the sampling signal698to open (e.g., to turn off) the switch510. In yet another example, the sampled signal is held on the capacitor522. In yet another example, a sampled and held signal620is generated at the capacitor522and received by the error amplifier520(e.g., at an inverting terminal). In yet another example, the error amplifier520also receives a reference signal606(e.g., Vref) and generates an amplified signal608which is associated with a difference between the signal620and the reference signal606. The amplified signal608is used for adjusting switching frequency and for affecting peak values of a primary current630that flows through the primary winding560so as to affect the power delivered to the output, in some embodiments.

According to another embodiment, the feedback signal604is received by at least the demagnetization detector526and the oscillator528. For example, the exponential generator508receives a detection signal622from the demagnetization detector526and a clock signal624from the oscillator528, and outputs a signal680(e.g., Vramp) to the comparator506. In another example, the comparator506also receives the amplified signal608and outputs a comparison signal628to the logic component540in order to affect the switching frequency. In yet another example, the logic component540generates a signal632to the driving component542which outputs a signal699in order to close (e.g., to turn on) or open (e.g., to turn off) the switch566. In yet another example, the signal680(e.g., Vramp) is an exponential signal. In yet another example, the waveform of the signal699is substantially the same as the waveform of the signal632.

According to yet another embodiment, the primary current630that flows through the primary winding560is sensed by the current sensing resistor568, which in response outputs a current sensing signal610to the comparators544,546and548(e.g., through the LEB component550). For example, if the switch566is closed (e.g., being turned on), the transformer stores energy and the primary current630increases in magnitude (e.g., linearly), causing the current sensing signal610(e.g., Vcs) to also increase in magnitude (e.g., linearly). In another example, the comparator546also receives a signal612(e.g., Vctrl) which is generated by the signal conditioning component536and associated with the amplified signal608, and outputs a comparison signal636to the modulation component538. In yet another example, the comparator544also receives a threshold signal616(e.g., Vth_max) and outputs a comparison signal638to the modulation component538. In yet another example, the comparator548receives another threshold signal618(e.g., Vth_minwhich is smaller than Vth_maxin magnitude) and outputs a comparison signal640to the modulation component538.

As shown inFIG. 4(a), the line sensing component530outputs a signal626which is associated with an input signal642(e.g., Vin) in certain embodiments. For example, the voltage-mode component504receives the signals612,626and632and outputs a signal644which is received by the modulation component538. In yet another example, the modulation component538outputs a modulation signal646to the logic component540which outputs the signal632to close (e.g., to turn on) or to open (e.g., to turn off) the switch566in order to affect the primary current630. In yet another example, the signal626is proportional to the signal642in magnitude.

FIG. 4(b)is a simplified diagram showing certain components of the power conversion system500according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As shown inFIG. 4(b), the system controller502further includes a low pass filter708and a capacitor710. The voltage-mode component504includes a signal generator702, comparators704and706, and a low pass filter708. For example, the signal conditioning component536includes the capacitor710. In another example, the switch566is a bipolar junction transistor.

As shown inFIG. 4(a)andFIG. 4(b), the amplified signal608is attenuated and filtered by a compensation network including the resistors532and534, the capacitor710and the low pass filter708, and a filtered signal712is received by the comparator704(e.g., at a non-inverting terminal), in some embodiments. For example, the signal generator702receives the signals626and632and outputs a signal714(e.g., Vramp1) to the comparators704and706. In another example, the comparator704outputs a signal716to the modulation component538, and the comparator706which also receives a threshold signal720(e.g., V_min) outputs a signal718to the modulation component538. In yet another example, the signal644is generated by an OR gate that receives the signals716and718as inputs. The signal714is a ramping signal associated with a ramping period which includes a ramping-up period, a ramping-down period, and an off period in some embodiments. For example, during the ramping-up period, the signal714increases in magnitude; during the ramping-down period, the signal714decreases in magnitude; and during the off period, the signal714keeps at a low magnitude (e.g., zero).

According to one embodiment, a switching period of the switch566includes an on-time period during which the switch566is closed (e.g., being turned on) and an off-time period during which the switch566is open (e.g., being turned off). For example, the duration of the on-time period in each switching period and peak values of the primary current630are affected by the signal646generated from the modulation component538, and thus are affected by the comparison of the signal712and the signal714. For example, the signal714is a ramping signal which increases in magnitude at a slope P in each switching period, and the slope P of the signal714changes with the signal626. In another example, the slope P increases as the signal626increases in magnitude, while the slope P decreases as the signal626decreases in magnitude. In yet another example, the signal714is triggered in response to the signal632during each switching period. In yet another example, the signal714begins to increase in magnitude when the signal632changes from a logic low level to a logic high level.

According to another embodiment, the off-time period in each switching period is used to adjust switching frequency associated with the switching period. For example, the duration of the off-time period in each switching period is affected by the comparison signal628and thus is affected by the comparison of the signal608and the signal680(e.g., Vramp) generated by the exponential generator508. In another example, the exponential generator508includes a switch-capacitor circuit that is affected by the clock signal624generated by the oscillator528(e.g., with a fixed frequency). In yet another example, the signal680is determined according to the following equation:

Vramp⁡(n)=(Vrefb-Vrefa)×ⅇnTτ+Vrefa(Equation⁢⁢6)
where Vrefbrepresents an upper limit of the signal608, Vrefarepresents a lower limit of the signal608, T represents a clock period of the clock signal624corresponding to the fixed frequency of the oscillator528, n represents the number of the clock period, and τ represents a time constant. As an example, τ is determined according to the following equation.

As discussed above and further emphasized here,FIG. 4(a)andFIG. 4(b)are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the switch566is an IGBT. In another example, the switch566is a MOSFET, as shown inFIG. 4(c).

FIG. 4(c)is a simplified diagram showing a power conversion system that adjusts switching frequency and peak current in response to output current according to yet another embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As shown inFIG. 4(c), the switch566is a MOSFET. According to one embodiment, the logic component540generates the signal632to the driving component542which outputs a voltage signal (e.g., the signal699) in order to close (e.g., to turn on) or open (e.g., to turn off) the switch566.

As discussed above and further emphasized here,FIG. 4(c)is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the switch566is an IGBT instead of a MOSFET.

Also, as discussed above and further emphasized here,FIGS. 3, 4(a),4(b) and4(c) are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, a resistor is added to couple between the LEB component350and the comparator346. In another example, a resistor is added to couple between the LEB component550and the comparator546.

FIG. 5is a simplified timing diagram for the power conversion system500according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As shown inFIG. 5, the waveform802represents the signal699(e.g., DRV) as a function of time, the waveform804represents the signal680(e.g., Vramp) as a function of time, the waveform806represents the amplified signal608(e.g., Vea) as a function of time, and the waveform808represents the feedback signal604as a function of time. Additionally, the waveform810represents the current sensing signal610(e.g., Vcs) as a function of time, the waveform812represents the threshold signal616(e.g., Vth_max) as a function of time, and the waveform814represents the signal612(e.g., Vctrl) as a function of time. For example, when the signal699(e.g., DRV) is at a logic high level (e.g., as shown by the waveform802), the switch566is closed (e.g., being turned on). In another example, when the signal699(e.g., DRV) is at a logic low level (e.g., as shown by the waveform802), the switch566is open (e.g., being turned off). In yet another example, the waveform802is substantially the same as the waveform of the signal632.

As shown inFIG. 5, when the switch566is closed (e.g., being turned on), the transformer including the primary winding560and the secondary winding562stores energy, and the primary current630increases in magnitude (e.g., linearly), according to one embodiment. For example, the current sensing signal610increases in magnitude, and when the signal610reaches a limit (e.g., the signal612or the threshold signal616), the switch566is caused to be open (e.g., being turned off). In yet another example, if the signal612(e.g., Vctrl) is larger than the threshold signal618(e.g., Vth_min) but smaller than the threshold signal616(e.g., Vth_max) in magnitude, the peak magnitude of the current sensing signal610(e.g., Vcscorresponding the waveform810) is limited to the magnitude of the signal612(e.g., Vctrlcorresponding to the waveform814).

According to another embodiment, when the switch566is open, the transformer that includes the primary winding560and the secondary winding562outputs energy to the output terminal. For example, the demagnetization process begins (e.g., at time t1), and the secondary current694that flows through the secondary winding562decreases in magnitude (e.g., linearly). The signal680(e.g., Vrampcorresponding to the waveform804) is restored to an initial value (e.g., Vrefb), but after the demagnetization process is completed (e.g., at time t2), the signal680decreases exponentially in one embodiment. For example, if the signal680becomes smaller than the amplified signal608(e.g., Veacorresponding to the waveform806) in magnitude, the comparator506changes the comparison signal628in order to cause the switch566to be turned on. In another example, the signal608(e.g., Vea) is larger in magnitude at heavy load conditions, and the duration of the off-time period associated with the switch566is shorter. In yet another example, the signal608(e.g., Vea) is smaller in magnitude at light load conditions, and the duration of the off-time period associated with the switch566is longer which results in a lower switching frequency. Referring back toFIG. 2(a), the switching frequency has a lower limit (e.g., fmin) and an upper limit (e.g., fmax) in some embodiments. For example, at no load or light load conditions, the switching frequency is fixed at the lower limit (e.g., fmin).

FIG. 6is a simplified diagram showing certain components of the power conversion system500including the voltage-mode component504according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The voltage-mode component504includes a current source738, a capacitor730, a transistor732, comparators704and706, and OR gates734and745. For example, the transistor732is an N-channel field effect transistor. In another example, the signal generator702includes the current source738, the capacitor730and the transistor732. In yet another example, the LEB component550includes a resistor752and a transistor756.

According to one embodiment, during the on-time period of a switching period associated with the switch566, the transistor732is turned off in response to the signal736, and the capacitor730is charged in response to the signal626. For example, the signal714(e.g., Vramp1) increases in magnitude linearly at a slope P. The slope P may be determined according to the following equation, as an example:

P=I_vinC2(Equation⁢⁢8)
where I_vin represents the signal626, and C2represents the capacitance of the capacitor730. In another example, the signal626changes with the input line voltage and thus the slope P changes with the input line voltage.

According to another embodiment, the signal714is received by the comparators704and706which outputs signals716and718respectively. For example, the OR gate734receives the signals716and718and outputs a signal747to the OR gate745. In another example, the OR gate745receives a control signal782(e.g., LEB_b) and outputs a signal744to the modulation component538in order to affect the duration of the on-time period associated with the switch566. In yet another example, if the signal712(e.g., Vctrl1) is larger than the threshold signal720(e.g., V_min) in magnitude, the duration of the on-time period is determined by the signal712(e.g., Vctrl1). In yet another example, if the signal712(e.g., Vctrl1) is smaller than the threshold signal720(e.g., V_min) in magnitude, the duration of the on-time period is determined by the signal720(e.g., V_min). In yet another example, during the off-time period of the switching period associated with the switch566, the transistor732is turned on in response to the signal736, and the capacitor730is discharged. In yet another example, the signal714(e.g., Vramp1) decreases to a low magnitude (e.g., zero). In yet another example, the signal744is the same as the signal644.

According to yet another embodiment, the LEB component550that includes the resistor752and the transistor756is affected by a control signal780(e.g., LEB), and outputs the current sensing signal610to the comparator546. For example, the comparator546outputs a comparison signal784to an OR gate750which also receives the control signal780(e.g., LEB). In another example, the OR gate750outputs a signal786to the modulation component538in order to affect the status of the switch566. In yet another example, if the control signal780is at the logic high level, the control signal782is at the logic low level, and if the control signal780is at the logic low level, the control signal782is at the logic high level. In yet another example, the control signal780(e.g., LEB) is an input signal of the LEB component550. In yet another example, the control signal780(e.g., LEB) and the control signal782(e.g., LEB_b) are associated with a blanking time period during which the leading edge blanking is carried out. In yet another example, during the blanking time period, the control signal780(e.g., LEB) is at the logic high level and the control signal782(e.g., LEB_b) is at the logic low level. In yet another example, the modulation component538outputs the signal646to the logic component540which receives the signal628and outputs the signal632(e.g., DR1). The signal632(e.g., DR1) is used as shown inFIG. 4(a),FIG. 4(b)andFIG. 4(c)according to certain embodiments.

As discussed above, the slope P of the signal626affects the duration of the on-time period of a switching period. For example, the duration of the on-time period corresponds to the pulse width of the signal699(or the signal499). In another example, the pulse width of the signal699(or the signal499) increases if the slope P decreases, and the pulse width of the signal699(or the signal499) decreases if the slope P increases. In yet another example, the pulse width of the signal699increases if the input voltage642decreases and if the output voltage602and the output current694remain constant. In yet another example, the pulse width of the signal699decreases if the input voltage642increases and if the output voltage602and the output current694remain constant.

As discussed above and further emphasized here,FIG. 6is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the OR gate734, the OR gate745and the OR gate750are included in the modulation component538. In another example, the resistor754is removed so that the terminal610is directly coupled with the resistor752and the transistor756.

FIG. 7(a)is a simplified timing diagram for the voltage-mode component504as part of the power conversion system500if the signal712is larger than the threshold signal720in magnitude according to an embodiment of the present invention, andFIG. 7(b)is a simplified timing diagram for the voltage-mode component504as part of the power conversion system500if the signal712is smaller than the threshold signal720in magnitude according to another embodiment of the present invention. These diagrams are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.

As shown inFIG. 7(a), the waveform902represents the signal699(e.g., DRV) as a function of time, the waveform904represents the signal680(e.g., Vramp) as a function of time, and the waveform906represents the amplified signal608(e.g., Vea) as a function of time. Additionally, the waveform908represents the signal712(e.g., Vctrl1) as a function of time, the waveform910represents the signal714(e.g., Vramp1) as a function of time, and the waveform912represents the threshold signal720(e.g., V_min) as a function of time. For example, when the signal699(e.g., DRV) is at a logic high level (e.g., as shown by the waveform902), the switch566is closed (e.g., being turned on). In another example, when the signal699(e.g., DRV) is at a logic low level (e.g., as shown by the waveform902), the switch566is open (e.g., being turned off). In yet another example, the waveform902is substantially the same as the waveform of the signal632.

When the switch566is closed (e.g., being turned on), the transformer including the primary winding560and the secondary winding562stores energy, and the primary current630increases in magnitude (e.g., linearly), according to one embodiment. For example, the transistor732is turned off in response to the signal736, and the capacitor730is charged in response to the signal626. In another example, the signal714(e.g., Vramp1) increases in magnitude (e.g., linearly) as shown by the waveform910. Because the signal712(e.g., Vctrl1) is larger than the threshold signal720(e.g., V_min) in magnitude, when the signal714becomes approximately equal to the signal712(e.g., Vctrl1) in magnitude, the comparator706changes the signal718in order to cause the switch566to be opened (e.g., to be turned off), in some embodiments. For example, the duration of the on-time period increases with the magnitude of the signal712(e.g., Vctrl1).

When the switch566is open (e.g., being turned off), the transformer that includes the primary winding560and the secondary winding562outputs energy to the output terminal according to another embodiment. For example, the demagnetization process begins (e.g., at time t4), and the secondary current694that flows through the secondary winding562decreases in magnitude (e.g., linearly). In another example, the signal680(e.g., Vrampcorresponding to the waveform904) is restored to an initial value (e.g., Vrefb), but after the demagnetization process is completed (e.g., at time t5), the signal680decreases exponentially as shown by the waveform904. In yet another example, when the switch566is open (e.g., at t4), the transistor732is turned on in response to the signal736, and the capacitor730is discharged. In yet another example, the signal714(e.g., Vramp1) decreases to a low magnitude (e.g., zero) as shown by the waveform910.

As shown inFIG. 7(b), the waveform1002represents the signal699(e.g., DRV) as a function of time, the waveform1004represents the signal680(e.g., Vramp) as a function of time, and the waveform1006represents the amplified signal608(e.g., Vea) as a function of time. Additionally, the waveform1008represents the signal712(e.g., Vctrl1) as a function of time, the waveform1010represents the signal714(e.g., Vramp1) as a function of time, and the waveform1012represents the threshold signal720(e.g., V_min) as a function of time. For example, when the signal699(e.g., DRV) is at a logic high level (e.g., as shown by the waveform1002), the switch566is closed (e.g., being turned on). In another example, when the signal699(e.g., DRV) is at a logic low level (e.g., as shown by the waveform1002), the switch566is open (e.g., being turned off). In yet another example, the waveform1002is substantially the same as the waveform of the signal632.

When the switch566is closed (e.g., being turned on), the transformer including the primary winding560and the secondary winding562stores energy, and the primary current630increases in magnitude (e.g., linearly), according to one embodiment. For example, the transistor732is turned off in response to the signal736, and the capacitor730is charged in response to the signal626. In another example, the signal714(e.g., Vramp1) increases in magnitude (e.g., linearly) as shown by the waveform1010. Because the signal712(e.g., Vctrl1) is smaller than the threshold signal720(e.g., V_min) in magnitude, when the signal714becomes approximately equal to the signal720(e.g., V_min) in magnitude, the comparator704changes the signal716in order to cause the switch566to be opened (e.g., to be turned off), in some embodiments. For example, the duration of the on-time period increases with the magnitude of the signal720(e.g., V_min).

When the switch566is open (e.g., being turned off), the transformer that includes the primary winding560and the secondary winding562outputs energy to the output terminal according to another embodiment. For example, the demagnetization process begins (e.g., at time t8), and the secondary current694that flows through the secondary winding562decreases in magnitude (e.g., linearly). In another example, the signal680(e.g., Vrampcorresponding to the waveform1004) is restored to an initial value (e.g., Vrefb), but after the demagnetization process is completed (e.g., at time t9), the signal680decreases exponentially as shown by the waveform1004. In yet another example, when the switch566is open (e.g., at t8), the transistor732is turned on in response to the signal736, and the capacitor730is discharged. In yet another example, the signal714(e.g., Vramp1) decreases to a low magnitude (e.g., zero) as shown by the waveform1010.

As discussed above and further emphasized here,FIGS. 3 and 6are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the power conversion system300includes all the components as shown inFIG. 6. In another example, the voltage-mode component304operates in the same manner as the voltage-mode component504as shown inFIGS. 7(a) and (b). In one embodiment, the voltage-mode component304includes the OR gate734, and outputs the signal444based on at least information associated with the signals712and720without directly comparing the signals712and720. In another embodiment, the voltage-mode component304is configured to, without directly comparing the signals712and720, if the signal712(e.g., Vctrl1) is larger than the signal720(e.g., V_min) in magnitude and the signal714(e.g., Vramp1) is smaller than the signal712(e.g., Vctrl1), generate the signal444in order to close the switch, and if the signal712(e.g., Vctrl1) is smaller than the signal720(e.g., V_min) in magnitude and the signal714(e.g., Vramp1) is smaller than the signal720(e.g., V_min), generate the signal444in order to close the switch.

According to another embodiment, a system controller for regulating an output of a power conversion system includes a signal generator and a modulation and drive component. The signal generator is configured to receive at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system and receive a second signal indicating a magnitude of a primary current flowing through the primary winding, and generate a third signal. The modulation and drive component is configured to receive at least the third signal, generate a drive signal based on at least information associated with the third signal, and output the drive signal to a switch to affect the primary current. The signal generator and the modulation and drive component are further configured to, if an output voltage of the power conversion system is constant and an output current of the power conversion system falls within a first predetermined range, generate a modulation signal as the drive signal based on at least information associated with the magnitude of the input voltage without taking into account the magnitude of the primary current flowing through the primary winding, and if the output voltage is constant and the output current falls within a second predetermined range, generate the modulation signal as the drive signal based on at least information associated with the magnitude of the primary current without taking into account the magnitude of the input voltage. For example, the system controller is implemented according to at leastFIG. 2(a),FIG. 2(b),FIG. 3,FIG. 4(a),FIG. 4(b), and/orFIG. 4(c).

According to yet another embodiment, a system controller for regulating an output of a power conversion system includes a signal generator and a modulation and drive component. The signal generator is configured to receive at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, process information associated with the first signal, and generate a second signal based on at least information associated with the first signal. The modulation and drive component is configured to receive at least the second signal, generate a drive signal based on at least information associated with the second signal, and output the drive signal to a switch to affect a primary current flowing through the primary winding. The signal generator and the modulation and drive component are further configured to, if an output voltage of the power conversion system is constant and an output current of the power conversion system falls within a first predetermined range, generate a pulse-width-modulation signal corresponding to a pulse width and a modulation frequency as the drive signal. The pulse width decreases if the input voltage increases and if the output voltage and the output current remain constant. For example, the system controller is implemented according to at leastFIG. 2(a),FIG. 2(b),FIG. 3,FIG. 4(a),FIG. 4(b), and/orFIG. 4(c).

According to yet another embodiment, a system controller for regulating an output of a power conversion system includes a signal generator, a first comparator, a second comparator, and a modulation and drive component. The signal generator is configured to receive at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, process information associated with the first signal, and generate a second signal based on at least information associated with the first signal. The first comparator is configured to receive the second signal and a third signal associated with a feedback signal of the power conversion system and generate a first comparison signal based on at least information associated with the second signal and the third signal. The second comparator is configured to receive the second signal and a threshold signal and generate a second comparison signal based on at least information associated with the second signal and the threshold signal. The modulation and drive component is configured to receive at least the first comparison signal and the second comparison signal, generate a drive signal based on at least information associated with the first comparison signal and the second comparison signal, and output the drive signal to a switch to affect a primary current flowing through the primary winding. The modulation and drive component is further configured to, if the third signal is larger than the threshold signal in magnitude, output the drive signal to close the switch if the second signal is smaller than the third signal, and if the threshold signal is larger than the third signal in magnitude, output the drive signal to close the switch if the second signal is smaller than the threshold signal. For example, the system controller is implemented according to at leastFIG. 4(a),FIG. 4(b),FIG. 4(c),FIG. 5,FIG. 6,FIG. 7(a)and/orFIG. 7(b).

In one embodiment, a method for regulating an output of a power conversion system includes receiving at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, receiving a second signal indicating a magnitude of a primary current flowing through the primary winding, and processing information associated with the first signal and the second signal. The method further includes generating a third signal, receiving at least the third signal, and processing information associated with the third signal. In addition, the method includes generating a drive signal based on at least information associated with the third signal, and outputting the drive signal to a switch to affect the primary current. The process for generating a drive signal based on at least information associated with the third signal includes, if an output voltage of the power conversion system is constant and an output current of the power conversion system falls within a first predetermined range, generating a modulation signal as the drive signal based on at least information associated with the magnitude of the input voltage without taking into account the magnitude of the primary current flowing through the primary winding, and if the output voltage is constant and the output current falls within a second predetermined range, generating the modulation signal as the drive signal based on at least information associated with the magnitude of the primary current without taking into account the magnitude of the input voltage. For example, the method is implemented according to at leastFIG. 2(a),FIG. 2(b),FIG. 3,FIG. 4(a),FIG. 4(b), and/orFIG. 4(c).

In another embodiment, a method for regulating an output of a power conversion system includes receiving at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, processing information associated with the first signal, and generating a second signal based on at least information associated with the first signal. The method further includes receiving at least the second signal, processing information associated with the second signal, generating a drive signal based on at least information associated with the second signal, and outputting the drive signal to a switch to affect a primary current flowing through the primary winding. The process for generating a drive signal based on at least information associated with the second signal includes, if an output voltage of the power conversion system is constant and an output current of the power conversion system falls within a first predetermined range, generating a pulse-width-modulation signal corresponding to a pulse width and a modulation frequency as the drive signal. The pulse width decreases if the input voltage increases and if the output voltage and the output current remain constant. For example, the method is implemented according to at leastFIG. 2(a),FIG. 2(b),FIG. 3,FIG. 4(a),FIG. 4(b), and/orFIG. 4(c).

In yet another embodiment, a method for regulating an output of a power conversion system includes receiving at least a first signal indicating a magnitude of an input voltage received by a primary winding of a power conversion system, processing information associated with the first signal, and generating a second signal based on at least information associated with the first signal. The method further includes receiving the second signal and a third signal associated with a feedback signal of the power conversion system, processing information associated with the second signal and the third signal, and generating a first comparison signal based on at least information associated with the second signal and the third signal. In addition, the method includes receiving the second signal and a threshold signal, processing information associated with the second signal and the threshold signal, and generating a second comparison signal based on at least information associated with the second signal and the threshold signal. Moreover, the method includes receiving at least the first comparison signal and the second comparison signal, processing information associated with the first comparison signal and the second comparison signal, generating a drive signal based on at least information associated with the first comparison signal and the second comparison signal, and outputting the drive signal to a switch to affect a primary current flowing through the primary winding. The process for outputting the drive signal to a switch to affect a primary current flowing through the primary winding includes, if the third signal is larger than the threshold signal in magnitude, outputting the drive signal to close the switch if the second signal is smaller than the third signal, and if the threshold signal is larger than the third signal in magnitude, outputting the drive signal to close the switch if the second signal is smaller than the threshold signal. For example, the method is implemented according to at leastFIG. 4(a),FIG. 4(b),FIG. 4(c),FIG. 5,FIG. 6,FIG. 7(a)and/orFIG. 7(b).

For example, some or all components of various embodiments of the present invention each are, individually and/or in combination with at least another component, implemented using one or more software components, one or more hardware components, and/or one or more combinations of software and hardware components. In another example, some or all components of various embodiments of the present invention each are, individually and/or in combination with at least another component, implemented in one or more circuits, such as one or more analog circuits and/or one or more digital circuits. In yet another example, various embodiments and/or examples of the present invention can be combined.