JP2007244088A - Power supply control circuit and power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To construct a semiconductor integrated circuit for power supply control of a low-withstand voltage device to reduce the power consumption of the circuit in a switching control AC-DC converter, and also to reduce the cost and the size of the converter. <P>SOLUTION: A power supply control circuit is provided with: a circuit (22) that shapes the waveform of an alternating-current signal obtained by dividing input alternating-current voltage by a resistor to generate a pulse signal synchronized with input and detects a rising edge or a falling edge of the pulse signal; and a ramp waveform generation circuit (21) that is triggered by a detection signal from the detection circuit and generates a waveform varying at a constant speed. The output of the waveform generation circuit and a feedback voltage of the output voltage are compared with each other with a comparator (24) to generate a phase-controlled PWM pulse, and a switching element (SW1) is driven based on this PWM pulse. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an AC-DC converter that converts an AC voltage into a DC voltage, and more particularly, a power supply control circuit that constitutes an AC-DC converter that performs AC-DC conversion by switching control, and a power supply device such as an AC adapter using the same. It is related to effective technology.

  As a power supply device that generates a desired DC power supply voltage using an AC voltage as an input voltage, for example, there is a power supply device such as an AC adapter that generates a DC voltage such as 5V by stepping down a commercial AC power supply such as AC100V. Since an AC-DC converter used in such a power supply apparatus uses a high voltage such as AC 100 V as an input voltage, when a switching control type converter is used as the AC-DC converter, a high breakdown voltage is applied to the elements constituting the control circuit. It is necessary to use an element.

  Conventionally, a control circuit in a switching control type AC-DC converter is composed of a high voltage IC or a discrete component. For this reason, there is a problem that the power consumption of the control circuit is large, thereby reducing the power efficiency of the power supply device, and it is difficult to reduce the cost and size.

  In addition, in the control in the switching power supply device, there is a drive system in which the pulse width of the drive signal of the switching element is changed by PWM control. However, a conventional drive circuit by PWM control is a circuit for generating a triangular wave or the like of a predetermined frequency. Since an oscillation circuit was required inside, the power consumption in the oscillation circuit was large.

  The present invention has been made paying attention to the above-described problems, and an object of the present invention is to make it possible to configure a power supply control semiconductor integrated circuit with low breakdown voltage elements in a switching control type AC-DC converter. Thus, the power consumption of the circuit is reduced, the cost is reduced, and the size of the apparatus is reduced.

  In order to achieve the above object, the present invention generates a pulse signal synchronized with an input by shaping an AC signal obtained by dividing an input AC voltage using a resistor, and detects a rising or falling edge of the pulse signal. And a ramp waveform generation circuit that generates a waveform that changes at a constant speed using the detection signal of the detection circuit as a trigger, and compares the output of the waveform generation circuit and the feedback voltage of the output voltage with a comparator to control the phase The generated PWM pulse is generated, and the switching element provided between the input terminal and the output terminal is driven based on the PWM pulse.

  Specifically, a synchronization pulse generation circuit that receives a voltage obtained by dividing the input AC voltage or the pulsating voltage and generates a synchronization pulse synchronized with the input AC voltage, and a rising edge of the synchronization pulse generated by the synchronization pulse generation circuit Alternatively, a waveform generation circuit that generates a waveform having a predetermined slope in synchronization with the falling edge, an error amplification circuit that receives a voltage obtained by dividing the output DC voltage, and outputs a voltage corresponding to a potential difference from the predetermined voltage, A power supply control circuit is constituted by a comparator that compares the output of the error amplifier circuit with the output of the waveform generation circuit to generate and output a control pulse.

  According to the configuration as described above, the control circuit can be configured with low-breakdown-voltage elements, and an oscillation circuit is not necessary, so that power consumption of the circuit can be reduced. Further, when the power supply control circuit is formed as a semiconductor integrated circuit, the chip size can be reduced, so that the cost and the size of the device can be reduced.

  In this case, it is preferable that an edge detection circuit for detecting a rising edge or a falling edge of the synchronization pulse is provided, and the waveform generation circuit generates a ramp waveform having a predetermined slope by using an output signal of the edge detection circuit as an activation signal. Configure. Thereby, the generation of the ramp waveform by the waveform generation circuit can be started reliably and accurately.

  The waveform generation circuit, the error amplification circuit, and the comparator are formed as a semiconductor integrated circuit on one semiconductor chip, and the synchronization pulse generated by the synchronization pulse generation circuit is waveformd on the semiconductor chip. A waveform shaping circuit which is shaped and supplied to the edge detection circuit is provided. This makes it possible to reliably detect the rising edge or falling edge of the synchronization pulse.

  Further, the waveform generating circuit includes a capacitive element, a switch transistor that rapidly charges the capacitive element, and a constant current source that discharges the capacitive element at a predetermined rate. The capacitive element is connected as an external element of the semiconductor integrated circuit. As a result, a circuit that generates a ramp waveform with a relatively simple circuit can be realized, and the chip size can be reduced.

  Another invention of the present application includes a power supply control circuit configured as described above, a switching element connected between an input terminal to which an input AC voltage or a pulsating voltage is applied, and an output terminal, and the output terminal A smoothing capacitor connected between the input terminal and the constant potential point; a first resistance voltage dividing circuit that divides the voltage applied to the input terminal; and a second resistance voltage dividing circuit that divides the voltage of the output terminal. The voltage divided by the first resistance voltage dividing circuit is input to the synchronization pulse generating circuit, the voltage divided by the second resistance voltage dividing circuit is input to the error amplification circuit, and the power supply control The power supply device is configured to drive the switching element based on the control pulse generated by a circuit. By configuring the power supply control circuit as a semiconductor integrated circuit composed of low-breakdown-voltage elements, it is possible to realize a small-sized and low-cost power supply apparatus capable of PWM driving by phase control.

  Here, preferably, a silicon controlled rectifier is used as the switching element. By using the silicon control rectifier, it is not necessary to consider the timing of turning off the silicon control rectifier in the generation of the control pulse, the power supply control circuit can be simplified, and the chip size can be reduced.

  Furthermore, preferably, a rectifier circuit that full-wave rectifies the input AC voltage is provided, and a pulsating voltage rectified by the rectifier circuit is applied to the input terminal. As a result, it is possible to obtain a power supply apparatus that directly uses a commercial AC power supply as an input voltage.

  Further, a DC-DC converter connected to the output terminal and converting the DC voltage of the output terminal into a DC voltage of a different potential is provided. Thereby, even if the output voltage of the AC-DC converter in the previous stage is an unstable voltage having ripples, a power supply device that generates a stable DC voltage can be obtained.

  As described above, according to the present invention, in a switching control type AC-DC converter, a power-control semiconductor integrated circuit circuit can be configured with low-breakdown-voltage elements, reducing the power consumption of the circuit and reducing the cost. There is an effect that the apparatus can be miniaturized.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of an AC-DC converter to which the present invention is applied.

  The AC-DC converter of this embodiment is connected between an input terminal IN to which an AC voltage Vin such as AC100V is input and an output terminal OUT from which a DC voltage Vout such as 10V subjected to AC-DC conversion is output. Switching element SW1, the smoothing capacitor C1 connected between the output terminal OUT and the ground point, resistors R1 and R2 that divide the input AC voltage Vin, and the waveform of the divided AC voltage. A pulse generation circuit 10 that generates a synchronizing pulse SP synchronized with the AC voltage Vin, resistors R3 and R4 that divide the output DC voltage Vout to generate a feedback voltage VFB, the divided DC voltage VFB and the pulse generation circuit From a control circuit 20 that generates a control signal for turning on and off the switching element SW1 based on the synchronization pulse SP from It is configured.

  In this embodiment, the switching element SW1 is not particularly limited, but a thyristor (silicon controlled rectifier) is used. This thyristor is an element that, once turned on by a control signal from the control circuit 20, continues to flow until the input AC voltage Vin becomes a predetermined voltage or less. The control circuit 20 constituting the AC-DC converter is configured as a semiconductor integrated circuit (IC) on a semiconductor chip, and discrete components and elements are used for the switching element SW1, the smoothing capacitor C1, and the resistors R1 to R4. It has been. The pulse generation circuit 10 may be an IC or a circuit configured on a printed circuit board by discrete components and elements.

  FIG. 2 shows a specific circuit example of the control circuit 20 constituting the AC-DC converter of FIG.

  The control circuit 20 of this embodiment includes, as external terminals, a power supply terminal P1 that receives a power supply voltage VDD such as 5 V, an input terminal P2 that receives the synchronization pulse SP generated by the pulse generation circuit 10, and the resistors R3 and R3. An input terminal P3 to which a feedback voltage VFB generated by dividing the output DC voltage Vout by R4 is input, an output terminal P4 for outputting a PWM control pulse Ppwm generated by the control circuit 20, and an external capacitor C2 A terminal P5 to be connected and a ground terminal (not shown) to which a ground potential is applied are provided.

  The control circuit 20 includes an external waveform C2 connected to the external terminal P5 and a constant current source CS as an internal circuit, and a ramp waveform generation circuit 21 that forms a waveform having a predetermined slope, and the pulse A start signal generation circuit 22 that generates a start signal of the ramp waveform generation circuit 21 based on the synchronization pulse SP input from the generation circuit 10 to the input terminal P2, and a feedback voltage VFB input to the input terminal P3. An error amplifying circuit 23 that outputs a voltage, a PWM comparator 24 that generates a PWM control pulse by comparing the output of the error amplifying circuit 23 and the output of the ramp waveform generating circuit 21, and the output of the comparator 24 is inverted. The inverter 25 etc. which shape-shape and output to the terminal P4 are provided.

  The activation signal generation circuit 22 compares the synchronization pulse SP input to the input terminal P2 with a predetermined reference voltage Vref3, thereby generating a comparator CMP1 that generates a pulse whose waveform is shaped so that the rising and falling edges are steep. The circuit includes an NAND gate G1, G2, a capacitor C0, a resistor R0, and the like, and an edge detection circuit EDC that detects the rising of the output of the comparator CMP1, an output inverter G3, and the like. The edge detection circuit EDC is a kind of differentiation circuit, and outputs a one-shot pulse synchronized with the rising edge of the output of the comparator CMP1.

  Specifically, the output of the comparator CMP1 is used as one input of the NAND gate G1, and the capacitance C0 and the NAND gate G2 connected between the output terminal of the NAND gate G1 and the first input terminal of the NAND gate G2 are connected. The output of the NAND gate G1 is differentiated by a differentiating circuit including a resistor R0 connected between the first input terminal and the power supply voltage terminal VDD, and this is input to the NAND gate G2. The NAND gate G2 has a second input terminal connected to the ground point, and functions as an inverter. The output of the NAND gate G2 is fed back to the second input terminal of the first-stage NAND gate G1.

  In addition to the constant current source CS, the ramp waveform generation circuit 21 includes a switch MOSFET M1 that rapidly charges the external capacitor C2 with the output of the output inverter G3. The error amplifying circuit 23 also outputs resistors R7 and R8 that divide the feedback voltage VFB, and a differential amplifier AMP1 that outputs a voltage proportional to the potential difference between the voltage divided by the resistors R7 and R8 and a predetermined reference voltage Vref2. With.

  Next, the operation of the control circuit 20 of FIG. 2 will be described using the time chart of FIG.

  The pulse generation circuit 10 generates a synchronization pulse SP synchronized with the input AC voltage Vin as shown in FIG. 3B based on the voltage divided by the resistors R1 and R2. The synchronization pulse SP is compared with the reference voltage Vref3 by the comparator CMP1, thereby generating a rectangular pulse having a waveform as shown in FIG. The falling edge of the rectangular pulse is detected by a differentiating circuit composed of a capacitor C0 and a resistor R0, and a whisker-like signal as shown in FIG. 3E is generated.

  The whisker of this signal has a very narrow temporal width, and it is not possible to sufficiently charge the external capacitor C2 by turning on the switch MOSFET M2 in the subsequent stage, so that the output of the NAND gate G2 is used as the NAND gate in the first stage. By feeding back to G1, a one-shot pulse Vd having a desired pulse width as shown in FIG. 3F is generated. The switch MOSFET M1 is turned on by this one-shot pulse Vd, the external capacitor C2 is rapidly charged to a predetermined level, and then the charge of the capacitor C2 is discharged by the current I2 of the constant current source CS.

  At this time, by setting the current I2 and the capacitor C2 of the constant current source CS to appropriate values, the potential Vn1 of the node N1 connected to the external terminal P4 rises with a predetermined slope as shown in FIG. To be lowered. The potential Vn1 and the output of the error amplifier circuit 23 are compared by the PWM comparator 24, whereby a pulse Vp as shown in FIG. 3 (H) is generated, inverted by the inverter 25, and output as a PWM pulse Ppwm. 1 is turned on by the PWM pulse Ppwm, and the smoothing capacitor C1 is charged.

  In the control circuit of this embodiment, the PWM pulse Ppwm is generated based on the synchronization pulse SP synchronized with the input AC voltage Vin as described above. Therefore, if the output of the error amplification circuit 23 is constant, the PWM pulse Ppwm Of the input AC voltage Vin is always controlled to be earlier than the zero cross point of the input AC voltage Vin by a predetermined phase. When the feedback voltage VFB proportional to the output voltage Vout changes according to the output voltage, the pulse width of the PWM pulse Ppwm is changed and the on-time of the switching element SW1 is changed, so that the output voltage Vout is controlled to be constant. The

  Specifically, when the output voltage Vout decreases, the output Ve of the error amplifying circuit 23 indicated by a broken line in FIG. 3G decreases, so that the rising timing of the pulse Vp in FIG. The pulse width of this portion is widened, whereby the on-time of the switching element SW1 is lengthened and the output voltage Vout is increased. On the other hand, when the output voltage Vout increases, the output Ve of the error amplifying circuit 23 shown by the broken line in FIG. 3G increases, so that the rising timing of the pulse Vp in FIG. The pulse width is narrowed, whereby the ON time of the switching element SW1 is shortened and the output voltage Vout is lowered.

  As is well known, since a commercial AC power supply (50 Hz or 60 Hz) has a relatively low cycle accuracy, when a PWM pulse is generated using an oscillation signal with a high frequency accuracy generated by a circuit such as an oscillation circuit, an input AC voltage is generated. Due to the phase shift from Vin, the timing at which the switching element SW1 is turned on with respect to Vin shifts, causing the output voltage Vout to fluctuate. According to the control circuit of this embodiment, the PWM pulse Ppwm is generated based on the synchronization pulse SP synchronized with the input AC voltage Vin, so that the ON timing of the switching element SW1 with respect to Vin can be stabilized, and the input AC It is possible to stabilize the operation of the control circuit against a phase shift from the voltage Vin and fluctuations in the cycle, and to reduce fluctuations in the output voltage Vout.

  If the switching element SW1 can be turned on / off at the power supply voltage VDD of 5 V of the control circuit 20 of this embodiment, the switching element SW1 can be directly controlled by the output of the control circuit. However, when the switching element SW1 is formed of a thyristor as in this embodiment, a voltage higher than 5 V is required to turn on and off the switching element SW1, so that the output of the inverter 25 is connected to a driver circuit (illustrated). The switching element SW1 is driven by the output of the driver circuit.

  The switching element SW1 can be a bipolar transistor or MOSFET instead of a thyristor. However, since the thyristor is automatically turned off when the input AC voltage Vin falls below a predetermined voltage, the switching element SW1 shown in FIG. Such a pulse Vp (/ Ppwm) in which only the rising timing is controlled can be used. On the other hand, when a bipolar transistor or MOSFET is used as the switching element SW1, the switching element is turned off by lowering the pulse Vp (/ Ppwm) before the input AC voltage Vin reaches a predetermined potential (eg, 0 V). Therefore, the control circuit shown in FIG. 2 needs to be slightly changed accordingly.

  FIG. 4 shows another embodiment of the AC-DC converter to which the present invention is applied.

  In this embodiment, a rectifier circuit D1 for full-wave rectification of an input AC voltage Vin is provided on the input side of the converter of the embodiment of FIG. 1, and a DC-DC converter 30 including a switching regulator is provided on the output side. It is. The output voltage of the AC-DC converter of FIG. 1 has a ripple due to fluctuations in the AC power supply, so it is difficult to obtain a stable DC voltage. However, by providing a DC-DC converter 30 in the subsequent stage, the converter 1 A stable DC voltage can be output as compared with a power supply device having only one stage.

  Here, as the DC-DC converter 30 at the subsequent stage, it is desirable to use a step-down switching regulator using a transformer. As a power supply device that generates a DC voltage of 1/10 or less such as 2.5 to 9V from an AC power supply such as 100V, two stages of converters are connected as in this embodiment, and the preceding stage is as in the above embodiment. By using a simple non-insulated AC-DC converter, it is possible to step down to 10V at a stroke, and an insulating switching regulator is provided in the subsequent stage to further reduce the voltage, thereby realizing a very power efficient power supply device can do.

  In the present embodiment, the voltage input to the pulse generation circuit 10 is a pulsating voltage unlike FIG. 1, but a pulse as shown in FIG. 3B is generated and output every other pulsating flow. By configuring the pulse generation circuit 10 to the above, the control circuit (IC) 20 shown in FIG. 2 can be used as it is. In the converter of FIG. 1, a synchronization pulse having a frequency twice that of the synchronization pulse SP input from the pulse generation circuit 10 to the control circuit 20 is generated by the pulse generation circuit 10 and input to the control circuit 20. Good. Even in such a case, a circuit having the same configuration as that shown in FIG. 2 can be used as the control circuit (IC) 20.

  Although the preferred embodiments of the invention made by the present inventors have been described above, various modifications can be made by those skilled in the art without departing from the gist of the present invention. For example, in the above-described embodiment, the pulse generation circuit 10 is configured as an IC separate from the control circuit 20, but may be formed on the same semiconductor chip. In the embodiment, a MOSFET is used as a transistor constituting the circuit. However, a bipolar transistor may be used.

  Further, in the above embodiment, the ramp waveform generating circuit 21 is constituted by the constant current source CS, the external capacitor C2, and the switch MOSFET M1, but has a predetermined slope by charging the external capacitor with the constant current source. A circuit such as an integration circuit for forming a waveform may be used.

  In the embodiment, in addition to the resistors R1 and R2 that divide the output voltage Vout to generate the feedback voltage VFB, the resistor R7 that further divides VFB into the chip of the control circuit 20 and inputs it to the error amplifier 23. , R8 may be provided, but the resistors R7, R8 may be omitted and the voltage divided by the external resistors R1, R2 may be input to the error amplifier 23. Further, the reference voltages Vref3 and Vref2 input to the comparator CMP1 and the error amplifier 23 may be generated by providing a reference voltage circuit inside the chip, but may be configured to be supplied from the outside of the chip.

  Although the example which applied this invention to the AC-DC converter was demonstrated in the above description, this invention is not limited to it, It can utilize also for a DC-DC converter.

FIG. 1 is a block diagram showing an embodiment of an AC-DC converter to which the present invention is applied. FIG. 2 is a block diagram showing an example of a specific circuit of the control circuit constituting the AC-DC converter of the embodiment. FIG. 3 is a time chart showing changes in signals and potentials at various parts of the AC-DC converter and control circuit of the embodiment. FIG. 4 is a block diagram showing another embodiment of the AC-DC converter to which the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pulse generation circuit 20 Control circuit 21 Ramp waveform generation circuit 22 Startup signal generation circuit 23 Error amplification circuit 24 PWM comparator SW1 Switching element (thyristor, silicon control rectifier)
C1 smoothing capacity

Claims (9)

  A synchronization pulse generation circuit that receives a voltage obtained by dividing the input AC voltage or pulsating voltage and generates a synchronization pulse synchronized with the input AC voltage, and is synchronized with the rising or falling edge of the synchronization pulse generated by the synchronization pulse generation circuit A waveform generation circuit that generates a waveform having a predetermined slope, an error amplification circuit that receives a voltage obtained by dividing the output DC voltage and outputs a voltage corresponding to a potential difference from the predetermined voltage, and the error amplification circuit A power supply control circuit comprising: a comparator that compares an output with an output of the waveform generation circuit to generate and output a control pulse.   An edge detection circuit for detecting a rising edge or a falling edge of the synchronization pulse, and the waveform generation circuit is configured to generate a waveform having a predetermined slope using an output signal of the edge detection circuit as an activation signal. The power supply control circuit according to claim 1, wherein:   The waveform generation circuit, the error amplification circuit, and the comparator are formed as a semiconductor integrated circuit on one semiconductor chip, and the semiconductor chip shapes the synchronization pulse generated by the synchronization pulse generation circuit. The power supply control circuit according to claim 2, further comprising a waveform shaping circuit that supplies the edge detection circuit.   The waveform generation circuit includes a capacitive element, a switch transistor that rapidly charges the capacitive element, and a constant current source that discharges the capacitive element at a predetermined speed, and the switch transistor is an output of the edge detection circuit. The power supply control circuit according to claim 3, wherein the power supply control circuit is configured to be turned on and off by a signal.   The power supply control circuit according to claim 4, wherein the capacitive element is connected as an external element of the semiconductor integrated circuit.   The power supply control circuit according to any one of claims 1 to 5, a switching element connected between an input terminal and an output terminal to which an AC voltage or a pulsating voltage is applied to an input, the output terminal and a constant potential A smoothing capacitor connected to a point; a first resistance voltage dividing circuit that divides the voltage applied to the input terminal; and a second resistance voltage dividing circuit that divides the voltage of the output terminal. The voltage divided by the first resistance voltage dividing circuit is input to the synchronization pulse generating circuit, the voltage divided by the second resistance voltage dividing circuit is input to the error amplification circuit, and the power supply control circuit A power supply apparatus configured to drive the switching element based on the generated control pulse.   The power supply apparatus according to claim 6, wherein the switching element is a silicon controlled rectifier.   8. The power supply device according to claim 6, further comprising a rectifier circuit that performs full-wave rectification of the input AC voltage, and a pulsating voltage rectified by the rectifier circuit is applied to the input terminal. The power supply apparatus according to claim 6, further comprising a DC-DC converter connected to the output terminal and converting a DC voltage of the output terminal into a DC voltage having a different potential.

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