JP2553784Y2 - Overvoltage protection circuit for ringing choke converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an overvoltage protection circuit for a ringing choke converter.

[Prior art] A conventional ringing choke converter (hereinafter referred to as R
The overvoltage protection circuit described as C.C detects an output overvoltage on the secondary side, transmits a detection signal to the input side (primary side), and cuts off the input voltage on the input side or causes the output to droop. It had a circuit configuration such as providing a functional circuit.

[Problems to be solved by the invention]

The conventional R, C, C overvoltage protection circuit described above detects an output overvoltage on the secondary side, transmits a detection signal to the input side (primary side), and cuts off the input voltage on the input side. In addition, since the circuit configuration is such that a circuit having an output drooping function is provided, there is a disadvantage that the whole circuit is complicated and the cost is high for a small, low-cost RCC.

[Means for solving the problem]

The R / C / C overvoltage protection circuit of the present invention includes a main switching transistor that generates a rectangular waveform current from an input DC voltage through a primary winding of a transformer, a base winding on a primary side of the transformer, A first terminal connected between the base winding and the base of the main switching transistor;
And a second resistor constituting a base drive circuit of the main switching transistor, an auxiliary winding on a primary side of the transformer, a first diode of a rectifier circuit, and a first capacitor, and a drive voltage for the main switching transistor. And a second diode and a second capacitor that rectify the voltage generated by the secondary winding of the transformer and output an output voltage.
An overvoltage protection circuit in the choke converter, wherein an overvoltage detection circuit for detecting an overvoltage of electric charge accumulated in the first capacitor from the auxiliary winding; and A switch with a latch function for short-circuiting between a base and an emitter of a main switch transistor, and detecting an output voltage of the first diode and the first capacitor of the rectifier circuit of a voltage from the auxiliary winding by the overvoltage detection. A base voltage of the main switching transistor is controlled by detection by a circuit.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an R, C, and C to which an embodiment of the present invention is applied.
It is a circuit diagram of C.

In FIG. 1, this application example uses an input DC voltage as a transformer.
A main switching transistor 2 for generating a current having a rectangular waveform via a primary winding 11 of the transformer 10, a base winding 12 on the primary side of the transformer 10, a resistor 4, and a base drive circuit for the main switching transistor 2 A drive transistor 6 for generating a drive voltage for the main switching transistor 2 by a resistor 5, an auxiliary winding 13 and a diode 8 and a capacitor 7 of a rectifying circuit;
An overvoltage protection circuit 20 according to an embodiment of the present invention, which controls the base voltage of the main switching transistor 2 by detecting the output voltage of the diode 8 and the capacitor 7 of the rectifier circuit of the voltage from 13, and the secondary winding 14 of the transformer 10 And a capacitor 17 that rectifies the voltage generated by the diode and outputs an output voltage.

The overvoltage protection circuit 20 according to the present embodiment includes an overvoltage detection circuit 16 that detects an overvoltage accumulated in the electric charge from the auxiliary winding 13, and an overvoltage detection circuit 16 that detects the overvoltage that is equal to or higher than a predetermined voltage. And a switch 15 with a latch function for driving the base.

 Next, the overvoltage protection operation of this application example will be described.

The voltage is applied to the capacitor 7 when the main switching transistor 2 is turned off. At this time, the voltage across the capacitor 17 which is the output voltage and the voltage across the capacitor 7 in the base drive circuit are changed by the transformer 10.
Is proportional to the turns ratio between the secondary winding 14 and the auxiliary winding 13, and by detecting the voltage of the capacitor 7,
It is possible to indirectly detect the output voltage.

Now, for example, if an overvoltage occurs in the output voltage of the secondary winding 14 due to a failure of the control circuit 3, the voltage across the capacitor 7 also increases. This is detected by the overvoltage detection circuit 16,
It operates by sending a signal to the switch 15 with a latch function, and steals the base current contained in the base of the main switching transistor 2 from the base winding 12, thereby turning off the main switching transistor 2 and generating an output overvoltage. To block.

[Effect of the invention]

As described above, the present invention detects a voltage higher than a preset voltage across a capacitor for storing charge for base drive for a main switching transistor in a base switching circuit of a main switching transistor of a ringing choke converter. An overvoltage detection circuit, and a switch for turning off a main switching transistor by detecting a voltage of the overvoltage detection circuit, include a small part in a base drive circuit for suppressing a rapid increase in power consumption due to an increase in input voltage. It can be configured on the primary side of the power supply circuit only by adding it, so there is no need to consider primary and secondary insulation, and it is also advantageous for circuit board pattern design. This has the effect of eliminating the need to provide an overvoltage protection circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a ringing choke converter to which one embodiment of the present invention is applied. 1. Start-up resistance 2. Main switching transistor 3. Control circuit 4. Base resistance 5. Resistance
6 ... Drive transistor, 7 ... Capacitor, 8 ...
... Diode, 9 ... Diode, 10 ... Transformer, 11
... primary winding, 12 ... base winding, 13 ... auxiliary winding, 14
…… Secondary winding, 15… Switch with latch function, 16 …… Overvoltage detection circuit, 17 …… Capacitor, 20 …… Overvoltage protection circuit.

Claims (1)

(57) [Scope of request for utility model registration] 1. A main switching transistor for generating a rectangular waveform current from an input DC voltage via a primary winding of a transformer, a base winding on a primary side of the transformer, the base winding and the main switching transistor. A first resistor connected between the bases of the main switching transistor,
, A drive transistor for generating a drive voltage for the main switching transistor by a first diode and a first capacitor of a rectifier circuit, an auxiliary winding on the primary side of the transformer, and a secondary winding of the transformer. An overvoltage protection circuit in a ringing choke converter comprising a second diode and a second capacitor for rectifying a voltage and outputting an output voltage, wherein the first diode from the auxiliary winding is provided. An overvoltage detection circuit that detects an overvoltage of electric charge accumulated by the capacitor, and a switch with a latch function that short-circuits between the base and the emitter of the main switch transistor when the overvoltage detection circuit detects an overvoltage equal to or higher than a predetermined voltage. , The first diode of the rectifier circuit for the voltage from the auxiliary winding. The first ringing choke converter overvoltage protection circuit and controlling the base voltage of the main switching transistor the output voltage by the detection by the overvoltage detection circuit of a capacitor.