JPH02211055A - Abnormal operation detecting circuit of dc/dc converter - Google Patents

Abstract

PURPOSE:To eliminate the limits unabling to detect abnormalities by monitoring an error voltage of a load voltage controlling circuit to detect load voltage abnormalities. CONSTITUTION:A DC power supply 1 is switched by a transistor 3, and it is boosted rectified and smoothed by means of a transformer 16 to supply to a load 12. In case an overcurrent is supplied, an abnormal current is detected by resistance 24 to hang down the load voltage by narrowing the width of a pulse. An error signal of a shunt regulator 9 in that time is voltage increasing signal because of lack of the load voltage, but a current of a photo-coupler 7 of the signal current reaches zero because of not rising of the load voltage. The signal current is detected by resistance 22, and a transistor 4 is turned OFF. According to the constitution, a capacitor 15 is charged through resistance 23, and when it reaches a prescribed voltage after the elapse of a certain time, a signal is transmitted a controlling circuit 11 through the resistance 23, and the load voltage is cut off.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to DC (direct current) required for computers, etc.
The present invention relates to an abnormal operation detection circuit for a DC/DC converter that converts and stabilizes an unstable DC voltage into a voltage.

[Conventional technology]

Conventionally (as shown in Fig. 4), an unstable DC 1tif*1 is switched by a power transistor 3, its pulse power is insulated by a transformer 16, and the voltage is converted, rectified by a diode 5, and smoothed by a capacitor 13. It was connected to supply voltage to the load 12.

In order to stabilize the voltage of the load 12, the voltage is detected by resistors 18 and 19, and the error current signal is isolated using a shunt regulator that has an internal reference voltage and compares the voltages and amplifies the error. Photocoupler 17
and sends it to the feedback terminal FB of the control circuit 11.

Here, the general operation of the control circuit 11 will be explained.

A resistor 21 and a capacitor 14 connected to terminals Rf and Cf
It has a triangular wave oscillation circuit section with a unique frequency determined by the pulse width modulation (P
WM) into a pulse signal and output it from the terminal OUT. Terminal OC is a detection terminal of an overcurrent droop protection circuit that prevents excessive current regardless of terminal FB by inputting a signal that tends to exceed a specific low voltage and thereby reducing the pulse width. Terminal Ov is a terminal for abruptly shutting off the circuit in the event of an abnormality. When a -degree cutoff signal is input, the cutoff state is maintained even if the signal is stopped while DC power supply 2 is applied to terminal Vcc. There is.

In FIG. 4, an overvoltage detection circuit consisting of a constant voltage diode lO and a resistor 20, or transistors 43 and 44, a constant voltage diode 45, a diode 42, and a capacitor 5 is shown.
When an undervoltage detection circuit consisting of resistors 46, 47, 48 and 49 malfunctions, a signal is sent to the terminal OV of the control circuit 11 through the photocoupler 8 to cut off the voltage being supplied to the load. By detecting the emitter current of the transistor 3 using the resistor 24, when an abnormal overcurrent is about to flow into the load 12, the terminal OC of the control circuit 11 causes the load voltage to drop to prevent the overcurrent from flowing. For protection, if the abnormal load condition continues for a longer time than the time constant of the resistor 46 and the capacitor 50, the undervoltage circuit will cut off the load voltage and disconnect the transformer 16, diode 5, etc. Protected from danger caused by abnormal heat generation of parts.

[Problem that the invention seeks to solve]

The operating point of the undervoltage detection circuit is the constant voltage diode 4.
5, and must be set separately from the output voltage values set by resistors 18 and 19 and shunt regulator 9, etc., and the output voltage during normal operation, including variations in individual parts. It was necessary to set the value with sufficient margin from the voltage.

Furthermore, when it is necessary to vary the output voltage, the operating setting value of the undervoltage detection circuit needs to have a sufficient margin from the variable lower limit condition. Even if the load voltage 51 was allowed to drop, the abnormal operation continued without being cut off in the abnormality detection impossible range up to the undervoltage detection value 54.

An object of the present invention is to provide a safer C/DC converter by eliminating the abnormality detection range.

[Means for solving problems]

The present invention solves the above problem by not detecting the load voltage, but detecting an abnormality in the error signal, which is a control signal for detecting the load voltage and stabilizing the voltage. It is.

In other words, the present invention has a DC power source, a transformer's primary winding, and a switching element such as a transistor connected in series, and a DC voltage rectified by a diode, a capacitor, etc. to the transformer's secondary winding can be supplied to the load. a circuit that detects the load voltage and compares it with a reference voltage; a circuit that converts the error signal into a pulse width; a circuit that determines whether the value of the error signal is a normal value; and the switching element. This is an abnormal operation detection circuit for a DC/DC converter, characterized in that the circuit is connected to the cutoff circuit through a time delay function when the normal value determination circuit is not normal.

〔Example〕

FIG. 1 shows one embodiment of the invention.

Switching to pulse voltage with a power transistor,
Shunt regulator 9, control circuit 11 and diode 5
, a capacitor 13, etc., to convert it into a stabilized voltage and supply it to the load, which is the same as in the conventional FIG. 4.

If the current flows up to the overcurrent detection value shown in FIG. 5 due to an abnormality in the load, the abnormal current is detected by the resistor 24, and the pulse width is narrowed to cause the load voltage 51 to drop.

At this time, the error signal of the shunt regulator 9 becomes a voltage increase signal due to insufficient load voltage, but since the load voltage does not increase, the current of the photocoupler bluff of that signal current is zero (
The load voltage rises further from the maximum signal to reach the upper limit)
Therefore, the signal current is detected by the resistor 22 and the transistor 4 is turned off. The capacitor 15 is charged by the resistor 23, and if the abnormal state continues for a certain period of time determined by the resistor 23, a signal is sent to the terminal Ov of the control circuit 11 through the diode 6 to cut off the load voltage.

Therefore, unlike the conventional method, the abnormality undetectable range 58 shown in FIG. 5 does not exist.

Also, as shown in Fig. 2, a resistor 20 and a constant voltage diode 1 are connected.
Even if 0, photocoupler 8, and diode 6 are removed, overvoltage detection is not possible when the load voltage stabilization control circuit is abnormal, such as when the resistor 17 is disconnected.
Since an abnormality in the current of the photocoupler 7 is detected, the overvoltage is cut off without continuing for a long time. This is not possible with conventional undervoltage detection methods, and provides double protection in the event of overvoltage, ensuring safety even if the overvoltage detection circuit fails.

Although the control circuit in FIG. 3 is different from that in FIGS. 1 and 2, the operation is exactly the same, and the present invention involves the resistor 30, capacitor 33, and constant voltage 40.

When the voltage at terminal 2 of the control circuit 35 is normal, it is within a certain voltage range, but when there is an overcurrent droop due to an abnormality in the load, or an abnormality due to a component failure, the voltage at terminal 2 of the control circuit 35 is within a certain voltage range. If the voltage continues to exceed the time determined by the resistor 30 and capacitor 33, a signal is sent to the gate of the thyristor 38 through the constant voltage diode 40, and even if the voltage exceeds the voltage limit, the photocoupler 8 will not operate during overvoltage operation. The basic content is the same, only with a delay.

In addition, although the flyback converter is shown in Figures 1, 2, and 3, there are also forward converters,
It is obvious that similar effects can be obtained with push-pull converters, half-bridge converters, full-bridge converters, and double-switch forward converters.

〔Effect of the invention〕

According to the present invention, unlike conventional undervoltage detection methods,
There is no need to design or adjust parts considering variations, etc., and it becomes possible to provide highly effective abnormal operation protection, which not only improves workability during manufacturing but also provides highly safe DC/DC.
You can make a DC converter.

Further, it is also possible to detect a case where the load voltage drops to a small enough extent that it does not affect the operation of the load due to an abnormal drop in the DC voltage l, and it is also possible to protect against input undervoltage abnormalities.

[Brief explanation of the drawing]

1, 2, and 3 are circuit diagrams showing one embodiment of the present invention. FIG. 4 is a conventional circuit diagram. FIG. 5 is a voltage/current characteristic diagram of the load. 1 and 2 are DC power supplies, 3, 4, 37, 43 and 44 are transistors, 5, 6 and 42 are diodes, 7 and 8 are photocouplers, 9 is a shunt regulator, 10, 39, 40 and 4
5 is a constant voltage diode, 11 and 35 are a control circuit, 12 is a load, 13, 14, 15, 32, 33, and 50 are capacitors, 16 is a transformer, 17, 18, 19, 20, 21, 22, 23, and 24 and 25 and 26 and 27 and 28 and 29 and 3
0, 31, 46, 47, 48 and 49 are resistors, 34 and 36
is an error amplifier circuit, 38 is a cyrisk, 51 is a load voltage,
52 is load current, 53 is overcurrent detection value, 54 is undervoltage detection value, 55 is normal voltage value, 56 is overvoltage detection value, 5
7 is the normal current upper limit, and 58 is the range where abnormality cannot be detected. Figure Figure Figure Figure Figure

Claims (1)

[Claims] The DC power supply, the primary winding of the transformer, and switching elements such as transistors are connected in series, and the two
D rectified by a diode and capacitor in the next winding
A circuit that connects the C voltage to the load, detects the load voltage, compares it with the reference voltage, and amplifies it, a circuit that converts the error signal into a pulse width, and checks whether the value of the error signal is a normal value. An abnormal operation detection circuit for a DC/DC converter, comprising: a circuit for determining, a circuit for cutting off the switching element, and a circuit connected to the cutting circuit through a time delay function when the normal value judgment circuit is not normal.