JP3007723B2 - Overvoltage protection circuit and distributed power supply system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overvoltage protection circuit in a switching regulator and a distributed power supply system using the same.

[0002]

2. Description of the Related Art The simplest overvoltage protection circuit in a conventional switching regulator is, as exemplified in FIG. 3, an input filter 1, a pulse width control circuit 2, a main switch 3, a transformer 4, a rectifying / smoothing circuit 5, and the like. The zener diode 6 is added to the output of the switching regulator including the photocoupler 9 and the error amplifier circuit 10, and the output at the time of overvoltage is clamped to the zener voltage.

As shown in FIG. 4, a conventional overvoltage protection circuit in a switching regulator requiring high reliability is a secondary side overvoltage detection circuit 21 added to a switching regulator similar to that shown in FIG. The overvoltage is detected, and the signal is output to 1 via photocouplers 9a and 9b.
The output at the time of overvoltage is stopped by feeding back to the next side to stop the pulse width control circuit 2, and a latch circuit 22 is provided in front of the pulse width control circuit 2 to maintain this state. A conventional overvoltage protection circuit for this type of switching regulator is described in, for example, "Switching Regulator Design Know-how" by Akira Hasegawa.
(CQ Publishing Co., Ltd. (1985) p. 136).

[0004]

In the prior art shown in FIG. 3, the switching regulator operates so that the output at the time of overvoltage is clamped by a Zener diode to protect the load. However, a large current exceeding the rating of the Zener diode is used. When a small-capacity Zener diode is used, the Zener diode is destroyed in the open mode, and as a result, there is a problem that the output of the switching regulator rises and the load may be destroyed. There is also a method of using a zener diode having the same power level as that of a switching regulator in order to prevent the overvoltage breakdown of the load, but there is a problem that the size cannot be reduced. In addition, FIG.
Although the prior art of the present invention operates reliably for the purpose of load protection, this includes the overvoltage detection circuit 21 and the photocoupler 9a,
9b and the number of components of the latch circuit 22 are increased.
There is a problem that it is disadvantageous in terms of miniaturization and economy compared to the prior art.

An object of the present invention is to provide an overvoltage protection circuit of a switching regulator which can surely protect a load with a small number of components. It is another object of the present invention to provide a distributed power supply system using such a switching regulator.

[0006]

In order to achieve the above object, an overvoltage protection circuit for a switching regulator according to the present invention includes a zener diode in parallel with a load and a zener diode in a path for supplying power to the load. Provide a thermal fuse that opens faster than the Zener diode opens due to the heat generated by the overvoltage applied to the zener diode, and mount or form these Zener diode and thermal fuse on a high thermal conductivity plate such as alumina material. It is something to do. Furthermore, the distributed power supply system of the present invention uses a switching regulator equipped with such an overvoltage protection circuit.

[0007]

The overvoltage protection circuit of the switching regulator is configured such that when an error occurs in a component controlling the output of the switching regulator and the output becomes overvoltage, the output voltage is clamped to the zener voltage and the zener diode is simultaneously output. Then, a large current flows to increase the junction temperature, and this heat is transmitted to the thermal fuse through a high thermal conductivity plate mounted or formed with a Zener diode, and the fuse temperature becomes close to the junction temperature. If this thermal fuse is selected at a temperature lower than the junction breakdown temperature of the Zener diode, the thermal fuse will be blown earlier than the Zener diode opens, thus reliably protecting the load. Further, since the distributed power supply system uses a switching regulator equipped with the present overvoltage protection circuit, hardware for performing other services can be mounted in a small space.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram of a switching regulator showing an example of an overvoltage protection circuit of the switching regulator according to the present invention. In FIG. 1, 1 is an input filter, 2 is a pulse width control circuit, 3 is a main switch, 4 is a transformer, 5 is a rectifying / smoothing circuit, 6 is a Zener diode, 7 is a thermal fuse, 8 is a high thermal conductivity plate, 9 Is a photocoupler, 10 is an error amplifier circuit, 11 is an overvoltage protection circuit,
The Zener diode 6 and the thermal fuse 7 of the overvoltage protection circuit 11 are mounted or formed on a high thermal conductivity plate 8.

In this configuration, when a voltage is applied to the input of the switching regulator, power is supplied to the pulse width control circuit 2 through the input filter 1, and the pulse width control circuit 2 and the main switch 3 connected thereto are supplied. Starts switching. By this switching, the transformer 4 connected in series with the main switch 3 transmits the primary-side power to the secondary side, and since the power transmitted to the secondary side is AC, it is converted to DC by the rectifying / smoothing circuit 5. Supply power to the load. Further, the output is amplified by the error amplifier circuit 10 so that the output voltage becomes constant with respect to the fluctuation of the input voltage and the load, and the signal is fed back to the primary side pulse width control circuit 2 via the photocoupler 9. The pulse is controlled so that the output becomes constant.

Here, if a component constituting the feedback loop fails, the output becomes overvoltage without pulse width control being activated, but when the voltage becomes overvoltage, the output voltage is reduced by a Zener diode 6 provided in parallel with the load. Is clamped to the Zener voltage. At the same time, a large current flows through the Zener diode 6 and the junction temperature rises, and the heat generated by the Zener diode 6 is transmitted to the thermal fuse 7 through a high thermal conductivity plate 8 such as an alumina material. Approaches junction temperature. Therefore, if the temperature selection of the thermal fuse 7 provided in the path for supplying power to the load of the overvoltage protection circuit 11 is set to a temperature lower than the junction breakdown temperature of the Zener diode 6, the Zener diode will be thermally destroyed and the short-circuit state will occur. Later, the thermal fuse 7 is blown before the Zener diode is opened, and the power supply to the load is stopped.

In this embodiment, the overvoltage protection circuit 11 is provided at the output of the switching regulator on the secondary side of the transformer, but the location of the overvoltage protection circuit 11 is not limited to this.

FIG. 2 is a perspective view showing an example of the distributed power supply system according to the present invention. In FIG. 2, 16 is a main power supply device, 17 is an electronic exchange device, 18 is a package, and 19 is a distributed power supply. In this configuration, the electronic exchange device 17 or the like that requires high reliability has a large-capacity main power supply device 16 separately from this device, and the distributed power supply 1
9 are arranged in a distributed manner so that even if one distributed power supply 19 fails, the system does not go down. A switching regulator equipped with the overvoltage protection circuit 11 as shown in FIG. 1 is applied to a distributed power supply 19 used in such a distributed power supply system.

[0013]

As described above, according to the overvoltage protection circuit of the switching regulator of the present invention, the thermal fuse of the conductor supplying power to the load is blown, so that the load can be protected reliably. Since the overvoltage protection circuit is composed of two parts, the Zener diode and the thermal fuse, the switching regulator can be made smaller and more economical. Further, according to the distributed power supply system of the present invention, it is possible to mount hardware for performing other services in a space where the switching regulator of the distributed power supply is small.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of an overvoltage protection circuit of a switching regulator according to the present invention.

FIG. 2 is a perspective view showing one embodiment of a distributed power supply system according to the present invention.

FIG. 3 is a diagram showing a configuration of an overvoltage protection circuit according to the related art;

FIG. 4 is a diagram showing a configuration of an overvoltage protection circuit according to the related art, which requires high reliability.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input filter, 2 ... Pulse width control circuit, 3 ... Main switch, 4 ... Transformer, 5 ... Rectifier / smoothing circuit, 6 ... Zener diode, 7 ... Thermal fuse, 8 ... High thermal conductivity plate,
Reference numeral 9: photocoupler, 10: error amplifier circuit, 11: overvoltage protection circuit, 16: main power supply device, 17: electronic exchange device, 1
8 Package, 19 Distributed power supply, 21 Overvoltage detection circuit, 22 Latch circuit

Claims (2)

(57) [Claims] 1. A Zener diode mounted or formed on a high thermal conductivity material such as silicon or alumina in a switching regulator, and heat generated by an overvoltage applied to the Zener diode causes the Zener diode to open earlier. An overvoltage protection circuit for a switching regulator, provided with an open thermal fuse. 2. A switching regulator, comprising:
Mounted on high thermal conductivity material such as recon or alumina
Created Zener Diode and Zener Diode
Heat generated by the overvoltage applied to the
The temperature at which the diode opens earlier than it opens
Switching level
Switching regulator with regulator overvoltage protection circuit
Distributed power supply system using a regulator .