JP2003333841A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a separately excited switching power supply 21 having a circuit 22 for controlling a switching operation depending on a secondary output voltage Vo in which an operation is stopped in safety without generating noise in the output voltage Vo and without generating an undesired high current even in the power supply 21 arranged to stop the operation stably by interrupting power to the control circuit 22 when the output voltage from a rectifying circuit is lowered by a voltage detecting circuit 24 and a switch circuit 25. <P>SOLUTION: Since a detection voltage is lowered by an amount corresponding to a voltage division ratio as compared with a case where the detection voltage is imparted directly to the voltage detecting circuit 24 from the joint of starting resistors R1 and R2, power to the control circuit 22 is interrupted at a relatively early stage even when a high voltage is used and a switching operation is stopped. Consequently, an undesired high current is generated in a primary circuit and an operation can be stopped in safety. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a so-called AC-D.
The present invention relates to a switching power supply device preferably implemented as a C converter, and particularly to a separately excited switching power supply device.

[0002]

2. Description of the Related Art FIG. 11 is an electric circuit diagram of a typical prior art switching power supply device 1. This switching power supply device 1 is the above-mentioned separately-excited basic switching power supply device that uses an integrated circuit dedicated control circuit 2 for controlling switching. The AC voltage Vin applied between the terminals p1 and p2 passes through a fuse f and a filter circuit for EMI countermeasures formed by the filter capacitors c1 and c2 and the filter coil l, and then a bridge circuit including diodes d1 to d4 and It is rectified and smoothed by the smoothing capacitor c3. The direct current voltage Vc3 thus obtained is applied to the FE and the primary winding n1 of the transformer n.
The induced voltage is applied to the secondary winding n2 of the transformer n by being applied to the series circuit with the main switching element q made of T, and the main switching element q is switched at a high frequency by the control circuit 2 as described later. Occurs. The induced voltage is rectified and smoothed by the diode d5 and the smoothing capacitor c4, and output from the terminals p3 and p4 to a load (not shown).

The output voltage Vo from the terminals p3 and p4 is monitored by the output voltage detection circuit 3,
The detection result is the photodiode d of the photocoupler pc.
It is sent from 6 to the phototransistor tr1 and fed back to the control circuit 2 on the primary side. The control circuit 2 controls the duty of the main switching element q based on the fed back information of the output voltage Vo, and thus the output voltage Vo of the switching power supply device 1 is stabilized.

On the other hand, a capacitor c5 is provided as a power source for the control circuit 2. The capacitor c5 is connected to the diode d when the voltage induced in the sub winding n3 of the transformer n is applied.
It is charged by being given via 7. Further, the DC voltage Vc3 rectified and smoothed by the bridge circuit and the smoothing capacitor c3 is applied to the capacitor c5 via the starting resistors r1 and r2. This starting resistance r
1 and r2 have two stages so that the high voltage of the smoothing capacitor c3 is not directly applied to the control circuit 2 even if they are short-circuited during the short-circuit / open test of each circuit component.

FIG. 12 is a waveform diagram for explaining the operation of the switching power supply device 1 configured as described above when the power is turned on. At time t1, when an AC power source is connected to the terminals p1 and p2, the charging voltage Vc3 of the smoothing capacitor c3 gradually rises, and the power source voltage Vcc of the control circuit 2 due to the capacitor c5 also rises and the control circuit 2 When the operation start voltage is reached, the control circuit 2 starts its operation, and at time t2, sends a control signal to the main switching element q to start the switching operation as described above. As a result, the secondary output voltage Vo also rises.
After starting in this way, the control circuit 2 continues to operate with the current supplied through the diode d7 as the main power source.

FIG. 13 is a waveform diagram for explaining the operation of the switching power supply device 1 when the power supply is cut off. The power input is turned off, and the charging voltage Vc3 of the smoothing capacitor c3
Decrease, the output voltage Vo decreases, the voltage induced in the sub winding n3 also decreases, the power supply voltage Vcc of the control circuit 2 due to the capacitor c5 also decreases, and the control circuit 2 once operates at time t3. Stop.

However, when switching is stopped, the electric charge remaining in the smoothing capacitor c3 is changed to the starting resistance r.
1 and r2 to the capacitor c5, the power supply voltage Vcc of the control circuit 2 rises, and the starting resistors r1 and r2
At a time t4 after the time determined by the capacitor c5 and, for example, 3 seconds has elapsed, the control circuit 2
Restarts, and spike noise is generated in the output voltage Vo. At this time, since the power supply input remains off, the output voltage Vo immediately drops.

When the control circuit 2 is restarted after the power is turned off and noise appears in the output voltage Vo in this way, there is a problem that the equipment connected in the subsequent stage malfunctions. For example,
When the device is an audio device, a clicking sound is generated from a speaker, or in a device that stores data, the data is erased.

Therefore, as another conventional technique for solving such a problem, a switching power supply device 11 shown in FIG. 14 is used. This switching power supply 1
1 is similar to the switching power supply device 1 described above,
Corresponding parts are designated by the same reference numerals and the description thereof will be omitted. This switching power supply device 11 is provided with a voltage detection circuit 12 that detects the voltage Vc3, and a switch circuit 13 that holds the power supply of the control circuit 2 while the power supply of the control circuit 2 is cut off when the detected voltage becomes lower than a predetermined voltage. Has been.

The voltage detecting circuit 12 comprises zener diodes zd1 and zd2 and bias resistors r3 and r4 thereof. On the other hand, the switch circuit 13
Includes a short-circuit resistor r5, a transistor tr2 that is a short-circuit switch, and a diode d8.

The zener diodes zd1 and zd2 and the bias resistors r3 and r4 are connected in series with each other, and the cathode side of the zener diode zd1 is connected to the primary winding n1.
Of the smoothing capacitor c3, and the bias resistor r4 side is connected to the low-level side power line of the sub winding n3. The connection point between the Zener diode zd2 and the bias resistor r3 is connected to the cathode of the diode d8, and the anode of this diode d8 is connected to the base of the transistor tr2. The power supply voltage Vcc is applied to the emitter of the PNP type transistor tr2 from the capacitor c5 via the short-circuit resistor r5, and the collector is grounded.

Therefore, when the charging voltage Vc3 of the smoothing capacitor c3 is sufficiently high, the Zener diode zd
1, zd2 breaks down, and the currents flowing through the Zener diodes zd1 and zd2 are bias resistors r3 and r4.
Is converted into a voltage by the PNP transistor tr.
2 becomes a high level and the transistor tr2
Is turned off, the power supply voltage Vcc is supplied to the control circuit 2, and the control circuit 2 is operating.

Like the starting resistors r1 and r2, the bias resistors r3 and r4 have two stages so that the base of the transistor tr2 is not ground-faulted even if a short circuit occurs during a short-circuit / open test of each circuit component. There is. The Zener voltage of the Zener diodes zd1 and zd2 is generally 3
Since 6 V is the upper limit, it has two stages in order to set the desired off-voltage at the time of power-off, which will be described later.

When the power is turned on, the Zener diode zd1,
Since zd2 is not broken down, the voltage on the cathode side of the diode d8 becomes lower than that on the anode side and the diode d8 turns on. As a result, the base of the transistor tr2 is grounded via the bias resistors r3 and r4, the base voltage becomes lower than the emitter voltage, and the transistor tr2 is turned on. As a result, the power supply of the control circuit 2 is short-circuited via the short-circuit resistance r5, and the power supply voltage Vcc is less than the saturation voltage of the main switching element q.
The voltage has dropped to about 2V and the control circuit 2 has stopped operating. Then, the charging voltage Vc3 of the smoothing capacitor c3
Becomes equal to or higher than the off voltage of 72 V, the zener diodes zd1 and zd2 break down to turn off the transistor tr2, and the control circuit 2 starts its operation by the supply of the power supply voltage Vcc by the starting resistors r1 and r2.

On the other hand, FIG. 15 is a waveform diagram for explaining the operation of the switching power supply device 11 when the power supply is cut off. The power supply input is turned off and the smoothing capacitor c3
When the charging voltage Vc3 of the power supply voltage Vc3 decreases and becomes lower than 72V at time t3, the Zener diodes zd1 and zd2 turn off, the transistor tr2 turns on, the power supply voltage Vcc is grounded, and the control circuit 2 stops operating. After that, since the power supply voltage Vcc remains grounded, the control circuit 2 remains stopped operating, and malfunctions such as the clicking noise are prevented.

[0016]

In the switching power supply device 11 configured as described above, if the power supply is compatible with various power supply voltages, that is, world wide support, the primary power is cut off when used at a high voltage. The current flowing through the side circuit may increase, and the main switching element q and the fuse f may be damaged. This is because the control circuit 2 controls so that the energy converted to the secondary side by switching becomes the same, and the power supply voltage Vi is cut off by shutting off the power supply.
This is because when n decreases, the primary-side current increases in inverse proportion to it.

For example, in order to enable use at a power supply voltage Vin of 100V, Zener diodes zd1 and zd1
When the off voltage due to d2 is set to 72V, the power supply voltage Vin (effective value) is set to 50V at which the peak value is 72V.
The switch circuit 13 cuts off the power supply of the control circuit 2 at the time when the power supply voltage has decreased. However, even when the switching power supply device 11 is used at 230V, the switch circuit 13 does not shut off the power supply of the control circuit 2 unless the power supply voltage Vin (effective value) drops to 50V, so that the smoothing capacitor c3 is charged. The voltage Vc3 changes from 230V to 5
A large current continues to flow until the voltage drops to 0V. Then, the primary side current is 230 V of normal operation.
Compared with the time, 230/5 at the time of 50V immediately before the stop of operation
It becomes 0 times.

An object of the present invention is to stably stop the operation without generating noise in the output voltage, and to safely stop the operation without causing an undesired large current even in the power supply device. It is to provide a switching power supply device capable of performing.

[0019]

In the switching power supply device of the present invention, a DC voltage obtained by rectifying an input AC voltage by a rectifying circuit is switched by a main switching element, and the control means is
In a switching power supply device that stabilizes the output voltage to a desired value by controlling the switching in accordance with the output voltage on the secondary side, the output voltage of the rectifier circuit falls below a predetermined level. Then, the power supply control means for cutting off the power supply to the control means and the first and second resistors are connected in series to each other, and the output voltage of the rectifier circuit is supplied as the power supply to the control means. At the same time, a switching power supply device is included, which includes a starting resistance for applying a determination voltage for determining interruption of the power supply to the power supply control means from a connection point of the first resistance and the second resistance. .

According to the above configuration, the separately excited switching power supply device is provided with the control means for controlling the switching of the main switching element according to the output voltage on the secondary side so as to stabilize the output voltage to a desired value. In the above, when the output voltage of the rectifier circuit falls below a predetermined level, the power supply to the control means is cut off, so that the power supply control means for stably stopping the operation without generating noise in the output voltage. In order to provide, the starting resistance for supplying the output voltage of the rectifier circuit as a power source to the control means when the power source is turned on is composed of two groups of a first resistor and a second resistor connected in series with each other. , The voltage at their connection points,
That is, the output voltage of the rectifier circuit is set to the first and second
The voltage divided by the resistor is applied to the power supply control means as a judgment voltage for judging the interruption of the power supply.

Therefore, the resistance value of the first resistor is set to R
1, the resistance value of the second resistor is R2, the desired arbitrary voltage division ratio of the determination voltage to the output voltage of the rectifier circuit is X, and the input AC voltage (effective value) is Vin,
For example, the zener voltage of the zener diode for judging whether or not the judgment voltage is lower than a predetermined level is Vz, and the power supply voltage of the control means (usually about 20V) is Vz.
When cc is set, R1 / R2 = {(√2Vin × X−Vcc) / Vz} −1 can be set to obtain the desired partial pressure ratio X.

As a result, as compared with the case where the output voltage of the rectifier circuit is directly applied as the judgment voltage, the judgment voltage can be lowered to the voltage division ratio X, for example, 70%, which corresponds to various power supply voltages. In this regard, even when used at a high voltage, the power supply control means cuts off the power supply to the control means at a relatively early stage after the power supply is cut off, thereby stopping the operation of the control means and thus the switching operation of the main switching element. The operation can be safely stopped without causing an undesired large current in the primary side circuit.

Further, by lowering the determination voltage, it is possible to reduce the number of stages of the Zener diode and its bias resistor for determining whether or not the determination voltage is lower than a predetermined level in the power supply control means. it can.

Further, in the switching power supply device of the present invention, the power supply control means breaks down when the judgment voltage is higher than a predetermined level and turns off when the judgment voltage is lower than the predetermined level, and a bias resistance of the zener diode. A voltage detection circuit for detecting that the output voltage of the rectifier circuit has dropped below a predetermined level, and turning on / off in response to a detection result taken from a connection point between the Zener diode and a bias resistor. A short-circuit switch that is turned off, and a short-circuit resistance that is interposed in series between the short-circuit switch and the power supply line of the control means,
And a switch circuit that controls the power supply to the control means in response to the detection result of the voltage detection circuit.

According to the above configuration, the voltage level representing the detection result given from the voltage detection circuit to the short-circuit switch can be lowered by the voltage division by the voltage-dividing resistor, and the short-circuit switch generally has a high withstand voltage. The switch circuit can be configured by using the conventional transistor as it is, and it is not necessary to use special parts.

Furthermore, in the switching power supply device of the present invention, the power supply control means breaks down when the determination voltage is a predetermined level or higher and turns off when the determination voltage is lower than the predetermined level, and a bias of the zener diode. A voltage detection circuit having a resistor for detecting that the output voltage of the rectifier circuit has dropped below a predetermined level, and is turned on in response to a detection result taken out from a connection point between the Zener diode and a bias resistor. A turning-off Darlington circuit, and a current limiting resistor that is interposed in series between the control transistor on the preceding stage side of the Darlington circuit and the power supply line of the control means.
And a switch circuit that controls the power supply to the control means in response to the detection result of the voltage detection circuit.

According to the above construction, since the Darlington circuit is used for short-circuiting the power supply line of the control means in the switch circuit, the direct current amplification factor per transistor is reduced, and the direct current amplification factor due to changes in ambient temperature is reduced. It is possible to stabilize the switch operation against the fluctuation of

Further, in the switching power supply device of the present invention, in the power supply control means, the voltage detection circuit is
It further has a resistor interposed between the Zener diode and a bias resistor, and the short circuit switch of the switch circuit receives and inputs the detection result from a connection point of the resistor and the bias resistor. Characterize.

According to the above configuration, the voltage level representing the detection result given from the voltage detection circuit to the short circuit switch can be lowered by the resistance interposed between the Zener diode and the bias resistor, and the short circuit As the switch, a general transistor having a high breakdown voltage can be used as it is, or a transistor having a low breakdown voltage and a diode for protecting the breakdown voltage can be used, and it is not necessary to use a special component.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is an electric circuit diagram of a switching power supply device 21 according to the first embodiment of the present invention. The switching power supply device 21 is a separately-excited switching power supply device that uses a dedicated control circuit 22 that is an integrated circuit that controls switching. The AC voltage Vin applied between the terminals P1 and P2 passes through a fuse F and a filter circuit for EMI countermeasures composed of filter capacitors C1 and C2 and a filter coil L, and then a bridge circuit including diodes D1 to D4 and It is rectified and smoothed by the smoothing capacitor C3. The DC voltage VC3 thus obtained is applied to the primary winding N1 of the transformer N and the FET.
Is applied to the series circuit with the main switching element Q, and the induced voltage is applied to the secondary winding N2 of the transformer N by the main switching element Q being switched at a high frequency by the control circuit 22 as described later. Occur. The induced voltage is generated by the diode D5 and the smoothing capacitor C4.
It is rectified and smoothed by and is output from the terminals P3 and P4 to a load (not shown).

The output voltage Vo from the terminals P3 and P4 is monitored by the output voltage detection circuit 23, and the detection result is sent from the photodiode D6 of the photocoupler PC to the phototransistor TR1 and the primary side of the above is detected. It is fed back to the control circuit 22. The control circuit 22 controls the duty of the main switching element Q based on the fed back information of the output voltage Vo, and the output voltage Vo of the switching power supply device 21 is thus stabilized.

On the other hand, a capacitor C5 is provided as a power source for the control circuit 22. The capacitor C5 is charged by the voltage induced in the sub winding N3 of the transformer N being given through the diode D7. The DC voltage VC3 rectified and smoothed by the bridge circuit and the smoothing capacitor C3 is applied to the capacitor C5 via the starting resistors R1 and R2. These starting resistors R1 and R2 prevent the smoothing capacitor C from being added to the control circuit 22 even if they are short-circuited during the short-circuit / open test of each circuit component.
There are two stages so that the high voltage of 3 is not directly applied.

Further, in relation to the control circuit 22, a voltage detection circuit 24 for detecting the voltage VC3, and the detection voltage is given as a power shutoff determination voltage and becomes lower than a predetermined voltage, the control circuit And a switch circuit 25 for holding the power source of the power source 22 with the power source cut off. The voltage detection circuit 24 includes a Zener diode ZD.
And a bias resistor R3 thereof.
On the other hand, the switch circuit 25 includes a short circuit resistor R4, a transistor TR2 which is a short circuit switch, and a diode D8.
And is configured.

It should be noted that in the present invention, the Zener diode ZD and the bias resistor R3 are connected in series with each other, the cathode side of the Zener diode ZD is connected to the connection point of the starting resistors R1 and R2, and the bias resistor R3.
Is connected to the power line on the low level side of the auxiliary winding N3. Therefore, the smoothing capacitor C3
The charging voltage VC3 is divided and input to the voltage detection circuit 24 as the determination voltage.

The connection point between the Zener diode ZD and the bias resistor R3 is connected to the cathode of the diode D8, and the anode of the diode D8 is the transistor TR.
2 connected to the base. PNP type transistor TR
A capacitor C5 is connected to the emitter of 2 through a short-circuit resistor R4.
Is applied with the power supply voltage Vcc, and the collector is grounded.

Therefore, when the charging voltage VC3 of the smoothing capacitor C3 is sufficiently high, the Zener diode ZD breaks down, the current flowing through the Zener diode ZD is converted into a voltage by the bias resistor R3, and PN
The base of the P-type transistor TR2 becomes high level, the transistor TR2 is turned off, the power supply voltage Vcc is supplied to the control circuit 22, and the control circuit 22 is operating.

Further, when the power is turned on, the Zener diode ZD is not broken down, so that the voltage on the cathode side of the diode D8 becomes lower than that on the anode side and the diode D8 is turned on. As a result, the base of the transistor TR2 is grounded via the bias resistor R3, the base voltage becomes lower than the emitter voltage, and the transistor TR2 is turned on. As a result, the control circuit 22
Is short-circuited via the short-circuit resistor R4, and the power supply voltage Vc
c decreases to about 0.2 V, which is lower than the saturation voltage of the main switching element Q, and the control circuit 22 stops operating. After that, when the charging voltage VC3 of the smoothing capacitor C3 gradually rises and the power supply voltage Vcc of the control circuit 22 due to the capacitor C5 also rises and reaches the operation start voltage of the control circuit 22, the control circuit 22 operates. Start and
A control signal is sent to the main switching element Q to start the switching operation. As a result, the secondary output voltage Vo
Also stands up. After starting in this way, the transistor TR2 is turned off as described above, and the diode D7 is turned on.
The control circuit 22 uses the current supplied via
Will continue to operate.

Furthermore, when the power supply is cut off, the charging voltage VC3 of the smoothing capacitor C3 decreases, and when the breakdown voltage becomes lower than 36V, for example, the Zener diode ZD turns off and the transistor TR2 turns on, and the control circuit 22 is turned on. The power supply is short-circuited via the short-circuit resistor R4, and the control circuit 22 stops operating. After that, since the power supply voltage Vcc remains at the ground potential, the control circuit 22 remains stopped operating, and malfunctions such as the clicking noise are prevented.

Here, the desired voltage division ratio of the input voltage to the voltage detection circuit 24 with respect to the charging voltage VC3 is X, the input AC voltage (effective value) is Vin, and the Zener voltage of the Zener diode ZD is Vz. , R1 = R2 = {(√2Vin × X-Vs) / Vz} -1 (1) when the charging voltage of the capacitor C5 is Vs (= power supply voltage Vcc of the control circuit 22 (normally about 20V)) By setting to, the desired partial pressure ratio X can be obtained.

That is, the voltage V2 at the connection point of the starting resistors R1 and R2 is V2 = {R2 / (R1 + R2)} (√2Vin × X-Vs) + Vs (2), and the transistor TR2 is turned on. An approximate expression of the voltage V2 when the control circuit 22 is stopped is V2 = Vs + Vz (3), which is the expression 1.

With this configuration, the voltage detection circuit 24 shuts off the power supply to the control circuit 22 when the input AC voltage Vin falls below a predetermined level, so that noise is not generated in the output voltage Vo. The load side circuit can be stably stopped without malfunctioning.

When the voltage detection circuit 24 is provided, the voltage at the connection point between the starting resistors R1 and R2, that is, the voltage obtained by dividing the charging voltage VC3 by the starting resistors R1 and R2 is determined by the voltage detecting circuit 24. Since the charging voltage VC3 is applied as a voltage, the judgment voltage is divided by the voltage division ratio X, for example, 7 compared with the case where the charging voltage VC3 is directly applied as the judgment voltage.
It can be as low as 0%. Therefore, in responding to various power supply voltages, the voltage detection circuit 24 and the switch circuit 25 shut off the power supply to the control circuit 22 at a relatively early stage after the power is shut off, even when used at a high voltage. Since the operation of 22 and hence the switching operation of the main switching element Q is stopped, the operation can be safely stopped without causing an undesired large current in the primary side circuit.

Furthermore, by lowering the judgment voltage, the withstand voltage of the Zener diode ZD for judging whether or not the judgment voltage becomes lower than a predetermined level can be reduced, and it is a general 1/2 level. The power consumption of the bias resistor R3 realized by a watt resistor can be reduced, and the number of these stages can be reduced. That is, the switching power supply device 11 shown in FIG. 14 has two stages of zd1, zd2 and r3, r4, whereas the switching power supply device 21 has one stage. In addition,
The Zener diode ZD and the bias resistor R3 may be configured by serially connecting a plurality of stages having a low withstand voltage. In this case as well, the switching power supply device 21 has a higher number of stages than the switching power supply device 11 described above. Can be reduced.

FIG. 2 shows the second embodiment of the present invention.
The explanation is based on the following.

FIG. 2 is an electric circuit diagram of the switching power supply device 31 according to the second embodiment of the present invention. The switching power supply 31 is the same as the switching power supply 2 described above.
Similar to 1 and corresponding parts are designated by the same reference numerals, and description thereof will be omitted. It should be noted that, in the switching power supply device 31, in the voltage detection circuit 34, a resistor R5 is added between the zener diode ZD and the bias resistor R3, and the resistor R5 is connected between the resistor R5 and the bias resistor R3. That is, the cathode of the diode D8 is connected.

Therefore, the cathode voltage of the diode D8 is further divided by the bias resistor R3 and the resistor R5 to be further lowered, and a diode having a low withstand voltage should be used as the diode D8 which is a withstand voltage protection diode of the transistor TR2. You can For example, 500V
It is possible to change from a withstand voltage product to a general withstand voltage of 50 V, which makes it possible to use inexpensive and small parts.

FIG. 3 shows the third embodiment of the present invention.
The explanation is based on the following.

FIG. 3 is an electric circuit diagram of a switching power supply device 41 according to the third embodiment of the present invention. This switching power supply device 41 is the same as the switching power supply device 2 described above.
Similar to 1 and corresponding parts are designated by the same reference numerals, and description thereof will be omitted. It should be noted that in the switching power supply device 41, in the switch circuit 45, the transistor T having a higher breakdown voltage than the transistor TR2 is used.
By using R2a, the breakdown voltage protection diode D8 of the transistor TR2 is not provided.

That is, since the base voltage of the transistor TR2a is lowered by omitting the diode D8, a transistor having a high breakdown voltage (about 100V) is adopted as the transistor TR2a. However, in the conventional switching power supply device 11 of FIG. 14, when Vin = 230V, the base voltage of the transistor tr2 becomes about 330V, so that it cannot be realized with general parts and special parts are used, resulting in cost reduction. 10
The switching power supply device 41 has a double size and a large size.
As described above, the base voltage of the transistor TR2a is set to about 230V by the voltage division by the starting resistors R1 and R2.
(As X = 70%),
The diode D8 can be omitted by adopting a high withstand voltage product among general components.

FIG. 4 shows the fourth embodiment of the present invention.
The explanation is based on the following.

FIG. 4 is an electric circuit diagram of a switching power supply device 51 according to the fourth embodiment of the present invention. This switching power supply device 51 is the same as the switching power supply device 3 described above.
Similar to 1,41. It should be noted that even in the switching power supply device 51, in the switch circuit 55, the transistor T having a higher breakdown voltage than the transistor TR2 is used.
By using R2b, the breakdown voltage protection diode D8 of the transistor TR2 is not provided.

The resistor R is provided in the voltage detection circuit 34.
5 is provided, the base voltage of the transistor TR2b can be further reduced as compared with the voltage detection circuit 44 in which the diode D8 is omitted, and the breakdown voltage of the transistor TR2b is, for example, 80V.
It can be a degree.

FIG. 5 shows the fifth embodiment of the present invention.
The explanation is based on the following.

FIG. 5 is an electric circuit diagram of a switching power supply device 61 according to the fifth embodiment of the present invention. This switching power supply device 61 is the same as the switching power supply device 2 described above.
Similar to 1. It should be noted that in the switching power supply device 61, in the switch circuit 65, the transistor TR2 is used for control, and another PNP type transistor TR3 controlled by the transistor TR2 is provided, and the control is performed by the transistor TR3. The power supply of the circuit 22 is short-circuited. That is, the transistors TR2 and TR3 form a Darlington circuit.

As a result, the switch operation can be stabilized against variations in the direct current amplification factor due to changes in ambient temperature. Particularly, in the case of a power supply device having a large output of 100 W or more, the outflow current from the sub winding N3 of the transformer N is 1
Since the auxiliary winding N3 has a low impedance of about 0 A, it was difficult to realize a reliable switching operation only with the transistor TR2. However, by using the Darlington circuit, a reliable switching operation can be realized. . That is, the DC current amplification factor of the transistor is the ratio of the collector current value to the base current value, and when the outflow current from the sub winding N3 becomes large as described above, the switching operation becomes unstable due to the change in the ambient temperature. By using the Darlington circuit, the DC current amplification factor per transistor can be reduced, and reliable operation can be realized.

Incidentally, the capacitor C5 and the transistor TR
A current limiting resistor R6 is provided between the base of the transistor TR2 and the emitter of the transistor TR2. The current limiting resistor R6 acts to limit the emitter current of the transistor TR2, and the current limiting resistor R6 is provided. Otherwise, the transistor TR2 may become overcurrent and may be destroyed.

FIG. 6 shows the sixth embodiment of the present invention.
The explanation is based on the following.

FIG. 6 is an electric circuit diagram of a switching power supply device 71 according to the sixth embodiment of the present invention. This switching power supply device 71 is the same as the switching power supply device 3 described above.
Similar to 1,61. Therefore, in this switching power supply device 71, by using the voltage detection circuit 34,
The diode D8 has a low withstand voltage, and the switching circuit 65 is used to realize a reliable switching operation.

FIG. 7 shows the seventh embodiment of the present invention.
The explanation is based on the following.

FIG. 7 is an electric circuit diagram of a switching power supply device 81 according to a seventh embodiment of the present invention. This switching power supply device 81 is the same as the switching power supply device 4 described above.
Similar to 1,61. Therefore, in the switching power supply device 81, the switch circuit 85 uses the transistor TR2a having a high breakdown voltage in the switch circuit 45, omits the diode D8, and uses the transistor TR3 in the switch circuit 65 to cause the transistor TR2a. And the transistor TR3
The Darlington circuit is configured by and to realize a reliable switching operation.

FIG. 8 shows the eighth embodiment of the present invention.
The explanation is based on the following.

FIG. 8 is an electric circuit diagram of a switching power supply device 91 according to the eighth embodiment of the present invention. This switching power supply device 91 is the same as the switching power supply device 3 described above.
Similar to 1,81. Therefore, in this switching power supply device 91, by using the switch circuit 85,
The diode D8 is omitted, a reliable switching operation is realized, and the voltage detection circuit 34 is used to further lower the base voltage of the transistor TR2a and lower the withstand voltage of the transistor TR2a.

FIG. 9 shows the ninth embodiment of the present invention.
The explanation is based on the following.

FIG. 9 is an electric circuit diagram of a switching power supply device 101 according to the ninth embodiment of the present invention. The switching power supply device 101 is similar to the switching power supply devices 41 and 81 described above. It should be noted that in the switching power supply device 101, the transistor TR
2, TR2a and TR3 are PNP type transistors, whereas the transistors TR20 and TR30 used in the switch circuit 105 are changed to NPN type transistors.

Therefore, when the charging voltage VC3 of the smoothing capacitor C3 is sufficiently high, the Zener diode ZD breaks down, the current flowing through the Zener diode ZD is converted into a voltage by the bias resistor R3, and NP
The base of the N-type transistor TR20 becomes high level and the transistor TR20 is turned on, whereby the base of the transistor TR30 becomes low level and the transistor TR30 is turned off, and the power supply voltage Vcc is supplied to the control circuit 22. Then, the control circuit 22 is operating.

When the power is turned on, the Zener diode ZD is not broken down. Therefore, the base of the transistor TR20 is grounded via the bias resistor R3, the base voltage becomes substantially equal to the emitter voltage, and the transistor TR20 is turned off. To do. At this time, the charging voltage VC3 of the smoothing capacitor C3 and the power supply voltage Vcc of the control circuit 22 by the capacitor C5 have not risen,
The control circuit 22 has stopped operating. After that, the charging voltage VC3 of the smoothing capacitor C3 gradually rises,
Further, the power supply voltage Vc of the control circuit 22 by the capacitor C5
When c also rises and reaches the operation start voltage of the control circuit 22, the control circuit 22 starts operation, sends a control signal to the main switching element Q, and starts switching operation. As a result, the secondary output voltage Vo also rises. After the start-up in this way, when the Zener diode ZD breaks down as described above, the transistor TR2
0 is turned on, whereby the base voltage of the transistor TR30 becomes the ground level, the transistor TR30 is turned off, and the control circuit 22 continues to operate using the current supplied through the diode D7 as the main power source.

Furthermore, when the power supply is cut off, the charging voltage VC3 of the smoothing capacitor C3 drops, and when it becomes lower than the breakdown voltage, for example, 36 V, the Zener diode ZD turns off and the transistor TR20 turns off, which causes the capacitor C5. High level power supply voltage Vcc
Is given to the base of the transistor TR30 via the current limiting resistor R6 to turn on the transistor TR30, the power supply of the control circuit 22 is short-circuited, and the control circuit 22 stops its operation. After that, since the power supply voltage Vcc remains at the ground potential, the control circuit 22 remains stopped operating,
Malfunctions such as the clicking noise are prevented.

With such a configuration, N with a good response can be obtained.
The switch circuit 105 can be configured using the PN type transistors TR20 and TR30. Further, since the operation of the transistor TR20 is opposite to that of the transistor TR2, the diode D8 can be omitted.

The tenth embodiment of the present invention will be described below with reference to FIG.

FIG. 10 is an electric circuit diagram of a switching power supply device 111 according to the tenth embodiment of the present invention. The switching power supply device 111 is similar to the switching power supply devices 51 and 101 described above. Therefore, in the switching power supply device 111, the voltage detection circuit 3
4, the base voltage of the transistor TR20 is lowered to lower the breakdown voltage of the transistor TR20, and the Darlington circuit of the NPN transistors TR20 and TR30 by the switch circuit 105 is used.

Incidentally, Japanese Patent Laid-Open No. 5-83933 discloses that
Although it has been shown that the soft-start circuit controls the dead time in response to the detection result of the AC voltage after rectification to limit the primary-side current when the power is turned on again, the present invention does not work when the power is shut off. The current limitation is performed by the switching control circuit 22 and the current limitation is performed by shutting off the power supply of the switching control circuit 22, which is different from the prior art.

[0073]

As described above, the switching power supply device of the present invention controls the switching of the main switching element according to the secondary side output voltage so as to stabilize the output voltage to a desired value. In the separately-excited switching power supply device including, when the output voltage of the rectifier circuit falls below a predetermined level, the power supply to the control means is cut off, without generating noise in the output voltage.
In providing the power supply control means for stably stopping the operation, the starting resistances that supply the output voltage of the rectifier circuit as the power supply to the control means when the power is turned on are first resistors connected in series with each other. And a second resistor, and a voltage at a connection point between them, that is, a voltage obtained by dividing the output voltage of the rectifier circuit by the first and second resistors is supplied to the power supply control means as a power supply. It is given as a cutoff judgment voltage.

Therefore, as compared with the case where the output voltage of the rectifier circuit is directly applied as the detection voltage, the judgment voltage can be made lower, and in responding to various power supply voltages, the power supply can be used even at a high voltage. Since the control means cuts off the power supply to the control means at a relatively early stage after the power is cut off and stops the operation of the control means, and thus the switching operation of the main switching element, an undesired large current flows in the primary circuit. It is possible to stop the operation safely without occurring.

Further, since the judgment voltage becomes low, the number of stages of the Zener diode and its bias resistor for judging whether or not the judgment voltage becomes lower than a predetermined level in the power supply control means can be reduced. it can.

Further, the switching power supply device of the present invention is
As described above, the power supply control means includes the Zener diode that breaks down when the determination voltage is equal to or higher than the predetermined level and is turned off when the determination voltage is lower than the predetermined level, and the bias resistance of the Zener diode. Voltage detection circuit that detects that the output voltage of the device has dropped below a predetermined level, a short-circuit switch that turns on / off in response to a detection result taken from a connection point between the Zener diode and a bias resistor, and the short circuit A switch circuit having a short-circuit resistance interposed in series between the switch and the power supply line of the control means, and controlling the power supply to the control means in response to the detection result of the voltage detection circuit. Constitute.

Therefore, the voltage level representing the detection result given from the voltage detecting circuit to the short circuit switch can be lowered by the voltage division by the voltage dividing resistor, and a general transistor having a high withstand voltage can be used as the short circuit switch. The switch circuit can be configured as it is without using special parts.

Furthermore, in the switching power supply device of the present invention, as described above, the zener diode that breaks down the power supply control means when the determination voltage is equal to or higher than a predetermined level and turns off when the determination voltage is lower than the predetermined level. A voltage detection circuit that has a bias resistance of the Zener diode and that detects that the output voltage of the rectifier circuit has dropped below a predetermined level, and a detection result extracted from the connection point between the Zener diode and the bias resistor. The voltage detection circuit, which has a Darlington circuit which is turned on / off in response to the current, and a current limiting resistor which is interposed in series between the control transistor on the preceding stage side of the Darlington circuit and the power supply line of the control means. And a switch circuit that controls the power supply to the control means in response to the detection result in (1).

Therefore, since the Darlington circuit is used for short-circuiting the power supply line of the control means in the switch circuit,
For changes in DC current gain due to changes in ambient temperature,
The switch operation can be stabilized.

Further, the switching power supply device of the present invention is
As described above, in the power supply control means, the voltage detection circuit further includes a resistor interposed between the Zener diode and the bias resistor, and the short circuit switch of the switch circuit is connected to the resistor and the bias resistor. The detection result is extracted from the connection point with and input.

Therefore, the voltage level given to the short-circuit switch from the voltage detection circuit and representing the detection result can be lowered by the resistance interposed between the Zener diode and the bias resistor, and the high-voltage of the short-circuit switch is high. A general transistor having a breakdown voltage can be used as it is, or a general transistor having a low breakdown voltage and a diode for protecting the breakdown voltage can be used, and it is not necessary to use a special component.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a switching power supply device according to a first embodiment of the present invention.

FIG. 2 is an electric circuit diagram of a switching power supply device according to a second embodiment of the present invention.

FIG. 3 is an electric circuit diagram of a switching power supply device according to a third embodiment of the present invention.

FIG. 4 is an electric circuit diagram of a switching power supply device according to a fourth embodiment of the present invention.

FIG. 5 is an electric circuit diagram of a switching power supply device according to a fifth embodiment of the present invention.

FIG. 6 is an electric circuit diagram of a switching power supply device according to a sixth embodiment of the present invention.

FIG. 7 is an electric circuit diagram of a switching power supply device according to a seventh embodiment of the present invention.

FIG. 8 is an electric circuit diagram of a switching power supply device according to an eighth embodiment of the present invention.

FIG. 9 is an electric circuit diagram of a switching power supply device according to a ninth embodiment of the present invention.

FIG. 10 is an electric circuit diagram of a switching power supply device according to a tenth embodiment of the present invention.

FIG. 11 is an electrical circuit diagram of a typical prior art switching power supply.

FIG. 12 is a waveform diagram for explaining the operation of the switching power supply device shown in FIG. 11 when the power is turned on.

13 is a waveform diagram for explaining the operation of the switching power supply device shown in FIG. 11 when the power supply is cut off.

FIG. 14 is an electric circuit diagram of another conventional switching power supply device.

15 is a waveform diagram for explaining the operation of the switching power supply device shown in FIG. 14 when the power supply is cut off.

[Explanation of symbols]

21, 31, 41, 51, 61, 71, 81, 91, 1
01,111 Switching power supply device 22 Control circuit (control means) 23 Output voltage detection circuit 24,34 Voltage detection circuit (power supply control means) 25,45,55,65,85,105 Switch circuit (power supply control means) C1, C2 Filter capacitor C3 Smoothing capacitor (rectifier circuit) C4 Smoothing capacitor C5 Capacitors D1 to D4 Diodes (rectifier circuit) D5, D7, D8 Diode D6 Photodiode F Fuse L Filter coil N Transformer P1, P2; P3, P4 Terminal PC Photocoupler Q Main switching element R1 Starting resistance (first resistance) R2 Starting resistance (second resistance) R3 Bias resistance R4 Short circuit resistance R5 Resistance R6 Current limiting resistance TR1 Phototransistor TR2, TR2a, TR2b Transistor (short circuit switch, Darlington switch) ) TR3 transistor (Darlington circuit) TR 20 transistor (Darlington circuit) TR30 transistor (Darlington circuit) ZD Zener diode

Claims (4)

[Claims] 1. A desired DC voltage obtained by rectifying an input AC voltage by a rectifier circuit is switched by a main switching element, and a control means controls the switching according to an output voltage on a secondary side. In the switching power supply device, the power supply control means for shutting off power supply to the control means when the output voltage of the rectifier circuit falls below a predetermined level, the first and second The resistors are connected in series to each other, and the output voltage of the rectifier circuit is supplied as a power source to the control means, and the connection point between the first resistor and the second resistor is connected to the power source control means. A switching power supply device, comprising: a starting resistance that provides a determination voltage for determining the cutoff of the power supply. 2. The rectifier circuit, wherein the power supply control means has a Zener diode that breaks down when the determination voltage is a predetermined level or higher and turns off when the determination voltage is lower than the predetermined level, and a bias resistance of the Zener diode. A voltage detection circuit that detects that the output voltage of the device has dropped below a predetermined level, a short-circuit switch that turns on / off in response to a detection result obtained from a connection point between the zener diode and a bias resistor, and the short circuit A switch circuit having a short-circuit resistance interposed in series between the switch and the power supply line of the control means, and controlling the power supply to the control means in response to the detection result of the voltage detection circuit. The switching power supply device according to claim 1, wherein the switching power supply device is configured. 3. The rectifier circuit, wherein the power supply control means has a Zener diode that breaks down when the determination voltage is equal to or higher than a predetermined level and turns off when the determination voltage is lower than the predetermined level, and a bias resistance of the Zener diode. Voltage detection circuit for detecting that the output voltage of the device has dropped below a predetermined level, a Darlington circuit for turning on / off in response to a detection result taken from a connection point of the Zener diode and a bias resistor, and the Darlington circuit. A current limiting resistor that is interposed in series between the control transistor on the preceding stage side of the circuit and the power supply line of the control means, and supplies power to the control means in response to the detection result of the voltage detection circuit. The switching power supply device according to claim 1, wherein the switching power supply device comprises a switch circuit for controlling supply. 4. In the power supply control means, the voltage detection circuit further has a resistor interposed between the zener diode and a bias resistor, and the short circuit switch of the switch circuit is provided with the resistor and the bias resistor. The switching power supply device according to claim 2 or 3, wherein the detection result is extracted from a connection point with and input.