Feedback circuit

The present invention particularly discloses a novel feedback circuit, mainly comprising: a signal sampling unit, a feedback unit, a signal concerting unit, and a signal adjusting unit. During the operation of the feedback circuit, a current-mode error amplifier unit is configured to output a current error signal based on a current sampling signal and a dimming signal outputted by the signal converting unit, so as to activate a PWM controlling unit to stabilize an output current of a LED driver circuit. In the meantime, a voltage-mode error amplifier unit cooperates with the PWM controlling unit to adaptively regulate an output voltage of the LED driver circuit based on a voltage sampling signal and an adjustment signal outputted by the signal adjusting unit, in order to facilitate the LED driver circuit provides a constant output power.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the technology field of electronic circuits, and more particularly to a feedback circuit applied in power converters and power supply devices.

2. Description of the Prior Art

With the continuous advance of electronic sciences and technologies, various electronic devices and products have been development and widely applied in human life. Traditionally, linear power supply devices are adopted for outputting voltage or current to power corresponding electronic devices. However, owing to linear power supply devices possessing many disadvantages such as large volume and poor power conversion rate, switch mode power supply (SMPS) device is invented by Neti R. M. Rao and disclosed in U.S. Pat. No. 4,253,137.

SMPS technology is also applied for designing and manufacturing LED driver circuits. Please refer toFIG. 1, there is provided a circuit block diagram of a conventional LED driver circuit. AsFIG. 1shows, the conventional LED driver circuit1′ comprises: an electromagnetic interference (EMI) filtering unit10′ coupling to a voltage source VS′, a rectifying unit11′, a power factor correction (PFC) unit12′, a power switch13′, a transformer unit14′, an output rectifying/filtering unit15′, a feedback unit16′, a pulse width modulation (PWM) controlling unit17′, and a dimming unit19′, wherein the said feedback unit16′ is constituted by an error amplifier unit161′ and a photo-coupler162′. Moreover, engineers skilled in development and manufacture of power electronic circuits should know that the error amplifier unit161′ used in the LED driver circuit1′ commonly consists of voltage-mode error amplifier1611′ and current-mode error amplifier1612′.

According to disclosures about a specific feedback control technique proposed by U.S. patent publication No. 2013/0127356 A1, it is able to know that the voltage-mode error amplifier1611′ and the current-mode error amplifier1612′ shown inFIG. 1are able to receive a voltage sampling signal and a current sampling signal through a voltage sensing unit VSU′ and a current sensing unit CSU′, respectively. Furthermore, after receiving an error signal from a OR gate1613′ of the error amplifier unit161′ via the photo-coupler162′, the PWM controlling unit17′ correspondingly generates a PWM controlling signal to the power switch13′, so as to facilitate the LED driver circuit1′ steadily supply an output current/voltage to an LED lighting device2′ based on the periodic ON-OFF switching of the power switch13′.

FromFIG. 1, electronic engineers skilled in development and manufacture of LED driver circuit can also understand that, the current-mode error amplifier1612′ is configured to generate a current error signal to the PWM controlling unit17′ based on a dimming signal outputted by the dimming unit19′ and the current sampling signal. Similarly, the voltage-mode error amplifier1611′ is configured to generate a voltage error signal to the PWM controlling unit17′ based on the dimming signal and the voltage sampling signal. Moreover, it is worth noting that, only the current error signal or the voltage error signal for informing the PWM controlling unit17′ to reduce the output current/voltage would be outputted by the OR gate1613′.

Clearly, based on the received dimming signal and the current/voltage sampling signal, conventional technology (i.e., the specific feedback control technique) mainly utilizes the error amplifier unit161′ constituted by the voltage-mode error amplifier1611′, the current-mode error amplifier1612′ and the OR gate1613′ to activate the PWM controlling unit17′ to stabilize the output current/voltage of the LED driver circuit1′. However, owing to the feedback unit16′ and the PWM controlling unit17′ can only singly reduce the output current or the output voltage of the LED driver circuit1′, such feedback control technique cannot make the LED driver circuit1′ provide a constant power even if the LED driver circuit1′ is able to output a constant driving current or a constant driving voltage to the LED lighting device2′ under the domination of the specific feedback controlling mechanism.

In view of the fact that the conventional feedback control technology can make the LED driver circuit1′ output a constant driving current or a constant driving voltage but fail to stabilize the output power of the LED driver circuit1′, inventors of the present application have made great efforts to make inventive research thereon and eventually provided a feedback circuit for use in power converters, power supply devices, and LED drivers.

SUMMARY OF THE INVENTION

Differing from conventional feedback controlling circuit can only make a LED driver circuit provide a constant output current and/or a constant output current, the primary objective of the present invention is to provide a novel feedback circuit, which can not only activate a PWM controlling unit to stabilize the output current and the output voltage of the LED driver circuit, but also can facilitate the LED driver circuit provide a constant output power. This feedback circuit comprises: a signal sampling unit, a feedback unit, a signal concerting unit, and a signal adjusting unit. During the operation of the feedback circuit, a current-mode error amplifier unit is configured to output a current error signal based on a current sampling signal and a dimming signal outputted by the signal converting unit, so as to activate the PWM controlling unit to stabilize the output current of the LED driver circuit. In the meantime, a voltage-mode error amplifier unit cooperates with the PWM controlling unit to adaptively regulate the output voltage of the LED driver circuit based on a voltage sampling signal and an adjustment signal outputted by the signal adjusting unit, in order to facilitate the LED driver circuit provides a constant output power.

For achieving the primary objective of the present invention, the inventor of the present invention provides an embodiment for the feedback circuit applied in an LED power supply device; wherein the LED power supply device comprises a rectifying unit, a power switch, a transformer unit, an output rectifying/filtering unit, and a pulse width modulation (PWM) controlling unit; moreover, the feedback circuit comprises:a signal sampling unit, being coupled to output terminals of the LED power supply device for sensing a voltage sampling signal and a current sampling signal;a feedback unit, being coupled to the signal sampling unit, and comprising a current-mode error amplifier and a voltage-mode error amplifier;a signal converting unit, being coupled to the current-mode error amplifier and an external dimming circuit, and configured for converting a dimming control signal outputted from the dimming circuit to a dimming signal, so as to transmit the dimming signal to the current-mode error amplifier;a signal adjusting unit, being coupled to the signal converting unit and the voltage-mode error amplifier, and used for applying a signal adjusting process to a reference signal based on the dimming signal and then outputting an adjusted reference signal to the voltage-mode error amplifier;wherein the current-mode error amplifier is configured to output a current error signal to the PWM controlling unit based on the current sampling signal and the dimming signal, such that the PWM controlling unit correspondingly generates a first PWM signal to the power switch, so as to facilitate the LED power supply device steadily supply an output current to an external LED lighting device based on the periodic ON-OFF switching of the power switch;wherein the voltage-mode error amplifier is configured to output a voltage error signal to the PWM controlling unit based on the voltage sampling signal and the adjusted reference signal, such that the PWM controlling unit correspondingly generates a second PWM signal to the power switch, so as to facilitate the LED power supply device provides a constant output power by adaptively regulating an output voltage of the LED power supply device with the variation of the output current.

Moreover, in order to achieve the primary objective of the present invention, the inventor of the present invention further provides another one embodiment for the feedback circuit applied in an LED power supply device; wherein the LED power supply device comprises a rectifying unit, a power switch, a transformer unit, an output rectifying/filtering unit, and a pulse width modulation (PWM) controlling unit; moreover, the feedback circuit comprises:a signal sampling unit, being coupled to output terminals of the LED power supply device for sensing a voltage sampling signal and a current sampling signal;a feedback unit, being coupled to the signal sampling unit, and comprising a current-mode error amplifier and a voltage-mode error amplifier;a signal converting unit, being coupled to the current-mode error amplifier and an external dimming circuit, and configured for converting a dimming control signal outputted from the dimming circuit to a dimming signal, so as to transmit the dimming signal to the current-mode error amplifier;a signal adjusting unit, being coupled to the signal converting unit and the voltage-mode error amplifier, and used for applying a signal adjusting process to a reference signal based on the dimming signal and then outputting an adjusted reference signal to the voltage-mode error amplifier;wherein the current-mode error amplifier is configured to output a current error signal to the PWM controlling unit based on the current sampling signal and the dimming signal, such that the PWM controlling unit correspondingly generates a first PWM signal to the power switch, so as to facilitate the LED power supply device steadily supply an output current to an external LED lighting device based on the periodic ON-OFF switching of the power switch;wherein the voltage-mode error amplifier is configured to output a voltage error signal to the PWM controlling unit based on the voltage sampling signal, a reference signal and the adjusted reference signal, such that the PWM controlling unit correspondingly generates a second PWM signal to the power switch, so as to facilitate the LED power supply device provides a constant output power by adaptively regulating an output voltage of the LED power supply device with the variation of the output current.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To more clearly describe a feedback circuit for use in power converters, power supply devices, and LED drivers according to the present invention, embodiments of the present invention will be described in detail with reference to the attached drawings hereinafter.

First Embodiment

With reference toFIG. 2, there is provided a circuit block diagram of an LED power supply device having a feedback circuit of the present invention. AsFIG. 2shows, the LED power supply device2comprises: an electromagnetic interference (EMI) filtering unit20coupling to a voltage source VS, a rectifying unit21, a power factor correction (PFC) unit22, a power switch23, a transformer unit24, an output rectifying/filtering unit25, and a pulse width modulation (PWM) controlling unit27.

The feedback circuit1of the present invention is mainly used in the LED power supply device2for cooperating with the PWM control unit27so as to stabilize the output current, the output voltage and the output power of the LED power supply device2. Briefly speaking, this feedback circuit1is particularly designed to provide an assistance on facilitating the LED power supply device2provide constant current and/or constant voltage to an LED lighting device3under the maintenance of constant output power. AsFIG. 2shows, the feedback circuit1is constituted by a signal sampling unit10, a feedback unit11, a signal converting unit12, and a signal adjusting unit13. Moreover,FIG. 3shows a circuit framework view of the first embodiment of the feedback circuit. FromFIG. 2andFIG. 3, it is found that the signal sampling unit10consists of an output current sampling unit101and an output voltage sampling unit102, wherein the output current sampling unit101comprises a current sensing resistor Rsen and a signal sampling resistor Rsam. Moreover, the current sensing resistor Rsen is coupled to the output terminal of the LED power supply device2by one end thereof, and the two ends of the signal sampling resistor Rsam are coupled to the other end of the current sensing resistor Rsen and a circuit ground GND of the LED power supply device2, respectively.

On the other hand, the output voltage sampling unit102comprises a first voltage dividing resistor Rv1and a second voltage dividing resistor Rv2, wherein the first voltage dividing resistor Rv1is coupled to the output terminal of the LED power supply device2by one end thereof. Moreover, the two ends of the second voltage dividing resistor Rv2are coupled to the other end of the first voltage dividing resistor Rv1and the circuit ground GND, respectively. Similar to conventional feedback circuits, the feedback unit11of this feedback circuit1is coupled to the signal sampling unit10and comprises a current-mode error amplifier111, a voltage-mode error amplifier112and a photo-coupler113. However, what is different from the conventional feedback circuits is that, the present invention particularly arranges a signal converting unit12to electrically connected to an external dimming circuit4, wherein the signal converting unit12is configured for converting a dimming control signal outputted from the dimming circuit4to a dimming signal, so as to transmit the dimming signal to the current-mode error amplifier111and the signal adjusting unit13. In brief, the current-mode error amplifier111does not be directly electrically connected to the dimming circuit4according to particular circuit design of the present invention. By such circuit arrangements, the current-mode error amplifier111is able to output a current error signal to the PWM controlling unit27based on the current sampling signal and the dimming signal, such that the PWM controlling unit correspondingly generates a first PWM signal to the power switch23, so as to facilitate the LED power supply device2steadily supply an output current to the LED lighting device3based on the periodic ON-OFF switching of the power switch23.

Moreover, asFIG. 2andFIG. 3show, the signal adjusting unit13is coupled to the signal converting unit12and the voltage-mode error amplifier112, and used for applying a signal adjusting process to a reference signal based on the dimming signal generated by the signal converting unit12, and then outputting an adjusted reference signal to the voltage-mode error amplifier. Thus, based on the voltage sampling signal and the adjusted reference signal, the voltage-mode error amplifier112outputs a voltage error signal for making the PWM controlling unit27correspondingly generates a second PWM signal to the power switch23, so as to facilitate the LED power supply device2provides a constant output power by adaptively regulating an output voltage of the LED power supply device2with the variation of the output current. It is worth explaining that, since the present invention particularly utilizes the signal converting unit12to convert the said dimming control signal generated by the external dimming circuit4to the dimming signal, it is ensured that the signal adjusting unit and the current-mode error amplifier111can receive the same dimming signal, such that signal distortion or transmission error can be prevented from occurring between the different circuit units coupled to each other.

According to circuit diagram ofFIG. 3, it is able to know that the signal converting unit12comprises a first signal converting resistor Rx1and a second signal converting resistor Rx2, wherein the first signal converting resistor Rx1is coupled to the dimming circuit4by one end thereof. Moreover, two ends of the second signal converting resistor Rx2are coupled to the other end of the first signal converting resistor Rx1and the circuit ground GND of the LED power supply device2. It is worth noting that, a non-linear dimming unit17, such as in-line package (DIP) switch or variable resistor, can be additionally coupled to the two ends of the first signal converting resistor Rx1according to particular circuit design of the present invention. Thus, users can apply a non-linear dimming control to the LED lighting device3by operating the non-linear dimming unit17. Herein it needs to explain that the said dimming circuit4can be a variable resistor dimming circuit, a DC dimming circuit (1-10 VDC), a PWM dimming circuit, a digital dimming circuit with decoding interface (DALI DIM), or a touch-type dimming circuit (TOUCH DIM); wherein any one of these dimming circuit is used for applying a linear dimming control to the LED lighting device3by outputting the dimming control signal to the signal converting unit12.

It is worth explaining that, in order to prevent the dimming signal from being directly inputted into the current-mode error amplifier111and the signal adjusting unit13, an isolation unit15is further arranged in the feedback circuit1for being coupled between the signal converting unit12and the current-mode error amplifier111as well as the signal adjusting unit13. Moreover, asFIG. 3shows, the current-mode error amplifier111consists of a first input buffer1112coupled to the isolation unit15and a first error amplifier1113, wherein the first error amplifier1113is coupled to the signal sampling resistor Rsam and the first input buffer1112by its one negative input terminal and one positive input terminal, respectively. In addition, one output terminal of the first error amplifier1113is coupled to the photo-coupler113.

Please continuously refer toFIG. 3, wherein the signal adjusting unit13comprises a differential amplifier131, a voltage regulating unit133and a voltage comparator132, wherein the differential amplifier131is coupled to the isolation unit15by one negative input terminal; moreover, one positive input terminal of the differential amplifier131is coupled to a first reference voltage VREF1. On the other hand, the voltage comparator132comprises an operational amplifier OP, a first resistor R514, a second resistor R151, a diode Di, and a third resistor R515. FromFIG. 3, it is found that the operational amplifier OP is coupled to a second reference voltage VREF2by one positive input terminal; moreover, one negative input terminal of the operational amplifier OP is coupled to the isolation unit15via a voltage dividing resistor set constituted by the first resistor R514and the second resistor R515. Moreover, one output terminal of the operational amplifier OP is coupled to the positive input terminal of the differential amplifier131via the diode Di and the third resistor serially connected to the diode Di. In addition, the voltage regulating unit133is coupled to output terminal of the differential amplifier131.

On the other hand, the voltage-mode error amplifier112comprises a second buffer1121coupled to the signal adjusting unit13and a second error amplifier1122, wherein the second error amplifier1122is coupled to the output terminal of the differential amplifier131via the voltage regulating unit133by one positive input terminal thereof; moreover, one negative input terminal and one output terminal of the second error amplifier1122are coupled to the output voltage sampling unit102and the photo-coupler113, respectively. Herein, it needs to further explain that, the purpose of connecting the voltage regulating unit133and the voltage comparator132to the differential amplifier131is to stabilize the adjusted reference signal generated by the signal adjusting unit13, so as to cancel the signal drift effect.

Therefore, above descriptions have introduced the circuit framework and the constitutions of the feedback circuit1proposed by the present invention. Next, following paragraphs will further describe the practicability of the feedback circuit1under the assistance of experimental data.FIG. 4exhibits a curve graph of output current versus output voltage, wherein related information of four curves shown inFIG. 4are integrated in following Table (1).

TABLE 1CurvesInformationAConstant output voltage provided by an LED power supplydevice 2 having this novel feedback circuit 1.BConstant output current provided by an LED power supplydevice 2 having this novel feedback circuit 1.CDuring the operation of the LED power supply device 2having the novel feedback circuit 1, the current-mode erroramplifier 111 activates the PWM controlling unit 27 tostabilize the output current of the LED power supply device2. In the meantime, the voltage-mode error amplifier unit112 cooperates with the PWM controlling unit 27 toadaptively regulate the output voltage of the LED powersupply device 2 based on a voltage sampling signal and anadjustment signal, so as to facilitate the LED power supplydevice 2 provides a constant output power.DDuring the operation of the LED power supply device 2having the novel feedback circuit 1, the current-mode erroramplifier 111 activates the PWM controlling unit 27 tostabilize the output current of the LED power supply device2. In the meantime, the voltage-mode error amplifier unit112 cooperates with the PWM controlling unit 27 toadaptively regulate the output voltage of the LED powersupply device 2 based on a voltage sampling signal and anadjustment signal, so as to facilitate the LED power supplydevice 2 provides a constant output power.

It must particularly emphasize that, curve C is a real simulation data of the LED power supply device2having the feedback circuit1of the present invention; on the contrary, curve D is an ideal data. Apparently, experimental data have improved that, this novel feedback circuit1can indeed be helpful to facilitate the LED power supply device2provides constant current and/or constant voltage to an LED lighting device3under the maintenance of constant output power.

Second Embodiment

Continuously referring toFIG. 5andFIG. 6, whereinFIG. 5illustrates a circuit framework view of a second embodiment of the feedback circuit, andFIG. 6shows a circuit block diagram of the LED power supply device having the feedback circuit of the present invention. After comparingFIG. 5withFIG. 3, it can find that the second embodiment of the feedback circuit1comprises: a signal sampling unit10, a feedback unit11, a signal converting unit12, and a signal adjusting unit13. Moreover, differing from the signal adjusting unit13of the first embodiment is constituted by a differential amplifier131, a voltage regulating unit133and a voltage comparator132, the signal adjusting unit13of the second embodiment is an error detection unit.

FromFIG. 5andFIG. 6, it is able to know that, the signal adjusting unit13comprises: an operational amplifier OP′, a third voltage dividing resistor Rv3, a fourth voltage dividing resistor Rv4, a first diode D1, and a second diode D2, wherein the operational amplifier OP′ is coupled to the signal converting unit12by one positive input terminal thereof. Moreover, the third voltage dividing resistor Rv3is coupled to one negative input terminal of the operational amplifier OP′ by one end thereof, and the fourth voltage dividing resistor Rv4is coupled to the other end of the third voltage dividing resistor Rv3. On the other hand, the first diode D1is coupled to the other end of the fourth voltage dividing resistor Rv4by one negative end thereof, and the positive end of the first diode D1is coupled to one output terminal of the operational amplifier OP′. In addition, the second diode D2is coupled to the output terminal of the operational amplifier OP′ by one positive end thereof, and the negative end of the second diode D2is coupled to the voltage-mode error amplifier112.

Electronic engineers should know that, the operational amplifier OP′, the third voltage dividing resistor Rv3and the fourth voltage dividing resistor Rv4form the main circuit framework of the error detector130. Moreover, a first diode D1and a second diode D2are disposed between the output terminal of the operational amplifier OP′ and the fourth voltage dividing resistor Rv4. By such circuit arrangement, the signal adjusting unit is able to steadily output an adjusted reference signal to the voltage-mode error amplifier112after applying a signal adjusting process to a reference signal VREFbased on the dimming signal, without inducing any signal drift phenomenon. One the other hand, asFIG. 5shows, the main circuit framework of the voltage-mode error amplifier1112is a an error amplifier Eop, which is configured to receive the reference signal VREFby one positive input terminal thereof; moreover, one negative input terminal and one output terminal of the error amplifier Eop are coupled to the signal adjusting unit13and the photo-coupler113, respectively.

Therefore, through above descriptions, the feedback circuit1for use in power converters, power supply devices, and LED drivers proposed by the present invention have been introduced completely and clearly; in summary, the present invention includes the advantages of:

(1) Differing from conventional feedback controlling circuit (asFIG. 1shows) can only make a LED driver circuit provide a constant output current and/or a constant output current, the present invention particularly discloses a novel feedback circuit1, which can not only activate a PWM controlling unit27to stabilize the output current and the output voltage of an LED power supply device2, but also can facilitate the LED power supply device2provide a constant output power. This feedback circuit1comprises: a signal sampling unit10, a feedback unit11, a signal concerting unit12, and a signal adjusting unit13. During the operation of the feedback circuit1, a current-mode error amplifier unit111is configured to output a current error signal based on a current sampling signal and a dimming signal outputted by the signal converting unit12, so as to activate the PWM controlling unit27to stabilize the output current of the LED power supply device2. In the meantime, a voltage-mode error amplifier unit112cooperates with the PWM controlling unit27to adaptively regulate the output voltage of the LED power supply device2based on a voltage sampling signal and an adjustment signal outputted by the signal adjusting unit13, so as to facilitate the LED power supply device2provides a constant output power.

(2) Moreover, it is worth explaining that, experimental data have improved that, this novel feedback circuit1can indeed be helpful to facilitate the LED power supply device2provides constant current and/or constant voltage to an LED lighting device3under the maintenance of constant output power.

The above description is made on embodiments of the present invention. However, the embodiments are not intended to limit scope of the present invention, and all equivalent implementations or alterations within the spirit of the present invention still fall within the scope of the present invention.