JPH10337019A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fluctuation of rising at the time of restart by controlling the control voltage to a constant level at the time of waiting through a high breakdown strength preregulator. SOLUTION: In the switching power supply employing a flyback type converter, the converter comprises a preregulator section 20 for supplying a control circuit with a control voltage controlled to a constant level at the time of starting and waiting, an on/off logic section 30 for controlling the converter to stop under conducting state or restarting the stopping converter, a pulse width modulation control section 40 for controlling the output voltage by regulating the oscillation frequency and the ON interval of a main switching element, and a logic section 50 for controlling the main switching element by processing the output signals from the pulse width modulation control section 40 and the on/off logic section 30. Fluctuation of rising is suppressed at the time of restart by controlling the control voltage to a constant level at the time of waiting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a switching power supply, and more particularly to an improvement in a restart characteristic when a standby state is changed to a use state.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an example of a conventional switching power supply using a commercially available flyback type converter. A high-voltage DC voltage (DC input) is applied to the primary side of the transformer T1, and the other side of the primary side is connected to the drain D of the flyback converter FC which is formed into an IC, and is driven by a built-in MOSFET.

The flyback type converter FC is a linear / current-cycle converter having a built-in main switching element MOSFET and a control circuit, and having an open-drain output and a self-bias and self-protection function.

A clamp circuit composed of a Zener diode VR1 and a diode D1 connected in parallel to the primary side of a transformer is used to limit the leading edge spike voltage of the transformer.

The output of the secondary winding of the transformer is a Zener diode D3, a capacitor C2, and an inductance L.
1. DC voltage can be obtained from the output terminal after being rectified and smoothed by the capacitor C3.

The output of the bias winding of the transformer T1 is rectified and smoothed by a diode D2, a resistor R1, and a capacitor C5, and applied to a control terminal P of a converter FC. The voltage applied to the capacitor C5 is determined by the converter F
Controlled by C.

When the capacitor C5 discharges to the lower threshold, the MOSFET is turned off, and the control circuit enters a low current standby state. When the high withstand voltage current source built in the converter is turned on and starts charging the external capacitor C5 (the total capacity is Ct) again, the auto-restart comparator having hysteresis as shown in FIG. By turning on / off, the voltage of the control pin (hereinafter referred to as control voltage) Vc is maintained between 4.7 and 5.7V.

[0008] The auto-restart circuit has a divide-by-8 counter. As shown in FIG.
It is prevented from turning on again before the charge / discharge cycle ends. The counter limits the power consumption of the IC by keeping the duty cycle of auto-restart to 5%. This auto restart operation is repeatedly performed until the output power is controlled again.

[0009]

In the standby state of such a conventional switching power supply, the main switching element is stopped, and at the same time, the IC repeatedly starts and stops by supplying a constant current from a high voltage after commercial voltage rectification. Therefore, there is a problem that the time from the restart signal to when the output rises varies depending on the value of the control voltage Vc.

In view of the above, an object of the present invention is to control the standby control voltage (Vcc in the present invention) to a constant value by a high withstand voltage pre-regulator, so that a restart An object of the present invention is to provide a switching power supply capable of improving the variation. Another object of the present invention is to provide a switching power supply that can be restarted in a short time by controlling the control voltage Vcc during standby to a value higher than the start voltage and lower than the control voltage.

[0011]

In order to achieve the above object, according to the present invention, an output of a bias winding of a transformer is received and a main switching element connected in series to a primary winding of the transformer is driven. In a switching power supply using a flyback type converter, the flyback type converter includes a pre-regulator for supplying a constant control voltage to a control circuit when the power supply is started and when the output voltage becomes zero while the power is on. Unit, an on / off logic unit for controlling the converter to stop the converter in the energized state or to restart the stopped converter, and a pulse for controlling the output voltage by adjusting the oscillation frequency and the on period of the main switching element. A width modulation control unit, and processing the output signals of the pulse width modulation control unit and the on / off logic unit to generate the main signal. Comprises a logic unit for controlling the switching element, characterized by being constructed as the rise of the variation at the time of re-starting is reduced by controlling the control voltage constant during standby.

[0012]

The Vcc voltage during standby is controlled to be constant. As a result, when switching from the standby state to the activation state, there is no variation in the time until the steady state is reached.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of a switching power supply according to the present invention. In the figure, T1 is a transformer, and 10 is a converter control unit that can switch between an operating state and a standby state.

A high voltage DC voltage VIN is applied to one of the primary windings Np of the transformer T1, and a series circuit of a main switching element Q10 and a resistor is connected to the other. The secondary winding Ns has a diode D20 and a capacitor C
Twenty smoothing circuits are connected. The output of the bias winding Nb of the transformer T1 is connected to a diode D2,
It is rectified by the capacitor C12.

The converter control section 10 includes a pre-regulator section 20, an on / off logic section (hereinafter referred to as ON / OFF logic section) 30, a pulse width modulation control section (hereinafter referred to as PWM control section) 40, and an out logic section (hereinafter referred to as OUT). And an output driver 60.

The pre-regulator unit 20 is used when the power supply is started and when the output voltage becomes zero while the power supply is kept on.
Control circuit (ON / OFF logic unit 30, PWM control unit 40, OUT
The power is supplied to the logic unit 50 and the output driver 60). The ON / OFF logic unit 30 performs control for stopping the converter in the energized state or restarting the stopped converter.

The PWM control unit 40 controls the oscillation frequency and the output voltage, and the OUT logic unit 50 processes the signals of each unit and controls the main switching element of the converter. The OUT logic unit 50 processes the signals of each unit and controls the main switching element of the converter.

Hereinafter, each part will be described in more detail. The pre-regulator unit 20 includes a constant current circuit 201, a start control circuit 202, and a malfunction prevention circuit (Under Voltage Lock Out (UV
LO) circuit 203, a standby voltage control circuit 204, and a reference voltage circuit (Vref circuit) 205.

The constant current circuit 201 is a circuit for supplying power to the control circuit with a constant current at the time of start-up and standby, and a switching element Q1 for limiting the supply current.
And a resistor R1 for supplying a drive voltage to the gate of Q1.
And a resistor R2 for detecting a current flowing in Q1, and a switching element Q2 for controlling a gate voltage of Q1 to make the current flowing in Q1 a constant current.

The high-voltage DC voltage VIN is applied to the drain of the switching element Q1, and the source is connected to the resistor R2. The other end of the resistor R2 is connected to a Vcc terminal (control voltage Vcc line). The gate of the switching element Q1 is connected to a resistor R1 having one end to which VIN is applied.
Is connected, and the collector of the switching element Q2 is connected. The gate of the switching element Q2 is connected to the source of the switching element Q1, and the emitter is a resistor R
2 is connected to the other end.

When the control terminal voltage Vcc reaches the comparison voltage of the comparator CP1 at startup, the startup control circuit 202 turns off the switching element Q1 to stop the current supply. Turn on Q1 to supply.

The start control circuit 202 includes resistors R3, R
The switching circuit Q1 is controlled by a comparator CP1 having a hysteresis in which the Vcc voltage is detected by the series circuit of No. 4 and the detection level is high at the time of startup and becomes low after startup.

The UVLO circuit 203 is a voltage level setting circuit that prevents the OUT logic unit 30 from outputting an output signal when the Vcc voltage is equal to or lower than a desired voltage. , Set voltage after startup (S
The top voltage) has hysteresis.

The standby voltage control circuit 204 outputs V
This is a constant current circuit that controls the cc voltage to be equal to or higher than the start voltage value and supplies power to the Vref circuit 205. The Vref circuit 205 supplies power to each logic unit at a constant voltage (for example, 5 V).

The ON / OFF logic unit 30 has a flip-flop 301 for generating a signal for switching from the operating state to the standby state or from the standby state to the operating state, and inverters INV1, INV2, and INV3 for inverting signals. The output of the inverter INV1 is the flip-flop 30
01 is connected to the reset (R) terminal, and the output of the inverter INV2 is connected to the set (S) terminal. The input terminals of the inverters INV1 and INV2 are pulled up to the output terminal (constant voltage power supply) of the Vref circuit 205 via the resistors R8 and R9, respectively.

The ON / OFF logic section 3 thus configured
At 0, the data terminal D and the clock terminal CLKT of the flip-flop 301 attain a high level at the time of startup. However, a delay circuit Delay1 is provided before the CLK terminal so that the CLK terminal voltage always becomes higher than the D terminal voltage to ensure that the flip-flop 301 can be started.

A set terminal (SE) is connected by an external switch SW2.
When the T terminal is set to the low level, the PON terminal is set to the low level, and at the same time, the output Q of the flip-flop 301 is set.
Becomes High level, and the converter is activated by this. Reset terminal by switch SW1 (RESET terminal)
Becomes low level, the output Q of the flip-flop 301 becomes low level, and the converter enters a standby state.

The PWM control section 40 comprises an oscillation circuit 401 and an output voltage control circuit 402. The oscillating circuit 401 oscillates at a frequency determined by a time constant of an external resistor R10 and a capacitor C10.

The output voltage control circuit 402 compares the output voltage of the smoothing circuit connected to the secondary winding of the transformer (hereinafter simply referred to as the output voltage) with the source current of the main switching element Q10 to determine the ON period of Q10. This is a current mode control circuit that controls the output voltage by adjusting it, and has the following configuration.

An error amplifier AMP for detecting an output voltage and amplifying a minute fluctuation to set a voltage for correcting an error.
1, a voltage correction circuit 403 for matching the output voltage of the error amplifier AMP1 with the input voltage level of the comparator CP3, and a comparator for comparing a signal obtained by converting the source current of Q10 into a voltage by the resistor R15 with the output voltage of the amplifier AMP1. It is composed of CP3.

To detect the output voltage, the output voltage Nb / N
There are a winding feedback method for detecting a Vcc voltage equal to s times the voltage, and a method for directly detecting an output voltage and feeding it back with a photocoupler. In the winding feedback method shown in FIG. 1, the Vcc voltage is divided by resistors R15 and R16, and the voltage is divided by an error amplifier A.
The signal is input to the inverting input terminal EIN of MP1 and amplified. The figure shows a case where C11 is externally attached as an example of the phase compensation.

FIG. 2 shows a case in which feedback is performed by a photocoupler (other means may be used if isolation is possible). The output voltage is divided by resistors R20 and R21 and this voltage is divided by a shunt regulator U20. To convert the current. U20 adjusts the photocurrent of the diode of the photocoupler OC and controls the transistor of the photocoupler OC. The collector terminal of the photocoupler OC is connected to the EO terminal of the converter, the output of the amplifier AMP1 is directly controlled, and the current waveform of the main switching element Q10 is compared by the comparator CP3.

The OUT logic section 50 controls the main switching element Q10 based on each signal from the ON / OFF logic section 30, the PWM control section 40, and the UVLO circuit 2003, and is a logic element for processing each signal. It is composed of a group 502 and an SR flip-flop 501 which is set / reset by the output of the logical element group.

The output driver 60 includes the OUT logic unit 50
Is amplified to drive the main switching element Q10.

The operation of the above configuration will now be described. FIG. 3 is a waveform chart of each part in each operation mode. (1) First, the operation at the time of startup will be described. When a DC voltage is applied, the switching element Q of the constant current circuit 201
Current flows through 1. This current is detected by the resistor R2, and the switching element Q2 controls the gate voltage of Q1 in accordance with the current, whereby the current flowing through Q1 is made constant and the current is supplied to Vcc.

When a current is supplied to Vcc, power is supplied to the Vref circuit 205 through the switching element Q3, and a 5V reference voltage is generated from the output. However,
Until the reference voltage reaches the operating voltage of each unit, each unit is kept stopped by a low-voltage malfunction prevention UVLO signal so that the circuit of each unit does not malfunction.

When the reference voltage reaches a predetermined operating voltage, UVLO
The signal is released and the control unit (ON / OFF logic unit 30, PWM
The control section 40 and the OUT logic section 50) operate, and the gate drive of the main switching element Q10 is started as shown in FIG. As a result, power is supplied from the bias winding Nb, and the Vcc voltage becomes higher than the Start voltage (FIG. 3B).

When the voltage becomes higher than the Start voltage, the comparator CP1 of the start control circuit 202 lowers the gate of the switching element Q1 of the constant current circuit 201 to suppress the drain current of Q1. With such control, the transformer T1
, A constant DC output voltage is obtained from the output side.

(2) Next, the operation at the time of transition from the operating state to the standby state will be described. Turn on the external switch SW1 to set the RESET terminal to the low level ((e) in FIG. 3), and
A reset signal (Low level) is given to the reset terminal of the flip-flop 301 of the N / OFF logic unit 30. As a result, the output Q of the flip-flop 301 goes high.

Based on the Q signal, the logic element group gives a low level signal to the set (S) terminal and a high level signal to the reset (RESET) terminal of the SR flip-flop 501. As a result, the output Q of the SR flip-flop 501 becomes low, the gate signal of the main switching element Q10 becomes as shown in FIG. 3 (g), and Q10 is turned off.

At this time, the power consumption of the control circuit is kept low, a very small current is supplied from the switching element Q1, and the control voltage Vcc as shown in FIG. Is maintained at a voltage higher than the start voltage and lower than the control voltage (referred to as a pre-regulator control voltage). It has been experimentally confirmed that the power loss in the standby state is 0.5 W or less.

(3) Next, the operation at the time of transition from the standby state to the operation state will be described. Turn on the external SET switch, set the SET terminal to Low as shown in FIG.
The set signal is input to the S terminal of the flip-flop 301 of the N / OFF logic unit 30.

As a result, the output Q of the flip-flop 301 changes to a low state. Upon receiving this signal, the S terminal of the SR flip-flop 501 changes to high, the R terminal changes to low, and the output Q changes to high. As a result, a drive signal is applied to the gate of the main switching element Q10 as shown in FIG. 3G, and the switching element Q10 is driven.

(4) The operation at the time of stop will be described below. DC voltage input disappears, VIN decreases, and Vcc + (resistance R
2) + (Drain-source voltage of Q1)
Then, the control voltage Vcc starts to decrease. When Vcc reaches the Stop voltage, the UVLO operates as shown in FIG. 3D to stop each part of the control circuit and turn off the main switching element Q10. When Vcc reaches (output voltage of Vref circuit 205) + (drain-source voltage of switching element Q3), Vref voltage also decreases.

The magnitude relationship between the voltages in each operation mode is as follows. Stop voltage <Start voltage <Pre-regulator control voltage <Vcc voltage

It should be noted that the foregoing description has been directed to specific preferred embodiments for the purpose of illustration and illustration of the invention. Therefore, the present invention is not limited to the above-described embodiments, and includes many more modifications without departing from the spirit thereof.
This includes deformation.

For example, as the high-voltage DC voltage VIN, FIG.
A high-voltage DC voltage obtained from a commercial AC power supply may be used by using a rectifying / smoothing circuit including a rectifying diode bridge circuit D1 and a smoothing capacitor C1 as shown in FIG.

[0048]

As described above, according to the present invention, the following effects can be obtained. By controlling the Vcc voltage during standby to be constant, it is possible to easily eliminate variations at the time of restart. By controlling the Vcc voltage during standby to be equal to or higher than the start voltage and equal to or lower than the control voltage, it is possible to restart in a short time. Since the pre-regulator after start-up passes only a small current, the efficiency of the power supply during operation can be improved, and the loss of the power supply during standby can be suppressed to a sufficiently low level (for example, 0.5 W or less).

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a switching power supply according to the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a waveform chart for explaining operation.

FIG. 4 is a configuration diagram of a rectifying / smoothing circuit applied to the present invention.

FIG. 5 is a configuration diagram showing an example of a conventional switching power supply.

FIG. 6 is an operation waveform diagram in the switching power supply of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Converter control part 20 Pre-regulator part 30 ON / OFF logic part 40 PWM control part 50 OUT logic part 60 Output driver 201 Constant current circuit 202 Start control circuit 203 UVLO circuit 204 Standby voltage control circuit 205 Vref circuit 301, 501 Flip-flop 401 oscillation circuit 402 output voltage control circuit 502 logic element group T1 transformer Q1, Q3 switching element Q10 main switching element D1 diode bridge circuit D2 diode C12 capacitor

Claims (6)

[Claims] 1. A switching power supply using a flyback converter that receives an output of a bias winding of a transformer and drives a main switching element connected in series to a primary winding of the transformer. A pre-regulator section that supplies a constant control voltage to the control circuit when the power is turned on and when the output voltage becomes zero while the power is on, and a converter that stops the converter while the power is on or restarts the stopped converter. An on / off logic unit for performing control for activation, a pulse width modulation control unit for controlling an output voltage by adjusting an oscillation frequency and an on period of a main switching element, the pulse width modulation control unit, and the on / off A logic section for processing the output signal of the logic section to control the main switching element, Switching power supply, characterized in that constructed as rising variation on restart is reduced by controlling the trawl voltage constant. 2. The switching power supply according to claim 1, wherein the control voltage during standby is controlled to a voltage higher than a start voltage and lower than a control voltage. 3. A pre-regulator unit comprising: a constant current circuit for supplying power to a control circuit with a constant current at the time of start-up and standby; and when the control voltage is lower than a predetermined voltage, no output signal is output from the logic unit. A malfunction prevention circuit configured to turn off the main switching element when the control voltage reaches the comparison voltage at the time of startup to stop the current supply, and to start the current supply when the control voltage decreases to fall below the comparison voltage after the startup. A control circuit, a reference voltage circuit that supplies power to each part at a constant voltage, and a standby voltage control circuit that controls the control voltage to a start voltage value or more and supplies power to the reference voltage circuit during standby. The switching power supply according to claim 1 or 2, wherein 4. The pulse width modulation control section compares an output voltage with a voltage corresponding to a source current of the main switching element, and compares the output voltage with a voltage corresponding to a source current of the main switching element. 4. The switching power supply according to claim 1, further comprising a comparator that outputs a pulse width signal. 5. The switching device according to claim 4, wherein said output voltage is obtained from a means for dividing an output of a bias winding of said transformer by a ratio of a bias winding to a secondary winding. Power supply. 6. The switching power supply according to claim 4, wherein said output voltage is directly detected by an output voltage of a secondary winding of said transformer and taken in through an isolation means.