JPH02241359A - Switching regulator - Google Patents

Abstract

PURPOSE:To enable switching working to be performed in a high-frequency range by varying the inductance of a transformer during the conduction of a main switching element, according to the fluctuation of output current to a load. CONSTITUTION:In an output current fluctuation detecting circuit 10, a shunt regulator (a shunt type stabilized power-supply element) 11 is an error amplifier, and the reference voltage Vref and output voltage VOUT are detected with resistors 12, 13, and the variation of a cathode current IK flowing in the light emitting diode 14 of a photo-coupler accompanying the variation of cathode voltage VK due to the difference of the reference and output voltages Vref and VOUT is transmitted to an inductance controlling circuit 20. The inductance controlling circuit 20 is connected to the output current fluctuation detecting circuit 10 through the photo-coupler, and according to the variation of the cathode current IK, the impedance of the photo-transistor 21 of the photo-coupler varies. According to the variation, the current I flowing in the tertiary winding 2 of a power converting transformer 1 varies, and an inductance is variably controlled.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to switching regulators.

[Conventional technology]

In conventional switching regulators, the induced voltage induced in the power conversion transformer when the main switching element is turned off and the reset time of the transformer are set by an absorber connected to the transformer or by a reset winding of the transformer.

Next, a conventional example will be explained with reference to the drawings. The switching regulator shown in Fig. 4 has a resistor 30 and a capacitor 3.
1 and a diode 32.
is connected to the primary winding of the power conversion transformer 34, and the power energy stored in the primary winding 36 is consumed by the resistor 3o via the diode 32 when the main switching element 35 is non-conductive. By changing the amount of energy consumed depending on the impedance of this absorber 33, the induced voltage Vl of the transformer 34 can be controlled.

V2 and the reset time T of the transformer 34 change (6th
In addition, as the load connected to the output terminals 37 and 38 changes, the induced voltages Vl and V2 and the reset time T change as shown in FIG.

In addition, in FIG. 4, diodes 40 and 41 connected to the secondary winding 39 of the transformer 34 and a chiyoke coil 42
and a capacitor 43 are normal elements constituting a forward switching regulator. Further, the main switching element 35 is driven by a pulse width control circuit (not shown) according to fluctuations in the output voltage to the load.

The switching regulator shown in FIG. 5 has a reset winding 44 connected to the primary winding 36 of a power conversion transformer 34 so as to have opposite polarity. Main switching element 35
Since the transformer 34 has a reverse potential when the input capacitor 46 is out of conduction, a reset current flows through the input capacitor 46. Since the voltage of the reset winding 44 is clamped to the power supply voltage VIN, the voltage induced in the negative winding 36 is the value obtained by multiplying the ratio of the number of turns of the primary winding 36 and the number of turns of the reset winding 44 by the voltage VIN. The voltage that is the sum of this voltage and the voltage VIN is the induced voltage Vl that is applied when the main switching element 35 is non-conductive.
, becomes V2. Even with the reset method using the reset winding 44, the amount of change in the magnetic flux of the transformer 34 within one cycle must be equal, so if the number of turns of the reset winding 44 is reduced, the reset will be completed in a shorter time; The induced voltage becomes a high value. Note that, like the above-mentioned regulator, the induced voltage of this regulator changes as shown in FIG. 6 as the load changes. FIG. 7 shows the relationship among the number of turns of the reset winding 44, induced voltage, and reset time.

[Problem to be solved by the invention]

In the conventional switching regulator mentioned above,
When used in a high frequency region, the power energy stored in the power conversion transformer is absorbed by the line capacitance of the power conversion transformer and the junction capacitance of the main switching element, and the induced voltage applied to the main switching element is determined by the inductance and capacitance. Therefore, there is a problem that the absorber-length beam set winding does not work effectively.

[Means to solve the problem]

The present invention provides a switching regulator that supplies power induced in a secondary winding of a power conversion transformer to a load according to the operation of a main switching element connected to a primary winding of a power conversion transformer, in which the main switching element is turned on. In this configuration, means for making the inductance of the transformer variable in accordance with fluctuations in the output current to the load is connected to the tertiary winding of the transformer.

〔Example〕

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

Referring to FIG. 1 showing one embodiment of the present invention, an output current fluctuation detection circuit 10 uses a shunt regulator (shunt type stabilized power supply element) 11 as an error amplifier, and a reference voltage V
r e f and output voltage■. UT is detected by resistors 12 and 13, and the change in cathode current Ik flowing through the light emitting diode 14 of the photocoupler due to the change in cathode voltage Vk due to the difference is sent to the inductance control circuit 20.

A resistor 15 limits the cathode current Ik. The capacitor 16 lowers the gain of alternating current, and operates stably against low frequency oscillations. The inductance control circuit 20 is coupled to the output current fluctuation detection circuit 10 by a photocoupler, and the impedance of the phototransistor 21 of the photocoupler changes in accordance with changes in the cathode current Ik. Along with this, the current I flowing through the tertiary winding 2 of the power conversion transformer 1 changes, and the inductance is variably controlled. Resistor 22 is for current limiting. Figure 2 shows the relationship between output current and inductance.

In order to perform the above-mentioned control, the power conversion transformer 1 uses a core material whose magnetic permeability (μ) changes linearly, changes the direct current flowing through the tertiary winding 2, and adjusts the bias point of the B-H characteristic curve. The inductance can be varied by shifting the bias point. FIG. 3 shows the relationship between ampere turns (NI) and magnetic permeability (μ).

A main switching element 3 driven by a pulse width control circuit (not shown) is connected to the primary winding of the transformer 1.
A diode 4.5, a choke coil 6 and a capacitor 7 are connected to the secondary winding to constitute a forward switching regulator.

〔Effect of the invention〕

As explained above, according to the present invention, the induced voltage applied to the main switching element can be easily adjusted by making the inductance of the power conversion transformer variable in accordance with fluctuations in the output current. As a result, regardless of the input capacitance selected as the main switching element, switching operation in a high frequency region can be made possible.

[Brief explanation of drawings]

FIGS. 1, 2, and 3 are diagrams showing an embodiment of the present invention, and FIGS. 4, 5, 6, and 7 are diagrams for explaining a conventional example. 1... Power conversion transformer, 2... Tertiary winding, 3...
・Main switching element, 10...output current detection circuit,
20...Inductance control circuit.

Claims (1)

[Claims] In a switching regulator that supplies power induced in a secondary winding of the transformer to a load according to the operation of a main switching element connected to a primary winding of a power conversion transformer, the power of the transformer when the main switching element is conductive is A switching regulator characterized in that means for making the inductance variable in accordance with fluctuations in the output current to the load is connected to the tertiary winding of the transformer.