JP2762907B2 - Overcurrent protection device for switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection device for a switching regulator which performs separately-excited control, and more particularly to an overcurrent protection device using a current transformer for detecting a current value.

[0002]

2. Description of the Related Art FIG. 3 shows a typical example of an overcurrent protection device in a conventional switching regulator. As shown, a current flowing through a primary side main winding T1 is detected by a sense resistor R and input to a control circuit IC. According to the detected current, the main winding T1
Is used to control over-current protection.

[0003]

However, according to the above method, it is necessary to provide the main transformer T with an auxiliary winding T2 for driving the control circuit IC in addition to the main winding T1. The structure of T becomes complicated.

Further, considering safety standards, in addition to the complexity of the main transformer T due to the auxiliary winding T2, the primary
The shape of the main transformer T is further enlarged by securing an insulation distance between the secondary and the like.

In addition, there are unstable factors such as the fact that the voltage generated in the auxiliary winding T2 is affected by the load fluctuation on the secondary side, or the voltage is not generated due to the short circuit of the secondary side load. There is a disadvantage that the operation of the circuit IC becomes unstable.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching regulator overcurrent protection device which is small in size and excellent in stability while improving the above-mentioned disadvantages.

[0007]

In the present invention, attention has been paid to the fact that the current flowing through the primary side main winding is a pulse.

That is, in an overcurrent protection device for a switching regulator that performs separately-excited control, a current flowing through a primary main winding is detected using a current transformer, and a voltage generated in the current transformer is detected using the overcurrent protection device. It was used as a power supply for driving the control circuit.

[0009]

[Operation] When a pulse current flows through the primary side main winding, a corresponding pulse voltage is generated in the current transformer. This is divided into two systems, one of which is used for overcurrent detection, and the control circuit operates to control the current flowing through the primary side main winding according to the detected current.
The other voltage is rectified and used as a drive power supply for the control circuit.

[0010]

FIG. 1 shows an embodiment of a circuit configuration of an overcurrent protection device for a switching regulator according to the present invention.

In FIG. 1, an AC input is rectified and smoothed by a rectifier D3 and a capacitor C2, and is connected to a primary side main winding T1 of a main transformer T. A transistor Q is connected to the main winding T1 and is driven by a drive signal DV from the control circuit IC. A current transformer CT is connected to the output of the transistor Q, and the output is divided into two systems by two diodes D1 and D2.

A capacitor C1 is connected to one diode D1 side, and is connected to a power supply terminal Vcc of the control circuit IC. The other diode D2 has a resistor R1,
And R2 are connected to the overcurrent input terminals OC of the control circuit IC.

The operation of the overcurrent protection device for a switching regulator according to the present invention is as follows with the above configuration.

As shown in FIG. 2, when the main winding T1 is excited, a pulse current flows through the transistor Q, and the pulse current generates a pulse voltage in the winding of the current transformer CT. Then, the voltage extracted by the diode D1 is smoothed by the capacitor C1, and supplied to the control circuit IC as a DC voltage. On the other hand, the voltage taken out by D2 is divided into appropriate voltage values by resistors R1 and R2 and input to an overcurrent input terminal OC of the control circuit IC, and an output terminal according to the current value (divided voltage value). The drive signal DV is output from OUT, and the excitation of the primary winding by the transistor Q is controlled.

[0015]

As described above, according to the present invention, the value of the current flowing through the primary main winding of the main transformer is detected using the current transformer, and at the same time, the voltage generated in the current transformer is used to drive the control circuit. Since the main transformer is used as a power supply, there is no need to provide an auxiliary winding for a drive power supply in the main transformer, so that the configuration is simplified and the transformer can be downsized.

Further, considering the problem of the insulation distance between primary and secondary in the safety standard, the elimination of the auxiliary winding is more effective for miniaturization.

Further, the power supply for driving the control circuit obtained by employing the current transformer is much more stable against load fluctuations on the secondary side and load short-circuiting than the method using the auxiliary winding. And the need for a sense resistor for current detection, unlike the conventional method, is eliminated, so that power consumption is eliminated and the efficiency of the switching regulator is increased, so that its performance is further improved.

[Brief description of the drawings]

FIG. 1 shows a circuit configuration of an overcurrent protection device for a switching regulator according to the present invention.

FIG. 2 shows waveforms at various parts of an overcurrent protection device for a switching regulator.

FIG. 3 shows a representative example of an overcurrent protection device in a conventional switching regulator.

[Explanation of symbols]

 CT current transformer IC control circuit T main transformer T1 main winding

──────────────────────────────────────────────────続 き Continued from the front page (56) References JP-A-64-77472 (JP, A) JP-A-60-93493 (JP, U) JP-A-54-141421 (JP, U) JP-A-4-141 97480 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H02M 3/00-3/44

Claims (1)

(57) [Claims] An overcurrent protection device for a switching regulator that performs separately-excited control by a control circuit (IC) detects a current flowing through a primary main winding (T1) using a current transformer (CT), The voltage generated by the current transformer (CT) is supplied to the control circuit (I
An overcurrent protection device for a switching regulator, wherein the driving power source is used in C).