JP2005124248A - Switching power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply circuit outputting positive and negative power supply voltages individually and stably to a load. <P>SOLUTION: The switching power supply circuit comprises an energy storage section 1 connected in parallel with the negative electrode side output terminal and the positive electrode side output terminal of an input power supply PW through a first switch SW1 and a second switch SW2, respectively, and outputting stored energy with negative voltage by turning only the first switch SW1 on and outputting stored energy with positive voltage by turning only the second switch SW2 on, and a timing pulse generating section 4 for turning the first and second switches SW1 and SW2 on/off such that the energy storage section 1 repeats storage of energy and output of stored energy with positive voltage, and storage of energy and output of stored energy with negative voltage alternately. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a switching power supply circuit capable of generating and outputting positive and negative voltages from a single power supply voltage.

  Conventionally, electronic devices such as audio devices may require positive and negative power supply voltages in addition to a single power supply voltage in order to ensure a sufficient dynamic range and high sound quality. In general, a so-called step-up type switching power supply circuit and an inverting type switching power supply circuit are respectively used as circuits for outputting a positive voltage and a negative voltage. However, in this configuration, since it is necessary to provide switching power supply circuits for positive voltage and negative voltage, respectively, it is necessary to provide a plurality of inductances, switching elements or their peripheral circuits that are normally used in a boost type switching power supply circuit. There is a problem that the cost becomes high.

Therefore, as shown in Patent Document 1, a switching power supply circuit that can output a positive voltage and a negative voltage using a common inductance has been proposed.
JP-A-10-84672

  The configuration of the switching power supply circuit will be briefly described. As shown in FIG. 6, the switching power supply circuit includes a switching element 21 connected in series between an input power supply terminal 20 to which a DC voltage Vin is input and a ground. And the choke coil 22, the control circuit 23 for controlling on / off of the switching element 21, the coupling capacitor 24 connected to the midpoint (point A) of the switching element 21 and the choke coil 22, the output of the coupling capacitor 24 and the positive electrode A coil 26 interposed between the terminals 25, a diode 27 connected between the connection point of the coupling capacitor 24 and the coil 26 and the ground, a capacitor 28 connected between the output terminal 25 and the ground, A diode 30 interposed between the point (point A) and the negative output terminal 29, and an output terminal 9 and a smoothing capacitor 31 connected between the ground, is schematically constituted by parallel-connected resistor 32 to the smoothing capacitor 31,.

  The coupling capacitor 24 to the smoothing capacitor 28 are circuits for outputting the DC energy accumulated in the choke coil 22 from the output terminal 25 with a positive voltage, and the diode 30 and the smoothing capacitor 31 represent the DC energy accumulated in the choke coil 22. This is a circuit for outputting a negative voltage from the output terminal 29. The resistor 32 is a circuit that detects the output voltage of the output terminal 29 and inputs it to the control circuit 23. The control circuit 23 performs on / off control of the switching element 21 based on the detected value of the output voltage at the output terminal 29.

  According to this configuration, when the switching element 21 is turned on, the DC voltage Vin input from the input power supply terminal 20 is applied to the choke coil 22, and DC energy is accumulated in the choke coil 22 during the ON period of the switching element 21. When the switching element 21 is turned off, the energy supply to the choke coil 22 is cut off, and the direct current energy accumulated in the choke coil 22 during the off period of the switching element 21 is positively composed of the coupling capacitor 24 to the capacitor 28. The voltage output circuit and the negative voltage output circuit composed of the diode 30 and the smoothing capacitor 31 are discharged.

  In the negative voltage output circuit, when the switching element 21 is in the OFF state, a voltage is generated in the choke coil 22 so that the point A is lower than the ground level, and the diode 30 becomes conductive. The energy stored in 22 is discharged to the smoothing capacitor 31, and the smoothing capacitor 31 is charged so that the side connected to the output terminal 29 has a negative potential. On the other hand, when the switching element 21 is in the ON state, a voltage is generated in the choke coil 22 so that the point A is higher than the ground level, and the diode 30 becomes non-conductive. Is discharged to the output terminal 29. Hereinafter, charging and discharging of the smoothing capacitor 31 are repeated each time the switching element 21 is repeatedly turned on and off. However, since the potential connected to the output terminal 29 of the smoothing capacitor 31 is held at a negative potential, the negative electrode From the output terminal 29, a negative voltage generated at point A is smoothed by the smoothing capacitor 31 and output.

  In the positive voltage output circuit, when the switching element 21 is in the off state, the point A becomes a potential lower than the ground level, and the diode 27 becomes conductive, so that the energy accumulated in the choke coil 22 is coupled to the coupling capacitor 24. The coupling capacitor 24 is charged such that the side connected to the choke coil 26 has a positive potential. On the other hand, when the switching element 21 is in the ON state, the point A becomes a potential higher than the ground level, so that the plus potential on the side of the coupling capacitor 24 connected to the choke coil 26 becomes a higher potential (that is, at the point A). The positive voltage is boosted), and the electric charge accumulated in the coupling capacitor 24 in this potential state is discharged by the series circuit of the choke coil 26 and the smoothing capacitor 28. Hereinafter, every time the switching element 21 is repeatedly turned on and off, the coupling capacitor 24 is repeatedly charged and discharged. However, since the potential of the coupling capacitor 24 connected to the choke coil 26 is maintained at a positive potential, From the output terminal 27, the positive voltage generated at point A is boosted by the coupling capacitor 24, and the boosted positive voltage is smoothed and output by a low-pass filter comprising a coil 26 and a capacitor 28.

  However, in the switching power supply circuit shown in FIG. 6, a positive voltage output circuit and a negative voltage output circuit are connected in parallel to the choke coil 22, and the DC energy to the choke coil 22 is controlled by turning on and off the switching element 21. Since the positive voltage output circuit and the negative voltage output circuit generate a positive voltage and a negative voltage at the same time during each energy release period when accumulation and discharge are repeated, the positive and negative voltages are respectively There is a drawback that it cannot be individually controlled. For this reason, when the positive and negative voltages cause fluctuations due to the load, these fluctuations cannot be suppressed individually. In particular, since the resistor 32 is configured to perform on / off control of the switching element 21 based on the detected value of the negative side output voltage, when output control is performed with respect to load fluctuation on the negative voltage side, the control contents This also affects the output voltage on the positive side, and the output value of the positive voltage fluctuates unnecessarily.

  The present invention has been conceived under the circumstances described above, and provides a switching power supply circuit capable of individually and stably outputting positive and negative power supply voltages to a load. Let it be an issue.

  In order to solve the above problems, the present invention takes the following technical means.

  The switching power supply circuit provided by the present invention generates a positive voltage power source and a negative voltage power source from a DC power source, and outputs two outputs, a positive voltage output from the positive voltage power source and a negative voltage output from the negative voltage power source. A switching power supply circuit that outputs from each end, and is connected in parallel to the negative-side output terminal and the positive-side output terminal of the DC power supply via first switch means and second switch means, respectively, Energy supplied from the DC power source is stored by turning on the first and second switch means, and energy stored by turning on only the first switch means is stored in the second state. A negative voltage is output from the connection point with the switch means, and the energy stored by turning on only the second switch means is transferred to the first switch means. An energy storage means for outputting a positive voltage from a connection point; a first smoothing provided between the first switch means and the positive voltage output terminal for smoothing the positive voltage output from the energy storage means Means, a second smoothing means provided between the second switch means and the negative voltage output terminal for smoothing the negative voltage output from the energy storage means, and output from the two output terminals On / off switching control signal is generated based on the positive voltage and the negative voltage that are generated, and based on this control signal, the energy storage means stores energy and the positive voltage output of the stored energy and energy storage and Control means for controlling on / off switching of the first and second switch means so as to alternately repeat the negative voltage output of the stored energy. There.

  As a preferred embodiment of the present invention, the energy storage means may be constituted by a choke coil, and the first and second smoothing means may be constituted by a capacitor. Further, the control means compares a first signal having a first output voltage waveform based on a differential voltage between a positive voltage and a negative voltage output from the two output terminals with a predetermined reference wave signal. And a second signal having a second output voltage waveform based on a difference voltage between a positive voltage and a negative voltage output from the two output terminals. And a second pulse signal generating means for generating a second pulse signal by comparing the reference wave signal with the first pulse signal generated by the first pulse signal generating means. The on / off switching of the first switch means may be controlled, and the on / off switching of the second switch means may be controlled by the second pulse signal generated by the second pulse signal generating means. .

  According to the present invention, when the first and second switch means are turned on, the energy supplied from the DC power supply is stored in the energy storage means. Further, when the first switch means is in the off state and the second switch means is in the on state, the energy stored in the energy storage means is released to the first smoothing means with a positive voltage from the connection point with the first switch means. When the first switch means is on and the second switch means is off, the energy stored in the energy storage means is released to the second smoothing means as a negative voltage from the connection point with the second switch means. Is done. The positive voltage is smoothed by the first smoothing means and output from the positive voltage output terminal, and the negative voltage is smoothed by the second smoothing means and output from the negative voltage output terminal.

  The first and second switch means are configured so that the energy storage means alternately repeats the storage of energy and the positive voltage output of the stored energy and the storage of energy and the negative voltage output of the stored energy by the control means, that is, On / off control is performed so that the on / off states of the first and second switch means are switched in the order of (on, on), (off, on), (on, on), (on, off). Therefore, since the positive voltage output and the negative voltage output are alternately repeated, the positive voltage and the negative voltage are substantially output at the same time. The on / off switching control signals of the first and second switch means are generated based on the positive voltage and the negative voltage output from the two output terminals, so that the load on the positive voltage output terminal side or Even when the output voltage at each output end fluctuates due to fluctuations in the load on the negative voltage output end side, control signals for the first and second switch means can be generated exceptionally according to each fluctuation, thereby Positive voltage output and negative voltage output can be controlled independently.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the accompanying drawings.

  FIG. 1 is a block diagram of a switching power supply circuit according to the present invention. This switching power supply circuit stabilizes the positive and negative power supply voltages individually when outputting positive and negative power supply voltages to the load by controlling on / off of the input power supply PW at a predetermined timing. Output.

  The switching power supply circuit includes an energy storage unit 1 that stores energy supplied from an input power source PW, a positive power supply smoothing unit 2 that smoothes a positive power supply voltage based on energy released from the energy storage unit 1, and an energy A negative power source smoothing unit 3 that smoothes a negative power source voltage based on energy released from the storage unit 1, and first to fourth switches SW1, SW2, and SW3 for storing and releasing energy in the energy storage unit 1 , SW4, and a timing pulse generator 4 that controls on / off of the first and second switches SW1, SW2 at a predetermined timing. Note that one of the third and fourth switches SW3 and SW4 is turned on according to the potential of the output voltage when the stored energy is released from the energy storage unit 1. More specifically, the third switch SW3 is turned on when the output voltage of the energy storage unit 1 is a positive voltage, and the fourth switch SW4 is turned on when the output voltage of the energy storage unit 1 is a negative voltage.

  The energy storage unit 1 is configured by an inductance, for example, and is connected to the input power source PW when the first and second switches SW1 and SW2 are in an on state. The energy storage unit 1 is connected to the input power source PW, is supplied with energy from the input power source PW, and stores the supplied energy while the first and second switches SW1 and SW2 are in the ON state. Further, when only the second switch SW2 is turned on after the energy is stored, the energy storage unit 1 releases the stored energy to the positive power supply smoothing unit 2 with a positive voltage. Furthermore, when only the first switch SW1 is turned on after the energy is stored, the energy storage unit 1 releases the stored energy to the negative power supply smoothing unit 3 with a negative voltage.

  The third and fourth switches SW3 and SW4 are made of diodes, for example. The diode of the third switch SW3 is connected so that the anode terminal is on the first switch SW1 side, and the diode of the fourth switch SW4 is connected so that the cathode terminal is on the second switch SW2 side. When only the second switch SW2 is turned on and a positive voltage is output from the energy storage unit 1, the third switch SW3 is turned on and the energy stored in the energy storage unit 1 is released to the positive power supply smoothing unit 2. . When only the first switch SW1 is turned on and a negative voltage is output from the energy storage unit 1, the fourth switch SW4 is turned on and the energy stored in the energy storage unit 1 is released to the negative power source smoothing unit 2. Is done.

  The positive power supply smoothing unit 2 and the negative power supply smoothing unit 3 are constituted by, for example, a smoothing capacitor. When a positive voltage is output from the energy storage unit 1, the positive power supply smoothing unit 2 smoothes the positive voltage with a smoothing capacitor, and outputs a positive power supply voltage output terminal OUT1 (hereinafter, “positive power supply output terminal OUT1”). Output from.

  Similarly to the positive power supply smoothing unit 2, the negative power supply smoothing unit 3 smoothes the negative voltage with a smoothing capacitor when a negative voltage is output from the energy storage unit 1, and outputs the negative power supply voltage output terminal OUT2 (hereinafter referred to as the negative power supply voltage output terminal OUT2). , “Output terminal OUT2 of negative power supply”).

  The timing pulse generation unit 4 simultaneously turns on the first and second switches SW1 and SW2 when the energy storage unit 1 stores energy. The timing pulse generation unit 4 stores only energy in the energy storage unit 1 and then turns off only the first switch SW1 when releasing energy through the positive power supply smoothing unit 2. The timing pulse generator 4 turns off only the second switch SW2 when energy is stored in the energy storage unit 1 and then released through the negative power supply smoothing unit 3.

  The timing pulse generator 4 is connected to the output terminal OUT1 of the positive power supply and the output terminal OUT2 of the negative power supply, respectively, and uses the positive voltage and the negative voltage output from both the output terminals OUT1 and OUT2. The control signal (timing pulse signal) is generated so that the ON / OFF relationship of the second switches SW1 and SW2 is the above-described relationship. In addition, when the output positive power supply voltage and negative power supply voltage fluctuate due to the influence of a load (not shown), the timing pulse generator 4 outputs them from the positive power supply output terminal OUT1 and the negative power supply output terminal OUT2. The amount of energy stored in the energy storage unit 1 is controlled by controlling the ON operation period of the first and second switches SW1 and SW2 so that the positive power supply voltage and the negative power supply voltage become substantially constant voltages by feedback. adjust.

  For example, when the power supply voltage at the output terminal OUT1 of the positive power supply decreases, the ON operation period of the first and second switches SW1 and SW2 for storing the energy released to the positive power supply smoothing section 2 in the energy storage section 1 is lengthened. Then, the energy stored in the energy storage unit 1 is increased. Then, if the timing pulse generator 4 subsequently turns off only the first switch SW1 to release the energy stored in the energy storage unit 1, the power supply voltage at the output terminal OUT1 of the positive power supply increases. The power supply voltage at the output terminal OUT1 can be kept substantially constant.

  FIG. 2 is a timing chart showing the relationship between the operation of the first to fourth switches SW1, SW2, SW3, SW4, the energy storage / release operation of the energy storage unit 1, and the output voltage of the output terminals OUT1, OUT2. According to the figure, the timing pulse generator 4 connects the input power source PW and the energy storage unit 1 by turning on the first and second switches SW1 and SW2 (see period T1). Thereby, the energy supplied from the input power source PW is stored in the energy storage unit 1.

  Next, the timing pulse generator 4 turns off only the first switch SW1 (see period T2). Thereby, the connection end of the energy storage unit 1 with the first switch SW1 becomes a positive voltage, the third switch SW3 is turned on, and the stored energy is released to the positive power supply smoothing unit 2. The positive voltage input to the positive power supply smoothing unit 2 is smoothed and output from the output terminal OUT1 of the positive power supply. Therefore, the energy accumulated in the period T1 is output as a positive voltage from the output terminal OUT1 of the positive power source.

  Next, the timing pulse generation unit 4 connects the input power source PW and the energy storage unit 1 by turning on the first switch SW1 again (see period T3), and stores energy in the energy storage unit 1.

  Next, the timing pulse generator 4 turns off only the second switch SW2 (see period T4). Thereby, the connection end of the energy storage unit 1 with the second switch SW2 becomes a negative voltage, the fourth switch SW4 is turned on, and the stored energy is released to the negative power source smoothing unit 3. The negative voltage input to the negative power supply smoothing unit 3 is smoothed and output from the output terminal OUT2 of the negative power supply. Therefore, the energy accumulated in the period T3 is output as a negative voltage from the output terminal OUT2 of the negative power source. Thereafter, the same switching control is repeatedly performed with the above switching control as one cycle.

  In this case, the ON / OFF control of the first and second switches SW1 and SW2 by the timing pulse generator 4 is performed by feeding back voltage fluctuations at the output terminal OUT1 of the positive power supply and the output terminal OUT2 of the negative power supply. For example, when there is a voltage fluctuation at the output terminal OUT1 of the positive power source, the timing pulse generator 4 is a period during which both the first and second switches SW1 and SW2 are on (energy storage time of the energy storage unit 1). Adjust. As a result, the energy storage time changes, the amount of energy increases or decreases, and the amount of energy released increases or decreases accordingly, which is fed back to the output terminal OUT1 of the positive power supply and is output at the output terminal OUT1 of the positive power supply. Voltage fluctuation can be suppressed.

  In this way, voltage fluctuations at the output terminal OUT1 of the positive power supply and the output terminal OUT2 of the negative power supply are fed back, and the energy storage time is adjusted at the positive power supply voltage and the negative power supply voltage, respectively. Then, based on the adjusted time, energy storage and release are alternately repeated with the positive power supply voltage and the negative power supply voltage, so that the positive power supply is based on the single input power supply PW. A predetermined power supply voltage (for example, ± 8 V) is output from the output terminal OUT1 and the output terminal OUT2 of the negative power supply. Therefore, the positive and negative power supply voltages can be output individually and stably.

  FIG. 3 is a circuit more specifically showing the block configuration of the switching power supply circuit shown in FIG. FIG. 4 is a diagram showing a more detailed circuit configuration of the timing pulse generator 4.

  In FIG. 3, the inductance L corresponds to the energy storage unit 4 shown in FIG. Further, the smoothing capacitor C1 corresponds to the positive power supply smoothing unit 2, and the smoothing capacitor C2 corresponds to the negative power supply smoothing unit 3. The first switch element FET1 and the second switch element FET2 correspond to the first switch SW1 and the second switch SW2 shown in FIG. 1, respectively, and the diode D1 and the diode D2 are the third switch shown in FIG. This corresponds to SW3 and fourth switch SW4.

  The connection relationship of the circuit of FIG. 3 will be described. The positive side of the input power supply PW is connected to the source terminal of a P-channel second field effect transistor (hereinafter referred to as “second switch element FET2”). Note that the negative side of the input power supply PW is connected to the ground. The gate terminal of the second switch element FET2 is connected to a timing pulse generator 4 (see FIG. 4 for details) (in FIG. 3, the timing pulse generator 4 is divided into two for convenience of explanation). ing). The drain terminal of the second switch element FET2 is connected to one end of the inductance L.

  One end of the inductance L is connected to the cathode terminal of the diode D2. The diode D2 is for reverse current prevention, and its anode terminal is connected to one end of the smoothing capacitor C2. Further, the smoothing capacitor C2 corresponds to the negative power supply smoothing unit 3 shown in FIG. One end of the smoothing capacitor C2 is connected to a resistor RL2 as a load via an output terminal OUT2 of a negative power source. The other end of the smoothing capacitor C2 is connected to the ground.

  The other end of the inductance L is connected to the anode terminal of the diode D1. The cathode terminal of the diode D1 is connected to one end of the smoothing capacitor C1. One end of the smoothing capacitor C1 is connected to a resistor RL1 as a load via an output terminal OUT1 of a positive power source. The other end of the smoothing capacitor C1 is connected to the ground.

  The other end of the inductance L is connected to the drain terminal of an N-channel first field effect transistor (hereinafter referred to as “first switch element FET1”). The gate terminal of the first switch element FET1 is connected to the timing pulse generator 4 (see FIG. 4 for details). The source terminal of the first switch element FET1 is connected to the ground.

  The first switch element FET1 and the second switch element FET2 described above correspond to the first and second switches SW1 and SW2 shown in FIG.

  Next, the detailed circuit of the timing pulse generator 4 will be described with reference to FIG. 4. The timing pulse generator 4 feeds back the output voltages at the output terminal OUT1 of the positive power source and the output terminal OUT2 of the negative power source, The switch element FET1 and the second switch element FET2 are turned on and off.

  Resistors R1 and R2 are connected in series between the positive power supply output terminal OUT1 and the negative power supply output terminal OUT2. Resistors R3 and R4 are connected in series with the resistors R1 and R2 between the output terminal OUT1 of the positive power source and the output terminal OUT2 of the negative power source. That is, the resistors R1 to R4 are bridge-connected.

The middle point of the resistors R1 and R2 is connected to the negative input terminal of the first operational amplifier OP1. That is, if the output voltage of the output terminal OUT1 of the positive power supply is V1 (> 0) and the output voltage of the output terminal OUT2 of the negative power supply is V2 (<0), Va = (V1−V2) · R1 / (R1
+ R2) is input to the negative input terminal of the first operational amplifier OP1. A power supply circuit P1 that outputs a predetermined reference voltage Vr1 (for example, 3.5 V) is connected to the plus side input terminal of the first operational amplifier OP1. A resistor R5 is connected between the negative input terminal and the output terminal of the first operational amplifier OP1, and thereby the first operational amplifier OP1 and the resistor R5 constitute a differential amplifier. That is, the first operational amplifier OP1 amplifies and outputs the difference voltage (Vr1−Va) between the voltage Va and the reference voltage Vr1. This output signal (see S1 in FIG. 4) is input to the plus side input terminal of the second operational amplifier OP2.

  When the positive voltage output from the output terminal OUT1 or the negative voltage output from the output terminal OUT2 changes due to a load change, the voltage obtained by dividing the voltage between the output terminals by the resistors R1 and R2 changes. The difference voltage from the reference voltage output from OP1 also changes. Therefore, the fluctuation of the output voltage is detected by the differential amplifier composed of the first operational amplifier OP1.

  A triangular wave generating circuit 10 is connected to the negative input terminal of the second operational amplifier OP2. The triangular wave generation circuit 10 outputs a reference signal for comparison with a differential voltage S1 output from the first operational amplifier OP1 and a differential voltage S2 output from a third operational amplifier OP3 described later. A triangular wave is used as the reference signal. Is generated.

  The second operational amplifier OP2 operates as a comparator and outputs a high-level pulse signal when the differential voltage S1 is larger than the triangular wave of the reference signal. The gate terminal of the first switch element FET1 shown in FIG. 3 is connected to the output terminal (see G1 in FIG. 4) of the second operational amplifier OP2. That is, the second operational amplifier OP2 outputs a control signal for controlling on / off switching of the first switch element FET1.

  On the other hand, the middle point of the resistors R3 and R4 is connected to the negative input terminal of the third operational amplifier OP3. That is, the voltage Vb = (V1−V2) · R3 / (R3 + R4) is input to the negative input terminal of the third operational amplifier OP3. A power supply circuit P2 that outputs a predetermined reference voltage Vr2 (for example, 3.5 V) is connected to the positive input terminal of the third operational amplifier OP3. A resistor R6 is connected between the minus side input terminal and the output terminal of the third operational amplifier OP3, and thereby the third operational amplifier OP3 and the resistor R6 constitute a differential amplifier. That is, the third operational amplifier OP3 amplifies and outputs the difference voltage (Vr2-Vb) between the voltage Vb and the reference voltage Vr2. This output signal (see S2 in FIG. 4) is input to the plus side input terminal of the fourth operational amplifier OP4. Similarly to the differential amplifier composed of the first operational amplifier OP1, the differential amplifier composed of the third operational amplifier OP3 detects the fluctuation of the output voltage.

  A triangular wave generation circuit 10 is connected to the negative input terminal of the fourth operational amplifier OP4. The fourth operational amplifier OP4 operates as a comparator, and outputs a pulse signal that becomes a high level when the differential voltage S2 is larger than the triangular wave of the reference signal. The gate terminal of the second switch element FET2 shown in FIG. 3 is connected to the output terminal (see G2 in FIG. 4) of the fourth operational amplifier OP4. That is, the fourth operational amplifier OP4 outputs a control signal for controlling on / off switching of the second switch element FET2.

  Next, the operation of the above switching power supply circuit will be described with reference to the timing chart shown in FIG.

  First, the first operation OP1 of the timing pulse generator 4 compares the voltage at the output terminal OUT1 of the positive power supply (see OUT1 in FIG. 5 (a)) with the reference voltage output from the power supply circuit P1, and outputs the result. The voltage at the terminal (see S1 in FIG. 4) is applied to the positive input terminal of the second operational amplifier OP2. The second operational amplifier OP2 compares the output voltage S1 of the first operational amplifier OP1 with the triangular wave S output from the triangular wave generating circuit 10, and the comparison result (see G1 in FIG. 4) is applied to the gate terminal of the first switch element FET1. input.

  The second operational amplifier OP2 outputs “HIGH” when the output voltage S1 of the first operational amplifier OP1 is larger than the triangular wave S. When the output voltage S1 of the first operational amplifier OP1 is smaller than the triangular wave S, “LOW” is output. Accordingly, as shown in FIG. 5B, the second switch element FET2 is turned on / off by a pulse signal in which the “HIGH” period is relatively longer than the “LOW” period.

  On the other hand, the third operational amplifier OP3 shown in FIG. 4 compares the voltage at the output terminal OUT2 of the negative power supply (see OUT2 in FIG. 5A) with the reference voltage output from the power supply circuit P2, and at the output terminal thereof. A voltage (see point S2 in FIG. 4) is applied to the positive input terminal of the fourth operational amplifier OP4. The fourth operational amplifier OP4 compares the output voltage S2 of the third operational amplifier OP3 with the triangular wave S output from the triangular wave generation circuit 10, and the comparison result (see G2 in FIG. 4) is applied to the gate terminal of the second switch element FET2. input.

  The fourth operational amplifier OP4 outputs “HIGH” when the output voltage S2 of the third operational amplifier OP3 is larger than the triangular wave S. When the output voltage S2 of the third operational amplifier OP3 is smaller than the triangular wave S, “LOW” is output. Thereby, as shown in FIG. 5C, the second switch element FET2 has a period of “HIGH” that is relatively shorter than a period of “LOW” and is compared with the pulse signal output from the second operational amplifier OP2. An ON / OFF operation is performed by a pulse signal having a short “HIGH” period.

  Thus, the first switch element FET1 is turned on / off by the output of the second operational amplifier OP2, and the second switch element FET2 is turned on / off by the output of the fourth operational amplifier OP4. In this case, since the first switch element FET1 and the second switch element FET2 are N-channel type and P-channel type, respectively, the first switch element FET1 is turned off when the gate terminal is “LOW”. ”To turn on. On the other hand, the second switch element FET2 is turned on when the gate terminal is "LOW" and turned off when "HIGH".

  Here, when both switch elements FET1 and FET2 are on (see period T1 in FIG. 5), the input power source PW is supplied to the inductance L which is the energy storage unit 1, and the energy of the input power source PW is stored. At this time, at both ends of the inductance L, as shown in FIG. 5D, the terminal side of the second switch element FET2 (see LM in FIG. 4) is the terminal side of the first switch element FET1 (see LP in FIG. 4). The potential is higher. FIG. 5 (e) is a diagram showing the current flowing through the inductance L. In the period T1, the current flowing through the inductance L gradually increases, that is, the energy of the input power supply PW becomes the inductance L. Accumulated.

  Next, when the first switch element FET1 is turned off (see period T2 in FIG. 5), the energy accumulated in the inductance L is released, and this is a resistance as a load from the output terminal OUT1 of the positive power supply via the diode D1. RL1 is supplied. At this time, at both ends of the inductance L, as shown in FIG. 5 (d), the terminal side of the first switch element FET1 has a higher potential on the terminal side of the second switch element FET2, and becomes forward biased with respect to the diode D1. Since the reverse bias is applied to the diode D2, the stored energy of the inductance L is released only to the smoothing capacitor C1.

  Here, the period T1 during which both the switch elements FET1 and FET2 are turned on is changed by the timing pulse generator 4 based on the voltage fluctuation of the load, whereby the amount of increase in the amount of energy accumulated in the inductance L is also changed. The That is, since the energy released in the period T2 is also changed based on the voltage fluctuation of the load, the voltage value output to the output terminal OUT1 of the positive power supply can be maintained at a substantially constant voltage.

  Next, when both switch elements FET1 and FET2 are turned on again (see period T3 in FIG. 5), the input power source PW is supplied to the inductance L, and the energy of the input power source PW is accumulated. At this time, at both ends of the inductance L, as shown in FIG. 5 (d), the terminal side of the second switch element FET2 is at a higher potential than the terminal side of the first switch element FET1, as shown in FIG. 5 (e). Thus, in the period T3, the current flowing through the inductance L gradually increases, that is, the energy of the input power source PW is accumulated.

  Then, when the second switch element FET2 is turned off (see period T4 in FIG. 5), the energy accumulated in the inductance L is released, and this is a resistance as a load from the output terminal OUT2 of the negative power supply via the diode D2. RL2 is supplied. At this time, at both ends of the inductance L, as shown in FIG. 5 (d), the terminal side of the first switch element FET1 has a lower potential on the terminal side of the second switch element FET2, and becomes forward biased with respect to the diode D2. Since the diode D1 is reverse-biased, the stored energy of the inductance L is released only to the smoothing capacitor C2.

  Here, the period T3 is changed based on the voltage fluctuation of the load by the timing pulse generator 4, and thereby the amount of increase in the amount of energy accumulated in the inductance L is also changed. That is, since the energy released in the period T4 is also changed based on the voltage fluctuation of the load, the voltage value output to the output terminal OUT2 of the negative power source can be maintained at a substantially constant voltage.

  Thereafter, as described above, both switch elements FET1 and FET2 are (ON, ON), (OFF, ON), (ON, ON), (ON, OFF), (ON, ON), (OFF, ON). Since the ON / OFF operation is controlled as shown in FIG. 6B, a positive voltage and a negative voltage are alternately generated from the stored energy of the inductance L using a common inductance L. By controlling, the positive voltage and the negative voltage can be controlled independently. Therefore, the power supply voltages output from the output terminal OUT1 of the positive power supply and the output terminal OUT2 of the negative power supply can be output individually and stably.

  Thus, according to this embodiment, voltage fluctuations at the output terminal OUT1 of the positive power supply and the output terminal OUT2 of the negative power supply are fed back, and the energy storage time is adjusted at the positive voltage and the negative voltage, respectively. Then, based on the adjusted time, the release of energy is alternately repeated between the positive power source and the negative power source, so that the output terminal OUT1 of the positive power source and the negative power source are based on the single input power source PW. A predetermined power supply voltage (for example, ± 8 V) is output at the output terminal OUT2. Therefore, the positive and negative power supplies can be output individually and stably.

  Of course, the scope of the present invention is not limited to the embodiment described above. For example, the configuration of the switching power supply circuit is not limited to the configuration described above.

It is a block block diagram of the switching power supply circuit concerning this invention. It is a timing chart which shows the relationship between the operation | movement of a 1st thru | or 4th switch, the operation | movement of accumulation | storage / release of the energy of an energy storage part, and the output voltage of an output terminal. It is a detailed circuit diagram of the switching power supply circuit shown in FIG. It is a detailed circuit diagram of a timing pulse generator. 4 is a timing chart of the switching power supply circuit shown in FIG. 3. It is a circuit diagram which shows the conventional switching power supply circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Energy storage part 2 Positive power supply smoothing part 3 Negative power supply smoothing part 4 Timing pulse generation part FET1 1st switch element FET2 2nd switch element L Inductance C1, C2 Smoothing capacitor PW Input power supply SW1 1st switch SW2 2nd switch SW3 3rd Switch SW4 4th switch

Claims (3)

A switching power supply circuit that generates a positive voltage power supply and a negative voltage power supply from a DC power supply, and outputs a positive voltage output from the positive voltage power supply and a negative voltage output from the negative voltage power supply from two output terminals, respectively. ,
The DC power supply is connected in parallel to the negative-side output terminal and the positive-side output terminal via a first switch means and a second switch means, respectively, and the first and second switch means are turned on. To store the energy supplied from the DC power supply, and output only the negative energy from the connection point with the second switch means by turning on only the first switch means. Energy storage means for outputting a positive voltage from the connection point with the first switch means by storing only the second switch means in an ON state;
First smoothing means that is provided between the first switch means and the positive voltage output terminal and smoothes the positive voltage output from the energy storage means;
A second smoothing means provided between the second switch means and the negative voltage output terminal for smoothing the negative voltage output from the energy storage means;
An on / off switching control signal is generated based on the positive voltage and the negative voltage output from the two output terminals, and based on the control signal, the energy storage means stores the energy and the positive of the stored energy. Control means for controlling on / off switching of the first and second switch means so as to alternately repeat voltage output and energy accumulation and negative voltage output of the accumulated energy;
A switching power supply circuit comprising:   2. The switching power supply circuit according to claim 1, wherein the energy storage unit includes a choke coil, and the first and second smoothing units include a capacitor. The control means includes
A first pulse signal is obtained by comparing a first signal having a first output voltage waveform based on a difference voltage between a positive voltage and a negative voltage output from the two output terminals with a predetermined reference wave signal. First pulse signal generating means for generating;
A second pulse signal is generated by comparing a second signal having a second output voltage waveform based on a difference voltage between a positive voltage and a negative voltage output from the two output terminals and the reference wave signal. Second pulse signal generation means
The first pulse signal generated by the first pulse signal generation means controls on / off switching of the first switch means, and the second pulse signal generated by the second pulse signal generation means The switching power supply circuit according to claim 1 or 2, wherein on / off switching of the second switch means is controlled by the control.

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