JPH03293924A - Short-circuit protective device for power circuit - Google Patents

Abstract

PURPOSE:To speed up the operation of short-circuit protection by increasing the resistance value of a resistor of a pattern shape by the heat generation of an output transistor at the time of a short circuit, lowering the VBE of a detecting transistor in a control IC and improving the sensitibity of the detection of overcurrents. CONSTITUTION:When the output voltage of an output voltage section V01 is short-circuited, large currents are made to flow through an output transistor Q1 to generate heat, and the resistance value of a detecting resistor R10 formed near the output transistor Q1 is increased. Likewise, the VBE of a detecting transistor Q4 incorporated into an IC1 is lowered by the heat generation, the detecting transistor Q4 is turned ON, and a control circuit S is operated and the base of the output transistor Q1 is turned OFF. Accordingly, the protection of the short circuit of a power circuit can be realized while moving an operating point in response to the extent of heat generation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an output iodine protection device that is effective when applied to power supply circuits and the like.

2. Description of the Related Art In recent years, there has been an increase in the use of semiconductor circuit structures in place of fuses as output gate protection devices for power supply units. An example of the above-mentioned conventional power supply circuit short protection device will be described below with reference to the drawings.

FIG. 3 shows a circuit diagram of a conventional short protection device. In FIG. 3, 1 is an input DC voltage terminal, 2 is an output DC voltage terminal, 3 is an output power transistor, 4 is a short-circuit detection resistor, 6 is a short-circuit detection transistor,
6 is a control circuit for the stabilized DC power supply. In this configuration, in order to stabilize the output DC voltage, the output power transistor 3 and the control circuit 6 are operated to obtain a constant voltage power source.

The operation of the conventional Schiller (FFL) protection circuit configured as described above will be described below. First, the output DC
If the voltage (voltage at terminal 2) is short-circuited for some reason, for example due to a short-circuit on the load side, a large current flows through the output power transistor 3. At that time, when the voltage across the short detection resistor 4 exceeds vBE of the short detection transistor 6, the transistor turns on and the control circuit 6
A voltage is applied to the output power transistor 3, which cuts off the base of the output power transistor 3 and operates as a protection circuit.

Problems to be Solved by the Invention There are cases in which the circuit shown in FIG. 3 is constructed as a discrete circuit, and cases in which it is constructed in a monolithic IC (for example, a three-terminal power supply regulator). The conventional configuration uses the voltage drop across the short-circuit detection resistor 4 to turn on the vBE of the short-circuit detection transistor 5 and turn off the output power transistor due to the increase in current at the time of a short circuit.
C! ! Let's go.

In the case of a discrete configuration, since the components are assembled on a printed circuit board, heat conduction is poor, and the heat generated by the output power transistor does not increase the fixed resistance value, nor does it affect the decrease in vBE due to the heat generated by the detection transistor. Heat generated by short-circuiting of transistors cannot be actively used for short-circuit protection.

Furthermore, in a monolithic IC, the permissible power consumption of the detection resistor cannot be increased, and the increase in resistance due to heat generation cannot be utilized. Therefore, it is necessary to increase the size of the heat dissipation plate of the transistor to accommodate the increase in current in the half-short state immediately before the operating point of the short circuit protection circuit, and on the other hand, in a monolithic IC, a circuit configuration in which a thermal protection circuit is separately provided is required.

In view of the above problems, the present invention provides hybrid I on a metal substrate.
By using the C pattern resistance, the allowable power consumption of the resistor can be increased, and by utilizing the heat generated by the output transistor at the time of a short circuit without using any specific parts, the pattern resistance value increases and the vBE of the short detection transistor decreases, resulting in a short circuit. The present invention aims to provide a short-circuit protection device for a power supply circuit that speeds up the protection operation.

Means for Solving the Problems In order to solve the above problems, the present invention provides an output transistor, a control IC for controlling the output transistor, and a control IC connected to the main current in series on a metal substrate having good thermal conductivity. As described above, patterned resistors are provided close to each other, and heat is generated when the output transistor is short-circuited.

According to the above-described configuration, the resistance value of the patterned resistor increases due to the heat generated by the output transistor when short-circuited, and the vBE of the detection transistor in the control IC decreases, improving the overcurrent detection sensitivity. This allows the output current to be cut off (short-circuit protection operation) quickly.

EXAMPLE Hereinafter, a short circuit protection device according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a short protection device on a metal substrate according to a first embodiment of the present invention, and FIG. 2 is a circuit diagram of a power supply stabilizing circuit including the same. v-work N1 and v-work N2 are the first. Second input voltage section, vol, ■o2. v03
are the output voltage section and Ql, respectively.

Q2. Q3 is an output transistor, R1°.

R11 and Q5 are detection resistors for short-circuit detection, respectively, and detection transistors Q4 and Q5 are incorporated in the circuit C1. This embodiment is for the case of two input terminals and three output voltages.

On the metal substrate, near the output transistor Q1, a detection resistor R1° formed of a copper foil resistor is provided, one end of which is connected to the emitter of the output transistor Q1. It is provided. Both ends of the detection resistor R1o are connected to the emic and base of the detection transistor Q4 through pins 2 and 3 of the circuit C1. Similarly, a detection resistor R formed of a copper foil resistor whose one end is connected to the collector of the output transistor Q2 is provided near the output transistor Q2 on the metal plate. Both ends of the detection resistor R111 are connected to the emitter and base of the detection transistor Q6 via pins 9 and 1o of the IC1, respectively. Note that the detection resistors R1° and R11 are shown with hatching in FIG. In addition, the temperature coefficient of the copper foil resistance is +4400 PPM/℃, and the detection transistor 04,05
The temperature coefficient of vBE is -2mV2C.

The protection operation in the case of a short circuit in the above configuration will be explained. Output voltage section V. When the output voltage of 1 is short-circuited, a large current flows through the output transistor Q, generating heat, and the resistance value of the detection resistor R4゜(0,20) formed near it increases. The vBE of the detection transistor Q4 incorporated in the output transistor Q4 decreases, the detection transistor Q4 is turned on, and the control circuit S is activated to turn off the base of the output transistor Q1.

Output transistor Q2. The operation of the detection resistor R and the detection transistor Q6 when the output of Q3 is short-circuited.1 In a hybrid structure in which components are arranged with an insulating layer on the output transistor, a short-circuit detection resistor is provided near the output transistor using a copper foil resistor. , and the IC containing the detection transistor is placed nearby, so that the heat generated by the output transistor when the output is low is easily transmitted, thereby reducing the increase in resistance value due to temperature rise of the detection resistor and the increase in the detection transistor. Utilizing the decrease in vBE, short-circuit protection of the power supply circuit can be realized while moving the operating point according to the degree of heat generation. Therefore, optimal protective operation is possible not only when a complete short circuit occurs but also when an excessively loaded state close to a fault continues.

Effects of the Invention As described above, the present invention provides pattern-shaped resistors placed close to each other on a metal substrate and connected in series with the main current of the output transistor and the control IC 1 for controlling the output transistor, making it easy to set the resistance value. Therefore, it is possible to improve the overcurrent detection sensitivity by increasing the resistance value of the resistor and decreasing the vBE of the detection transistor in the control IC by using the temperature rise due to heat generation of the output transistor, and it is possible to improve the overcurrent detection sensitivity with a simple configuration. Can provide short circuit protection.

[Brief explanation of the drawing]

Fig. 1 is a component layout diagram on a metal substrate of a short-circuit protection device for a power supply circuit according to an embodiment of the present invention, Fig. 2 is a circuit diagram of main parts of this embodiment, and Fig. 3 is a conventional short-circuit protection device for a power supply circuit. It is a circuit diagram of a protection device. Q, Q O4-output transistor, Q4. Q51
21 3...Detection transistor, R1゜, R,,1...
・For anti-resistance.

Claims (1)

[Claims] An output transistor and a control IC for controlling the output transistor to obtain a constant voltage are provided close to each other on a metal substrate,
A pattern-shaped resistor is provided on the metal substrate close to the control IC of the output transistor, and this resistor is connected in series with the main current, and both ends of this resistor are connected to the detection transistor in the control IC. The overcurrent is detected by the amount of current flowing through the connected resistor, and the heat generated when an overcurrent flows through the output transistor causes the resistor and the detection transistor in the control IC that are nearby on the same metal substrate to be detected. 1. A short-circuit protection device for a power supply circuit, characterized in that the temperature is increased, the resistance value is increased, and the V_B_E of the transistor is decreased, thereby increasing overcurrent detection sensitivity and cutting off the output current at an early stage.