JPS6264258A - Excess current protective circuit - Google Patents

Abstract

PURPOSE:To reduce loss and improve efficiency and miniaturize a device, by detecting the excess current of a chopper type switching regulator, with an output side rectification diode and a resistance connected to the diode n series. CONSTITUTION:The output of a switching transistor (Tr1) is fed to a load 2 via a rectification diode D and a resistance R1. The voltage of the load 2 is detected by a control section 1, and the ON/OFF pulse range of the Tr1 is controlled, and output voltage is kept constant. So far as a transistor Tr2 is concerned, the value of voltage at the both ends of the diode D and the resistance R1 is applied between a base and an emitter, and load current is detected, nd when voltage BE between the base and the emitter exceeds a specified value, then the Tr2 is turned ON, and by the control section 1, the ON range of the Tr1 is diminished, and load current is diminished. By this method, the value of the resistance R1 is diminished by internal resistance, and loss is reduced, and efficiency is improved, and the device is miniaturized.

Description

[Detailed Description of the Invention] [Summary] When detecting overcurrent in a chopper type switching regulator, a rectifier diode inserted in series on the output side and a resistor connected in series with the rectifier diode are connected at both ends. By measuring and detecting the voltage, loss is reduced and the efficiency of the chopper switching regulator is improved.

[Industrial application field]

The present invention relates to an improvement in an overcurrent protection circuit for a chopper type switching regulator.

In a chopper type switching regulator, it is desirable that the input and output are grounded on the same line, so that overcurrent can be detected with less loss as a switching regulator.

[Conventional technology]

FIG. 3 is a circuit diagram of a conventional chopper type switching regulator.

In the figure, E is a DC power supply, l is a control unit, 2 is a load, L is an inductance, ]r1 is a switching transistor, Tr
2 is a transistor, D is a rectifier diode, R is a resistor,
C indicates a capacitor.

In Fig. 3, direct current flows through inductance L? By switching the source E with the switching transistor Tri, the switching transistor Trl
A rectifying diode D and a capacitor C rectify and smooth the repetitive pulse voltage generated at both ends of the circuit to supply constant voltage power to the load 2.

In this case, the control unit l detects the voltage of the load 2, and depending on the level of this voltage, the switching transistor 'T'rl
The on/off pulse width is controlled to keep the output voltage constant.

At this time, if the current flowing through the load 2 becomes an overcurrent, the switching regulator may be damaged, so the load current is detected by the voltage on both sides of the resistor R, that is, the voltage v0 between the base and emitter of the transistor Tr2. When the current becomes large, the control section 1 rapidly narrows the width of the switching transistor Tri turned on to reduce the load current, thereby protecting the chopper type switching regulator.

[Problem that the invention seeks to solve]

However, in the above-mentioned overcurrent detection method, since the DC current after rectification and smoothing is detected, the loss as a switching regulator is the sum of the loss due to the rectifier diode D and the resistor R, resulting in a large loss and low efficiency. There is a bad problem.

[Means for solving problems]

The above problem is solved by the overcurrent protection circuit of the present invention, which detects overcurrent using a rectifying diode on the output side and a resistor connected in series with the rectifying diode.

[Effect]

According to the present invention, overcurrent detection is performed by a rectifying diode and a resistor connected in series with the rectifying diode, so the resistance value of this resistor is determined by the resistance of the rectifying diode (
(forward voltage/load current), and the loss can be reduced by the amount of loss caused by the rectifying diode compared to the conventional method, improving efficiency.

[Seventh Example] FIG. 1 is a circuit diagram of a chopper type switching regulator according to an embodiment of the present invention.

In the figure, R1 represents a resistor, and the same reference numerals indicate the same functions throughout the figures.

The difference between Fig. 1 and Fig. 3 is that, except for the resistor R, a resistor R1, whose value is smaller than the resistor R by the resistance of the rectifying diode D, is connected in series with the rectifying diode D. The point is that the load current is detected based on the voltage V BE between the base and emitter of the transistor Tr2.

If this is done, the loss will be reduced by the loss caused by the rectifying diode D compared to the case shown in FIG. 3, and the efficiency will be reduced.

FIG. 2 is a circuit diagram of a chopper-type switching regulator with inverted polarity according to another embodiment of the present invention.

3 in the figure indicates a control section.

Figure 2 shows a circuit in which the polarity of the DC power supply E is reversed to supply constant voltage power to the load 2, and overcurrent detection in this case can be performed in the same way as in Figure 1. .

In this case, if the voltage of the load 2 increases, the control section 3
The ON width of the switching transistor Tri is reduced, and when an overcurrent is detected, the switching transistor T is
The ON width of ri is rapidly reduced to protect the switching regulator.

Therefore, in the case of FIG. 2, as in the case of FIG. 1, the loss is reduced by the loss due to the rectifying diode D, and the efficiency is improved.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the loss can be reduced by the loss caused by the rectifying diode, the efficiency can be improved, and the device can be made smaller.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a chopper type switching regulator according to an embodiment of the present invention, Fig. 2 is a circuit diagram of a chopper type switching regulator with inverted polarity according to another embodiment of the present invention, and Fig. 3 is a circuit diagram of a chopper type switching regulator of a conventional example. FIG. 2 is a circuit diagram of a type switching regulator. In the figure, E is a DC power supply, 1.3 is a control unit, 2 is a load, L is an inductance, Tri is a switching transistor, Tr2 is a transistor, D is a rectifier diode, R and R1 are resistors, 4-Courage KK riff of the example of the disaster prevention village 1. The temple of Muteyotsuba Ikken phi.

Claims (1)

[Claims] When detecting overcurrent in a chopper type switching regulator, detection is performed using a rectifying diode (D) on the output side and a resistor (R1) connected in series with the rectifying diode (D). An overcurrent protection circuit characterized by: