JPS6051417A - Overcurrent protecting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION fa) TECHNICAL FIELD OF THE INVENTION The present invention relates to an overcurrent protection circuit in a ringing choke converter current circuit.

(bl Background of the Technology) Conventionally, power supplies that supply electronic equipment have increased power consumption as the functions of electronic equipment have increased, and the power supply has also become large. A converter power supply circuit system has been widely put into practical use.This ringing choke converter power supply circuit system is.

After the commercial power source is rectified into DC at one end by a rectifying element and a power rectifying and smoothing circuit via a transformer, the switching element is turned on/off.
In this method, the power source is turned off, the DC power source is turned on and off to create a DC intermittent wave, and this DC intermittent wave is further transformed by a transformer, and then rectified by the next power rectification and smoothing circuit to be supplied as DC current. Recently, the load capacity of electronic equipment has increased, and there is a high demand for high-power, low-voltage DC power supplies. . A ringing choke converter power supply circuit system is adopted.

This ringing choke converter power supply circuit type power supply device is provided with an overcurrent protection circuit in order to protect the main switching elements that turn on/off the DC input power supply from failure due to overcurrent.

tel Conventional technology and problems A conventional overcurrent protection circuit of this type will be explained.

FIG. 1 shows a block diagram of the circuit configuration of a conventional ringing choke converter power supply with an overcurrent protection circuit.

In normal operation, a base current is supplied from the start resistor 1 to the switching transistor 2, and when switching 1 to transistor 2 are turned on, a voltage is induced in the winding 31) of the transformer 3, and a base current is applied to the base of the switching transistor 1 to transistor 2. ~
Sumi current is supplied, but switching] ・Langistor 2
As the collector current increases, the base current becomes insufficient, the switching transistor 2 turns off, and the winding 3c of the transformer 3
transfer energy to. After this energy is released, the switching transistor 2 is again transferred from the star l/resistor 1 to the switching transistor 2.
A base current is supplied to the switching transistor 2, and the switching transistor 2 is turned on. By repeating the above operations, the power from the DC input power source 4 is output as a DC intermittent wave to the winding 3C of the transformer 3.

If an overcurrent flows through the switching transistor 2 due to some abnormality that has occurred, the overcurrent will flow through the overcurrent detection resistor 6 of the overcurrent protection circuit 5, and the potential will be detected by the voltage drop of the overcurrent detection resistor 6. Since the transistor 7 is turned on and the collector side of the detection transistor 7 is connected to the base side of the switching transistor 2, the base current of the switching transistor 2 is cut off and the switching transistor 2 is turned off. For example, if the output on the winding 3c side of the transformer 3 is short-circuited, the winding 3b of the transformer 3
The energy stored in is released in a short time, and again,
From start resistor 1 to switching transistor 2
The switching transistor 2 turns on and repeats the above operation, so if the overcurrent condition is maintained, the switching transistor 2 continuously turns on and off, and as the loss of the switching transistor 2 increases. However, the switching transistor 2 has the disadvantage of being damaged.

(dl OBJECT OF THE INVENTION The present invention aims to solve this conventional drawback.

tel Structure of the Invention The above object is to include a switching element that turns on/off a DC input power source, a current detection resistor that is connected in series with the switching element and detects a flowing current, and a voltage drop potential of the current detection resistor to generate electric charge. It includes a charging capacitor and a detection transistor that is turned on by the charging potential of the capacitor.

A ringing choke having an overcurrent protection function that turns off the switching element by the detection transistor.
In the converter, when an overcurrent state occurs, the capacitor is charged with a potential of a voltage drop that occurs in proportion to the current flowing through the overcurrent detection resistor, and the charging voltage of the capacitor is used to charge the capacitor. This is achieved by the present invention, which is configured to keep the detection transistor on and turn off the switching element.

That is, the capacitor is charged by the voltage drop potential of the overcurrent detection resistor, and the charging voltage of the capacitor is:

Discharges while supplying base current to the detection transistor,
When the detection transistor turns on, it turns off the switching element, and the charging voltage of the capacitor gradually decreases, so even if an overcurrent condition is maintained, the detection transistor turns on and off intermittently, so the switching element also turns off. It works.

The present invention provides a protection circuit that can prevent damage to switching elements.

(fl Embodiment of the Invention An embodiment of the present invention will be described below. FIG. 2 shows a circuit configuration block diagram of an overcurrent protection circuit according to the present invention.
In this figure, the same objects are.

Indicated by the same reference numerals as in FIG. 8 is an overcurrent protection circuit.

9 is a diode, 10 is a capacitor, and 11 is a resistor. The anodes of the diodes 1 and 9 are connected to the ten potentials of the overcurrent detection resistor 6 connected in series to the emitter of the switching transistor 2, and the diode 9 and the capacitor 10 are connected in series. resistance 6
Along with connecting one potential of.

Connect to one potential of the DC input power source 4. The base of the detection transistor 1-Rangistaf is connected to the cathode of the diode 9 via the resistor 11, the emitter of the detection transistor 7 is connected to one potential of the overcurrent detection resistor 6, and the voltage of the detection transistor 7 is connected to the one potential of the switching transistor 2. Connect to Hose.

The normal operation in the configuration shown in FIG. 2 is the same as that described above, so a description thereof will be omitted. The overcurrent protection circuit according to the present invention operates if an overcurrent flows through the switching transistor 2 due to some abnormality that occurs.

An overcurrent flows through the overcurrent detection resistor 6, and a proportional voltage is generated in the overcurrent detection resistor 6 due to the voltage drop caused by the current.
The capacitor 10 is charged via the diode 9 and discharged while supplying a base current to the detection transistor 7 via the resistor 11. When the detection transistor 7 is turned on, the base current of the switching transistor 2 is cut off, and the switching transistor 2 is turned off. Moreover, once the detection transistor 7 is turned on, the voltage between the hemisphere and the emitter of the detection transistor 7 is VBB, the voltage of the capacitor 10 is Vc, the resistance value of the resistor 11 is Ilh, and the Hesmi current of the detection transistor 7 is Ib. given that.

Since the detection transistor 7 remains on until VBE -Vc-RbXrb, the switching transistor 2 remains off during this time. Therefore.

By performing intermittent operation even if the overcurrent condition persists, it is possible to prevent and protect the switching transistor 2 from damage. The on-time duration of the detection l-rangistaph is selected based on the electrical constants of the overcurrent detection resistor 6, capacitor 10, and resistor 11, and the characteristics of the detection l-rangistaph, so that the safe intermittent time of the switching transistor 2 can be determined. can be set.

(As explained in detail about the invention, a conventional overcurrent protection circuit is provided with a capacitor that is charged by the voltage drop of the overcurrent detection resistor. Even if the overcurrent state is maintained, the detection transistor is intermittently Since the switching I transistor is turned on and off periodically, the switching I transistor operates intermittently, and is effective as an overcurrent protection circuit that prevents damage to the switching I transistor.

[Brief explanation of the drawing]

FIG. 1 shows a circuit configuration block diagram of a ringing choke converter power supply having a conventional overcurrent protection circuit, and FIG. 2 shows a circuit configuration block diagram of an overcurrent protection circuit according to the present invention. In the drawings, 1 is a start resistor, 2 is a switching transistor, 6 is an overcurrent detection Il+resistance, 7 is a detection transistor, 8 is an overcurrent protection circuit, 9 is a diode, and 10 is a capacitor.

Claims (1)

[Scope of Claims] A switching element that turns on/off a DC input power supply, a current detection resistor that is connected in series with the switching element and detects a flowing current, and a charge that is charged by a voltage drop potential of the current detection resistor. A ringing choke converter comprising a capacitor and a detection transistor that is turned on by the charged potential of the capacitor, and has an overcurrent protection function in which the switching element is turned off by the detection transistor, when an overcurrent condition occurs. . charging the capacitor with a potential of a voltage drop that occurs in proportion to the current flowing through the overcurrent detection resistor;
Due to the charging voltage of said capacitor. An overcurrent protection circuit characterized in that the overcurrent protection circuit is configured to keep the detection transistor turned on and turn off the switching element.