JPH06153505A - Ringing choke converter - Google Patents

Abstract

PURPOSE:To suppress the variation of the dropping point of the fold-back current characteristic caused by the variation of input voltage, concerning to an RCC circuit which uses a MOSFET. CONSTITUTION:Variation of a dropping point by the variation of input voltage can be suppressed, since the peak voltage of a triangular wave of a capacitor rises by inserting an emitter resistor 27 into the emitter of a control transistor 10, and the rate-of-change of oscillation frequency becomes smaller than that of input voltage. Besides, similar effect can be obtained by inserting a base resistor into the base of the control transistor 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-stone converter, and more particularly to an improvement of an output control circuit of a ringing choke converter (RCC) having a simple structure.

[0002]

2. Description of the Related Art A general RCC circuit has a voltage conversion function but does not have an output control function. Therefore, the present applicant previously provided an inexpensive converter having an efficient output voltage control function and an overcurrent protection function.

FIG. 3 shows an example of this circuit.
Is a voltage detection unit and a control circuit unit (2). First, the voltage detection section A is a shunt regulator 22 having a built-in reference voltage and a photocoupler-light emitting section 2 for outputting the shunt regulator 22.
1 and resistors 24 and 25 for dividing the output voltage (E0). In the control circuit section B, 10 is a control transistor connected between the gate and source of the MOS transistor 26, and 12 is a Zener diode which forms a time constant circuit together with a resistor 13 and a capacitor 11. , And is connected to both ends of the feedback winding 17, and the Zener diode 12
The connection point (a) of the capacitor 12 and the capacitor 12 is connected to the base of the control transistor 10. Next, 14 is a light receiving portion of the photocoupler connected between one end of the feedback winding 17 and the connection point (a), and the charging time constant of the capacitor 11 is adjusted by this.

The basic operation of this circuit is to output the energy stored in the transformer T when the MOS transistor 26 is turned on through the rectifying diode 18 when it is turned off. In addition, M
In the OFF operation of the OS transistor 26, the potential flowing at the point (a) in the time constant circuit of the capacitor 11 and the current flowing through the photocoupler-light receiving portion 14, the Zener diode 12 and the resistor 13 exceeds the voltage (VBE) of the control transistor 10. Then, the transistor 10 is turned on, which turns off the MOS transistor 26. Therefore, the output voltage E0 can be kept constant by detecting the output voltage and varying the current of the photocoupler to control the on-time.

When the output voltage is controlled to be constant as described above, the ON time of the MOS transistor 26 is increased by increasing the load current or decreasing the input voltage (E1). That is, when the input voltage (Ei) is the lowest and the maximum load current, the on-time is the maximum, and at this time, the photocoupler-light receiving unit 14 via the voltage detecting unit A
If the current is set to zero, the charging time constant of the capacitor 11 becomes maximum for output currents higher than this. Therefore, the output voltage-current characteristic of this circuit obtains a so-called fold-down characteristic.

(3)

2. Description of the Related Art In the conventional RCC circuit,
The oscillation frequency is determined by the capacitor 11 and the charging current, and the switching device uses a MOS transistor (hereinafter MOSF).
When ET) 26 is used, when the control transistor turns on, it turns off in a short time. Therefore, as the input voltage increases, the charging current of the capacitor 11 increases and the oscillation frequency changes to the higher side, so that the current value at the drooping point of the fold-back characteristic becomes aa ', as shown in FIG. By using the MOSFET in the conventional RCC circuit as described above,
There is a drawback that the variation of the drooping point due to the variation of the input voltage becomes large.

[0007]

SUMMARY OF THE INVENTION The present invention is an RCC using a MOSFET.
It is an object of the present invention to provide a converter which prevents a drooping point from varying due to a variation in input voltage in a circuit.

[0008]

According to the present invention, the peak voltage of the triangular wave of the capacitor is raised by inserting the emitter resistor 27 into the emitter of the control transistor 10, and the rate of change of the oscillation frequency is higher than the rate of change of the input voltage. Is made small to suppress the fluctuation of the drooping point due to the fluctuation of the input voltage. In addition, the base of the control transistor 10
You may add resistance.

[0009]

1 is an embodiment of the present invention, in which 26 is a MOSFET which is a switching device, 10 is a control transistor, 11 is a capacitor for determining an oscillation frequency, 14 and 21 are feedback photocouplers, and 15 and 16. , 17 are primary windings, secondary windings, and feedback windings of the transformer T, and 27 is an emitter resistance for lowering gm of the control transistor 10. The oscillation frequency of RCC is Zener diode 12
Current, the current of photocoupler 14 and the capacity of capacitor 11, the charging current changes depending on the load (4), the current from the photocoupler disappears when drooping, and the charging current from the Zener diode only. Is.

The triangular wave peak voltage of the capacitor 11 raises the base potential when the control transistor 10 is turned on. This means that the peak voltage of the triangular wave of the capacitor 11 rises, and the oscillation frequency at the same input voltage becomes lower than that when the emitter resistor 11 is not provided.

FIG. 2 is a circuit diagram of another embodiment of the present invention, in which a base resistor 28 is connected in place of the emitter resistor 27, and the same action and effect can be obtained by this. be able to.

[0012]

By incorporating the emitter resistor 27 or the base resistor 28 in the emitter or the base of the control transistor 10, the rate of change of the oscillation frequency becomes smaller than the rate of change of the input voltage. As shown, the variation of the drooping point due to the variation of the input voltage can be suppressed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of another embodiment of the present invention.

FIG. 3 Conventional circuit diagram

FIG. 4 is an output characteristic diagram of the circuit of the present invention.

FIG. 5: Output characteristic diagram of conventional circuit (5)

[Explanation of symbols]

 T Output transformer 15 Primary winding 16 Secondary winding 17 Feedback winding 26 Field effect transistor (MOSFET) 18 Rectifying diode 10 Controlling transistor 11 Capacitor 12 Zener diode 13 Resistor 14 Photoreceptor 22 Series-regulated -Ter 21 Light emitting part 27 Emitter resistance 28 Base resistance

Claims (1)

[Claims] 1. An output transformer having a primary winding, a secondary winding and a feedback winding, a drain connected to the primary winding, and a gate and a source connected between the feedback windings. In a ringing choke converter having a field-effect transistor, a rectifying diode connected to the secondary winding side, and a control circuit section for the field-effect transistor, the control circuit section includes a control circuit section for the field-effect transistor. A control transistor connected between the gate and the source, a base or an emitter resistor directly connected to the base or emitter of the control transistor, and a feedback winding. A time constant circuit composed of a resistor, a Zener diode, and a capacitor, and a connection point of the Zener diode and the capacitor is directly connected to the base of the control transistor or the base resistance is connected to the control transistor. A ringing choke converter comprising: a circuit connected via the circuit; and an adjusting circuit for adjusting a charging time constant of the capacitor according to an output voltage.