High efficiency charging circuit and power supply system having such high efficiency charging circuit

A charging circuit includes a main power circuit, a DC-to-DC converting circuit, a detection circuit and a controller. The main power circuit is electrically connected to a power source for converting an input voltage from the power source into a first voltage. The DC-to-DC converting circuit is electrically connected to the main power circuit for converting the first voltage into a second voltage to charge the energy storage element. The detection circuit is electrically connected to the main power circuit and the DC-to-DC converting circuit for detecting a terminal voltage of the energy storage element and the first voltage from the main power circuit, thereby generating a feedback signal. The controller is electrically connected to the detection circuit and the main power circuit for controlling operations of the first switching element in response to the feedback signal, so that the first voltage is adjustable according to the second voltage.

FIELD OF THE INVENTION

The present invention relates to a charging circuit, and more particularly to a high efficiency charging circuit. The present invention also relates to a power supply system having such a high efficiency charging circuit.

BACKGROUND OF THE INVENTION

Recently, the general trends in designing portable electronic devices are toward small size, light weightiness and easy portability. The portable electronic devices such as mobile phones, personal digital assistants (PDAs), digital still cameras, digital video cameras, notebook computers and the like have built-in batteries. If no external power supply apparatus is provided to power the portable electronic device, the built-in battery is usually used as the main power source. If the power supplied from the battery is insufficient, the user needs to charge the built-in battery.

FIG. 1is a schematic circuit block diagram of a conventional charging circuit. The charging circuit1ofFIG. 1principally includes an AC-to-DC converting circuit11, a DC-to-DC converting circuit12and a filter capacitor Cbus. The AC-to-DC converting circuit11is electrically connected to the DC-to-DC converting circuit12and the filter capacitor Cbus. The DC-to-DC converting circuit12is electrically connected to a charger. An input AC voltage Vinis received and converted by the AC-to-DC converting circuit11into a high DC voltage. The noise contained in the high DC voltage is filtered off by the filter capacitor Cbus, thereby creating a first DC voltage Vbus. The first DC voltage Vbusis then converted by the DC-to-DC converting circuit12into a regulated DC voltage required for charging the battery13.

In the conventional charging circuit1, the battery is charged by a constant current. In other words, the current Iboutputted from the DC-to-DC converting circuit12is substantially constant in order to continuously and stably charge the battery13. As the charge capacity of the battery13is increased, however, the voltage difference Vbbetween both terminals of the battery13is increased. If the current Iboutputted from the DC-to-DC converting circuit12continuously and stably charge the battery13, the voltage difference Vbbetween both terminals of the battery13is continuously increased.

Furthermore, the first DC voltage Vbusoutputted from the AC-to-DC converting circuit11is usually constant. By the DC-to-DC converting circuit12, the first DC voltage Vbusis converted into the regulated second DC voltage, which is equal to the voltage difference Vbbetween both terminals of the battery13. As a consequence, the magnitude of the second DC voltage is changed as the charge capacity of the battery13. Generally, the relation between the first DC voltage Vbusand the second DC voltage Vbcan be written as a formula: Vb=Vbus×D×N, where D is a duty cycle and N is a turn ratio. Since the first DC voltage Vbusand the turn ratio N in the above formula are constant values, the second DC voltage Vbis in direct proportion to the duty cycle D. In a case that the battery13has the minimum charge capacity, the voltage difference between both terminals of the battery13is minimum and thus the second DC voltage Vband the duty cycle D are minimum. Whereas, in a case that the battery13has the maximum charge capacity, the voltage difference between both terminals of the battery13is maximum and thus the second DC voltage Vband the duty cycle D are maximum.

Generally, the operating efficiency of the DC-to-DC converting circuit12is dependent on the duty cycle D. If the DC-to-DC converting circuit12is operated at a high duty cycle D, the operating efficiency is relatively higher. Whereas, if the DC-to-DC converting circuit12is operated at a low duty cycle D, the operating efficiency is relatively lower. Under this circumstance, the operating efficiency of the DC-to-DC converting circuit12is dependent on the charge capacity of the battery13. That is, the charging circuit1has a low operating efficiency when the battery13has low charge capacity but a high operating efficiency when the battery13has high charge capacity. On the whole, the operating efficiency of the charging circuit1is unsatisfactory.

Therefore, there is a need of providing a high efficiency charging circuit so as to obviate the drawbacks encountered from the prior art.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide charging circuit, having a high operating efficiency independent of the charge capacity of the battery so as to obviate the drawbacks encountered from the prior art.

The present invention also relates to a power supply system having such a high efficiency charging circuit.

In accordance with an aspect of the present invention, there is provided a charging circuit for charging an energy storage element. The charging circuit includes a main power circuit, a DC-to-DC converting circuit, a detection circuit and a controller. The main power circuit includes at least a first switching element and is electrically connected to a power source for converting an input voltage from the power source into a first voltage. The DC-to-DC converting circuit is electrically connected to the main power circuit for converting the first voltage into a second voltage to charge the energy storage element. The detection circuit is electrically connected to output terminals of the main power circuit and the DC-to-DC converting circuit for detecting a terminal voltage of the energy storage element and the first voltage from the main power circuit, thereby generating a feedback signal. The controller is electrically connected to the detection circuit and the first switching element of the main power circuit for controlling operations of the first switching element in response to the feedback signal, so that the first voltage is adjustable according to the second voltage.

In accordance with another aspect of the present invention, there is provided a power supply system. The power supply system includes a battery module, an AC-to-DC converter, a charging circuit, an inverter, a bypass, a changeover switch and a system controller. The battery module is used for storing electric power therein. The AC-to-DC converter is used for receiving a first AC voltage from a power input terminal and converting the first AC voltage into a DC voltage. The charging circuit is interconnected between the power input terminal and the battery module or between the AC-to-DC converter and the battery module for charging the battery module. The inverter is electrically connected to the AC-to-DC converter for converting the DC voltage into a second AC voltage. The bypass has an end connected to the power input terminal. The changeover switch is connected to the other end of the bypass, the inverter and a power output terminal. The system controller is electrically connected to the power input terminal, the AC-to-DC converter, the charging circuit and the inverter for controlling operations of the power supply system. The charging circuit includes a main power circuit, a DC-to-DC converting circuit, a detection circuit and a pulse width modulation controller. The main power circuit includes at least a first switching element for converting an input voltage into a first voltage. The DC-to-DC converting circuit is electrically connected to the main power circuit for converting the first voltage into a second voltage to charge the energy storage element. The detection circuit is electrically connected to output terminals of the main power circuit and the DC-to-DC converting circuit for detecting a terminal voltage of the battery module and the first voltage from the main power circuit, thereby generating a feedback signal. The pulse width modulation controller is electrically connected to the detection circuit and the first switching element of the main power circuit for controlling operations of the first switching element in response to the feedback signal, so that the first voltage is adjustable according to the second voltage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 2, a schematic circuit block diagram of a high efficiency charging circuit according to a preferred embodiment of the present invention is illustrated. This high efficiency charging circuit2is adapted to charge an energy storage element20. An example of the energy storage element20includes but is not limited to a battery. The high efficiency charging circuit2ofFIG. 2principally includes a main power circuit21, a DC-to-DC converting circuit22, a detection circuit23and a pulse width modulation (PWM) controller24. The main power circuit21is electrically connected to a power source so as to receive an input voltage Vin(e.g. an AC voltage or a DC voltage). By the main power circuit21, the input voltage Vinis converted into a first voltage Vbus(e.g. a DC voltage). The DC-to-DC converting circuit22is electrically connected to the main power circuit21and the energy storage element20. By the DC-to-DC converting circuit22, the first voltage Vbusoutputted from the main power circuit21is converted into a regulated DC voltage, i.e. a second voltage. The second voltage is substantially equal to the voltage difference Vbbetween both terminals of the energy storage element20. In the context, the voltage difference Vbbetween both terminals of the energy storage element20is also referred as the second voltage Vb. The detection circuit23is electrically connected to the output terminal of the main power circuit21and the output terminal of the DC-to-DC converting circuit22. When the first voltage Vbusoutputted from the main power circuit21and the voltage difference Vbbetween both terminals of the energy storage element20are detected by the detection circuit23, a feedback voltage Vfis generated. The PWM controller24is electrically connected to the detection circuit23and the main power circuit21. In response to the feedback voltage Vf, the first voltage Vbusoutputted from the main power circuit21is adjusted by the PWM controller24according to the second voltage Vb.

Please refer toFIG. 2again. The high efficiency charging circuit2further includes a filter capacitor Cbusand a feedback capacitor Cf. The filter capacitor Cbusis electrically connected to the output terminal of the main power circuit21for filtering off undesirable noise contained in the DC voltage outputted from the main power circuit21. The feedback capacitor Cfis electrically connected to the output terminal of the detection circuit23for filtering off undesirable noise contained in the feedback voltage Vf.

In the high efficiency charging circuit2, the second voltage Vbis increased as the charge capacity of the energy storage element20is increased. In accordance with a key feature of the present invention, the first voltage Vbusoutputted from the main power circuit21is adjusted according to the second voltage Vb. Likewise, the relation between the first voltage Vbusand the second voltage Vbcan be written as a formula: Vb=Vbus×D×N, where D is a duty cycle and N is a turn ratio. Since the first voltage Vbusreceived by the DC-to-DC converting circuit22is changed as the voltage difference Vbbetween both terminals of the energy storage element20, the DC-to-DC converting circuit22can be operated at a relatively higher duty cycle D so as to achieve a high operating efficiency.

In this embodiment, the first voltage Vbusoutputted from the main power circuit21is controlled by the PWM controller24. Moreover, the feedback voltage Vfgenerated from the detection circuit23is dependent on the first voltage Vbusoutputted from the main power circuit21and the voltage difference Vbbetween both terminals of the energy storage element20. As a consequence, the first voltage Vbusoutputted from the main power circuit21can be controlled at a proper level such that the DC-to-DC converting circuit22is operated at a relatively higher duty cycle D.

FIG. 3is a schematic detailed circuit block diagram of a high efficiency charging circuit according to a preferred embodiment of the present invention. As shown inFIG. 3, the main power circuit21of the high efficiency charging circuit2includes a first switching element Q1. The first switching element Q1is electrically connected to the PWM controller24. Whether the first switching element Q1is either turned on or turned off is controlled by the PWM controller24according to the voltage value of the feedback voltage Vf. An example of the first switching element Q1includes but is not limited to a bipolar junction transistor (BJT), a junction field effect transistor (JFET) or a metal oxide semiconductor field effect transistor (MOSFET).

Please refer toFIG. 3again. The main power circuit21further includes a bridge rectifier211, an input capacitor Cin, an inductor L, a diode D and an output capacitor Co. An input end of the bridge rectifier211is electrically connected to the power source. An output end of the bridge rectifier211is electrically connected to the input capacitor Cinand the inductor L. The input voltage Vinis received by the bridge rectifier211and rectified into DC voltage. The ripple voltage contained in the DC voltage is smoothed by the input capacitor Cin. The first switching element Q1is electrically connected with the positive end of the diode D, the inductor L and the PWM controller24. The negative end of the diode D is electrically connected to the output terminal of the main power circuit21and the output capacitor Co. In response to an enabling signal (e.g. a high-level voltage) issued from the PWM controller24, the first switching element Q1is conducted such that electrical energy transmitted from the PWM controller24is stored in the inductor L. In response to an disenabling signal (e.g. a low-level voltage) issued from the PWM controller24, the first switching element Q1is shut off such that energy stored in the inductor L is transmitted to the input terminal of the DC-to-DC converting circuit22through the diode D. Under this circumstance, the first voltage Vbusoutputted from the main power circuit21is equal to the sum of the voltage across the inductor L and the magnitude of the input voltage Vin, so that the main power circuit21has a function of boosting the voltage value. In other words, a proper value of the first voltage Vbusis obtained by controlling the on-off time of the first switching element Q1by the PWM controller24.

Please refer toFIG. 3again. The detection circuit23includes a first feedback resistor Rf1, a second feedback resistor Rf2, a third feedback resistor Rf3, a photo coupler231, a first resistor R1, a second resistor R2, a third resistor R3, a second switching element Q2, a first capacitor C1and a digital signal processor (DSP)232. The first feedback resistor Rf1, the second feedback resistor Rf2and the third feedback resistor Rf3are connected in series. The first feedback resistor Rf1has an end coupled to the output terminal of the main power circuit21and the other end coupled to the second feedback resistor Rf2and the output terminal of the detection circuit23. The output terminal of the photo coupler231is connected in parallel with the third feedback resistor Rf3. The input terminal of the photo coupler231is coupled with the collector and the emitter of the second switching element Q2. The first resistor R1is coupled with a DC driving power source Vcc(e.g. 12V) and the collector of the second switching element Q2. The second resistor R2and the first capacitor C1are interconnected between the base and the emitter of the second switching element Q2. The third resistor R3is coupled with the base of the second switching element Q2and the DSP232. The DSP232is coupled with the output terminal of the DC-to-DC converting circuit22and the third resistor R3.

The operations of the detection circuit23will be illustrated in more details as follows. For operating the DC-to-DC converting circuit22at a high duty cycle D, the feedback ratio k of the detection circuit23is changed according to the first voltage Vbusoutputted from the main power circuit21and the voltage difference Vbbetween both terminals of the energy storage element20. In a case that the energy storage element20has low charge capacity, the voltage difference Vbbetween both terminals of the energy storage element20is relatively low. According to the relation formula Vb=Vbus×D×N, the voltage value of the first voltage Vbusshould be low enough to have the DC-to-DC converting circuit22operated at a first high duty cycle D. In other words, in order to maintain the duty cycle D of operating the DC-to-DC converting circuit22at a constant high level, the first voltage Vbusoutputted from the main power circuit21needs to be lowered and thus a relatively low second voltage Vbis obtained. Whereas, in another case that the energy storage element20has high charge capacity, the voltage difference Vbbetween both terminals of the energy storage element20is relatively high. According to the relation formula Vb=Vbus×D×N, the voltage value of the first voltage Vbusshould be high enough to have the DC-to-DC converting circuit22operated at a second high duty cycle D. In other words, in order to maintain the duty cycle D of operating the DC-to-DC converting circuit22at a constant high level, the first voltage Vbusoutputted from the main power circuit21needs to be raised and thus a relatively high second voltage Vbis obtained. In some embodiments, the first high duty cycle D when the voltage difference Vbis low and the second high duty cycle D when the voltage difference Vbis high can be identical or different. According to the characteristics of the DC-to-DC converting circuit22and the energy storage element20, the first high duty cycle D and the second high duty cycle D are variable so that the operating efficiency of the DC-to-DC converting circuit22is enhanced.

In a case that a low voltage difference Vbbetween both terminals of the energy storage element20is detected by the DSP232of the detection circuit23, the second switching element Q2is controlled by the DSP232to be shut off. Under this circumstance, the photo coupler231is enabled and the third feedback resistor Rf3is bypassed, so that a low feedback ratio k=Rf2/(Rf1+Rf2) is obtained. Whereas, in another case that a high voltage difference Vbbetween both terminals of the energy storage element20is detected by the DSP232of the detection circuit23, the second switching element Q2is controlled by the DSP232to be conducted. Under this circumstance, the photo coupler231is disenabled and the third feedback resistor Rf3is no longer bypassed, so that a high feedback ratio k=(Rf2+Rf3)/(Rf1+Rf2+Rf3) is obtained.

For example, if the energy storage element20has low charge capacity, the voltage difference Vbbetween both terminals of the energy storage element20is 0.9V; otherwise, if the energy storage element20has high charge capacity, the voltage difference Vbbetween both terminals of the energy storage element20is 1.4V. Provided that the turn ratio N is 0.005 and the duty cycle D is intended to be maintained at about 0.9, the first voltage Vbusto be received by the DC-to-DC converting circuit22is preferably adjusted to about 200V when the voltage difference Vbis low (i.e. 0.9V) or adjusted to about 311V when the voltage difference Vbis high (i.e. 1.4V). Therefore, the charging circuit can be maintained at a high operating efficiency.

Please refer toFIG. 3again. The PWM controller24further includes a comparator241. The feedback voltage Vfand a reference voltage Vrefare inputted into the comparator241. By comparing the feedback voltage Vfwith the reference voltage Vrefby the comparator241, the PWM controller24controls on/off statuses of the first switching element Q1of the main power circuit21. Since Vf=k×Vbus, the first voltage Vbusoutputted from the main power circuit21is changeable by adjusting the feedback ratio k. Since the first voltage Vbusreceived by the DC-to-DC converting circuit22is changed as the voltage difference Vbbetween both terminals of the energy storage element20, the DC-to-DC converting circuit22can be operated at a high operating efficiency. In this embodiment, a low feedback ratio k=Rf2/(Rf1+Rf2) is obtained when the voltage difference Vbbetween both terminals of the energy storage element20is low; and a high feedback ratio k=(Rf2+Rf3)/(Rf1+Rf2+Rf3) is obtained when the voltage difference Vbbetween both terminals of the energy storage element20is high.

Furthermore, the feedback ratio k of the detection circuit23can be diverse by calculation or using a lookup table, so that the DC-to-DC converting circuit22is maintained at a relatively higher duty cycle D and a high operating efficiency is achieved. For example, the voltage difference Vbbetween both terminals of the energy storage element20and the first voltage Vbusoutputted from the main power circuit21can be obtained by an analog-to-digital converter. The voltage difference Vband the first voltage Vbusare processed by the DSP232through calculation or a lookup table, thereby obtaining a suitable feedback ratio k. At this feedback ratio k, the DC-to-DC converting circuit22can be maintained at a relatively higher duty cycle D. Afterwards, a corresponding feedback voltage Vfis obtained by using a digital-to-analog converter.

FIG. 4is a schematic circuit block diagram of an uninterruptible power supply system having the high efficiency charging circuit of the present invention. The uninterruptible power supply system4ofFIG. 4principally includes an AC-to-DC converter41, a high efficiency charging circuit2, a battery module42, a boost circuit43, an inverter44, a system controller45, a changeover switch46, a power input terminal41a, a DC bus bar41b, a power output terminal46aand a bypass47. The operations of the uninterruptible power supply system4will be illustrated in more details as follows.

An input voltage Vin(or a first AC voltage) is inputted into the power input terminal41a. The AC-to-DC converter41is interconnected between the power input terminal41aand the DC bus bar41bfor converting the input voltage Vininto a DC voltage of a predetermined voltage level. The high efficiency charging circuit2provided by the present invention is interconnected between the power input terminal41aand the battery module42for converting the input voltage Vininto a DC voltage required for charging the battery module42. The boost circuit43is for example a boost DC-to-DC converter. The boost circuit43is interconnected between the battery module42and the DC bus bar41bfor converting the output voltage from the battery module42into a DC voltage to be received by the inverter44. The inverter44is interconnected between the DC bus bar41band the changeover switch46for converting the DC voltage from the DC bus bar41binto a stable second AC voltage V1. The changeover switch46is connected to the bypass47, the inverter44and the power output terminal46a. An example of the changeover switch46includes but is not limited to a silicon-controlled rectifier (SCR), a bidirectional triode thyristor (TRIAC) switch, an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET) or a relay. The bypass47is interconnected between the changeover switch46and the power input terminal41a. The system controller45is connected to the power input terminal41a, the AC-to-DC converter41, the high efficiency charging circuit2, the boost circuit43and the inverter44for controlling operations of the uninterruptible power supply system4.

When the input voltage Vinis normally provided, under control of the system controller45, the input voltage Vininputted into the AC-to-DC converter41is converted into a DC voltage of a predetermined voltage level, which is transmitted to the inverter44. Under control of the system controller45, the DC voltage is converted by the inverter44into the stable second AC voltage V1. Through the changeover switch46, the second AC voltage V1is provided to the load48, in which the second AC voltage V1outputted from the inverter44is equal to the load voltage Vout. At the same time when the input voltage Vinis normally provided, the input voltage Vinis converted by the high efficiency charging circuit2into a DC voltage required for charging the battery module42.

When the input voltage Vinis unavailable or deteriorated, under control of the system controller45, the electric power stored in the battery module42is converted by the boost circuit43into a DC voltage to be received by the inverter44. Under control of the system controller45, the DC voltage is converted by the inverter44into the second AC voltage V1. Through the changeover switch46, the second AC voltage V1is provided to the load48. As a consequence, the electric power for use in the load48is supplied by the battery module42. In some embodiments, the battery module42includes a plurality of batteries. As the number of batteries is increased, the power supplying time is extended.

Since the input voltage Vinis converted by the charging circuit2into a DC voltage required for charging the battery module42at a high operating efficiency when the input voltage Vinis normally provided, the overall operating efficiency of the uninterruptible power supply system is enhanced. In this embodiment, the high efficiency charging circuit2can be interconnected between the power input terminal41aand the battery module42.

Moreover, the high efficiency charging circuit of the present invention can be used in the power supply apparatuses for outputting adjustable voltages required for powering a variety of loads. Consequently, the operating efficiencies of these power supply apparatuses are enhanced.

From the above description, the charging circuit can charge the battery module at a high operating efficiency because the first voltage Vbusoutputted from the main power circuit21is adjusted according to voltage difference Vbbetween both terminals of the energy storage element20. Regardless of whether the output voltage of the high efficiency charging circuit (i.e. the voltage difference Vbbetween both terminals of the energy storage element20) is high or low, the DC-to-DC converting circuit22is maintained at a relatively higher duty cycle D and thus a high operating efficiency is achieved. Moreover, the high efficiency charging circuit of the present invention can be used in the power supply apparatus so that the power supply apparatus can output a regulated DC voltage at a high operating efficiency.