JP7224953B2 - SWITCHING POWER SUPPLY DEVICE, POWER CONTROL CIRCUIT, AND SWITCHING POWER SUPPLY CONTROL METHOD - Google Patents

Description

The present invention relates to a switching power supply, a power supply control circuit, and a control method for a switching power supply.

Conventionally, the phase of the current flowing through the switching MOSFET is detected to determine whether the operation mode is the normal mode or the standby mode, and when the standby mode is determined, the burst mode operation is performed. A switching power supply device that starts is known (see, for example, Patent Document 1).

In such a conventional switching power supply device, power consumption is suppressed by performing burst operation of the oscillator when the feedback current increases at startup.

However, in this conventional switching power supply, the soft start time becomes long during such burst operation. As a result, the switching loss cannot be sufficiently reduced, and the switching frequency increases, resulting in a decrease in the efficiency of power supply to the secondary side of the transformer. was there.

JP 2010-206949

Therefore, the present invention adjusts and switches so that the soft-start state is shortened at the timing immediately after startup, and when a light load is detected in burst mode, the soft-start time is shortened and the switching frequency is quickly lowered. An object of the present invention is to provide a switching power supply device capable of improving the efficiency of power supply to the secondary side of a transformer.

A switching power supply device according to an aspect of the present invention includes:
a power input terminal to which a power supply voltage is supplied;
a first switch element having one end connected to the power supply input terminal and the other end connected to an output voltage node;
a second switch element having one end connected to the output voltage node and the other end connected to a fixed potential;
a primary coil connected between the output voltage node and the fixed potential;
a secondary coil that forms a transformer with the primary coil;
a load voltage terminal connected to a load and supplied with a voltage obtained by rectifying the voltage of the secondary coil of the transformer;
A first adjustment capacitor is connected between a reference voltage terminal and the fixed potential, and a reference voltage based on a charged voltage of the first adjustment capacitor charged with a constant current is applied to the reference voltage terminal. a voltage adjustment circuit for applying to and adjusting the reference voltage at the reference voltage terminal;
A soft start operation is performed to decrease the switching frequencies of the first and second switch elements as the reference voltage rises, and when the reference voltage reaches a preset reference voltage, the load a power supply control circuit that controls at a predetermined switching frequency to alternately turn on/off the first switching element and the second switching element so that the load voltage of the voltage terminal becomes a preset target voltage; , and
At startup, until the reference voltage first reaches the reference voltage, the voltage regulation circuit applies the reference voltage based on the charged voltage of the first regulation capacitor charged with a constant current to the reference voltage terminal. It is set to the initial state to apply,
after the reference voltage reaches the reference voltage,
The power control circuit is
setting the voltage adjustment circuit to maintain an adjustment state in which the reference voltage rises more steeply than the soft start operation;
during burst mode control, during a stop period for stopping the supply of power to the load voltage terminal, forcibly discharging the charge of the first adjustment capacitor;
It is characterized in that the reference voltage rises steeper than the soft start operation when the first adjustment capacitor is charged during an oscillation period during which power is supplied to the load voltage terminal.

In the switching power supply,
The voltage regulation circuit is
the first adjustment capacitor having one end connected to the reference voltage terminal;
a voltage adjustment resistor having one end connected to the other end of the first adjustment capacitor and the other end connected to the fixed potential;
a voltage adjustment switch element connected between the other end of the first adjustment capacitor and the fixed potential;
The power control circuit is
turning on the voltage regulating switch element to set the voltage regulating circuit to the initial state, and turning off the voltage regulating switch element to set the voltage regulating circuit to the regulated state. characterized by

In the switching power supply,
The voltage regulation circuit is
A second adjustment capacitor having one end connected to the reference voltage terminal and the other end connected to the fixed potential is further provided.

In the switching power supply,
The power control circuit is
The voltage adjustment circuit is reset to the initial state when an abnormal operation of the switching power supply is detected or when an overcurrent protection function is to be performed.

In the switching power supply,
The power control circuit is
During the stop period, the voltage of the reference voltage terminal is forcibly set to the fixed potential by discharging the charge of the first adjustment capacitor, thereby stopping the switching of the first and second switch elements. characterized by

In the switching power supply,
The power control circuit is
a first constant current source that supplies a first constant current to the reference voltage terminal;
a stop switch element connected between the reference voltage terminal and the fixed potential;
Turning on the switching element for stopping during the stopping period,
The switching element for stopping is turned off during the oscillation period.

In the switching power supply,
The voltage regulation circuit is
the first adjustment capacitor having one end connected to the reference voltage terminal and the other end connected to the fixed potential;
a second constant current source that outputs a second constant current;
a current adjusting switch element having one end connected to the output of the second constant current source and the other end connected to the reference voltage terminal;
The power control circuit is
turning on the current regulating switch element to set the voltage regulating circuit to the regulated state, and turning off the current regulating switch element to set the voltage regulating circuit to the initial state. characterized by

In the switching power supply,
The power control circuit is
an oscillator that outputs an oscillation signal for generating a switching pulse that controls the first switch element and the second switch element;
a burst mode switching circuit for setting the voltage so that the reference voltage rises steeper than the soft start operation when the first adjustment capacitor is charged during an oscillation period for supplying power to the load voltage terminal; ,
a control unit that controls the first switch element and the second switch element by a switching pulse generated from the oscillation signal output by the oscillator;
a voltage detection circuit that detects a detected voltage based on the power supply voltage and turns on/off the operation of the oscillator according to the detected voltage;
and a soft start circuit that sets the oscillation frequency of the oscillator gradually from a high frequency to a low frequency according to the reference voltage of the reference voltage terminal to execute a soft start.

In the switching power supply,
an output detection circuit that detects the load voltage;
a photocoupler that passes a detection current corresponding to the load voltage detected by the output detection circuit to a feedback terminal;
The oscillator controls the oscillation frequency of the switching pulse based on the load voltage of the load voltage terminal, with an oscillation frequency corresponding to the detected current of the feedback terminal applied via the photocoupler. and

In the switching power supply,
a resonance capacitor having one end connected to the primary coil;
a current detection resistor having one end connected to the other end of the resonance capacitor and the other end connected to the fixed potential;
The power control circuit is
It is characterized by further comprising an overcurrent protection circuit that detects the current flowing through the first switch element and the second switch element based on the current flowing through the current detection resistor.

In the switching power supply,
The soft start circuit is
the first constant current source that supplies the first constant current to the reference voltage terminal;
the stop switch element connected between the reference voltage terminal and the fixed potential;
A non-inverting input terminal is connected to the reference voltage terminal, an inverting input terminal is supplied with the reference voltage, and a comparison result signal corresponding to a result of comparing the reference voltage of the reference voltage terminal and the reference voltage is supplied to the and a comparator that outputs to the burst mode switching circuit,
The burst mode switching circuit is
while the comparison result signal indicates that the reference voltage is less than the reference voltage, turning on the voltage adjustment switch element to set the voltage adjustment circuit to the initial state;
After that, after the comparison result signal indicates that the reference voltage is equal to or higher than the reference voltage, turning off the voltage adjustment switch element to set the voltage adjustment circuit to the adjustment state,
After that, when an abnormal operation of the switching power supply is detected, or when the overcurrent protection function is to be executed, the voltage adjustment switch element is controlled to be ON, and the voltage adjustment circuit Y is forcibly operated. reset from the adjusted state to the initial state.

In the switching power supply,
The burst mode switching circuit is
a set terminal to which the comparison result signal output by the comparator is input; a first reset terminal to which a first reset signal indicating detection of abnormal operation of the switching power supply device is input; and overcurrent protection. a flip-flop circuit having a second reset terminal to which a second reset signal indicating execution of a functional operation is input, and an output terminal for outputting a logic signal;
a driver circuit that receives the logic signal output from the flip-flop circuit and outputs an adjustment signal based on the logic signal;
The voltage adjustment circuit is characterized in that the voltage adjustment switch element is controlled according to the adjustment signal to be set to the initial state or the adjustment state.

In the switching power supply,
The oscillator outputs a light load detection signal when the load state is a light load,
The stop switch element of the soft start circuit is turned on by the light load detection signal.

A power supply control circuit according to an aspect of the present invention includes:
a power supply input terminal to which a power supply voltage is supplied; a first switching element having one end connected to the power supply input terminal and the other end connected to an output voltage node; one end connected to the output voltage node; is connected to a fixed potential, a primary coil connected between the output voltage node and the fixed potential, and a secondary coil forming a transformer together with the primary coil , a load voltage terminal connected to a load and supplied with a voltage obtained by rectifying the voltage of the secondary coil of the transformer; and a first adjusting capacitor connected between a reference voltage terminal and the fixed potential. a voltage adjustment circuit that applies to the reference voltage terminal a reference voltage based on the charged voltage of the first adjustment capacitor that is charged with a constant current and adjusts the reference voltage of the reference voltage terminal; A power supply control circuit applied to a switching power supply device comprising
A soft start operation is performed to decrease the switching frequencies of the first and second switch elements as the reference voltage rises, and when the reference voltage reaches a preset reference voltage, the load The first switch element and the second switch element are alternately turned on/off at a predetermined switching frequency so that the load voltage at the voltage terminal becomes a preset target voltage. cage,
At startup, until the reference voltage first reaches the reference voltage, the voltage regulation circuit applies the reference voltage based on the charged voltage of the first regulation capacitor charged with a constant current to the reference voltage terminal. It is set to the initial state to apply,
after the reference voltage reaches the reference voltage,
setting the voltage adjustment circuit to maintain an adjustment state in which the reference voltage rises more steeply than the soft start operation;
during burst mode control, during a stop period for stopping the supply of power to the load voltage terminal, forcibly discharging the charge of the first adjustment capacitor;
It is characterized in that the reference voltage rises steeper than the soft start operation when the first adjustment capacitor is charged during an oscillation period during which power is supplied to the load voltage terminal.

A control method for a switching power supply device according to an aspect of the present invention includes:
a power supply input terminal to which a power supply voltage is supplied; a first switching element having one end connected to the power supply input terminal and the other end connected to an output voltage node; one end connected to the output voltage node; is connected to a fixed potential, a primary coil connected between the output voltage node and the fixed potential, and a secondary coil forming a transformer together with the primary coil , a load voltage terminal connected to a load and supplied with a voltage obtained by rectifying the voltage of the secondary coil of the transformer; and a first adjusting capacitor connected between a reference voltage terminal and the fixed potential. a voltage adjustment circuit that applies to the reference voltage terminal a reference voltage based on the charged voltage of the first adjustment capacitor that is charged with a constant current and adjusts the reference voltage of the reference voltage terminal; A soft start operation is performed to decrease the switching frequencies of the first and second switch elements as the reference voltage rises, and when the reference voltage reaches a preset reference voltage, the load a power supply control circuit that controls at a predetermined switching frequency to alternately turn on/off the first switching element and the second switching element so that the load voltage of the voltage terminal becomes a preset target voltage; A control method for a switching power supply device comprising
At startup, until the reference voltage first reaches the reference voltage, the voltage regulation circuit applies the reference voltage based on the charged voltage of the first regulation capacitor charged with a constant current to the reference voltage terminal. It is set to the initial state to apply,
after the reference voltage reaches the reference voltage,
The power control circuit is
setting the voltage adjustment circuit to maintain an adjustment state in which the reference voltage rises more steeply than the soft start operation;
during burst mode control, during a stop period for stopping the supply of power to the load voltage terminal, forcibly discharging the charge of the first adjustment capacitor;
It is characterized in that the reference voltage rises steeper than the soft start operation when the first adjustment capacitor is charged during an oscillation period during which power is supplied to the load voltage terminal.

A switching power supply device according to an aspect of the present invention includes a power supply input terminal to which a power supply voltage is supplied, a first switch element having one end connected to the power supply input terminal and the other end connected to an output voltage node, is connected to the output voltage node and the other end is connected to a fixed potential; a primary coil connected between the output voltage node and the fixed potential; the primary coil and the transformer; a secondary coil, a load voltage terminal connected to a load and supplied with a voltage obtained by rectifying the voltage of the secondary coil of the transformer, and a first voltage terminal connected between a reference voltage terminal and a fixed potential. a voltage adjustment circuit having an adjustment capacitor, applying a reference voltage based on the charged voltage of the first adjustment capacitor charged with a constant current to a reference voltage terminal, and adjusting the reference voltage of the reference voltage terminal; As the reference voltage rises, a soft start operation is performed to decrease the switching frequencies of the first and second switch elements. a power supply control circuit that controls at a predetermined switching frequency to alternately turn on/off the first switch element and the second switch element so that the voltage reaches a preset target voltage.

At the start-up, the voltage adjustment circuit is in an initial state in which the reference voltage based on the charged voltage of the first adjustment capacitor charged with a constant current is applied to the reference voltage terminal until the reference voltage first reaches the reference voltage. and after the reference voltage reaches the reference voltage, the power supply control circuit sets the voltage regulation circuit to hold it in a regulation state that causes the reference voltage to rise steeper than the soft-start operation. , during the burst mode control, the charge of the first adjustment capacitor is forcibly discharged during the stop period for stopping the supply of power to the load voltage terminal, and during the oscillation period during which power is supplied to the load voltage terminal, the first When the adjustment capacitor is charged, the reference voltage is made to rise steeper than the soft start operation.

As a result, according to the switching power supply device of the present invention, adjustment switching is performed so that the soft-start state is shortened at the timing immediately after startup, and when a light load is detected in the burst mode, the soft-start time is shortened and switching is performed. By lowering the frequency quickly, the efficiency of the power supply to the secondary side of the transformer can be improved.

FIG. 1 is a diagram showing an example of the configuration of a switching power supply device 100 according to this embodiment. FIG. 2 is a diagram showing an example of the configuration of the power supply control circuit 7 of the switching power supply device 100 shown in FIG. FIG. 3 is a diagram showing an example of a configuration including a configuration in the vicinity of the voltage adjustment circuit Y, the soft start circuit SF, and the burst mode switching circuit BM shown in FIG. 2, according to the first embodiment. FIG. 4 is a diagram illustrating an example of operation in the normal mode of the switching power supply device 100 according to the first embodiment. FIG. 5 is a diagram illustrating an example of burst mode operation of the switching power supply device 100 according to the first embodiment. FIG. 6 is a diagram showing an example of the configuration of the voltage adjustment circuit Y, soft start circuit SF, and burst mode switching circuit BM according to the second embodiment. FIG. 7 is a diagram illustrating an example of the waveform of the reference voltage VY at the reference voltage terminal SST according to the second embodiment. FIG. 8 is a diagram showing an example of configurations of the voltage adjustment circuit Y, soft start circuit SF, and burst mode switching circuit BM according to the third embodiment.

FIG. 1 is a diagram showing an example of the configuration of a switching power supply device 100 according to the first embodiment. 2 is a diagram showing an example of the configuration of the power supply control circuit 7 of the switching power supply device 100 shown in FIG. 1. As shown in FIG. Also, FIG. 3 is a diagram showing an example of a configuration including a configuration in the vicinity of the voltage adjustment circuit Y, the soft start circuit SF, and the burst mode switching circuit BM shown in FIG. 2, according to the first embodiment.

For example, as shown in FIG. 1, the switching power supply device 100 includes power supply input terminals 1a and 1b, a smoothing capacitor 2, an input power supply line 3, and a transformer 4 (a primary side coil Np1, secondary side coils Ns1 and Ns2 ), resonance capacitor 5, current detection resistor 6, power supply control circuit 7, voltage dividing circuit B (first voltage dividing resistor 8, second voltage dividing resistor 9), and first switch element 11 , second switch element 12, diodes 13 and 14, output power supply lines 15 and 16, smoothing capacitor 17, load voltage terminal TL, voltage adjustment circuit Y, output detection circuit 21, and photocoupler 22 , a capacitor 23 for oscillation adjustment, and a resistor 24 for oscillation adjustment.

A power supply voltage VIN is supplied to the power supply input terminal 1a as shown in FIG. 1, for example. The power input terminal 1a is connected to the input power line 3. As shown in FIG.

The power input terminal 1b is connected to a fixed potential (ground potential), for example, as shown in FIG. That is, the power input terminal 1b is grounded.

A smoothing capacitor 2 is connected between the power input terminal 1a and the power input terminal 1b.

The first switch element 11 has one end connected to the power supply input terminal 1a and the other end connected to the output voltage node A. As shown in FIG.

This first switch element 11 is, for example, a MOSFET as shown in FIG. A high-side switching pulse VGH is supplied from the VGH terminal of the power supply control circuit 7 to the gate of the first switch element 11 .

The second switch element 12 has one end connected to the output voltage node A and the other end connected to a fixed potential (ground potential).

This second switch element 12 is, for example, a MOSFET as shown in FIG. A low-side switching pulse VGL is supplied from the VGL terminal of the power supply control circuit 7 to the gate of the second switch element 12 .

Thus, the first switch element 11 and the second switch element 12 are connected in series between the input power supply line 3 and the ground.

For example, as shown in FIG. 1, the connection point (output voltage node A) between the first switch element 11 and the second switch element 12 is connected to the terminal Vs of the power supply control circuit 7 .

Also, the primary coil Np1 is connected between the output voltage node A and a fixed potential (ground potential).

One end of the resonance capacitor 5 is connected to the primary coil Np1, for example, as shown in FIG.

1, one end of the current detection resistor 6 is connected to the other end of the resonance capacitor 5, and the other end is connected to a fixed potential (ground potential).

Thus, the connection point (output voltage node A) between the first switch element 11 and the second switch element 12 is connected to one end of the primary coil Np1 of the transformer 4, and the primary coil Np1 of the transformer 4 is connected to one end. is grounded through a resonance capacitor 5 and a current detection resistor 6 .

Further, the secondary coils Ns1 and Ns2 constitute a primary coil Np1 and a transformer 4, as shown in FIG. 1, for example.

One end of the secondary coil Ns1 of the transformer 4 is connected to the anode of the diode 13, and one end of the secondary coil Ns2 of the transformer 4 is connected to the anode of the diode 14, as shown in FIG. ing.

Also, the cathode of the diode 13 and the cathode of the diode 14 are connected to the output power supply line 15 .

A connection point between the secondary coil Ns1 and the secondary coil Ns2 of the transformer 4 is connected to the output power supply line 16 . A smoothing capacitor 17 is connected between the output power line 15 and the output power line 16 .

A load 20 is connected between the output power supply line 15 and the output power supply line 16 (between the load voltage terminal TL and the ground potential).

Thus, the load voltage terminal TL is connected to the load 20, for example, as shown in FIG. .

Also, the voltage dividing circuit B includes, for example, a first voltage dividing resistor 8 and a second voltage dividing resistor 9, as shown in FIG.

That is, the voltage dividing circuit B outputs the divided voltage at the voltage dividing terminal to the voltage detecting circuit VD (FIG. 2) as the detected voltage.

The first voltage dividing resistor 8 has one end connected to the power input terminal 1a and the other end connected to a voltage dividing terminal (terminal Vsen of the power control circuit 7).

The second voltage dividing resistor 9 has one end connected to the voltage dividing terminal (the terminal Vsen of the power supply control circuit 7) and the other end connected to a fixed potential.

Thus, the first voltage dividing resistor 8 and the second voltage dividing resistor 9 are connected in series between the input power supply line 3 and the ground.

In this way, for example, as shown in FIG. supplied to Vsen.

Also, the output detection circuit 21 is adapted to detect the load voltage VL at the load voltage terminal TL, for example, as shown in FIG.

1, the photocoupler 22 causes a detection current corresponding to the load voltage VL detected by the output detection circuit 21 to flow through the feedback terminal FB of the power supply control circuit 7, for example.

Thus, the output between the output power supply line 15 and the output power supply line 16 is detected by the output detection circuit 21 . A detection output from the output detection circuit 21 is fed back to the FB terminal of the power supply control circuit 7 via the photocoupler 22 .

Also, the oscillation adjustment capacitor 23 is connected between the terminal Ct of the power supply control circuit 7 and the ground, for example, as shown in FIG.

Also, the oscillation adjusting resistor 24 is connected between the Rt terminal of the power supply control circuit 7 and the ground, as shown in FIG. 1, for example.

A ground terminal GND of the power supply control circuit 7 is grounded.

Here, in the switching power supply device 100, switching pulses VGH and VGL for the first switch element 11 on the high side and the second switch element 12 on the low side are output from the terminals VGH and VGL of the power supply control circuit 7. be.

These switching pulses VGH and VGL alternately switch the first switching element 11 on the high side and the second switching element 12 on the low side, and electromagnetic energy is accumulated in the primary coil Np1 of the transformer 4. Energy is transferred to the secondary coils Ns1, Ns2.

The secondary side output of the transformer 4 is rectified by the diodes 13 and 14 and sent to the load 20 .

Also, the output of the secondary side of the transformer 4 is detected by the output detection circuit 21 . This detection output is fed back to the feedback terminal FB of the power control circuit 7 via the photocoupler 22 .

The power control circuit 7 controls the frequency of the switching pulse based on the detected current fed back to the feedback terminal FB.

1 and 3, the voltage adjustment circuit Y has a first adjustment capacitor Css1 connected between the reference voltage terminal SST and a fixed potential (ground potential).

The voltage adjustment circuit Y applies a reference voltage based on the charging voltage of the first adjustment capacitor Css1 charged with a constant current to the reference voltage terminal SST, and adjusts the reference voltage VY of the reference voltage terminal SST. It has become.

The power supply control circuit 7 also performs a soft start operation to decrease the switching frequencies of the first and second switch elements 11 and 12 as the reference voltage VY rises.

When the reference voltage VY reaches a preset reference voltage VZ, the power supply control circuit 7 controls the first switch element 11 so that the load voltage VL at the load voltage terminal TL reaches a preset target voltage. and the second switch element 12 are alternately turned on/off at the switching frequency described above.

Here, for example, when the switching power supply device 100 (power supply control circuit 7) is started, the voltage adjustment circuit Y is charged with a constant current until the reference voltage VY first reaches the reference voltage VZ. An initial state is set in which the reference voltage VY based on the charging voltage of Css1 is applied to the reference voltage terminal SST.
After the reference voltage VY reaches the reference voltage VZ, the power supply control circuit 7 keeps the voltage adjustment circuit Y in an adjustment state in which the reference voltage VY rises steeper than the soft start operation. During the stop period during which the power supply to the load voltage terminal TL is stopped during burst mode control, the charge of the first adjustment capacitor Css1 is forcibly discharged and the power to the load voltage terminal TL is discharged. is supplied, the reference voltage VY rises steeper than the soft start operation when the first adjustment capacitor Css1 is charged.

Here, for example, as shown in FIGS. 1 and 3, this voltage adjustment circuit Y includes the above-described first adjustment capacitor Css1, voltage adjustment resistor Rss, and voltage adjustment switch element SWR. Prepare.

One end of the first adjustment capacitor Css1 is connected to the reference voltage terminal SST.

The voltage adjusting resistor Rss has one end connected to the other end of the first adjusting capacitor Css1 and the other end connected to a fixed potential (ground potential).

Also, the voltage adjustment switch element SWR is connected between the other end of the first adjustment capacitor Css1 and a fixed potential (ground potential).

For example, the power supply control circuit 7 outputs an adjustment signal via the terminal SSC to turn on the voltage adjustment switch element SWR, thereby setting the voltage adjustment circuit Y to the initial state.

On the other hand, the power supply control circuit 7 outputs an adjustment signal via the terminal SSC to turn off the voltage adjustment switch element SWR, thereby setting the voltage adjustment circuit Y to the adjustment state.

For example, when detecting an abnormal operation of the switching power supply device 100, or when executing the overcurrent protection function operation of the switching power supply device 100, the power supply control circuit 7 switches the voltage adjustment circuit Y to is reset to its initial state.

Further, the power supply control circuit 7 forcibly sets the voltage of the reference voltage terminal SST to a fixed potential (ground potential) by discharging the charge of the first adjustment capacitor Css1 during the stop period described above. The switching of the first and second switch elements 11 and 12 is stopped.

For example, as shown in FIG. 2, such a power supply control circuit 7 includes an oscillator OSC, a burst mode switching circuit BM, a soft start circuit SF, a control circuit (control section) CON, a voltage detection circuit VD, and an overcurrent protection circuit X.

The voltage detection circuit VD, for example, as shown in FIG. 2, detects a detection voltage Vsen based on the power supply voltage VIN, and turns on/off the operation of the oscillator OSC according to the detection voltage Vsen. there is

Also, the overcurrent protection circuit X detects the current flowing through the first switching element 11 and the second switching element 12 based on the current flowing through the current detection resistor 6 .

The overcurrent protection circuit X detects the phases of the currents flowing through the first and second switch elements 11 and 12, and determines whether the load 20 is heavy (normal mode) or light (standby mode). or is determined.

Further, the oscillator OSC outputs an oscillation signal for generating switching pulses VGH and VGL for controlling the first switch element 11 and the second switch element 12, for example, as shown in FIG. there is

The oscillator OSC controls the oscillation frequency of the switching pulses VGH and VGL based on the load voltage VL at the load voltage terminal TL and the oscillation frequency corresponding to the detected current at the feedback terminal FB applied via the photocoupler 22. .

Further, for example, this oscillator OSC outputs a light load detection signal SR when the load 20 is in a light load state.

On the other hand, the oscillator OSC does not output the light load detection signal SR when the load 20 is heavy (not light).

The time constant of this oscillator OSC can be set by a capacitor 23 connected to the terminal Ct and a resistor 24 connected to the terminal RT.

The control circuit CON controls the first switch element 11 and the second switch element 12 by switching pulses VGH and VGL generated from the oscillation signal output from the oscillator OSC, for example, as shown in FIG. It's becoming

Further, the soft start circuit SF gradually sets the oscillation frequency of the oscillator OSC from a high frequency to a low frequency according to the reference voltage VY of the reference voltage terminal SST (here, as the reference voltage VY rises). to perform a soft start.

The time constant of this soft start circuit SF is set by the voltage adjustment circuit Y connected to the reference voltage VY of the reference voltage terminal SST.

Here, for example, as shown in FIG. 3, the soft start circuit SF includes a first constant current source Iss1, a stop switch element SWC1, and a comparator COMP.

The first constant current source Iss1 supplies a first constant current to the reference voltage terminal SST.

The stop switch element SWC1 is connected between the reference voltage terminal SST and a fixed potential (ground potential).

The stop switch element SWC1 is turned on by the light load detection signal SR output by the oscillator OSC.

That is, the soft start circuit SF turns on the stop switch element SWC1 during the above-described stop period.

As a result, the charge of the first adjustment capacitor Css1 is discharged, and the voltage of the reference voltage terminal SST is forced to the fixed potential (ground potential).

On the other hand, the stop switch element SWC1 is turned off when the light load detection signal SR is not supplied from the oscillator OSC.

That is, the soft start circuit SF turns off the stop switch element SWC1 during the oscillation period described above.

As a result, the first adjustment capacitor Css1 is charged by the first constant current of the first constant current source Iss1, and the voltage of the reference voltage terminal SST rises.

The comparator COMP has a non-inverting input terminal connected to the reference voltage terminal SST and an inverting input terminal supplied with the reference voltage VZ.

The comparator COMP outputs a comparison result signal corresponding to the result of comparing the reference voltage VY of the reference voltage terminal SST and the reference voltage VZ to the burst mode switching circuit BM.

In addition, as shown in FIG. 2, the burst mode switching circuit BM, for example, during the oscillation period for supplying power to the load voltage terminal TL, when the first adjustment capacitor Css1 is charged, the reference voltage VY is soft-started. The voltage is set so that it rises steeper than

Here, for example, while the comparison result signal indicates that the reference voltage VY is less than the reference voltage VZ, the burst mode switching circuit BM turns on the voltage adjusting switch element SWR to turn on the voltage adjusting circuit Y. is set to the initial state.

After that, after the comparison result signal indicates that the reference voltage VY is equal to or higher than the reference voltage VZ, the burst mode switching circuit BM turns off the voltage adjusting switch element SWR to turn off the voltage adjusting circuit Y. It is set to the adjustment state.

After that, the burst mode switching circuit BM, for example, when detecting an abnormal operation of the switching power supply device 100 or when executing the overcurrent protection function operation, controls the voltage adjustment switching element SWR to ON. Then, the voltage regulation circuit Y is forcibly reset from the regulation state to the initial state.

This burst mode switching circuit BM includes, for example, a flip-flop circuit FF and a driver circuit (buffer) D, as shown in FIG.

The flip-flop circuit FF has a set terminal S to which the comparison result signal output by the comparator COMP is input, and a first reset signal SI to which a first reset signal SI indicating that an abnormal operation of the switching power supply device 100 has been detected is input. a second reset terminal R2 to which a second reset signal SH indicating execution of the overcurrent protection function operation is input; and an output terminal (inverted output) /Q for outputting a logic signal. , has

A driver circuit (buffer) D receives the logic signal output from the flip-flop circuit FF and outputs an adjustment signal based on the logic signal to a terminal SSC.

In the voltage adjustment circuit Y described above, the adjustment switch element SWR is controlled according to the adjustment signal output from the driver circuit D (that is, the output of the burst mode switching circuit BM), and the voltage adjustment circuit Y is set to the initial state or adjustment state. is set.

Next, an example of a control method for the switching power supply device 100 having the configuration as described above will be described.

Here, FIG. 4 is a diagram showing an example of the operation in the normal mode of the switching power supply device 100 according to the first embodiment. FIG. 5 is a diagram showing an example of the burst mode operation of the switching power supply device 100 according to the first embodiment.

As described above, in the switching power supply device 100, the switching pulses VGH and VGL are supplied from the terminals VGH and VGL of the power control circuit 7 to the first switch element 11 on the high side and the second switch element 12 on the low side. is output.

These switching pulses VGH and VGL alternately switch the first switching element 11 on the high side and the second switching element 12 on the low side, and electromagnetic energy is accumulated in the primary coil Np1 of the transformer 4. Energy is transferred to the secondary coils Ns1, Ns2.

The secondary side output of the transformer 4 is rectified by the diodes 13 and 14 and sent to the load 20 .

Also, the output of the secondary side of the transformer 4 is detected by the output detection circuit 21 . This detection output is fed back to the feedback terminal FB of the power control circuit 7 via the photocoupler 22 .

The power control circuit 7 controls the frequency of the switching pulse based on the detected current fed back to the feedback terminal FB.

Here, when the switching power supply device 100 (power supply control circuit 7) is started, for example, as shown from time t1 to time t2 in FIGS. The circuit Y is set to an initial state in which the reference voltage VY based on the charging voltage of the first adjusting capacitor Css1 charged with a constant current is applied to the reference voltage terminal SST.

As a result, the power supply control circuit 7 performs a soft start operation to decrease the switching frequencies of the first and second switch elements 11 and 12 as the reference voltage VY rises.

After the reference voltage VY reaches the reference voltage VZ (after time t2), the power supply control circuit 7 puts the voltage adjustment circuit Y into an adjustment state in which the reference voltage VY rises steeper than the soft start operation. , and during the stop period (for example, time ta to time tb in FIG. 5) in which the power supply to the load voltage terminal TL is stopped during burst mode control, the first adjustment capacitor During the oscillation period (time tb to time tc in FIG. 5) for forcibly discharging the charge of Css1 and supplying power to the load voltage terminal TL, when the first adjustment capacitor Css1 is charged, the reference voltage VY is set to the soft voltage. It is made to rise steeper than the start operation (time t1 to time t2 in FIG. 5).

At time t3 in FIGS. 5 and 6, the power supply control circuit 7, for example, detects an abnormal operation of the switching power supply device 100, or executes the overcurrent protection function operation of the switching power supply device 100. resets the voltage regulation circuit Y to the initial state described above.

Thereafter, similar operations are repeatedly performed.

As described above, the switching power supply device according to the first embodiment includes the power supply input terminal to which the power supply voltage is supplied, and the first switch having one end connected to the power supply input terminal and the other end connected to the output voltage node. an element, a second switch element having one end connected to an output voltage node and the other end connected to a fixed potential, a primary coil connected between the output voltage node and the fixed potential, and a primary side A coil and a secondary coil constituting a transformer, a load voltage terminal connected to a load and supplied with a voltage obtained by rectifying the voltage of the secondary coil of the transformer, and a reference voltage terminal and a fixed potential. A voltage for adjusting the reference voltage of the reference voltage terminal while applying to the reference voltage terminal a reference voltage based on the charged voltage of the first adjustment capacitor charged with a constant current. The adjustment circuit and the soft start operation are performed to decrease the switching frequencies of the first and second switch elements as the reference voltage rises, and when the reference voltage reaches a preset reference voltage, the load a power supply control circuit that controls at a predetermined switching frequency to alternately turn on/off the first switch element and the second switch element so that the load voltage of the voltage terminal becomes a preset target voltage; Prepare.

At the start-up, the voltage adjustment circuit is in an initial state in which the reference voltage based on the charged voltage of the first adjustment capacitor charged with a constant current is applied to the reference voltage terminal until the reference voltage first reaches the reference voltage. and after the reference voltage reaches the reference voltage, the power supply control circuit sets the voltage regulation circuit to hold it in a regulation state that causes the reference voltage to rise steeper than the soft-start operation. , during the burst mode control, the charge of the first adjustment capacitor is forcibly discharged during the stop period for stopping the supply of power to the load voltage terminal, and during the oscillation period during which power is supplied to the load voltage terminal, the first When the adjustment capacitor is charged, the reference voltage is made to rise steeper than the soft start operation.

That is, according to the switching power supply device according to the first embodiment, adjustment switching is performed so that the soft start state is shortened at the timing immediately after startup, and the soft start time is shortened when a light load is detected in the burst mode. , the switching frequency can be quickly lowered to improve the efficiency of the power supply to the secondary side of the transformer.

In a second embodiment, another configuration example of the voltage adjustment circuit Y of the switching power supply device 100 will be described. FIG. 6 is a diagram showing an example of the configuration of the voltage adjustment circuit Y, soft start circuit SF, and burst mode switching circuit BM according to the second embodiment. FIG. 7 is a diagram illustrating an example of the waveform of the reference voltage VY at the reference voltage terminal SST according to the second embodiment.

In the second embodiment, for example, as shown in FIG. 6, the voltage adjustment circuit Y has one end connected to the reference voltage terminal SST and the other end connected to a fixed potential ( and a second adjustment capacitor Css2 connected to ground potential).

Here, the burst mode switching circuit BM turns on the voltage adjusting switch element SWR while the comparison result signal output from the soft start circuit SF indicates that the reference voltage VY is less than the reference voltage VZ. to set the voltage adjustment circuit Y to the initial state.

As a result, the reference voltage VY of the reference voltage terminal SST is a charge charged by the first constant current output from the first constant current source Iss1 to the combined capacitance of the first and second adjustment capacitors Css1 and Css2. be based on.

After that, after the comparison result signal indicates that the reference voltage VY is equal to or higher than the reference voltage VZ, the burst mode switching circuit BM turns off the voltage adjusting switch element SWR to turn off the voltage adjusting circuit Y. Set to adjustment state.

As a result, the reference voltage VY of the reference voltage terminal SST is the combined capacitance of the first adjustment capacitor Css1 and the second adjustment capacitor Css2 to which the voltage adjustment resistor Rss is connected in series, which is the first constant current source. It is based on the charge charged by the first constant current output by Iss1 (FIG. 7).

The rest of the configuration of the switching power supply device 100 in the second embodiment is similar to that in the first embodiment.

That is, according to the switching power supply device according to the second embodiment, adjustment switching is performed so that the soft start state is shortened at the timing immediately after startup, and when a light load is detected in burst mode, the soft start time is shortened, By quickly lowering the switching frequency, the efficiency of supplying power to the secondary side of the transformer can be improved.

In Example 3, still another configuration example of the voltage adjustment circuit Y of the switching power supply device 100 will be described. FIG. 8 is a diagram showing an example of configurations of the voltage adjustment circuit Y, soft start circuit SF, and burst mode switching circuit BM according to the third embodiment.

In the third embodiment, the voltage adjustment circuit Y includes, for example, a first adjustment capacitor Css1, a second constant current source Iss2, and a current adjustment switch element SWC2, as shown in FIG. .

For example, as shown in FIG. 8, the first adjustment capacitor Css1 has one end connected to the reference voltage terminal SST and the other end connected to a fixed potential (ground potential).

Also, the second constant current source Iss2 outputs a second constant current.

The current adjusting switch element SWC2 has one end connected to the output of the second constant current source Iss2 and the other end connected to the reference voltage terminal SST.

Here, for example, the power supply control circuit 7 turns on the current adjustment switch element SWC2 so that the first adjustment capacitor Css1 is charged with the first and second constant currents, and the voltage adjustment circuit Y is set to the adjustment state described above.

Therefore, the charging time of the first adjustment capacitor Css1 is shortened, and the soft start time is shortened.

Thereby, the power supply control circuit 7 can set (set) the voltage adjustment circuit Y so as to hold the adjustment state in which the reference voltage VY rises more steeply than the soft start operation.

On the other hand, the power supply control circuit 7 turns off the current adjusting switch element SWC2 so that the first adjusting capacitor Css1 is charged with the first constant current, and the voltage adjusting circuit Y is set to the above-mentioned initial voltage. state.

The rest of the configuration of the switching power supply device 100 in the third embodiment is similar to that in the first embodiment.

That is, according to the switching power supply device 100 according to the third embodiment, adjustment switching is performed so that the soft-start state is shortened at the timing immediately after startup, and the soft-start time is shortened when a light load is detected in burst mode. , the switching frequency can be quickly lowered to improve the efficiency of the power supply to the secondary side of the transformer.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention as well as the scope of the invention described in the claims and equivalents thereof.

100 switching power supply 1a, 1b power supply input terminal 2 smoothing capacitor 3 input power supply line 4 transformer 5 resonance capacitor 6 current detection resistor 7 power supply control circuit 8 first voltage dividing resistor 9 second voltage dividing resistor 11 first switch Element 12 Second switch elements 13, 14 Diodes 15, 16 Output power supply line 17 Smoothing capacitor 21 Output detection circuit 22 Photocoupler 23 Oscillation adjustment capacitor 24 Oscillation adjustment resistor Np1 Primary side coils Ns1, Ns2 Secondary side Coil TL Load voltage terminal Y Voltage adjustment circuit Css1 First adjustment capacitor Rss Voltage adjustment resistor SWR Voltage adjustment switch element B Voltage dividing circuit OSC Oscillator BM Burst mode switching circuit FF Flip-flop circuit D Driver circuit (buffer)
SF Soft-start circuit Iss1 First constant current source Iss2 Second constant current source SWC1 Stop switch element COMP Comparator CON Control circuit (control unit)
VD Voltage detection circuit X Overcurrent protection circuit

Claims (15)

a power input terminal to which a power supply voltage is supplied;
a first switch element having one end connected to the power supply input terminal and the other end connected to an output voltage node;
a second switch element having one end connected to the output voltage node and the other end connected to a fixed potential;
a primary coil connected between the output voltage node and the fixed potential;
a secondary coil that forms a transformer with the primary coil;
a load voltage terminal connected to a load and supplied with a voltage obtained by rectifying the voltage of the secondary coil of the transformer;
A first adjustment capacitor is connected between a reference voltage terminal and the fixed potential, and a reference voltage based on a charged voltage of the first adjustment capacitor charged with a constant current is applied to the reference voltage terminal. a voltage adjustment circuit for applying to and adjusting the reference voltage at the reference voltage terminal;
A soft start operation is performed to decrease the switching frequencies of the first and second switch elements as the reference voltage rises, and when the reference voltage reaches a preset reference voltage, the load a power supply control circuit that controls at a predetermined switching frequency to alternately turn on/off the first switching element and the second switching element so that the load voltage of the voltage terminal becomes a preset target voltage; , and
At startup, until the reference voltage first reaches the reference voltage, the voltage regulation circuit applies the reference voltage based on the charged voltage of the first regulation capacitor charged with a constant current to the reference voltage terminal. It is set to the initial state to apply,
after the reference voltage reaches the reference voltage,
The power control circuit is
setting the voltage adjustment circuit to maintain an adjustment state in which the reference voltage rises more steeply than the soft start operation;
during burst mode control, during a stop period for stopping the supply of power to the load voltage terminal, forcibly discharging the charge of the first adjustment capacitor;
A switching power supply device, wherein the reference voltage rises more sharply than the soft start operation when charging the first adjustment capacitor during an oscillation period for supplying power to the load voltage terminal. The voltage regulation circuit is
the first adjustment capacitor having one end connected to the reference voltage terminal;
a voltage adjustment resistor having one end connected to the other end of the first adjustment capacitor and the other end connected to the fixed potential;
a voltage adjustment switch element connected between the other end of the first adjustment capacitor and the fixed potential;
The power control circuit is
turning on the voltage regulating switch element to set the voltage regulating circuit to the initial state, and turning off the voltage regulating switch element to set the voltage regulating circuit to the regulated state. The switching power supply device according to claim 1, characterized by: The voltage regulation circuit is
3. The switching power supply device according to claim 2, further comprising a second adjustment capacitor having one end connected to said reference voltage terminal and the other end connected to said fixed potential. The power control circuit is
2. The switching according to claim 1, wherein the voltage regulation circuit is reset to the initial state when an abnormal operation of the switching power supply is detected or when an overcurrent protection function operation is performed. Power supply. The power control circuit is
During the stop period, the voltage of the reference voltage terminal is forcibly set to the fixed potential by discharging the charge of the first adjustment capacitor, thereby stopping the switching of the first and second switch elements. 3. The switching power supply device according to claim 2, characterized by: The power control circuit is
a first constant current source that supplies a first constant current to the reference voltage terminal;
a stop switch element connected between the reference voltage terminal and the fixed potential;
Turning on the switching element for stopping during the stopping period,
6. The switching power supply device according to claim 5, wherein the stop switch element is turned off during the oscillation period. The voltage regulation circuit is
the first adjustment capacitor having one end connected to the reference voltage terminal and the other end connected to the fixed potential;
a second constant current source that outputs a second constant current;
a current adjusting switch element having one end connected to the output of the second constant current source and the other end connected to the reference voltage terminal;
The power control circuit is
turning on the current regulating switch element to set the voltage regulating circuit to the regulated state, and turning off the current regulating switch element to set the voltage regulating circuit to the initial state. 7. The switching power supply device according to claim 6, characterized by: The power control circuit is
an oscillator that outputs an oscillation signal for generating a switching pulse that controls the first switch element and the second switch element;
a burst mode switching circuit for setting the voltage so that the reference voltage rises steeper than the soft start operation when the first adjustment capacitor is charged during an oscillation period for supplying power to the load voltage terminal; ,
a control unit that controls the first switch element and the second switch element by a switching pulse generated from the oscillation signal output by the oscillator;
a voltage detection circuit that detects a detected voltage based on the power supply voltage and turns on/off the operation of the oscillator according to the detected voltage;
8. A soft start circuit that sets the oscillation frequency of the oscillator from a high frequency to a low frequency gradually according to the reference voltage of the reference voltage terminal, and executes a soft start. The switching power supply device according to . an output detection circuit that detects the load voltage;
a photocoupler that passes a detection current corresponding to the load voltage detected by the output detection circuit to a feedback terminal;
The oscillator controls the oscillation frequency of the switching pulse based on the load voltage of the load voltage terminal, with an oscillation frequency corresponding to the detected current of the feedback terminal applied via the photocoupler. 9. The switching power supply device according to claim 8. a resonance capacitor having one end connected to the primary coil;
a current detection resistor having one end connected to the other end of the resonance capacitor and the other end connected to the fixed potential;
The power control circuit is
2. The switching according to claim 1, further comprising an overcurrent protection circuit that detects a current flowing through the first switching element and the second switching element based on a current flowing through the current detection resistor. Power supply. The soft start circuit is
the first constant current source that supplies the first constant current to the reference voltage terminal;
the stop switch element connected between the reference voltage terminal and the fixed potential;
A non-inverting input terminal is connected to the reference voltage terminal, an inverting input terminal is supplied with the reference voltage, and a comparison result signal corresponding to a result of comparing the reference voltage of the reference voltage terminal and the reference voltage is supplied to the and a comparator that outputs to the burst mode switching circuit,
The burst mode switching circuit is
while the comparison result signal indicates that the reference voltage is less than the reference voltage, turning on the voltage adjustment switch element to set the voltage adjustment circuit to the initial state;
After that, after the comparison result signal indicates that the reference voltage is equal to or higher than the reference voltage, turning off the voltage adjustment switch element to set the voltage adjustment circuit to the adjustment state,
Thereafter, when an abnormal operation of the switching power supply is detected, or when the overcurrent protection function is to be executed, the voltage adjustment switch element is controlled to be ON to force the voltage adjustment circuit to operate. 9. The switching power supply device according to claim 8, wherein the adjustment state is reset to the initial state. The burst mode switching circuit is
a set terminal to which the comparison result signal output by the comparator is input; a first reset terminal to which a first reset signal indicating detection of abnormal operation of the switching power supply device is input; and overcurrent protection. a flip-flop circuit having a second reset terminal to which a second reset signal indicating execution of a functional operation is input, and an output terminal for outputting a logic signal;
a driver circuit that receives the logic signal output from the flip-flop circuit and outputs an adjustment signal based on the logic signal;
12. The switching power supply device according to claim 11, wherein the voltage adjustment circuit is set to the initial state or the adjustment state by controlling the voltage adjustment switch element according to the adjustment signal. The oscillator outputs a light load detection signal when the load state is a light load,
12. The switching power supply device according to claim 11, wherein the stop switch element of the soft start circuit is turned on by the light load detection signal. a power supply input terminal to which a power supply voltage is supplied; a first switching element having one end connected to the power supply input terminal and the other end connected to an output voltage node; one end connected to the output voltage node; is connected to a fixed potential, a primary coil connected between the output voltage node and the fixed potential, and a secondary coil forming a transformer together with the primary coil , a load voltage terminal connected to a load and supplied with a voltage obtained by rectifying the voltage of the secondary coil of the transformer; and a first adjusting capacitor connected between a reference voltage terminal and the fixed potential. a voltage adjustment circuit that applies to the reference voltage terminal a reference voltage based on the charged voltage of the first adjustment capacitor that is charged with a constant current and adjusts the reference voltage of the reference voltage terminal; A power supply control circuit applied to a switching power supply device comprising
A soft start operation is performed to decrease the switching frequencies of the first and second switch elements as the reference voltage rises, and when the reference voltage reaches a preset reference voltage, the load The first switch element and the second switch element are alternately turned on/off at a predetermined switching frequency so that the load voltage at the voltage terminal becomes a preset target voltage. cage,
At startup, until the reference voltage first reaches the reference voltage, the voltage regulation circuit applies the reference voltage based on the charged voltage of the first regulation capacitor charged with a constant current to the reference voltage terminal. It is set to the initial state to apply,
after the reference voltage reaches the reference voltage,
setting the voltage adjustment circuit to maintain an adjustment state in which the reference voltage rises more steeply than the soft start operation;
during burst mode control, during a stop period for stopping the supply of power to the load voltage terminal, forcibly discharging the charge of the first adjustment capacitor;
A power supply control circuit, wherein the reference voltage rises steeper than the soft start operation when the first adjustment capacitor is charged during an oscillation period during which power is supplied to the load voltage terminal. a power supply input terminal to which a power supply voltage is supplied; a first switching element having one end connected to the power supply input terminal and the other end connected to an output voltage node; one end connected to the output voltage node; is connected to a fixed potential, a primary coil connected between the output voltage node and the fixed potential, and a secondary coil forming a transformer together with the primary coil , a load voltage terminal connected to a load and supplied with a voltage obtained by rectifying the voltage of the secondary coil of the transformer; and a first adjusting capacitor connected between a reference voltage terminal and the fixed potential. a voltage adjustment circuit that applies to the reference voltage terminal a reference voltage based on the charged voltage of the first adjustment capacitor that is charged with a constant current and adjusts the reference voltage of the reference voltage terminal; A soft start operation is performed to decrease the switching frequencies of the first and second switch elements as the reference voltage rises, and when the reference voltage reaches a preset reference voltage, the load a power supply control circuit that controls at a predetermined switching frequency to alternately turn on/off the first switching element and the second switching element so that the load voltage of the voltage terminal becomes a preset target voltage; A control method for a switching power supply device comprising
At startup, until the reference voltage first reaches the reference voltage, the voltage regulation circuit applies the reference voltage based on the charged voltage of the first regulation capacitor charged with a constant current to the reference voltage terminal. It is set to the initial state to apply,
after the reference voltage reaches the reference voltage,
The power control circuit is
setting the voltage adjustment circuit to maintain an adjustment state in which the reference voltage rises more steeply than the soft start operation;
during burst mode control, during a stop period for stopping the supply of power to the load voltage terminal, forcibly discharging the charge of the first adjustment capacitor;
wherein the reference voltage rises steeper than the soft start operation when the first adjustment capacitor is charged during an oscillation period during which power is supplied to the load voltage terminal. control method.

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