JP2010148162A - Switching power source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To seek the reduction of the number of pins of an IC, the reduction of chip area, and the reduction of external parts, and the downsizing of equipment, by using a terminal in common to a charge circuit for soft start and a discharge circuit for protective operation, and to enable the further expansion of its function. <P>SOLUTION: A switching power source includes a soft operation executing circuit and a protective operation executing circuit at the same time. The soft operation executing circuit charges a capacitor with a first set current by a charge circuit, by connecting the capacitor to a single control terminal, and raises it to a set voltage value in a set time and executes soft start operation by the terminal voltage of the capacitor. The protective operation executing circuit detects the abnormal state of the operation of the switching power source, while keeping the voltage of the set voltage value, after finish of the soft start operation, and discharges the capacitor and stops the operation of the switching power source, when it detects the abnormal state successively for a prescribed time after start of charge of the capacitor from the set voltage value. Furthermore, it is possible to execute the soft start operation by discharging the capacitor since the voltage of a single control terminal after finish of the soft start operation is at a set voltage value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply, and more particularly to a switching power supply having a soft start operation function and a protection operation function at the time of startup.

  Conventionally, a switching power supply has compared an error amplification circuit that compares a divided voltage of an output voltage with a reference voltage, and compares the output signal of the error amplification circuit with a reference triangular wave signal to obtain the comparison result. A PWM comparator that generates a pulse signal with a corresponding duty cycle, and performs switching control of a transistor that forms a switching element in accordance with an output signal of the PWM comparator so that the output voltage becomes constant at a predetermined value. .

  When starting the switching power supply, it is common to increase the output voltage from 0 V in a light load state. At this time, the inrush current is suppressed to the input side power supply such as a battery. In order to reduce the burden, a soft start circuit that gradually increases the output voltage of the switching power supply is frequently used.

  This soft start circuit is realized by gradually increasing the voltage of the output signal of the error amplification circuit, which is a voltage to be compared with the reference triangular wave signal, in the PWM comparator. Specifically, many soft start circuits realize a soft start function by charging a capacitor with a constant current to generate a gradually increasing voltage and outputting the voltage to the error amplifier circuit.

  Further, as one of the protection circuits for the switching power supply, there is a latch protection circuit which is a timer latch type protection circuit. When an abnormality such as an output short-circuit occurs, the output voltage of the error amplifier circuit increases to the maximum value and exceeds the maximum voltage value of the reference triangular wave signal, that is, the duty cycle in PWM control reaches the maximum value. The state and the duration of the state are detected, and when the state continues for a predetermined period, it is latched and the operation of the switching power supply is stopped.

  In many cases, the delay time until the latch is determined by the charging time required for connecting the constant current source to the capacitor and setting the voltage of the capacitor to a predetermined voltage, as in the soft start.

  However, as shown in FIG. 8, in the conventional switching power supply as described above, the circuit for setting the soft start time (soft start circuit in the figure) and the circuit for setting the delay time of the timer latch type protection circuit (in the figure) Each has a latch protection circuit).

  Accordingly, two sets of comparators, current sources, and the like having the same configuration are required, and it is useless when considering the chip area when forming an IC.

  When a time setting capacitor is externally attached to the IC, the IC needs two IC pins for connecting these capacitors. In addition, as electric appliances and the like have been reduced in size, it has been necessary to reduce the area of the power supply by reducing the number of IC pins and external components.

For this reason, the time setting means included in the soft start circuit and the latch protection circuit are shared, and the purpose is to reduce the number of pins of the IC, reduce the chip area and external parts, and reduce the size of the device. A switching power supply is known (see, for example, Patent Document 1).
JP 2007-159316 A

  However, in the technique described in Patent Document 1, by sharing the time setting means, it is possible to reduce the number of IC pins, reduce the chip area, reduce external components, and reduce the size of the device. However, when sharing the time setting means, during the soft start operation, the protection operation is reset, prohibiting the execution of the protection operation, and after the soft start operation is completed, the reset is released and the protection operation is started. At the same time, since the soft start operation is prohibited until the start-up, it is difficult to protect the abnormal state of the switching power supply by directly controlling the common IC pin voltage after the soft start operation ends. In order to realize this, there is a problem that the circuit configuration becomes complicated, and the expandability of further functions is impaired.

  Therefore, the present invention has been made in view of the above-described problems, and a soft start charging circuit and a charge / discharge circuit for protection operation are used as a common terminal. A switching power supply that reduces the number of IC pins, reduces the chip area and external components, reduces the size of the device, and enables further function expansion by maintaining the specified voltage and performing control. The purpose is to provide.

  The present invention proposes the following matters in order to solve the above problems.

  (1) The present invention is a switching power supply that converts a DC voltage input to an input terminal into a predetermined constant voltage and outputs the voltage from the output terminal, and performs switching according to the input control signal; By the switching operation of the switching element, an inductor that accumulates electric power from the DC voltage, a rectifier circuit that discharges the electric power accumulated in the inductor, and an output voltage that is output from the output terminal become a predetermined voltage. A switching control circuit unit that performs switching control as described above, and a capacitor is connected to a single control terminal, and the capacitor is charged with a first set current by a charging circuit at the time of start-up to set the terminal voltage of the capacitor The voltage is increased to the set voltage value for a specified time, and switching control is performed by the terminal voltage of the capacitor. The soft operation execution circuit unit that executes the soft start operation, and after the soft start operation is completed, the abnormal state of the switching power supply operation is detected while maintaining the voltage of the set voltage value. And a protection operation execution circuit unit for discharging the capacitor by the discharge circuit and stopping the switching power supply operation when the abnormal state is continuously detected for a predetermined time after the charging of the capacitor is started. A switching power supply is proposed in which a soft start operation is performed by discharging the capacitor from the state of the set voltage value after the voltage of the single control terminal after the start operation is completed.

  According to the present invention, a capacitor is connected to a single control terminal, and a soft operation execution circuit unit that executes a soft start operation at the time of start-up, and in a state where the voltage of the set voltage value is maintained after the soft start operation is completed, When a state is continuously detected for a predetermined time, it is also provided with a protection operation execution circuit unit that stops the switching power supply operation.After the soft start operation is completed, the capacitor is removed from the state where the voltage of the single control terminal is the set voltage value. Since the soft start operation can be performed by discharging, it is possible to reduce the size of the device by reducing the number of pins of the IC and the number of external parts, and to further expand the protection function.

  (2) The present invention monitors the input DC voltage with respect to the switching power supply of (1), and when the DC voltage falls below a set voltage, the capacitor connected to the single control terminal is There has been proposed a switching power supply including an input low voltage detection circuit unit that performs a protective operation by discharging.

  According to the present invention, the input DC voltage is monitored, and when the DC voltage falls below the set voltage, a protective operation is performed by discharging the capacitor connected to the single control terminal. Therefore, by connecting the input low voltage detection circuit unit to a single control terminal, as an additional function, even when the input voltage becomes lower than the set voltage, the circuit protection operation is executed with one terminal. be able to.

  (3) The present invention detects the abnormal state of the switching power supply operation for the switching power source of (1), and after the abnormal state is canceled when the abnormal state is canceled within the predetermined time. 2. The switching power supply according to claim 1, wherein the capacitor is discharged to a voltage of the predetermined value after elapse of a predetermined timer period.

  According to the present invention, when the abnormal state of the switching power supply operation is detected and the abnormal state is canceled within a predetermined time, the capacitor is set to the predetermined time after the predetermined timer period elapses after the abnormal state is canceled. By discharging to a value voltage, the steady state can be restored in a short time.

  (4) The present invention detects the abnormal state of the switching power supply operation in the state where the voltage of the set voltage value is maintained for the switching power source of (1) and continuously detects the abnormal state. The capacitor is charged with a set current of 2, and when the single control terminal voltage reaches a second set voltage higher than the set voltage value, the switching power supply operation is stopped, and the third set current When the capacitor is discharged and the single control terminal voltage reaches a third set voltage smaller than the set voltage value, the switching power supply operation is started, and at the same time, the capacitor is charged with the first set current. The power supply to the output is resumed by a soft start operation, the single control terminal voltage is increased, and the single control terminal voltage is set to the set voltage value again. 2. The switching power supply according to claim 1, wherein when a higher second set voltage is reached, the switching power supply operation is stopped and a series of controls for discharging the capacitor by a third set current is repeated. Has proposed.

  According to the present invention, when the overload state continues, that is, when the terminal voltage of the capacitor reaches a predetermined set voltage that is higher than the steady voltage (first set voltage), the capacitor is quickly turned on. To stop the switching operation, and when the terminal voltage of the capacitor reaches a predetermined set voltage higher than 0 V, the capacitor is started to be charged and restarted intermittently, Protect the circuit.

  (5) In the switching power supply of (1), the present invention includes a latch circuit in the switching control circuit unit, and detects an abnormal state of the switching power supply operation while maintaining the voltage of the set voltage value. When the abnormal state is continuously detected, the capacitor is charged with a second set current, and when the single control terminal voltage reaches a second set voltage higher than the set voltage value, the latch circuit The switching power supply according to claim 1, wherein the switching power supply operation is stopped and the stopped state is maintained unless the latch circuit is reset.

  According to the present invention, when the protection operation execution circuit unit reaches a predetermined set voltage whose single control terminal voltage is higher than the steady voltage, the switching operation is stopped by the latch circuit, and the switching element is turned off to shut off the circuit. And the interrupted state is maintained unless the latch circuit is reset. Therefore, since the abnormal state is avoided and the restart is not performed until the latch circuit is reset, the circuit can be effectively protected.

  (6) In the switching power supply of (4), the present invention includes a counter and a latch circuit in the switching circuit unit, counts the number of times the counter reaches the second set voltage, and sets the count number When the switching power supply reaches the switching power supply operation, the switching power supply operation is stopped by the latch circuit, and the stopped state is maintained unless the latch circuit is reset.

  According to the present invention, the counter counts the number of times the predetermined set voltage higher than the steady voltage is reached, and when the counter reaches the set count number, the switching circuit unit stops the switching operation by the latch circuit. The switching element is turned off to be in the cutoff state, and the cutoff state is maintained unless the latch circuit is reset. Therefore, when the abnormal voltage is detected more than the set number of times, the abnormal state is avoided, and the circuit is effectively protected because the restart is not performed until the latch circuit is reset.

  (7) The present invention relates to the switching power supply of (1) to (6), wherein the charging circuit includes a constant current source, a constant voltage element in which an output of the constant current source determines the steady voltage, and the current source A switching power supply is proposed in which an anode is connected and a cathode is connected to a diode connected to the single control terminal.

  According to the present invention, the charging circuit includes a constant current source, a constant voltage element whose output is determined by a constant current source, a current source and an anode connected, and a cathode connected to a single control terminal. It consists of a diode. Therefore, an accurate charging circuit can be configured with a simple circuit configuration.

  (8) According to the present invention, for the switching power supply of (1) to (6), the charging circuit compares the single control terminal voltage with a reference power supply that determines the steady voltage, and the comparison result Accordingly, there is proposed a switching power supply comprising a buffer for supplying current to the capacitor, and a diode having an output connected to the anode and a cathode connected to the single control terminal. Yes.

  According to the present invention, the charging circuit includes a comparator that compares a single control terminal voltage and a reference power source that determines a steady voltage, a buffer that supplies current to the capacitor according to the comparison result, and an output of the buffer is an anode. And a cathode having a cathode connected to a single control terminal. Therefore, an accurate charging circuit can be configured with a simple circuit configuration.

  (9) According to the present invention, for the switching power supply of (1) to (6), the charging circuit compares the single control terminal voltage with a reference power supply that determines the steady voltage, and an output of the comparator 2 is connected to an output of a constant current source and an anode of a diode, a cathode of the diode is connected to the single control terminal, and supplies current to the capacitor according to the comparison result. The switching power supply according to claim 6 is proposed.

  According to the present invention, the charging circuit includes a comparator that compares a single control terminal voltage and a reference power source that determines a steady voltage, and the output of the comparator is connected to the output of the constant current source and the anode of the diode, and the cathode of the diode Is connected to the single control terminal and supplies current to the capacitor according to the comparison result. Therefore, an accurate charging circuit can be configured with a simple circuit configuration.

  According to the present invention, a capacitor is connected to a single control terminal, and a soft operation execution circuit unit that executes a soft start operation at start-up, and after the soft start operation is completed, an abnormal condition is maintained. When a state is continuously detected for a predetermined time, it is also provided with a protection operation execution circuit unit that stops the switching power supply operation.After the soft start operation is completed, the capacitor is removed from the state where the voltage of the single control terminal is the set voltage value. Since the soft start operation can be performed by discharging, the device can be reduced in size by reducing the number of IC pins and the number of external parts, and the protection function can be further expanded. is there.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Note that the constituent elements in the present embodiment can be appropriately replaced with existing constituent elements and the like, and various variations including combinations with other existing constituent elements are possible. Therefore, the description of the present embodiment does not limit the contents of the invention described in the claims.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS.

<Configuration of switching power supply>
As shown in FIG. 1, the switching power supply according to the present embodiment mainly includes an IC 101, input voltage detection resistors R101 and R102, a brownout detection (input low voltage detection) circuit 103, a timer capacitor C101, and a switching Transformer T101 composed of elements Q101 and Q102, primary winding Np and secondary windings Ns1 and Ns2, resonant capacitor C102, current detection resistor R103, rectifier diodes D201 and D202, rectifier capacitor C201, output voltage It comprises detection resistors R201 and R202, a shunt regulator IC201, and a photocoupler PC101.

  Further, in the IC 101, an SS charging circuit 101, a discharging circuit 102, an oscillation circuit 104, a driving circuit 105, an OCP comparator 106, and a control circuit 107 are provided.

  The switching power supply according to the present embodiment is a switching power supply that controls output power by frequency modulation. The output power is controlled by frequency modulation using the FB terminal current of the IC 101, and the SST terminal voltage of the IC 101 is also controlled. The control circuit 107 can perform frequency modulation in proportion to the output power and limit the output power.

  In the control by the SST terminal voltage, when the SST terminal voltage is low, the output power is limited by increasing the oscillation frequency. As the SST terminal voltage increases, the oscillation frequency is lowered and the output power restriction is relaxed. Further, when the voltage rises above the set voltage value, control is performed to release the restriction on the output power.

  Here, the timer capacitor C101 is connected to the SST terminal which is a functional terminal according to the present invention, and the SST terminal voltage is set by charging and discharging. The SS charging circuit 101 includes a constant current source that supplies a constant current Iss, a constant voltage element CL101 that determines a steady voltage, and a diode D101, and charges the capacitor C101 to execute a soft start function. Further, when an abnormal signal such as an overcurrent is detected, the switch connected to the current source Ira is turned on, and the voltage during steady operation set by the voltage of the constant voltage element CL101 and the forward voltage of the diode D101. On the other hand, by charging the timer capacitor C101, the SST terminal voltage is further increased with respect to the voltage during the steady operation.

  The discharge circuit 102 is a circuit for discharging the charge of the timer capacitor C101. The discharge circuit using the constant current Irf1 and the discharge circuit using the Irf2 current are connected to the SST terminal via a switch controlled by the control circuit 107. The switches are connected to each other and connected to the capacitor timer capacitor C101, and each switch is turned on while detecting an abnormal signal such as an overcurrent in which the SST terminal voltage is higher than the voltage during steady operation. Then, the SST terminal voltage is lowered by acting to extract the charge from the capacitor C101.

  The oscillation circuit 104 supplies a desired oscillation waveform to the drive circuit 105 via the control circuit 107 in accordance with a signal from the control circuit 107. For example, at the time of soft start, an oscillation frequency is gradually changed from a high frequency to a low frequency by a signal from the control circuit 107 and supplied, and when a reset signal is input, oscillation is quickly stopped.

  The drive circuit 105 drives the switching elements Q101 and Q102 by a signal supplied from the control circuit 107. The OCP comparator 106 monitors the switched current flowing through the resonance capacitor C102 by the current detection resistor R103, and generates an abnormal signal for the overcurrent of the switching current.

  The control circuit 107 controls the entire IC 101 according to a predetermined program. Specifically, the switching power supply protection operation is executed by detecting overcurrent of the switching current, Vcc voltage, abnormal heat generation of the IC, and the like. The brown-out detection (input low voltage detection) circuit 103 discharges electric charge from the capacitor C101 when the input voltage becomes lower than a predetermined voltage value, and lowers the voltage of the SST terminal, thereby oscillating the oscillation circuit 104. It has the function of protecting the circuit by increasing the frequency.

  Therefore, in the switching power supply according to this embodiment, a single SST terminal has both a soft start circuit and protection in the event of an abnormality such as overcurrent, and more easily connects a brownout detection circuit or the like to execute a protection operation. can do.

<Operation sequence of switching power supply>
Next, an operation sequence of the switching power supply according to the present embodiment will be described with reference to FIGS. 1 and 2.

  First, in the start-up (A in FIG. 2), when the DC input voltage VDCin is input and the input monitoring voltage Vsen becomes equal to or higher than the predetermined value Vssr, the current supplied from the SS charging circuit 101 (first set current Iss in FIG. 2) The capacitor C101 is gradually charged to raise the voltage of the SST terminal to a steady voltage (first set voltage Vss in FIG. 2), so that a so-called soft start operation is performed, and the oscillation frequency of the oscillation circuit 104 is lowered from a high frequency. Transition to frequency and gradually increase the output power of the switching power supply.

  At this time, the input monitoring voltage Vsen for monitoring the input voltage becomes equal to or higher than the predetermined value Vssr by starting, but if the input monitoring voltage Vsen becomes lower than the predetermined value Vssr for some reason, the transistor having the collector connected to the capacitor C101. Is turned on and rapid discharge is performed by drawing out the electric charge of the capacitor C101 by the discharge current Irf3 by the restart signal, and the voltage at the SST terminal is lowered.

  When the input monitoring voltage Vsen returns to the predetermined value Vssr or higher, the capacitor C101 is gradually charged again with the current supplied from the SS charging circuit 101 (first set current Iss in FIG. 2), and the SST terminal By raising the voltage to a steady voltage (first set voltage Vss in FIG. 2), a so-called soft start operation is performed, the oscillation frequency of the oscillation circuit 104 is changed from a high frequency to a low frequency, and the output power of the switching power supply is gradually increased. To rise.

  Next, in the case of a short-time overload state (“B” in FIG. 2), an abnormal signal is output from the OCP comparator 106 to the control circuit 107. At this time, the control circuit 107 closes a switch having one end connected to the SST terminal and the other end connected to the constant current source Ira (second set current Ira in FIG. 2), charges the capacitor C101, and outputs an abnormal signal. A voltage corresponding to the pulse width is generated as the SST terminal voltage.

  When the overload state is resolved by the abnormal signal, the refresh timer in the control circuit 107 is started. After the refresh timer period elapses, the constant current source Irf2 (fourth set current Irf2 in FIG. 2) rapidly Then, the charge of the timer capacitor C101 is pulled out, and the SST terminal voltage is set to a steady voltage (first set voltage Vss in FIG. 2).

  When the overload state continues (after “C” in FIG. 2), an abnormal signal is output from the OCP comparator 106 to the control circuit 107. At this time, the control circuit 107 closes a switch having one end connected to the SST terminal and the other end connected to the constant current source Ira (second set current Ira in FIG. 2), charges the capacitor C101, and outputs an abnormal signal. A voltage corresponding to the pulse width is generated as the SST terminal voltage.

  When the abnormal signal continues and the SST terminal voltage becomes equal to or higher than the second set voltage Vra, the oscillation is stopped, one end is the SST terminal, and the other end is the constant current source Ira (second set current in FIG. 2). The switch connected to Ira) is opened, the charge of the capacitor C101 is extracted by the constant current source Irf1 (third set current Irf1 in FIG. 2), and the SST terminal voltage is set to Vrs (third set voltage Vrs in FIG. 2). ) Discharge to voltage.

  Thereafter, when the overload state continues, the above operation is repeated. Therefore, in the switching power supply according to the present embodiment, when the overload state continues, that is, when the terminal voltage of the capacitor reaches a predetermined set voltage that is higher than the steady voltage (first set voltage). In this case, the capacitor is rapidly discharged to stop the oscillation, and when the capacitor terminal voltage reaches a predetermined set voltage higher than 0 V, the capacitor is started to be charged and restarted intermittently. Doing so protects the circuit.

<Detection and protection operation of abnormal state by SST terminal voltage>
The detection and protection operation of the abnormal state due to the SST terminal voltage will be described with reference to FIGS.

  FIG. 3 is a block diagram illustrating an example of a latch-type protection circuit. According to this figure, the latch-type protection circuit of this example includes a capacitor C101 connected to the SST terminal, a voltage detection circuit 111 for detecting the voltage of the capacitor C101, and a latch circuit 110.

  When the latch circuit 110 determines that an abnormal state is detected based on the voltage value detected by the voltage detection circuit 111, the latch circuit 110 outputs a latch signal to the drive circuit 105, stops the drive circuit 105, and protects the circuit. Note that to release the stop state of the drive circuit, it is necessary to output a reset signal from the control circuit 107 to the latch circuit 110. Therefore, since the abnormal state is avoided and the restart is not performed until the latch circuit is reset, the circuit can be effectively protected.

  FIG. 4 is a block diagram illustrating an example of a latch-type protection circuit. According to this figure, the latch-type protection circuit of this example counts the capacitor C101 connected to the SST terminal, the voltage detection circuit 111 that detects the voltage of the capacitor C101, and the detection result of the voltage detection circuit 111. The counter circuit 112 and the latch circuit 110 are included.

  The counter circuit 112 outputs a signal to the latch circuit 110 when the count value becomes a predetermined value or more. The latch circuit 110 outputs a latch signal to the driving circuit 105, stops the driving circuit 105, and protects the circuit. Note that to release the stop state of the drive circuit, it is necessary to output a reset signal from the control circuit 107 to the latch circuit 110. Therefore, when the abnormal voltage is detected more than the set number of times, the abnormal state is avoided, and the circuit is effectively protected because the restart is not performed until the latch circuit is reset.

<Modification of switching power supply>
FIG. 5 is a modification of the first embodiment. In the first embodiment, the brownout detection (input low voltage detection) circuit 103 is an external circuit of the IC 101. However, in this modification, the brownout detection (input low voltage detection) circuit is provided inside the IC101. 103 is built-in.

  By doing so, although the chip area of the IC 101 is slightly increased, the entire switching power supply can be reduced in size. Further, since the brownout detection (input low voltage detection) circuit 103 is built in the IC 101, it is not necessary for the user to configure the circuit externally, and it is possible to perform a high function without taking extra time. The switching power supply can be configured.

<Modification of SS charging circuit>
FIG. 6 is a diagram showing a modification of the SS charging circuit 101 shown in the first embodiment. According to this figure, in the SS charging circuit of this example, a constant current (Iss) source 201 is connected to a supply source of the inverter IC 202, and is connected to the constant current (Iss) source 201, and a predetermined reference voltage Vr3. And the SST terminal voltage are connected to a comparator IC203, and in response to the comparison result of the comparator IC203, an Iss current is supplied from the buffer 202 to the capacitor C101 via the diode D101 in the inverted logic. .

  That is, the function of the present charging circuit is the same as that of the first embodiment, and the charge is supplied to the capacitor C101 via the diode D101 at the time of start-up or the like when the SST terminal voltage is lower than the predetermined reference voltage Vr3. Thus, it has a function of charging.

  This charging circuit is slightly more complicated in its circuit configuration than the SS charging circuit 101 in the first embodiment, but can set a voltage with higher accuracy than the SS charging circuit 101 in the first embodiment. Has the advantage of being.

  FIG. 7 is a diagram showing another modification of the SS charging circuit 101 shown in the first embodiment. According to this figure, the SS charging circuit of this example includes a constant current (Iss) source 202, an open collector type comparator IC 204 that compares a predetermined reference voltage Vr3 and the SST terminal voltage, and a charging current to the capacitor C101. It is comprised from the diode D101 to supply.

  That is, the function of this charging circuit is the same as that of the first embodiment, and at the time of start-up or the like when the SST terminal voltage is lower than the predetermined reference voltage Vr3, the capacitor is connected from the constant current source 202 via the diode D101. It has a function of supplying a charge to C101 and charging it.

  This charging circuit is slightly more complicated in its circuit configuration than the SS charging circuit 101 in the first embodiment, but can set a voltage with higher accuracy than the SS charging circuit 101 in the first embodiment. Has the advantage of being.

  The embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to the embodiments, and includes designs and the like that do not depart from the gist of the present invention.

It is a figure which shows the structure of the switching power supply which concerns on 1st Embodiment. It is a sequence diagram which shows operation | movement of the switching power supply which concerns on 1st Embodiment. It is a figure which shows the structure of the latch type protection circuit of the switching power supply which concerns on 1st Embodiment. It is a figure which shows the structure of the latch type protection circuit of the switching power supply which concerns on 1st Embodiment. It is a figure which shows the structure of the switching power supply which concerns on a modification. It is a figure which shows the structure of the charging circuit which concerns on a modification. It is a figure which shows the structure of the charging circuit which concerns on a modification. It is the figure which showed the internal structure of the soft start / latch protection circuit which concerns on a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... SS charge circuit 102 ... Discharge circuit 103 ... Brown-out detection (input low voltage detection) circuit 104 ... Oscillation circuit 105 ... Drive circuit 106 ... OCP comparator 107 ... Control Circuit 110 ... Latch circuit 111 ... Voltage detection circuit 112 ... Counter circuit 201 ... Constant current source 202 ... Constant current source C101 ... Timer capacitor C102 ... Resonance capacitor C201 ... Rectifier capacitor D101 ... Diode D201 ... Rectifier diode D202 ... Rectifier diode IC101 ... Control IC
IC201 ... Shunt regulator IC202 ... Buffer IC203 ... Comparator IC204 ... Comparator Np ... Primary winding Ns1 ... Secondary winding Ns2 ... Secondary winding PC101 ... Photocoupler Q101 ... Switching element Q102 ... Switching element R101 ... Input voltage detection resistor R102 ... Input voltage detection resistor R103 ... Current detection resistor R201 ... Output voltage detection resistor R202 ... Output voltage detection Resistance T101 ... Transformer

Claims (9)

A switching power supply that converts a DC voltage input to an input terminal into a predetermined constant voltage and outputs it from an output terminal,
A switching element that performs switching in accordance with an input control signal, an inductor that accumulates power from the DC voltage by a switching operation of the switching element, and a rectifier circuit that discharges power accumulated in the inductor; A switching control circuit unit that performs switching control so that the output voltage output from the output terminal becomes a predetermined voltage,
A capacitor is connected to a single control terminal, and the capacitor is charged with a first set current by a charging circuit at the time of start-up, and the terminal voltage of the capacitor is increased to a set voltage value at a set time. A soft operation execution circuit unit that executes a soft start operation by performing switching control according to the terminal voltage, and detects the abnormal state of the switching power supply operation in a state where the voltage of the set voltage value is maintained after the soft start operation is completed. At the same time, when the charging of the capacitor is started from the set voltage value and the abnormal state is continuously detected for a predetermined time, the capacitor is discharged by a discharge circuit, and a protection operation execution circuit unit that stops the switching power supply operation and In addition,
Furthermore, the switching power supply is characterized in that the soft start operation is executed by discharging the capacitor from the state of the set voltage value when the voltage of the single control terminal after the soft start operation ends.   The input low voltage detection circuit unit that monitors the input DC voltage and performs a protection operation by discharging the capacitor connected to the single control terminal when the DC voltage is lower than a set voltage. The switching power supply according to claim 1, further comprising:   When the abnormal state of the switching power supply operation is detected and the abnormal state is canceled within the predetermined time, the capacitor is set to the predetermined value after a predetermined timer period elapses after the abnormal state is canceled. The switching power supply according to claim 1, wherein the switching power supply is discharged to a voltage of   In a state where the voltage of the set voltage value is maintained, an abnormal state of the switching power supply operation is detected, and when the abnormal state is continuously detected, the capacitor is charged by a second set current, and the single When the control terminal voltage reaches a second set voltage higher than the set voltage value, the switching power supply operation is stopped and the capacitor is discharged by a third set current, and the single control terminal voltage is When the third set voltage smaller than the set voltage value is reached, the switching power supply operation is started. At the same time, the capacitor is charged with the first set current and the power supply to the output is restarted by the soft start operation. When one control terminal voltage is increased and the single control terminal voltage reaches a second set voltage that is higher than the set voltage value again, the switching voltage is increased. It stops the operation, the switching power supply according to claim 1, characterized by repeating the sequence of control for discharge of the capacitor by a third set current. The switching control circuit unit includes a latch circuit,
In a state where the voltage of the set voltage value is maintained, an abnormal state of the switching power supply operation is detected, and when the abnormal state is continuously detected, the capacitor is charged by a second set current, and the single The switching power supply operation is stopped by the latch circuit when the control terminal voltage reaches a second set voltage higher than the set voltage value, and the stopped state is maintained unless the latch circuit is reset. The switching power supply according to 1. The switching circuit unit includes a counter and a latch circuit,
The counter counts the number of times the second set voltage is reached, and when the set count is reached, the switching power supply operation is stopped by the latch circuit, and the stopped state is maintained unless the latch circuit is reset. The switching power supply according to claim 4. The charging circuit is
A constant current source;
A constant voltage element in which the output of the constant current source determines the steady voltage;
A diode in which the current source and the anode are connected and a cathode is connected to the single control terminal;
The switching power supply according to any one of claims 1 to 6, characterized by comprising: The charging circuit is
A comparator that compares the single control terminal voltage with a reference power supply that defines the steady voltage;
A buffer for supplying a current to the capacitor according to the comparison result;
The switching power supply according to any one of claims 1 to 6, wherein an output of the buffer is connected to an anode, and a cathode is connected to the single control terminal. The charging circuit is
A comparator that compares the single control terminal voltage with a reference power supply that defines the steady voltage;
The output of the comparator is connected to the output of a constant current source and the anode of a diode, the cathode of the diode is connected to the single control terminal, and current is supplied to the capacitor according to the comparison result. The switching power supply according to any one of claims 1 to 6.

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