JP2003033014A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumed when high voltage is inputted, capable of preventing a starting miss. SOLUTION: This is a switching power supply device 100 where the switching operation of a switching FET 125 for switching the rectified smoothed output of a primary rectifying smoothing circuit 115 is controlled, by a switching control circuit 130 which has a hysteresis low-voltage malfunction preventing circuit. A starting circuit 140 by which starting current is supplied to the control circuit 130 is composed of a constant current circuit 141.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device which controls a switching operation of a switching element for switching a rectified and smoothed output of a primary side rectified and smoothed circuit by a switching control circuit having a hysteresis low voltage malfunction prevention circuit. And its starting method.

[0002]

2. Description of the Related Art Conventionally, a switching power supply device has been constructed in which a direct current obtained by rectifying and smoothing a commercial alternating current is switched at a high frequency of, for example, about 100 kHz and is converted into a desired voltage with a high efficiency by a transformer. Is widely used.

As a control method of the output voltage in the above switching power supply device, there is a pulse width modulation (P) which controls the duty ratio of the switching pulse according to the change of the output voltage.
A WM (Pulse Width Modulation) control method, a frequency control method such as resonance for controlling the frequency and phase of a switching pulse, and a phase control method are adopted.

FIG. 2 shows an example of a circuit configuration of a conventional switching power supply device adopting a PWM control system.

This switching power supply device 200 is provided with a primary side rectifying / smoothing circuit 215 for rectifying and smoothing an AC input supplied from a commercial power source AC through an AC filter 210. The primary side rectifying / smoothing circuit 215 has a converter transformer. Switching F through 220 primary winding 220A
The drain of ET225 is connected and the switching operation of the switching FET225 is PWM.
Power supply terminal 230 of switching control circuit 230 for controlling
A is connected to the primary side rectifying / smoothing circuit 215 via a starting circuit 240. The power supply terminal 230A is grounded via a capacitor 235. Further, the starting circuit 240 includes three resistors 240A, 2 connected in series.
It consists of 40B and 240C.

The switching control circuit 230 has a built-in hysteresis low voltage malfunction prevention circuit in order to prevent malfunction when the power supply voltage drops, and the power supply terminal 23 is provided.
When the power supply voltage Vcc applied to 0A rises from 0V, the operation starts at Vcc = 16.5V, and when the power supply voltage drops, the output is cut off at Vcc = 9.0V.

A secondary side rectifying / smoothing circuit 250 is connected to the secondary winding 220B of the converter transformer 220, and the secondary winding 220B of the converter transformer 220 is connected.
The converter output obtained at
50 is rectified and smoothed, and output through the output filter 255. The secondary side rectifying / smoothing circuit 25
0 is connected to an output detection circuit 270 via a resistance division circuit 260 for detecting an output voltage and a resistor 265 for detecting an output current, and a detection output of the output detection circuit 270 is output via a photocoupler 280. It is fed back to the switching control circuit 230. The output detection circuit 270 and the photocoupler 280 operate with the rectification / smoothing output by the rectification / smoothing circuit 290 connected to the secondary winding 220B of the converter transformer 220 as a driving power supply.

The switching control circuit 230 is started by supplying a starting current from the primary side rectifying / smoothing circuit 215 via the starting circuit 240 at the time of starting, and starts supplying a switching pulse to the switching FET 225, and after starting. Operates by using the rectifying / smoothing output by the rectifying / smoothing circuit 238 connected to the tertiary winding 220C of the converter transformer 220 as a driving power source, and responds to the detection output by the output detection circuit 270 fed back through the photocoupler 280. By changing the duty ratio of the switching pulse, the switching FET2
The switching operation of 25 is PWM-controlled to stabilize the converter output.

[0009]

By the way, in the conventional switching power supply device having the above-mentioned configuration, since the starting power is supplied through the resistors 240A, 240B and 240C of the starting circuit 240, the starting current of the starting current is reduced at the minimum input voltage. It is necessary to secure and confirm the allowable power resistance at the maximum voltage. Currently, a resistor 240A that secures a starting current and has an allowable power that is higher than the power generated at the maximum input voltage with its resistance value,
240B and 240C were selected.

In a power supply having a wide input permissible voltage of 80 V to 276 V AC, the resistors 240A, 240B, 24 of the starting circuit 240 are provided in order to secure the minimum starting current (1 mA).
0C is 1 when the input voltage is AC85V (DC110V)
A resistance value of 10 KΩ or less is required, and input voltage AC27
At 6V (DC390V), the power consumed by this resistor is 1.378W, and it is necessary to select an allowable value higher than that. Considering heat dissipation, the resistance becomes 3W or more. Since a high voltage is applied to each of the resistors 240A, 240B, 240C, it has been realized by connecting several resistors in series in consideration of the withstand voltage of the resistors.

When the power is turned on, the starting circuit 24 is always provided.
Since the resistors 240A, 240B, and 240C of 0 consume electric power, the proportion of the electric power consumption in the standby state is a big problem. For that reason, after starting, the method of stopping after confirming the operation of the main switching circuit is also adopted. This method is effective in reducing power consumption after startup, but it is effective in reducing power consumption at startup. There is no.

On the other hand, if it is attempted to increase the resistance value of the starting circuit 240 and reduce the power consumption, the starting current becomes insufficient and the starting error is likely to occur.

Therefore, in view of the above-mentioned conventional problems, the object of the present invention is to reliably start the system, and
It is an object of the present invention to provide a switching power supply device capable of reducing power consumption at startup and a startup method thereof.

[0014]

According to the present invention, a switching control circuit having a hysteresis low voltage malfunction prevention circuit controls a switching operation of a switching element for switching a rectified and smoothed output of a primary side rectified and smoothed circuit. In the power supply device, the starting circuit that supplies the starting current to the switching control circuit is configured by a constant current circuit, and the product of the transient response time of the switching power supply device, the driving current, and the minimum driving voltage is used to prevent the low voltage malfunction. It is characterized in that it is smaller than half the product of the squared difference of the hysteresis voltage of the circuit and the capacitance of the capacitor connected to the power supply terminal of the switching control circuit.

Further, according to the present invention, a switching control circuit having a hysteresis low voltage malfunction prevention circuit controls the switching operation of a switching element for switching the rectified and smoothed output of the primary side rectified and smoothed circuit. A method, wherein the product of the transient response time of the switching power supply device, the drive current and the minimum drive voltage is the square difference of the hysteresis voltage of the low voltage malfunction prevention circuit and the capacitor connected to the power supply terminal of the switching control circuit. It is characterized in that the switching control circuit is started by supplying a starting current from a constant current circuit while making the value smaller than half the product of the capacity.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The present invention is applied to a switching power supply device 100 having a structure as shown in FIG. 1, for example.

This switching power supply device 100 includes a primary side rectifying / smoothing circuit 115 for rectifying and smoothing an AC input supplied from a commercial power source AC via an AC filter 110. The primary side rectifying / smoothing circuit 115 has a converter transformer. Switching F through 120 primary winding 120A
The drain of ET125 is connected. Further, the switching control circuit 130 for PWM-controlling the switching operation of the switching FET 125 is provided, and the connection point between the AC filter 110 and the primary side rectifying / smoothing circuit 115 is connected to the switching control circuit 13 via a starting circuit 140.
0 is connected to the power supply terminal 130A.

This switching control circuit 130 has a built-in hysteresis low voltage malfunction prevention circuit in order to prevent malfunction when the power supply voltage drops, and when the power supply voltage Vcc applied to the power supply terminal 130A rises from 0V. ,
The operation is started at Vcc = 16.5V, and the control output is cut off at Vcc = 9.0V when the power supply voltage drops.

The starting circuit 140 includes a constant current circuit 141 connected to a connection point between the AC filter 110 and the primary side rectifying / smoothing circuit 115, and the constant current circuit 141 switches the switching via the backflow prevention diode 148. It is connected to the power supply terminal 130A of the control circuit 130. The power supply terminal 130A is grounded via the capacitor 135.

The constant current circuit 141 has first and second NPN transistors 144 and 44 whose collectors are connected to the connection points of the AC filter 110 and the primary side rectifying / smoothing circuit 115 via resistors 142 and 143, respectively. 145 and includes a base of the first NPN transistor 144 and a second NPN transistor 144.
Of the first NPN transistor 144 is connected to the collector, the emitter of the first NPN transistor 144 is connected to the base of the second NPN transistor 145, and the emitter of the first NPN transistor 144 and the second NPN transistor 145 are connected to each other. Is connected to the emitter of the second NPN transistor 145 via the current detecting resistor 146 and to the cathode of the backflow prevention diode 148.

In the constant current circuit 141, the voltage across the current detecting resistor 146 is applied to the second NPN transistor 145.
By controlling the current flowing from the resistor 143 to the base of the first NPN transistor 144, the constant current Ic is made to flow to the current detecting resistor 146.

A secondary side rectifying and smoothing circuit 150 is connected to the secondary winding 120B of the converter transformer 120, and the secondary winding 1 of the converter transformer 120 is connected.
The converter output obtained in 20B is rectified and smoothed by the secondary side rectifying and smoothing circuit 150 and output through the output filter 155. In the secondary side rectifying / smoothing circuit 150, the output detecting circuit 17 is connected via a resistor dividing circuit 160 for detecting an output voltage and a resistor 165 for detecting an output current.
0 is connected, and the detection output of the output detection circuit 170 is fed back to the switching control circuit 130 via the photocoupler 180. The output detection circuit 170
The photocoupler 180 is the converter transformer 1 described above.
Rectifying and smoothing circuit 19 connected to secondary winding 120B of 20
The rectified and smoothed output by 0 operates as a drive power source.

The switching control circuit 130 is started by supplying a starting current through the starting circuit 140 at the time of starting, starts supplying a switching pulse to the switching FET 125, and after starting, the converter transformer 120 is started. The rectifying / smoothing output from the rectifying / smoothing circuit 138 connected to the tertiary winding 120C operates as a driving power source, and the detection output from the output detection circuit 170 is fed back through the photocoupler 180, whereby the switching operation of the switching FET 125 is performed. PWM
Control to stabilize the converter output.

That is, this switching power supply device 10
At 0, when the AC input is supplied from the commercial power source, the resistor 142 of the starting circuit 140, the first NPN transistor 14
4, current detection resistor 146, backflow prevention diode 148
A constant current (Ic = 0.6 m
Pour A) and start charging.

Power supply terminal 1 of switching control circuit 130
The voltage Vcc applied to 30A gradually increases as the charging of the capacitor 135 progresses, and when the voltage exceeds the minimum start-up voltage (16.5V) of the low voltage malfunction prevention circuit, the switching control circuit 130 starts operation and a switching pulse is generated. Output to the switching FET 125. At this time, the current consumption of the switching control circuit 130 increases and the capacitor 1
Although the voltage across the terminals of 35 decreases, it is the minimum operating voltage (V1 = 9) due to the low voltage malfunction prevention circuit with hysteresis.
The switching operation continues until V).

Here, by charging the capacitor 135 with the current value Ic of the constant current circuit 141, the voltage Vcc applied to the power supply terminal 130A of the switching control circuit 130 rises, but the rise time to the minimum starting voltage is increased. Is within 5 seconds, for example. Then, the product of the transient response time, the drive current, and the minimum drive voltage is set to be smaller than half the product of the square difference of the hysteresis voltage of the low voltage malfunction prevention circuit and the capacitance of the capacitor 135. As a result, the switching power supply device 100 can reliably start up with less drive energy than the starting energy.

The current switched in the meantime passes through the converter transformer 120 and the secondary and tertiary windings 120B,
A high frequency current is passed through 120C. This high-frequency current is rectified by the secondary rectifying / smoothing circuit 150 and output from the output terminal as a converter output via the output filter 155.

Further, this voltage is compared with the reference voltage in the output detection circuit 170 via the resistance division circuit 160. When the output voltage is high, the light emitting diode of the photocoupler is turned on, and when it is low, it is turned off, and the primary side is turned off. The signal is transmitted to the switching control circuit 130, and the switching FE
The duty of the switching pulse applied to the gate of T125 is changed to control the output voltage Vout to a constant voltage.

On the other hand, the output from the tertiary winding 120C is rectified and smoothed by the rectification and smoothing circuit 120 on the primary side, charged in the capacitor 135, and supplied as a driving power source for the switching control circuit 130. The voltage Vcc (the voltage value in normal operation is 12V) is higher than the voltage from the starting circuit 140 (the voltage when starting is stable at 11V), and the backflow prevention diode 148 is connected to the starting circuit 140. The rectifying / smoothing output from the rectifying / smoothing circuit 138 does not flow back to the starting circuit.

As shown by the alternate long and short dash line in FIG. 1, the collector of the third NPN transistor 147 which is turned on by the rectifying and smoothing output by the rectifying and smoothing circuit 138 is connected to the base of the first NPN transistor 144 and the collector of the third NPN transistor 144. 2 N
By connecting to the connection point with the collector of the PN transistor 145, after starting, by stopping the power supply from the starting circuit 140, the starting circuit 140
It is also possible to reduce the power consumption in.

The voltage applied to the starting current limiting resistor 142 is low (0.6 mA × 150) due to the constant current operation.
(KΩ = 90V) It is not necessary to take measures to increase the withstand voltage by connecting resistors in series.

Further, the current required for the operation of the switching control circuit 130 is supplied as a constant current even at the time of start-up, and when it is not necessary, the start-up current limiting resistor 142 does not cause an unnecessarily large amount of current to flow, resulting in the power consumption of the conventional method. Less than

Further, even if the switching control circuit 130 is protected, the minimum latch current for maintaining the protection can be secured. Furthermore, in this switching power supply device 100, since the connection point between the AC filter 110 and the primary side rectifying / smoothing circuit 115 is connected to the power supply terminal 130A of the switching control circuit 130 via the starting circuit 140, the AC filter is connected. The starting circuit 140 can function as a discharge circuit for the X capacitors 110A and 110B of the 110.

In the above description, the present invention is applied to the switching power supply device adopting the PWM control method.
The present invention can also be applied to a switching power supply device that employs a frequency control method. Also, the constant current circuit
A configuration other than the above may be used, and an operational amplifier may be used to improve accuracy, and a constant current diode may be used if cost is taken into consideration.

[0036]

As described above, according to the present invention, the switching operation of the switching element for switching the rectified and smoothed output of the primary side rectified and smoothed circuit is controlled by the switching control circuit having the hysteresis low voltage malfunction prevention circuit. In activating the switching power supply device, the product of the transient response time of the switching power supply device, the drive current and the minimum drive voltage is set to the square difference of the hysteresis voltage of the low voltage malfunction prevention circuit and the power supply terminal of the switching control circuit. Keeping it smaller than half of the product of the capacity of the connected capacitor and supplying the starting current from the constant current circuit to start the switching control circuit reduces the start-up error and ensures the switching power supply device. Can be started.

Further, in the present invention, the starting current required for the operation of the switching control circuit can be made to flow at a constant current at the time of starting, and when it is not necessary, the starting current limiting resistor can prevent an excessive current from flowing. The power consumption can be reduced as compared with the conventional method. Since the voltage applied to the starting current limiting resistor is low due to the constant current operation,
There is no need to take measures to increase the withstand voltage by connecting resistors in series.

Further, in the present invention, the starting current is supplied from the constant current circuit to the power supply terminal of the switching control circuit through the backflow prevention diode, so that the power supply terminal of the switching control circuit is switched to the constant current circuit after the start-up. The drive power does not flow backwards.

Further, in the present invention, the constant current circuit is connected to a connection point between the AC filter connected to the commercial power source and the primary side rectifying / smoothing circuit, so that the discharging circuit for the X capacitor of the AC filter is used. The starting circuit can function.

Further, according to the present invention, by stopping the operation of the constant current circuit after the activation of the switching control circuit, it is possible to reduce the power consumption in the activation circuit after the activation.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of a conventional switching power supply device.

[Explanation of symbols]

100 switching power supply device, 110 AC filter, 115 primary side rectifying and smoothing circuit, 120 converter transformer, 120A primary winding, 120B secondary winding,
120C tertiary winding 120C, 125 switching F
ET, 130 switching control circuit, 130A power supply terminal, 135 capacitor, 140 starting circuit, 141
Constant current circuit, 142, 143 resistance, 144, 145
First and second NPN transistors, 146 Current detecting resistor, 147 Third NPN transistor, 148
Backflow prevention diode, 150 secondary side rectification smoothing circuit, 1
55 output filter, 160 resistance dividing circuit for detecting output voltage, 165 resistance for detecting output current, 170 output detecting circuit, 180 photo coupler, 190 rectifying and smoothing circuit

Claims (7)

[Claims] 1. A switching power supply device in which a switching control circuit having a hysteresis low voltage malfunction prevention circuit controls a switching operation of a switching element for switching a rectified and smoothed output of a primary side rectified and smoothed circuit, the switching power supply comprising: The starting circuit for supplying the starting current to the control circuit is configured by a constant current circuit, and the product of the transient response time of the switching power supply device, the driving current and the minimum driving voltage is the square difference of the hysteresis voltage of the low voltage malfunction prevention circuit. A switching power supply device, characterized in that it is smaller than half the product of the capacitance of a capacitor connected to the power supply terminal of the switching control circuit. 2. The constant current circuit supplies a starting current to a power supply terminal of the switching control circuit via a current limiting resistor, a first NPN transistor, and a current detecting resistor,
The voltage across the current detecting resistor is detected by the second NPN transistor, and the current flowing through the resistor to the base of the first NPN transistor is controlled so that the current is constant via the current detecting resistor. 2. The switching power supply device according to claim 1, wherein the starting current is supplied. 3. The switching power supply device according to claim 2, wherein the constant current circuit supplies the power supply terminal of the switching control circuit through a backflow prevention diode. 4. The switching power supply device according to claim 1, wherein the constant current circuit is connected to a connection point between an AC filter connected to a commercial power supply and the primary side rectifying and smoothing circuit. 5. The switching power supply device according to claim 1, wherein the starting circuit includes a switch element that stops the operation of the constant current circuit after the switching control circuit is started. 6. A method of starting a switching power supply device, wherein a switching control circuit having a hysteresis low voltage malfunction prevention circuit controls a switching operation of a switching element that switches a rectified and smoothed output of a primary side rectified and smoothed circuit. , The product of the transient response time of the switching power supply device, the drive current and the minimum drive voltage, the product of the square difference of the hysteresis voltage of the low voltage malfunction prevention circuit and the capacitance of the capacitor connected to the power supply terminal of the switching control circuit. The method for starting a switching power supply device is characterized in that the switching control circuit is started by supplying a starting current from a constant current circuit. 7. The method of starting a switching power supply device according to claim 6, wherein the operation of the constant current circuit is stopped after the switching control circuit is started.