JPH0250711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant frequency switching power supply device controlled by a saturable transformer.

[Conventional technology]

A self-oscillating output type switching power supply device using a bipolar transistor using a saturable transformer
It was proposed by JL Jensen, and its characteristics have also been analyzed (Transactions of the Institute of Electrical Engineers of Japan, C., published July 1980, p. 25-31).

The power supply proposed by Jensen is simple in construction, does not require an internal auxiliary power supply, has self-starting characteristics, and requires a small number of electronic components.

[Problem that the invention seeks to solve]

However, as seen in the above analysis, the fluctuation of the oscillation frequency is not only expressed by the linear equation of the power supply voltage and load resistance, but also strongly depends on the magnetic flux saturation characteristics of the saturable magnetic core, the temperature characteristics of the switching transistor, etc. Therefore, it was difficult to operate at a stable frequency.

For this reason, it is necessary to design or add an output voltage stabilization circuit and a noise removal filter, which is particularly difficult to remove complex noise derived from cross modulation with power supply noise due to fluctuations in oscillation frequency. It was hot.

[Means for solving problems]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a switching power supply device that performs oscillation operation at a stable frequency even with fluctuations in input voltage and output load.

In order to achieve the above object, the present invention provides an output of a differentiating circuit that converts a rectangular wave current generated in the secondary winding of an output transformer into a triangular wave current, and an oscillation system that identifies frequency fluctuations of the rectangular wave current. The output of the variable resistance circuit controlled by the frequency monitoring circuit is superimposed and applied to the input winding of the saturable magnetic core oscillation transformer, and oscillation is achieved by controlling the pulse width output from the saturable transformer. It is characterized by keeping the frequency constant.

[Effect]

With the above means, the superimposed current sent to the input winding of the saturable transformer is stabilized because the drive current waveform of the oscillation circuit is controlled in accordance with the fluctuations in the oscillation frequency, and fluctuations in the oscillation frequency are suppressed. It can continue to operate at a certain oscillation frequency.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.

The figure schematically shows a magnetically controlled constant frequency switching power supply circuit according to the present invention, in which a commercial wave power source E is input and DC output circuits SW1 and SW2, which will be described later, supply DC output to first and second loads RL1 and RL2, respectively. do.

1 is a rectifier circuit for the commercial frequency power supply E, and this rectifier circuit 1 includes reactors 10, 11, capacitors 12, 1
3 and 14, a bridge rectifier 15, and a smoothing capacitor 16. Capacitor 16 is bridge rectifier 15
The rectified DC is smoothed by

The oscillation circuit 2 is operated by this direct current, and performs an oscillation operation in cooperation with the saturable transformer 3 and the output transformer 4. One ends of the starting resistors 21 and 22 are connected to the bases of oscillation transistors 23 and 24, respectively.
The other end is connected to the collectors of these transistors 23 and 24. Bias diodes 25 and 26 connect capacitors 27 and 28 in parallel, respectively.
It is connected to the output side windings 32 and 33 of the saturable transformer 3 and the bases of the oscillation transistors 23 and 24.

Diodes 29 and 20 are connected to the collectors of the transistors 23 and 24, respectively, for controlling the base currents of the oscillation transistors 23 and 24, reducing storage time, and achieving high-speed operation.

The saturable transformer 3 receives the pulses generated by the output transformer 4 and supplies driving pulses to the transistors 23 and 24. The pulses in the input winding 31 induce voltages of opposite polarity in the output windings 32 and 33, respectively.

One end of the primary winding 41 of the output transformer 4 is connected to a common connection point between coupling capacitors 51 and 52, and the other end is connected to a connection point connecting the emitters and collectors of transistors 23 and 24.
3 and 24, a corresponding pulse is received and the secondary winding 42 generates a rectangular wave signal.
43, 44 and 45, 46 are output side secondary windings of the output transformer 4, and are connected to the first and second DC output circuits SW1 and SW2, respectively.

6 is a differentiating circuit, which connects the secondary winding 42 of the output transformer 4.
is inserted and connected between the output side of the saturable transformer 3 and the input side winding 31 of the saturable transformer 3, and converts the rectangular wave current generated by the secondary winding 42 into a triangular wave current,
supply to. 61 is a capacitor, 62 is a resistor,
The time constant is configured to have a sufficiently small value with respect to the period of the required oscillation frequency. It is configured to have a sufficiently small value.

7 is an oscillation frequency monitoring circuit, which includes resistors 701 and 70.
2 and a constant voltage diode 7 connected with reverse polarity
A series circuit of 02,704 is connected to the output side of the secondary winding 42. 705 is a small capacitor,
The constant voltage rectangular wave signal determined by the operation of the constant voltage diodes 703 and 704 is transmitted to the diodes 706 and 7.
The voltage is supplied to the voltage doubler rectifier circuit constituted by 07. 70
8 is a capacitor which smoothes the DC rectified by diodes 706 and 707 and connects it to transistor 70.
It is connected to supply the base of 9. Since the value of the capacitor 705 is selected to be small, the current flowing between the base and emitter of the transistor 709 varies in proportion to the variation in the oscillation frequency.

On the other hand, a rectifier circuit composed of a resistor 710, a variable resistor 711, and a diode 712 rectifies the half wave of the constant voltage generated by the constant voltage diodes 703 and 704 and the resistor 702, and
smoothes this direct current. Since the resistor 710 is connected to the base of the transistor 709, this direct current also flows between the base and emitter of the transistor 709, but the direction of the direct current is opposite to the direct current from the voltage doubler rectifier circuit. Therefore, by adjusting the variable resistor 711, the base-emitter current between the transistor 709 can be defined to a value corresponding to a desired oscillation frequency. The resistor 702 is used to compensate for detection errors in the frequency monitoring circuit 7 due to changes in the input current applied to the internal impedances of the constant voltage diodes 703, 704, diodes 706, 707, etc. due to fluctuations in the power supply input voltage. Resistors 710 and 711 are resistors for increasing and decreasing the current in the circuit according to the voltage drop.

A local power rectifier circuit consisting of resistors 714 and 715 and a diode 716 or a capacitor 717 is a circuit that amplifies the current between the collector and emitter when the transistor 709 operates, and the resistor 715 outputs an error from the oscillation frequency monitoring circuit 7 according to its terminal voltage. is output to the variable resistance circuit 8 as a collector current.

The variable resistance circuit 8 amplifies the output current of the oscillation frequency monitoring circuit 7 and the input winding 3 of the saturable transformer 3.
It controls the current flowing through capacitor 8.
1. The current sent through the resistor 82 in series is connected so as to be superimposed on the output of the differentiating circuit 6.
The base and emitter of transistor 83 are connected to resistor 7.
The collector is connected to the output terminal of the secondary winding 42 through resistors 84 and 85, the base-emitter of a transistor 86, and a bridge rectifier 87. 88 is a buffer capacitor.

The collector and emitter of the transistor 86 are connected to a bridge rectifier 87, respectively, and the secondary winding 4
Regardless of the polarity of the voltage generated by transistor 2, a voltage in a fixed direction is applied between the collector and emitter of transistor 86.

Next, the operation in the above configuration will be explained.

With the DC power rectified by the rectifier circuit 1,
If the transistor 23 becomes conductive via the starting resistor 21, the power supply voltage is applied to the primary winding 41 of the output transformer 4.
The voltage induced in the secondary winding 42 is applied to the primary winding 31 of the saturable transformer 3 via the differentiating circuit 6, and when the saturable transformer 3 is saturated, there is no change in magnetic flux, and the voltage that is induced in the secondary winding 42 is applied to the primary winding 31 of the saturable transformer 3. becomes non-conductive. Transistor 24 then becomes conductive, repeating this alternating operation. Therefore, the output transformer 4 generates a rectangular wave alternating current. Further, the rectangular wave voltage generated in the secondary winding 42 is applied to the constant voltage diodes 703 and 704 via resistors 710 and 702. The constant voltage rectangular wave signal determined by the constant voltage diodes 703 and 704 is applied through a capacitor 705 to a voltage doubler rectifier circuit made up of diodes 706 and 707, and the rectified direct current is smoothed by a capacitor 708 and sent to the base of a transistor 709. Added. The polarity of the current flowing through this base emitter is (+), and since the capacitor 705 is selected to have a small value, its value is determined by the voltage regulator diode 7.
03,704 and the frequency generated by the applied secondary winding 42.

In addition, the DC voltage rectified by the diode 712 and smoothed by the capacitor 713 is connected to the resistor 7.
11,710 to the base of the transistor 709. However, this direct current is in the opposite direction to the direct current caused by the capacitor 705 described above.

Therefore, the current flowing through the base and emitter of transistor 709 is determined by the sum of the two types of current. By adjusting the variable resistor 711, the base-emitter current is adjusted to a current value specified at a predetermined oscillation frequency, and the variable resistor circuit 8, which will be described later, outputs a current from the resistor 82 and the capacitor 81. The combined value of the current output from the resistor 62 and the capacitor 61 by the differentiating circuit 6 can set the pulse width generated by the saturable transformer 3 to a specified value, and the oscillation circuit 2 can oscillate at a predetermined oscillation frequency. can perform actions.

The base-emitter current of transistor 709 also defines the collector-emitter current.

When the oscillation frequency fluctuates and increases, the current between the base and emitter of the transistor 709 increases to (+), so the current between the collector and emitter of the transistor 83, which operates with the potential difference between both terminals of the resistor 715, also increases. The current between the collector and emitter of 86 also increases, and the variable resistance circuit 8
The output current from the resistor 82 and capacitor 81 increases.

Therefore, the combined pulse width of the output of the differentiating circuit 6 and the output of the variable resistance circuit 8 applied to the input winding 31 of the saturable transformer 3 increases, so the oscillation frequency decreases and returns to the specified frequency. .

Contrary to the above, when the oscillation frequency decreases, the current between the base and emitter of transistor 709 decreases, and the current between the collectors and emitters of transistors 83 and 86 decreases.
Since the current between the emitters is reduced, the pulse width due to the combined current applied to the input winding 31 of the saturable transformer 3 becomes smaller, and the oscillation frequency is increased and returned to the specified frequency.

In this way, the output transformer 4 drives the first and second DC output circuits at a constant oscillation frequency, so that the first and second loads RL1,
A predetermined voltage is supplied to RL2.

〔Effect of the invention〕

As explained above, by adding a simple oscillation frequency monitoring circuit, detecting fluctuations in the oscillation frequency, and feeding this back to the saturable transformer, the oscillation frequency can be held constant, reducing noise. There is no need to design or add a removal filter, and it is particularly effective in removing complex noise caused by cross-modulation with power supply noise due to fluctuations in oscillation frequency.

[Brief explanation of drawings]

The figure is a schematic diagram of a constant frequency switching power supply according to the present invention. 1 is a rectifier circuit, 2 is an oscillation circuit, 3 is a saturable transformer, 4 is an output transformer, 6 is a differentiation circuit, 7 is an oscillation frequency monitoring circuit, 8 is a variable resistance circuit, SW1, SW
2 are first and second DC output circuits, and RL1 and RL2 are first and second load circuits.

Claims (1)

[Claims] 1. In a self-oscillating output type switching power supply that uses an oscillation circuit controlled by a saturable magnetic core, the rectangular wave current generated in the secondary winding of the output transformer is converted into a triangular waveform output signal and supplied to the saturable magnetic core. an oscillation frequency monitoring circuit that detects frequency fluctuations of the rectangular wave current, and an output signal of a variable resistance circuit controlled by the output signal of this monitoring circuit is superimposed on the saturable magnetic core together with the output signal of the differentiating circuit. 1. A constant frequency switching power supply device comprising: a variable resistance circuit that supplies a constant frequency switching power source;