JPS5961469A - Overcurrent protecting circuit for dc/dc converter - Google Patents

Abstract

PURPOSE:To effectively operate a DC/DC converter even when a load is abruptly shortcircuited by protecting the primary or secondary coil current of a main transformer by utilizing the average value and the maximum value of the DC current corresponding to the primary or secondary coil current. CONSTITUTION:The input current of a DC/DC converter 1 is removed, a pulse width control circuit 2 is operated by the average current corresponding to the input current, thereby protecting the converter 1. The voltage corresponding to the maximum value of the input current of the converter is produced form a resistor RV2, and the difference between the voltage and the reference voltage E2 is obtained by a comparator 4. When the voltage corresponding to the maximum value of the input current of the converter 1 is larger than the reference voltage E2, a stop signal is immediately fed to a half-cycle stop circuit 5, and the vibration is stopped only during the half period.

Description

[Detailed Description of the Invention] ta+ Technical Field of the Invention The present invention relates to an overcurrent protection circuit for preventing damage to a DC-DC converter due to overcurrent, and is particularly capable of operating effectively even when a sudden load short-circuit occurs. DC-D
The present invention relates to an overcurrent protection circuit for a C converter.

(bl Prior Art and Problems) The overcurrent protection circuit of a conventional DC-DC converter will be explained below with reference to the diagram.

FIG. 1 is a diagram showing an example of a conventional overcurrent protection circuit for a DC-DC converter. In the figure, 1 is the DC-DC converter, 2 is the pulse width tlilJ control circuit, 3 is the operational amplifier, CT is the current transformer, RP
C is a rectifier composed of diodes D1, D2, D3, and D4, R1 and R2 are resistors, C is a capacitor, RV is a variable resistor, D5 is a diode, and El is a reference voltage.

FIG. 2 is a graph of voltage-current characteristics of a conventional DC-DC converter. In the figure, the horizontal axis V indicates voltage, and the vertical axis ■ indicates current.

In the conventional [>C-D (1: converter circuit), the first
As shown in the figure, a rectifier consisting of diodes D1 to D4 is installed in the secondary winding of the current transformer CT that detects the primary or secondary winding current of the main transformer of the converter circuit. By controlling the pulse width control circuit 2 based on the RV terminal voltage)
By shadowing the C-DC converter and giving it an inverted-shaped droop characteristic as shown in Figure 2, or by adding part of the cutting voltage to the reference voltage of operational amplifier 3 in Figure 1. As a result, a F-shaped drooping characteristic as shown by ■ in FIG. 2 was imparted.

However, since both of these use the average value of the current, fl
s l The capacitor C connected in parallel with the resistor F2 v causes a time delay, and as a result, the control circuit operates with a time delay, and therefore the load gradually increases over time. When this occurs, this can be sufficiently protected, but there is a drawback that it is difficult to protect the conversion element, such as a transistor, due to sudden load short circuits or biased magnetization of the main conversion transformer.

(C) Object of the Invention The object of the present invention is to eliminate the above-mentioned drawbacks and to provide an overcurrent protection circuit for a D(, -DC converter) which is good and responsive.

+d) Structure of the invention According to the present invention, the above object is achieved by
A current transformer for detecting the primary or secondary winding current of the main transformer of the circuit, and a rectifier circuit installed in the secondary winding of the transformer to detect the direct current corresponding to the primary or secondary winding current of the main transformer. This is achieved by providing an overcurrent protection circuit for a DC-DC converter, characterized in that the protection circuit is formed using the average value and maximum value of the DC current.

(Examples of 91 inventions Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a circuit diagram showing an embodiment of the present invention, in which the same symbols and numbers as in FIG. 1 indicate the same circuits or elements, RV2 is a variable resistor, and E2 is a reference. It is voltage.

FIG. 4 is a graph for explaining the function of the overcurrent protection circuit of the DC, -DC converter shown in FIG. 3 according to the present invention.

In Fig. 3, the input current of the DC-DC converter 1 is taken out, and the pulse 1 is calculated by the average value current corresponding to this.
Activating the fault control circuit 2 to protect the DC-DC converter is exactly the same as in the case shown in Figure 1, but in addition to this, as shown in the figure, the maximum input current of the DC-DC converter is The voltage corresponding to the value (terminal voltage of RV2) is extracted, and the difference between this voltage and the base tr-voltage E2 is determined by the comparator 4. That is, as shown in Figure 4, DC-DC
A reference voltage E2 in which a voltage corresponding to the maximum value of the input current of the converter 1 (indicated by the solid line marked ■ in FIG. 4) is set in advance.
(represented by ■ in Figure 4), immediately sends a stop signal like ■ in Figure 4 to the half-cycle stop circuit 5, and
As shown by the dotted line (■) in the figure, the vibration is stopped for only half a cycle.

Of course, since the level at which the vibration of the hole starts to stop is set at a level higher than the drooping point based on the average value, the half-cycle stop circuit 5 will not operate due to a gradually increasing overload.

However, this half-cycle stop circuit 5 is DC-DC as described above.
There is no time delay because it operates with a voltage corresponding to the maximum input current of the Conharc. Therefore, it is responsive;
It is possible to prevent damage to transistors etc. due to time delay.

ff) Effects of the Invention As explained in detail above, according to the present invention, unlike conventional overcurrent protection circuits, it does not operate effectively when an overload occurs gradually over time, but when an overload suddenly occurs. Even when it becomes
Works quickly. Moreover, in carrying out the present invention, one current transformer is required as before, and the present invention has the great effect of being realized with the addition of a small number of circuits.

[Brief Description of the Drawings] Figure 1 is a diagram showing an example of an overcurrent protection circuit of a conventional DC-DC converter, Figure 2 is a graph of voltage-current characteristics of a conventional DC-DC converter, and Figure 3 is a diagram showing an example of an overcurrent protection circuit of a conventional DC-DC converter. is a circuit diagram showing one embodiment of the present invention, and FIG. 4 is a circuit diagram showing an embodiment of the present invention.
It is a graph for explaining the function of an overcurrent protection circuit of a C-DC converter. In the figure, 1 is a DC-DC converter, 2 is a pulse width control circuit, 3 is an operational amplifier, 4 is a comparator, 5 is a half-cycle stop circuit, CT is a current transformer, D1 to D5 are rectifiers, R1 and R2 are A resistor, C is a capacitor, RV is a variable resistor, RV is a variable resistor, El is a reference voltage, and R2 is a reference voltage.

Claims (1)

[Claims] A current transformer that detects the primary or secondary winding current of the main transformer of the DC-DC converter circuit, and the secondary N! of the current transformer. A rectifying circuit is installed in the line to obtain a direct current corresponding to the primary or secondary winding current of the main transformer, and a protection circuit is formed using the average value and maximum value of the direct current. Overcurrent protection circuit for DC-DC converter.