JPH10336879A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To positively prevent an output voltage for being abnormally increased. SOLUTION: A switching power supply is applied to a configuration for stabilizing the output voltage of a DC output 5 by feeding back the error of the output voltage via an insulating element 6 and has an output voltage monitor circuit 9 for sending an abnormal detection signal when the output voltage exceeds the maximum value being set in advance and a stop control circuit 7 for suspending the switching operation of a primary side circuit 1 when the abnormal detection signal is led via a photocoupler 8.

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, such as an RCC type switching power supply, in which a primary circuit and a secondary circuit are insulated, and more specifically, an abnormal rise in output voltage. Sometimes, a special protection circuit
The present invention relates to a switching power supply for stopping a switching operation.

[0002]

2. Description of the Related Art In a switching power supply of the RCC type, when a failure occurs in a loop for stabilizing an output voltage, the output voltage may rise abnormally. On the other hand, when the output voltage rises abnormally, the load circuit may be broken. For this reason, the prior art shown in FIG. 3 has been proposed. That is, in addition to an error detection circuit that detects an error in the output voltage and feeds back the detected error to the primary side, an abnormality detection circuit 33 that detects an abnormal increase in the output voltage is provided. When detecting an abnormal rise in the output voltage, the abnormality detection circuit 33 grounds the emitter of the transistor Q31 of the error detection circuit. As a result, the base current of transistor Q31 increases, and the collector current increases. When the collector current of the transistor Q31 increases, the output current of the phototransistor of the photocoupler 32 increases in response to the increase of the collector current. Therefore, the control circuit 31 to which the output of the phototransistor is guided controls the operation of the switching circuit 34 in a direction to reduce the output voltage. For this reason, the output voltage is limited to a low voltage value.

[0003]

However, even when the above-mentioned configuration is used, the following problems have occurred. That is, when detecting an abnormal increase in the output voltage, the abnormality detection circuit 33 increases the current of the light emitting diode of the photocoupler 32 by grounding the emitter of the transistor Q31. However, if the cause of the abnormal rise of the output voltage is a defect of the photocoupler 32, a signal for suppressing the abnormal rise of the output voltage is not transmitted to the control circuit 31. For this reason, a situation has occurred in which the abnormal rise in the output voltage cannot be eliminated. On the other hand, if the cause of the abnormal increase in the output voltage is a defect in the control circuit 31, if the abnormal increase in the output voltage occurs, the output current of the phototransistor of the photocoupler 32 increases. However, even if the output current of the phototransistor increases, the control circuit 31
In this case, the operation of the switching circuit 34 cannot be controlled in the direction of decreasing the output voltage because of the occurrence of a problem. For this reason, a situation has occurred in which the abnormal rise in the output voltage cannot be eliminated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a dedicated switching device for stopping a switching operation on a primary side in response to an abnormal rise of an output voltage. An object of the present invention is to provide a switching power supply that can reliably prevent an abnormal increase in output voltage by providing a control loop. It is another object of the present invention to prevent the occurrence of intermittent switching operation by continuing control for stopping the switching operation after detecting an abnormal rise in output voltage. It is to provide a switching power supply that can be used.

[0005]

According to a first aspect of the present invention, there is provided a switching power supply in which a primary circuit and a secondary circuit are insulated from each other and an output voltage error is provided via an insulating element. Is applied to a switching power supply that stabilizes the output voltage of the DC output by feeding back to the primary side circuit, and outputs an abnormality detection signal when the output voltage exceeds a preset upper limit. A photocoupler in which the abnormality detection signal is guided to the light emitting diode, and a stop control circuit that stops the switching operation of the primary circuit when the abnormality detection signal is transmitted from a phototransistor of the photocoupler. Configuration. That is, when the output voltage abnormally rises due to a malfunction of a control loop for stabilizing the output voltage, the output voltage monitoring circuit outputs an abnormality detection signal. The abnormality detection signal output from the output voltage monitoring circuit is guided to a stop control circuit via a photocoupler. As a result, the stop control circuit stops the switching operation of the primary circuit, so that the output voltage becomes 0V.

According to a second aspect of the present invention, in the switching power supply, after the abnormality detection signal is transmitted from the phototransistor to stop the switching operation of the primary side circuit, the abnormality detection is performed by the stop control circuit. Even when the signal is no longer transmitted, the switching operation of the primary side circuit is kept stopped. In other words, since the abnormal detection signal was sent from the phototransistor,
When the stop control circuit stops the switching operation of the primary side circuit, the output voltage becomes 0V. Therefore, the output voltage monitoring circuit does not operate, and no abnormality detection signal is output. However, after the stop control circuit stops the switching operation of the primary circuit, the switching operation is not restarted because the switching operation of the primary circuit continues to be stopped even when the abnormality detection signal is no longer transmitted.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an electrical connection of a first embodiment of the switching power supply according to the present invention. This embodiment is mainly composed of a primary circuit 1, a secondary circuit 2, a stop control circuit 7, a photocoupler 8, and an output voltage monitoring circuit 9 when roughly classified.

The primary circuit 1 is a block for switching a current flowing through the primary coil 12 of the transformer 11 and performs a switching operation corresponding to an error in the output voltage of the DC output 5. The secondary side circuit 2 rectifies and smoothes the voltage generated in the secondary coil 14 so that the DC output 5
Is generated, and an error in the output voltage of the DC output 5 is fed back to the primary side circuit 1 via a photocoupler 6 which is an insulating element.

The output voltage monitoring circuit 9 is a block for monitoring an abnormal increase in the output voltage of the DC output 5. When the output voltage increases, for example, by more than 30% of the standard value of the output voltage, it is determined that the output voltage has abnormally increased. When it is determined that an abnormal rise has occurred in the output voltage, the abnormal detection signal is output to the photocoupler 8.
To the light emitting diode D3.

The stop control circuit 7 is a block for stopping the switching operation of the primary circuit 1 when an abnormality detection signal is transmitted from the phototransistor Q6 of the photocoupler 8. After the abnormality detection signal is transmitted from the phototransistor Q6 and the switching operation of the primary circuit 1 is stopped, the switching operation of the primary circuit 1 is stopped even if the phototransistor Q6 stops transmitting the abnormality detection signal. Keep stopping.

Hereinafter, each block will be described in detail. The plus level 3 of the primary side DC source obtained by rectifying and smoothing the commercial power supply is connected to one terminal of the primary coil 12 of the transformer 11. The other terminal of the primary coil 12 is connected to a collector of a switching transistor Q1 that switches a current flowing through the primary coil 12. The positive level 3 is guided to the base of the switching transistor Q1 via a resistor R1 that supplies a start-up current when the power is turned on. The emitter of the switching transistor Q1 is connected to the minus level 4 of the primary DC source.

The control transistor Q2 responds to an error in the output voltage of the DC output 5 and switches the switching transistor Q2.
1 is a transistor for controlling the base current. Therefore, the collector of the control transistor Q2 is connected to the base of the switching transistor Q1. The base of the control transistor Q2 is connected to the emitter of the phototransistor Q3 that outputs an error in the output voltage. The emitter of the control transistor Q2 is connected to the minus level 4.

One terminal of the auxiliary coil 13 for supplying a base current to the switching transistor Q1 is connected to the minus level 4. The other terminal of the auxiliary coil 13 includes a resistor R3 and a resistor R2 for limiting the base current.
, And is led to the base of the switching transistor Q1. The connection point between the resistors R2 and R3 is a current source for the phototransistor Q3. Therefore, the connection point between the resistors R2 and R3 is led to the collector of the phototransistor Q3.

The other terminal of the secondary coil 14, one terminal of which is grounded, is connected to a rectifying and smoothing circuit composed of a diode D4 and a capacitor C1. DC output 5
The cathode of a Zener diode D5 that generates a reference voltage is connected to the emitter of the transistor Q7 that detects an error in the output voltage of the transistor Q7. A resistor R11 is connected between the cathode of the Zener diode D5 and the DC output 5 to supply an operating current to the Zener diode D5. The anode of the Zener diode D5 is grounded.

The circuit composed of the resistor R10 and the variable resistor R12 is a voltage dividing circuit for dividing the output voltage of the DC output 5. Therefore, the output of the voltage dividing circuit including the resistor R10 and the variable resistor R12 is guided to the base of the transistor Q7. Further, the photocoupler 6 is an insulating element for feeding back the error of the output voltage to the primary circuit 1. Therefore, the cathode of the light emitting diode D1 of the photocoupler 6 is connected to the collector of the transistor Q7. The anode of the light emitting diode D1 is connected to the DC output 5 via a resistor R9 for limiting a current.

The Zener diode D6 is a voltage shifter that raises a voltage at which a current starts flowing to the base of the transistor Q8 to a predetermined voltage. The resistance R1
The circuit including the resistor 3 and the resistor R15 is a voltage dividing circuit for dividing the output voltage of the DC output 5. Therefore, the resistance R
The output of the voltage divider composed of the resistor 13 and the resistor R15 is connected to the cathode of the Zener diode D6. Also,
The anode of the Zener diode D6 is connected to the transistor Q
8 bases.

The photocoupler 8 is an insulating element for transmitting the abnormality detection signal output from the output voltage monitoring circuit 9 to the stop control circuit 7. Therefore, the photocoupler 8
The cathode of the light emitting diode D3 is connected to the collector of the transistor Q8 that outputs an abnormality detection signal.
The anode of the light emitting diode D3 is connected to the DC output 5 via the resistor R9. When no current flows through the Zener diode D6 between the base of the transistor Q8 and the ground level, the transistor Q8
A resistor R14 for preventing the base from being opened is connected. A capacitor C2 for absorbing noise and preventing malfunction is connected between the base of the transistor Q8 and the ground level.

The emitter of the transistor Q4 is connected to the plus level 3 via a current limiting resistor R4. Further, a resistor R5 for making the base voltage equal to the emitter voltage when the phototransistor Q6 is in the off state is connected between the emitter and the base of the transistor Q4. The collector of the phototransistor Q6 that sends out the abnormality detection signal is connected to the base of the transistor Q4. The collector of the transistor Q4 is connected to a resistor R7 and a resistor R8 for limiting the collector current.
And is connected to minus level 4. The emitter of the phototransistor Q6 is connected to the minus level 4.

A resistor R6 for limiting the base current of the transistor Q4 is connected between the collector of the transistor Q5 and the base of the transistor Q4. The cathode of the diode D2 is connected to the collector of the transistor Q5. The anode of the diode D2 is connected to the base of the switching transistor Q1. Further, the base of the transistor Q5 is led to a connection point between the resistors R7 and R8. The emitter of the transistor Q5 is connected to the minus level 4.

The transistors Q4 and Q5 are connected as described above. Therefore, when the transistor Q4 is turned on, a base current flows through the transistor Q5. When the transistor Q5 is turned on, a base current flows through the transistor Q4. That is, the transistor Q4 and the transistor Q
Reference numeral 5 indicates a connection for providing positive feedback. as a result,
When the transistor Q4 is turned on, both the transistor Q4 and the transistor Q5 are turned on,
Thereafter, the ON state is maintained until the voltage of the plus level 3 becomes 0V. That is, the connection is such that a latch operation is performed.

The operation of the embodiment having the above configuration will be described. When no trouble occurs, the primary side circuit 1 performs a switching operation according to the output current of the phototransistor Q3. Further, the secondary circuit 2 feeds back an error in the output voltage of the DC output 5 to the primary circuit 1 via the photocoupler 6. Therefore, the output voltage of the DC output 5 is in a stabilized state. At this time, the base current of the transistor Q8 is 0, and the transistor Q8 is off. Also, since the phototransistor Q6 is off,
Transistors Q4 and Q5 are both off.

In this state, a failure occurs in an error detecting circuit having the transistor Q7 as a main element, a photocoupler 6 for feeding back an error, and a control circuit having the control transistor Q2 as a main element. It is assumed that the output voltage has started rising abnormally. And the output voltage is
For example, 6.5 which is a voltage that exceeds 30% of the standard value of 5V
When the voltage becomes V, a current flows through the base of the transistor Q8. Therefore, a collector current flows through the transistor Q8 (output of an abnormality detection signal by the output voltage monitoring circuit 9). As a result, a current flows through the light emitting diode D3 and a current flows through the phototransistor Q6 (output of an abnormality detection signal by the phototransistor Q6). Therefore,
A current flows through the base of the transistor Q4.

When a current flows to the base of the transistor Q4, a current flows from the collector of the transistor Q4.
Part of the current flowing out of the collector of the transistor Q4 becomes the base current of the transistor Q5. Therefore, a current flows through the collector of the transistor Q5. When a current flows through the collector of the transistor Q5, the base current of the transistor Q4 increases. As a result, the collector current of transistor Q4 increases, and the base current of transistor Q5 increases. By this positive feedback operation, the transistors Q4 and Q5 immediately shift to the complete ON state.

When transistor Q5 is turned on, the base of switching transistor Q1 is connected to minus level 4 via diode D2 and transistor Q5. As a result, the base current of the switching transistor Q1 becomes 0, so that the switching transistor Q1 stops the switching operation. When the switching transistor Q1 stops the switching operation, the output voltage of the DC output 5 becomes 0V. Therefore, the collector current of the transistor Q8 becomes 0 (the output of the abnormality detection signal is stopped).

When the collector current of the transistor Q8 becomes zero, the output current of the phototransistor Q6 becomes zero.
Becomes However, since the transistor Q5 is on, a current flows through the base of the transistor Q4. Therefore, a current flows from the collector of the transistor Q4, and a part of the current flows as the base current of the transistor Q5, so that both the transistors Q4 and Q5 maintain the ON state. As a result, the base of the switching transistor Q1 is connected via the diode D2 and the transistor Q5 to
Keep connected to minus level 4. Therefore, the switching transistor Q1 continues to stop the switching operation.

FIG. 2 is a circuit diagram showing the electrical connection of a second embodiment of the switching power supply according to the present invention. In the figure, only parts having a configuration different from that of the first embodiment are shown, and illustration of the same parts is omitted. In the present embodiment, the resistor R1 of the first embodiment is used.
0 is divided into two resistors R16 and R17. Further, the connection point between the resistors R16 and R17 is
Connected to the cathode of Zener diode D6,
3 and the resistor R15 are omitted.

That is, in the first embodiment, the resistance R1
In the present embodiment, the voltage generated by the voltage dividing circuit including the resistor 3 and the resistor R15 is obtained from the connection point between the resistor R16 and the resistor R17. Therefore, the resistance R1
6, the values of R17 are set such that the voltage applied to the base of transistor Q7 and the voltage applied to the cathode of Zener diode D6 are equal to those in the first embodiment.

The second embodiment has the above-described configuration. Therefore, the operation of the second embodiment is the same as the operation of the first embodiment. That is, when the output voltage of the DC output 5 starts to increase abnormally and reaches a voltage of 6.5 V, which is a voltage exceeding the standard value of 5 V by 30%,
The base of the switching transistor Q1 is connected to the negative level 4 via the diode D2 and the transistor Q5.
Connected to. As a result, the switching transistor Q
Since the base current of 1 becomes 0, the switching transistor Q1 stops the switching operation.

As explained above, the second embodiment is
Compared to the first embodiment, the same operation and effect as in the first embodiment can be obtained despite the configuration in which the number of resistors is one less.

The present invention is not limited to the above embodiment, and the type of switching power supply to be applied
Although the description has been given of the case of using the C-type switching power supply, the present invention can be similarly applied to other switching power supplies such as a separately-excited switching power supply.

[0031]

According to the switching power supply of the present invention, the primary circuit and the secondary circuit are insulated from each other, and an error in the output voltage is fed back to the primary circuit through an insulating element. The present invention is applied to a switching power supply for stabilizing an output voltage of a DC output, and when the output voltage exceeds a preset upper limit value, an output voltage monitoring circuit for sending an abnormality detection signal, and the abnormality detection signal is supplied to the light emitting diode. And a stop control circuit that stops the switching operation of the primary circuit when the abnormality detection signal is transmitted from the phototransistor of the photocoupler. Therefore, if the output voltage rises abnormally, the output voltage monitoring circuit, photocoupler,
Further, the switching operation of the switching transistor is stopped by a dedicated control loop configured by the stop control circuit. For this reason, it is possible to reliably prevent an abnormal increase in the output voltage.

Further, in the switching power supply according to the second aspect of the present invention, after the abnormality detection signal is sent from the phototransistor to stop the switching operation of the primary side circuit, the abnormality detection is performed by the stop control circuit. Even when the signal is no longer transmitted, the switching operation of the primary side circuit is kept stopped. For this reason, after the abnormal rise of the output voltage is detected, the control for stopping the switching operation is continued even when the output voltage of the DC output becomes 0 V, thereby preventing the occurrence of the intermittent switching operation. It has become possible.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an electrical connection of a first embodiment of a switching power supply according to the present invention.

FIG. 2 is a circuit diagram showing an electrical connection of a switching power supply according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional electrical connection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Primary circuit 2 Secondary circuit 3 Positive level of primary DC source 4 Negative level of primary DC source 5 DC output 7 Stop control circuit 8 Photocoupler 9 Output voltage monitoring circuit D3 Light emitting diode Q6 Phototransistor

Claims (2)

[Claims] 1. A primary circuit and a secondary circuit are insulated from each other,
In a switching power supply that stabilizes the output voltage of the DC output by feeding back the error of the output voltage to the primary side circuit through an insulating element, when the output voltage exceeds a preset upper limit value, an abnormality is detected. An output voltage monitoring circuit for transmitting a signal; a photocoupler in which the abnormality detection signal is guided to the light emitting diode; and a switching operation of the primary circuit when the abnormality detection signal is transmitted from a phototransistor of the photocoupler. A switching power supply, comprising: a stop control circuit for stopping the switching power supply. 2. The stop control circuit according to claim 1, wherein after the abnormality detection signal is transmitted from the phototransistor and the switching operation of the primary side circuit is stopped, the primary control circuit also stops the primary detection circuit when the abnormality detection signal is not transmitted. The switching operation of the side circuit is continuously stopped.
The described switching power supply.