JP6035769B2 - Power circuit - Google Patents

Description

  The present invention relates to a power supply circuit for preventing an inrush current when power is turned on in an electronic device such as a switching power supply device.

  2. Description of the Related Art Conventionally, there is a switching power supply circuit as a power supply circuit shown in FIG. In this switching power supply circuit, when the power supply V1 is turned on, a large inrush current flows as a charging current for the capacitor C1 through the resistor R11 and the bridge-type diode circuit D1. This is because the capacitor C1 is not charged before the power is turned on and is in an empty zero state. Therefore, when the power source V1 is turned on, the charge is suddenly charged from the zero state, so that the current flows without restriction. It is.

  A resistor R11 is provided for the purpose of suppressing the maximum value of the inrush current. When the power is turned on, since the triac TC1 is in an off state, a current flows through the resistor R11 so that an inrush current is prevented. When the voltage of the capacitor C1 rises according to the current flowing through the resistor R11 and charging proceeds to the capacitor C2 via the resistor R1 in response to this rise, the SW (switching) power control IC (Integrated Circuit) ) 11 starts.

  As a result of this activation, a pulse voltage for performing SW power control is output from the output terminal Out of the SW power control IC 11, and this pulse voltage is supplied via a resistor R2 to a transistor Q1 by a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). Is supplied to the gate terminal. This supply causes the transistor Q1 to start a SW operation, and a voltage is induced in the transformer T1. This induced voltage applies a voltage to the load 12 connected to the secondary winding of the transformer T1. The induced voltage of the transformer T1 is charged to the capacitor C5 via the diode D5. This charging voltage is supplied to the gate terminal of the triac TC1 via the resistor R5, thereby turning on the triac TC1.

  After that, when the power supply V1 is turned off, the charging voltage of the capacitor C1 decreases, and the input voltage Vcc to the SW power supply control IC 11 becomes the off voltage, so that the transistor Q1 is turned off. When the discharge of the capacitor C5 starts from this off time, and the discharge voltage falls below the gate threshold voltage of the triac TC1, the triac TC1 is turned off.

  Instead of this triac TC1, a thyristor SC1 may be used as shown in FIG. The switching power supply circuit using this thyristor SC1 performs the same operation as described above. As this type of prior art, there is an inrush current reduction circuit described in Patent Document 1.

JP 2009-268244 A

  However, according to the switching power supply circuit shown in FIGS. 6 and 7, the transformer T1 needs another winding for driving the gate of the TRIAC TC1 or the thyristor SC1, and the number of pins of the transformer T1 is increased correspondingly. There is a problem that the overall scale increases.

  Further, since the discharge time of the capacitor C5 is determined by the time constant of the capacitor C5 and the resistor R5, if the time constant is poorly selected, the power supply V1 is turned off in a short time after the power supply V1 is turned off. The discharge of the capacitor C5 that sometimes occurs continues without being ended even when the capacitor C5 is turned on, and thus there is a state in which the triac TC1 remains on. Since the power supply V1 is turned on in this on state, the current from the power supply V1 flows in the circuit via the triac TC1. In this case, there arises a problem that an inrush current flows in the circuit.

  When an inrush current flows in this way, a switch (not shown) interposed immediately after the power supply V1 is welded or a diode of the diode circuit D1 is damaged. Furthermore, since the capacitor C1 having a large charge capacity is suddenly charged by the inrush current, the voltage of the power supply V1 temporarily decreases, and an electric or electronic device (not shown) connected to the path of the power supply V1 malfunctions. .

  In the switching power supply circuit, after the inrush current when the power supply V1 is turned on decreases, the triac TC1 or the thyristor SC1 is turned on, and the current from the power supply V1 is guided into the circuit via the triac TC1 or the thyristor SC1, and the power supply V1 When turning off, the TRIAC TC1 or the thyristor SC1 must be turned off immediately. However, depending on the time constant of the capacitor C5 and the resistor R5, as described above, the discharge of the capacitor C5 that occurs when the power source V1 is turned off may continue without ending even when the power source V1 is turned on. is there.

  Thus, since the condition for turning on the triac TC1 or thyristor SC1 and the condition for quickly turning off the triac TC1 or thyristor SC1 when the power supply V1 is turned off are in conflict, the time constant of the capacitor C5 and the resistor R5 is There is a problem that is difficult to select.

  The present invention has been made to solve the above-described problems, and it is possible to easily select a time constant in a small circuit and to quickly adapt to power on / off to prevent inrush current. An object of the present invention is to provide a power supply circuit that can be used.

In order to solve the above problems, the present invention operates at a predetermined operating frequency by applying a capacitor and a resistor connected to a power source to be turned on / off, and a charging voltage of the capacitor that is charged when the power source is turned on. A control unit that performs a pulse signal output from the control unit, a switching element that performs a switching operation based on the pulse signal from the control unit, and power of the power source that is supplied to the primary winding in accordance with the switching operation of the switching element And a transformer that transmits the current to the secondary winding, and in a power supply circuit that prevents the inrush current by flowing the current when the power is turned on to the resistor, the power supply circuit is connected in parallel to the resistor, A second switching element that is turned on when a voltage is applied; a diode whose anode is connected to an output terminal of a pulse signal of the control unit; And a second capacitor that is charged by a pulse signal of the control unit, and the charge voltage is supplied to the control terminal of the second switching element, and a second capacitor that discharges the charge of the second capacitor. The second resistor is connected in parallel with the diode .

According to this configuration, unlike the conventional circuit, a structure in which a control voltage is obtained by winding a separate winding around the transformer to control on / off of the switching element is not necessary. Can be scaled down.

In the present invention, the second switching element is a field effect transistor, a triac, or a thyristor .

As in this configuration, the second switching element can be configured in small size, and be driven at a lower voltage. Further, as in this configuration, the second switching element can be configured by a versatile active element.

  In the present invention, a photocoupler is connected between the second capacitor and a control terminal of the second switching element, and the photocoupler is turned on or off according to the presence or absence of a charging voltage of the second capacitor. Two switching elements are turned on or off.

  According to this configuration, even when the ground level of the circuit part on the power supply side including the second switching element and the circuit part of the control unit are different, the circuit part is insulated by the photocoupler, and the second switching element is It can be turned on / off properly.

In the present invention, the second resistor and the diode are provided in the control unit.

According to this configuration, since the second resistor and the diode can be configured in an integrated circuit such as an IC that forms the control unit, the entire inrush current prevention circuit can be reduced in size.

  According to the present invention, it is possible to provide an inrush current prevention circuit capable of easily selecting a time constant with a small circuit and quickly adapting to power on / off to prevent an inrush current. .

It is a circuit diagram which shows the structure of the switching power supply circuit which concerns on this embodiment. In the switching power supply circuit of this embodiment, (a) is a diagram showing a pulse voltage waveform output from a SW power supply control IC, and (b) is a diagram showing a gate voltage waveform of a transistor connected in parallel to a power supply together with a resistor. It is a circuit diagram which shows the structure of the switching power supply circuit which concerns on the modification 1 of this embodiment. It is a circuit diagram which shows the structure of the switching power supply circuit which concerns on the modification 2 of this embodiment. It is a circuit diagram which shows the structure of the switching power supply circuit which concerns on the modification 3 of this embodiment. It is a circuit diagram which shows the structure of the conventional switching power supply circuit. It is a circuit diagram which shows the other structure of the conventional switching power supply circuit.

Hereinafter, an embodiment for carrying out the present invention (hereinafter simply referred to as the present embodiment) will be described in detail with reference to the accompanying drawings.
(Configuration of the embodiment)
FIG. 1 is a circuit diagram showing a configuration of a switching power supply circuit according to the present embodiment. In the switching power supply circuit according to the present embodiment, a power supply V1 that is turned on or off by a switch (not shown) and supplies an AC voltage when turned on, and a plurality of diodes are bridged so as to rectify the voltage from the power supply V1. The combined diode circuit D1, capacitor C1, resistor R11, MOSFET transistor Q10, resistor R12, capacitor C10, resistor R10 and diode D10, SW power supply control IC 11, resistor R5, The MOSFET includes a transistor Q1, resistors R1 and R4, capacitors C4 and C2, diodes D4 and D2, and a transformer T11. The secondary winding terminals 5 and 6 of the transformer T11 include diodes D3 and A load 12 is connected via a capacitor C3.

  In these components, the input side of the diode circuit D1 is connected between the positive electrode and the negative electrode of the power supply V1, and the capacitor C1 and the resistor R11 are connected between the outputs of the diode circuit D1. A source terminal and a drain terminal of the transistor Q11 are connected to both ends of the resistor R11, and a resistor R12 and a capacitor C10 are connected between the gate terminal of the transistor Q12 and one output side of the diode circuit D1. A resistor R10 and a diode D10 are connected in parallel between one end of the capacitor C10 and the output terminal Out of the SW power supply control IC 11.

  A resistor R1 is connected between the application terminal of the input voltage Vcc of the SW power supply control IC 11 and the other output side of the diode circuit D1, and the application terminal and one output side of the diode circuit D1 are connected to the transformer T11. A diode D2 and a capacitor C2 are connected between the secondary winding terminals 3 and 4. The output terminal Out of the SW power supply control IC 11 is connected to the gate terminal of the transistor Q1 through a resistor R5. The source terminal and drain terminal of the transistor Q1 are connected to a diode D4, a capacitor C4, and a resistor R4 through a diode. Connected between both outputs of the circuit D1. The drain terminal of the transistor Q1 is connected to one winding terminal 2 on the primary side of the transformer T11, and the other winding terminal 1 is connected to the other output side of the diode circuit D1.

Furthermore, the output voltage Vout to the load 12 on the secondary side of the transformer T11 is fed back to the SW power supply control IC 11. Further, the part including the resistors R11 and R12 and the transistor Q10 surrounded by the broken line 21 is an inrush current preventing unit. A portion including the capacitor C10, the resistor R10, and the diode D10 surrounded by the broken line 22 is a time constant circuit portion.
(Operation of the embodiment)
Hereinafter, the operation of the switching power supply circuit according to the present embodiment shown in FIG. 1 will be described in detail. It is assumed that the power source V1 is connected to a commercial power source with a frequency of 50 Hz that outputs a voltage of AC (alternating current) 100V.

  When the power supply V1 is turned on, AC100V is rectified by the diode circuit D1, and a current flows in the order of the capacitor C1 and the resistor R11, thereby charging the capacitor C1. By this charging, the voltage of the capacitor C1 rises to about 141V which is the peak value of AC100V.

  At this time, as the voltage of the capacitor C1 rises, charging of the capacitor C2 is also started via the resistor R1 according to a time constant (for example, 500 ms) determined by the resistor R1 and the capacitor C2. This charging voltage is applied as the input voltage Vcc to the SW power supply control IC 11. When this applied voltage reaches the starting voltage (for example, 15 V) of the SW power control IC 11, the SW power control IC 11 operates at a predetermined operating frequency. Start. By this operation, a predetermined pulse voltage is output from the output terminal Out of the SW power supply control IC 11 and applied to the gate terminal of the transistor Q1 via the resistor R5.

  As a result, the transistor Q1 repeats an on / off operation at a predetermined SW frequency (for example, 50 KHz). By this SW operation, the current of the capacitor C1 flows from the terminal 1 to the terminal 2 of the transformer T11, and the secondary winding of the transformer T11 is wound. A voltage corresponding to the number of winding turns is induced in the wire terminals 5 and 6 and generated.

  Due to the voltage generated on the secondary side, the diode D3 is turned on to charge the capacitor C3, and the voltage is output to the load 12 as the output voltage Vout. At the same time, a voltage is induced in the winding terminals 3 and 4 on the secondary side of the transformer T11 according to the number of turns of the winding, and the diode D2 is turned on to charge the capacitor C2. . This charging voltage is supplied as the input voltage Vcc to the SW power supply control IC 11, and the SW power supply control IC 11 continues the SW operation.

  Since the operating frequency of the SW power supply control IC 11 is 50 KHz (period 20 μs), a signal having a pulse voltage waveform of a constant level of 15 V, for example, is output from the output terminal Out as shown in FIG. This pulse signal is formed by falling at the rising time t2 at the time t1, and this rising and falling is similarly performed at the times t3 and t4. At this time, the time between the times t1 and t4 of the two pulse signals is 20 μs, and further rises at time t5 1 ms after the time t4, and at times t6, t7, and t8, similarly to the time t1 to t4. A pulse signal is generated. This operation is repeated in the same manner after the power source V1 is turned on.

  The pulse signal is supplied to the capacitor C10 via the diode D10, whereby the voltage is charged in the capacitor C10. This charging voltage is supplied to the gate terminal of the transistor Q10, and the transistor Q10 is turned on. At this time, since the transistor Q10 is a MOSFET, the gate impedance is high, and therefore the potential of the capacitor C10 does not decrease.

  Therefore, in order to discharge the capacitor C10, the resistor R10 is connected to the capacitor C10. When no pulse signal as a drive signal is output from the output terminal Out of the SW power supply control IC 11, the resistor R10 causes the capacitor C10 to be discharged. The electric charge is discharged. The time constants of the capacitor C10 and the resistor R10 that determine the discharge time are set to a time that is significantly longer than the cycle 20 μs of the operating frequency of the SW power supply control IC 11 and shorter than the cycle 20 ms of the commercial frequency 50 Hz of the power supply V1. Yes. For example, the time is set to 2 ms, which is 1/10 of the cycle 20 ms.

  With this setting, when the power source V1 is turned off, the capacitor C10 finishes discharging in a time 2 ms shorter than the cycle 20 ms of the commercial frequency 50 Hz of the power source V1, thereby turning off the transistor Q10. Therefore, the transistor Q10 is surely turned off by the shortest time when the power supply V1 is turned on next.

In addition, after the pulse signal is applied to the gate terminal of the transistor Q10, the charging voltage of the capacitor C10 is discharged before the next pulse signal is applied. Since this discharge takes 2 ms, the time between the pulse signals is 2 μs. Is sufficiently long, as shown in FIG. 2B, the gate voltage does not fall below the voltage 5V of the threshold th1. Therefore, the transistor Q10 is in an on state while the power supply V1 is on.
(Effect of embodiment)
As described above, the switching power supply circuit as the power supply circuit according to the present embodiment charges the capacitor C1 and the resistor R11 connected to the power supply V1 that is turned on / off, and the capacitor C1 that is charged when the power supply V1 is turned on. A SW power supply control IC 11 as a control unit that operates at a predetermined operating frequency by applying a voltage and outputs a pulse signal; a transistor Q1 as a switching element that performs a switching operation by a pulse signal from the SW power supply control IC 11; A transformer T11 for transmitting the power of the power source V1 supplied to the primary windings 1 and 2 to the secondary windings 3, 4 and 5 and 6 in accordance with the switching operation of the transistor Q1; The current when V1 is turned on is passed through the resistor R11 to prevent an inrush current.

  A feature of the present embodiment is that the transistor Q10 as a second switching element connected in parallel to the resistor R11 and turned on by applying a voltage to the gate terminal as a control terminal, the gate terminal of the transistor Q10, and SW power control It is connected between the pulse signal output terminal Out of the IC 11 and includes a delay circuit for delaying the pulse signal and a capacitor C10 as a second capacitor. A time constant by the delay circuit and the capacitor C10 is set to the SW power control IC 11 The period is set longer than the period of the operating frequency and shorter than the period of the frequency of the power supply V1.

  According to this configuration, the pulse signal output from the SW power supply control IC 11 is charged to the capacitor C10 via the delay circuit, and this charging voltage is supplied to the control terminal of the transistor Q10. At this time, the charging voltage of the capacitor C10 is discharged by the delay circuit when no pulse signal is output, and this discharge time is determined by the time constant of the delay circuit and the capacitor C10. In this embodiment, the time constant is set to a time (for example, 2 ms) that is significantly longer than the period of the operating frequency of the control unit (for example, 20 μs) and shorter than the period of 20 ms for the frequency of the power source V1 (for example, commercial frequency 50 Hz). Therefore, when the power source V1 is turned off, the capacitor C10 finishes discharging in a time 2 ms shorter than the cycle 20 ms of the commercial frequency 50 Hz of the power source V1, and the transistor Q10 can be turned off. Thus, the transistor Q10 can be reliably turned off by the shortest time when the power source V1 is turned on next time.

  Therefore, like the conventional switching power supply circuit, the discharge of the capacitor C10 that occurs when the power supply V1 is turned off continues without ending even when the power supply V1 is turned on, so that the switching element remains on. The inrush current can be prevented from flowing in the circuit through the triac TC1 or thyristor SC1 as a switching element.

  Further, since the above time constant can be determined from the cycle of the operating frequency of the SW power supply control IC 11 and the cycle of the frequency of the power supply V1, the time constant can be easily selected.

  Further, unlike the conventional circuit, a structure in which a control voltage is obtained by winding another winding around the transformer T1 in order to control on / off of the triac TC1 or the thyristor SC1 as a switching element becomes unnecessary. The scale of the switching power supply circuit can be reduced.

  A delay circuit is formed by connecting a resistor R10 and a diode D10 in parallel. The diode D10 has an anode connected to the pulse signal output terminal Out of the SW power supply control IC 11 and a cathode connected to the capacitor C10. It has a configuration.

  According to this configuration, since the delay circuit can be configured with the resistor R10 and the diode D10 which are simple components, the time constant by the capacitor C10 and the resistor R10 can be easily set to the predetermined time constant described above. Is possible.

  The transistor Q10 is a field effect transistor (FET). As a result, the second switching element can be configured in a small size and can be driven at a lower voltage.

The power source V1 is an AC power source in the present embodiment, but may be a DC power source.
(Modification 1 of embodiment)
FIG. 3 is a circuit diagram showing a configuration of a switching power supply circuit according to Modification 1 of the present embodiment. The switching power supply circuit according to Modification 1 differs from the switching power supply circuit shown in FIG. 1 in that the ground level of the circuit part on the power supply V1 side including the transistor Q10 and the circuit part of the SW power supply control IC 11 are different. In addition, the photocoupler PC1 is used to insulate those circuit portions and drive the transistor Q10.

  That is, one output side of the diode circuit D1 is connected to one end of the light receiving element of the photocoupler PC1, the other end of the light receiving element is connected to the gate terminal of the transistor Q10 via the resistor R14, and this gate terminal is connected to the resistor R13. Is connected to the other output side of the diode circuit D1. The other end of the resistor R1 having one end connected to one output side of the diode circuit D1 is connected to one end of the light emitting element of the photocoupler PC1 through the resistor R5, and the other end of the light emitting element is bipolar. Connected to the collector terminal of the transistor Q2. The emitter terminal of the transistor Q2 is connected between the capacitor C1 and the resistor R11, the base terminal of the transistor Q2 is connected to the capacitor C10 via the resistor R9, and the capacitor C1 and the resistor R11 via the resistor R12. Connected in between.

  In such a configuration, when the power supply V1 is turned on, a pulse signal is output from the output terminal Out of the SW power supply control IC 11, and the capacitor C10 is charged accordingly, and this charging voltage is connected via the resistor R9. When applied to the base terminal of the transistor Q2, the transistor Q2 is turned on, and the light emitting element of the photocoupler PC1 emits light. When the light receiving element receives this emitted light, a current flows through the light receiving element. This current is applied as a voltage to the gate terminal of the transistor Q10 via the resistor R14, and the transistor Q10 is turned on.

  On the other hand, when the power supply V1 is turned off, the pulse signal of the SW power supply control IC 11 is not output, so that the charging voltage of the capacitor C10 is discharged through the resistor R10 in 2 ms, for example, as described above. As a result, the transistor Q2 is turned off and the light emission of the photocoupler PC1 is stopped, so that the voltage applied to the gate terminal of the transistor Q10 falls below the threshold value 5V, and the transistor Q10 is turned off.

  As described above, according to the switching power supply circuit of the first modification of the present embodiment, the photocoupler PC1 is connected between the capacitor C10 and the gate terminal of the transistor Q10, and the photo according to the presence or absence of the charging voltage of the capacitor C10. The coupler PC1 is turned on or off, and the transistor Q10 is turned on or off.

Therefore, even when the circuit level on the power supply V1 side including the transistor Q10 and the circuit level of the SW power supply control IC 11 are different from each other, the circuit portion is insulated by the photocoupler PC1 and the transistor Q10 is properly turned on / off. Can be turned off.
(Modification 2 of embodiment)
FIG. 4 is a circuit diagram showing a configuration of a switching power supply circuit according to Modification 2 of the present embodiment. The switching power supply circuit according to the modification 2 is different from the switching power supply circuit shown in FIG. 1 in that a triac TC1 is used instead of the transistor Q10, and the gate terminal of the triac TC1 is connected to the capacitor C10 via the resistor R13. Being connected. However, the resistor R10 and the cathode terminal of the diode D10 are also connected to the connection portion of the gate terminal to the capacitor C10 via the resistor R13.

In this configuration, the pulse signal output from the SW power supply control IC 11 is supplied to the capacitor C10 via the diode D10 and charged, and this charging voltage is supplied to the control terminal of the triac TC1 via the resistor R13. TC1 is turned on. When the power supply V1 is turned off and the pulse signal is turned off, the charge of the capacitor C10 is discharged according to the discharge time determined by the time constant by the resistor R10 and the capacitor C10, and the triac TC1 can be turned off. . Thus, the triac TC1 can be surely turned off by the shortest time when the power source V1 is turned on next time. Instead of the triac TC1, a thyristor SC1 may be used. Even in such a configuration, the same effect as the switching power supply circuit of FIG. 1 can be obtained. Furthermore, it can be configured using general-purpose active elements such as triac TC1 and thyristor SC1.
(Modification 3 of embodiment)
FIG. 5 is a circuit diagram showing a configuration of a switching power supply circuit according to Modification 3 of the present embodiment. The switching power supply circuit according to the modification 3 is different from the switching power supply circuit shown in FIG. 1 in that a function equivalent to that of the resistor R10 and the diode D10 connected in parallel is provided in the SW power supply control IC 11 with a delay circuit 11a. It is in having established as. Even in this configuration, the same effect as the switching power supply circuit shown in FIG. 1 can be obtained. Furthermore, since the delay circuit 11a can be configured in an integrated circuit such as an IC forming the control unit, the entire switching power supply circuit can be reduced in size.

  As mentioned above, although preferred embodiment of this invention was explained in full detail, it cannot be overemphasized that the technical range prediction of this invention is not limited to the range prediction as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiments. In addition, it is apparent from the description of the scope of claims that embodiments to which such changes or improvements are added can also be included in the scope of prediction of the present invention.

  D1, diode circuit, C1, C2, C3, C10, capacitor C1, R1, R4, R5, R10, R12, R13, resistor, Q1, Q10, transistor, D2, D3, D4, D10, diode, T11, transformer 11, SW power control, 11 a Delay circuit, 12 Load, 21 Inrush current prevention unit, 22 Time constant circuit unit

Claims (4)

A capacitor and a resistor connected to a power source to be turned on / off, a control unit that operates at a predetermined operating frequency by applying a charging voltage of the capacitor that is charged when the power source is turned on, and outputs a pulse signal; A switching element that performs a switching operation by a pulse signal from the control unit, and a transformer that transmits the power of the power source supplied to the primary winding in accordance with the switching operation of the switching element to the secondary winding. In the power supply circuit that prevents the inrush current by flowing the current when the power is turned on to the resistor,
A second switching element connected in parallel to the resistor and turned on by applying a voltage to the control terminal;
A diode whose anode is connected to an output terminal of a pulse signal of the control unit;
A cathode of the diode is connected, charged by a pulse signal of the control unit, and a second capacitor supplied with the charging voltage to a control terminal of the second switching element;
A second resistor for discharging the charge of the second capacitor,
The power supply circuit, wherein the second resistor is connected in parallel with the diode . The power supply circuit according to claim 1, wherein the second switching element is a field effect transistor, a triac, or a thyristor. A photocoupler is connected between the second capacitor and a control terminal of the second switching element, and the photocoupler is turned on or off according to the presence or absence of a charging voltage of the second capacitor, thereby switching the second switching element. The power supply circuit according to claim 1, wherein the power supply circuit is turned on or off. 4. The power supply circuit according to claim 1, wherein the second resistor and the diode are provided inside the control unit. 5.

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