JP3307576B2 - Power protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply protection circuit having a transistor, and more particularly to a power supply protection circuit which protects a power supply when a temperature of a transistor rises abnormally to prevent the power supply circuit from being destroyed. .

2. Description of the Related Art Conventionally, there has been provided a switching power supply in which when a voltage of a primary DC source exceeds a predetermined upper limit, a control transistor is turned off to prevent an abnormal rise in temperature. I have. In this switching power supply, as shown in FIG. 4, a fuse 8 is provided in the current path of the primary DC source, and the output voltage is controlled by controlling the base current of a switching transistor Q3 that switches the current flowing through the primary coil 2. The switching power supply to which the collector of the control transistor Q2 to be stabilized is connected is provided with an overvoltage control circuit 1 for turning off the control transistor Q2 when the voltage of the primary DC source exceeds a preset upper limit. . The overvoltage control circuit 1 includes a first resistor R1 having one terminal connected to the plus level 5 of the primary DC source, one terminal connected to the other terminal of the first resistor R1, and the other terminal connected to the other terminal. Is connected to a second resistor R2 whose terminal is connected to the minus level 6, a Zener diode D1 whose cathode is connected to a connection point between the first resistor R1 and the second resistor R2, and an assembler of a Zener diode D1 whose base is And a transistor Q1 whose collector is connected to the base of the control transistor Q2 and whose emitter is connected to the minus level 6.

In the above-mentioned conventional switching power supply, although the temperature is prevented from rising abnormally, in particular, the number of components in the overvoltage control circuit 1 is large and the structure is complicated. was there. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and to provide a power supply protection circuit having a simple structure and capable of protecting a power supply and preventing destruction of a power supply circuit when the temperature of a transistor rises abnormally. The purpose is.

In order to achieve the above-mentioned object, the invention according to the first aspect of the present invention provides a heat-shrinkable device that extends over a linear leg of a collector of a transistor and a linear leg of an emitter terminal. A tube is attached, and when the temperature of the transistor rises abnormally, the heat-shrinkable tube shrinks so that the linear leg of the collector of the transistor and the linear leg of the emitter terminal are short-circuited. The short circuit due to this contact cuts the fuse of the power supply circuit in which the transistor is disposed to eliminate the conductive state, protects the power supply on the primary side, and prevents secondary destruction of the power supply circuit, A radiator plate is provided on the transistor, and when the temperature of the transistor rises abnormally, the heat of the radiator plate generated by the temperature rise of the transistor causes the heat collection. Tube is contracted, it is characterized in that a linear leg portion of the linear legs of the collector and the emitter terminal of the transistor is to be shorted by contact.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a power supply protection circuit according to the present invention will be described with reference to the drawings. FIG.
FIG. 2 is a front view showing a state in which a heat-shrinkable tube is attached across the linear leg of the collector and the linear leg of the emitter terminal of the transistor in the power supply protection circuit according to the embodiment of the present invention, and FIG. FIG. 3 is a front view showing a state in which the linear leg of the collector and the linear leg of the emitter terminal are short-circuited due to shrinkage of the heat-shrinkable tube when the temperature of the battery rises abnormally. FIG. It is a circuit diagram. As shown in FIGS. 1 and 2, the power supply protection circuit 10 of the present embodiment includes a transistor 13 provided with a heat radiating plate 12 erected on the surface of a substrate 11. , A collector 15 and an emitter terminal 16, and the base terminal 14, the collector 15, and the emitter terminal 16 are provided with linear legs 17, 18, and 19 whose lower ends are soldered to the substrate 11. I have.
The linear legs 18 and 19 are preferably thin enough to be easily bent when the heat-shrinkable tube 20 described below is thermally contracted. Further, a heat-shrinkable tube 20 is attached across the linear leg 18 of the collector 15 and the linear leg 19 of the emitter terminal 16. This power supply protection circuit 10
As shown in FIG. 3, an outlet 21 for inserting a power supply (not shown), a rectifier circuit 22 connected to the outlet 21 for converting an AC current to a DC current, a fuse 23 connected thereto, A primary coil 25 of a transformer (transformer) 24 connected to 23 and a transistor 13 connected to the primary coil 24 are provided. Further, the transformer 24 is provided with two secondary coils 26 and 27. Transistor 1
3 has the base terminal 14 and the collector 1 as described above.
5 and an emitter terminal 16 are provided. Since the power supply protection circuit 10 of the present embodiment is configured as described above, when the temperature of the transistor 13 rises abnormally, as shown in FIG. The 15 linear legs 18 and the linear legs 19 of the emitter terminal 16 come into contact and short-circuit. Then, a short due to this contact causes the fuse 23
As a result, the conduction state disappears, the power supply on the primary side is protected, and the secondary destruction of the power supply circuit can be prevented. Further, since the heat sink 12 is provided in the transistor 13, when the temperature of the transistor 13 rises abnormally, heat is generated from the heat sink 12 due to the temperature rise of the transistor 13. The shrink tube 20 shrinks, causing the linear legs 18 of the collector 15 of the transistor 13 to shrink.
And the linear legs 19 of the emitter terminal 16 are short-circuited by contact, so that there is an advantage that the heat-shrinking action of the heat-shrinkable tube 20 can be promoted.

As described above, according to the first aspect of the present invention, the heat-shrinkable tube is attached across the linear leg of the collector of the transistor and the linear leg of the emitter terminal. As a result, when the temperature of the transistor rises abnormally, the heat-shrinkable tube shrinks, and the linear leg of the collector of the transistor and the linear leg of the emitter terminal are short-circuited. With a short circuit, the fuse of the power supply circuit in which the transistor is provided is blown to eliminate the conductive state, and the power supply on the primary side can be protected to prevent secondary destruction of the power supply circuit. Further, since the heat-shrinkable tube is simply attached over the linear leg of the collector of the transistor and the linear leg of the emitter terminal, the structure is simple and the repair is easy. Further, since the heat sink is provided on the transistor, when the temperature of the transistor rises abnormally, the heat shrink tube is shrunk by the heat of the heat sink generated by the temperature rise of the transistor. When the transistor temperature rises abnormally and is dangerous, the linear leg of the collector of the transistor and the linear leg of the emitter terminal can be reliably contacted and short-circuited. The power supply circuit fuse can be reliably blown to eliminate the conductive state, and the primary side power supply can be protected and protected.
Secondary destruction can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a front view showing a state in which a heat-shrinkable tube is attached across a linear leg of a collector and a linear leg of an emitter terminal of a transistor in a power supply protection circuit according to an embodiment of the present invention. .

FIG. 2 is a front view of a state in which the linear leg of the collector and the linear leg of the emitter terminal are short-circuited due to shrinkage of the heat-shrinkable tube when the temperature of the transistor rises abnormally.

FIG. 3 is a circuit diagram showing an internal structure of a power supply protection circuit according to the embodiment.

FIG. 4 is a perspective view of a conventional sealed battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply protection circuit 11 Substrate 12 Heat sink 13 Transistor 14 Base terminal 15 Collector 16 Emitter terminal 17 Base terminal linear leg 18 Collector linear leg 19 Emitter terminal linear leg 20 Heat shrinkable tube 23 Fuse

Claims (1)

(57) [Claims] 1. A heat-shrinkable tube is attached across a linear leg of a collector of a transistor and a linear leg of an emitter terminal, and when the temperature of the transistor rises abnormally,
The heat-shrinkable tube is configured to contract so that the linear leg of the collector of the transistor and the linear leg of the emitter terminal are brought into contact with each other and short-circuited. Blown the fuse of the power supply circuit to eliminate the conductive state, protect the power supply on the primary side to prevent secondary destruction of the power supply circuit , and
A heat sink is provided on the transistor, and the transistor is
When the temperature rises abnormally, the temperature of this transistor
The heat of the radiator plate generated by the rise
The shrink tube shrinks and the collector of the transistor
When the linear leg and the linear leg of the emitter terminal touch,
Power supply protection circuit which is characterized in that so as to bets.