JPS608558Y2 - Overcurrent protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates in particular to an overcurrent protection circuit for a converter, and more particularly to an overcurrent protection circuit for preventing damage to switching elements due to an abnormal increase in output current.

A block diagram of a converter circuit equipped with a conventional overcurrent protection circuit is shown in FIG.

The operating principle will be described based on FIG.

Input power is applied between input terminals 1 and 2, and is applied to a conversion transformer 5 and a transistor 6 via a protection circuit 3 and an input circuit 4 having a function of cutting off an input circuit.

The input power is converted to a predetermined voltage by the conversion transformer 5 by the switching operation of the transistor, and becomes the secondary winding voltage.The input power is passed through the primary winding of the rectifier 7 and the current detection transformer 8, and then through the rectifying and smoothing circuit 9. Appears as a DC output voltage.

The control circuit 12 monitors the output voltage and stabilizes the output voltage by controlling the conduction time of the transistor 6 using its output.

As such a control circuit, for example, the report rDEX-R1, DEX by Yamamura, Ohashi, and Hosoi described in Research and Practical Application Report No. 23S No. 5 (1974), pages 1039 to 1048, published by the Telecommunications Research Institute. -R device power supply system”
You can refer to FIG.

Figure 4 shows the control circuit described in this report, which is composed of an oscillation circuit having a unijunction transistor 35 and a differential amplifier, and each terminal 13 to 16 corresponds to each terminal 13 to 16 in Figure 1. do.

On the other hand, the secondary winding output voltage of the current detection transformer 8 is smoothed by a rectifying and smoothing circuit 18.

The output of the rectifying and smoothing circuit 18 is connected to the detection circuit 17.

The output of the detection circuit 17 is connected to the protection circuit 3.

If the output current increases abnormally, the current detection transformer 8
The secondary winding output voltage of increases.

Therefore, the output of the rectifying and smoothing circuit 18 increases and the detection circuit 17 operates.

When the detection circuit 17 operates, a signal for operating the protection circuit 3 is sent from the detection circuit 17 to the protection circuit 3.

The protection circuit 3 operates to cut off the input power, stop the operation of the entire converter circuit, and protect the converter circuit.

Protection circuit 3 and detection circuit 17 when the input power source is DC voltage
is shown in Figure 2.

When the output current increases abnormally, the relay 30 of the detection circuit 17 operates and the relay contact 29 closes.

When the relay contact 29 closes, the sirisk 26 is turned on and the input power source is terminated at the resistor 25.

Therefore, the fuse 24 is blown, the input power is cut off, the operation of the converter circuit is stopped, and the converter circuit is protected.

However, since the secondary output voltage of the overcurrent detection transformer 8 is smoothed by the rectifier circuit, the operation time of the overcurrent protection circuit is extremely long, and requires several hundred rLS to several seconds.

Therefore, the transistor 6 has to withstand the overload during this period, and the rating of the transistor 6 does not have enough margin, which has the drawback of causing damage.

The purpose of this invention is to provide a first overcurrent protection circuit that instantly suppresses the output current when the output current increases abnormally, and a first overcurrent protection circuit that instantly suppresses the output current when the output current increases abnormally.If the abnormal condition continues, the input power is cut off and the converter circuit stops operating. An object of the present invention is to provide an overcurrent protection circuit which is used in conjunction with a second overcurrent protection circuit to prevent damage to switching elements.

Next, the overcurrent protection circuit of the present invention will be explained based on FIG.

In FIG. 3, the operation of the converter circuit is the same as that in FIG. 1, so a description thereof will be omitted.

The AC signal is directly applied to the input of the first error amplifier circuit 21 without smoothing the secondary winding voltage of the current detection transformer 8.

An amplified AC signal is obtained at the output of the first error amplification circuit 21.

This AC signal is branched into two, and the control circuit 12 in FIG.
overcurrent detection terminals 22 and 23 and the second error amplification circuit 20
are given to each input.

Since there is no smoothing circuit on the input side of the first error amplifier circuit 21, there is almost no time delay.

If the output current increases abnormally, the first error amplifier circuit 2
1 output is applied between overcurrent detection terminals 22-23.

When a signal is applied between overcurrent detection terminals 22 and 23, the conduction time of switching transistor 6 is shortened.

When the conduction time of the switching transistor 6 is shortened, an increase in the output current can be suppressed.

Therefore, the increase in output current can be suppressed without any time delay.

On the other hand, since the input to the detection circuit 17 is given from the output of the second error amplification circuit 20 through the delay circuit 19, if the overcurrent condition continues for several cycles to several tens of cycles, the detection circuit 17
No. 7 relay 30 operates.

When the relay 30 of the detection circuit operates and the relay contact 29 closes, the fuse 24 shown in FIG. 2 is blown, as described above.
Turn off the input power to protect the converter circuit.

As mentioned above, the present invention is based on the first aspect. By configuring the second overcurrent protection circuit, it is possible to prevent damage to the switching element due to an abnormal increase in the output current.

Although FIGS. 1 and 2 show the case of DC input voltage, the present invention can also be applied to the case of AC input voltage if the input circuit 4 is equipped with a rectifier diode and a smoothing capacitor.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a converter circuit using a conventional overcurrent protection circuit, Fig. 2 is an electrical connection diagram between the protection circuit and the detection circuit, and Fig. 3 is a converter circuit diagram showing an embodiment of the present invention. The block diagram and FIG. 4 are circuit diagrams showing the control circuit. 1 to 3, 1, 2...input terminal, 3...protection circuit, 4...input circuit, 5...transformer, 6... Transistor, 7... Diode, 8... Current detection transformer, 9... Rectifier smoothing circuit, 10, 1
1... Output terminal, 12... Control circuit,
13, 14... Output voltage detection terminal, 15, 16
... Base current supply terminal, 17 ... Detection circuit, 18 ... Rectification/smoothing circuit, 19 ...
... Delay circuit, 20... Second error amplification circuit, 21... First error amplification circuit, 22, 23.
...Overcurrent detection terminal, 24...Fuse, 25.27.28.32...Resistor, 26...
...Thyristor, 29...Relay contact, 3
0...Relay, 31...Transistor, 33
...Thyristor, 34...Auxiliary power supply.

Claims (1)

[Scope of utility model registration request] a first transformer; a switching element having one end connected to one end of the primary winding of the first transformer; a rectifier circuit that rectifies the secondary output of the first transformer; a second transformer provided to the primary winding; a smoothing circuit for smoothing the secondary output of the first transformer provided via the rectifier circuit and the primary winding of the second transformer; A first error amplification circuit to which the secondary side output of the second transformer is given, a second error amplification circuit to which the output of the first error amplification circuit is given, and an output of the second error amplification circuit. a delay circuit that delays the output by a predetermined time; a detection circuit that detects whether the output of the delay circuit is greater than or equal to a predetermined value; a protection circuit that is supplied between the other end of the primary winding and the other end of the switching element and stops supplying the input voltage in response to detection of the input voltage being equal to or greater than the predetermined value of the detection circuit; An overcurrent protection circuit comprising: a control circuit that controls opening and closing times of the switching element in response to the output voltage of the smoothing circuit and the output voltage of the first error amplifier circuit.