JPS63117663A - Self-excited converter - Google Patents

Abstract

PURPOSE:To stabilize the output voltage of a self-excited converter by maintaining the ON period of a switching transistor constant and controlling the OFF period irrespective of a flyback voltage generating period. CONSTITUTION:A self-excited converter is composed of a main transformer 4 having a primary exciting winding 1 and the like, a self-excited oscillator having a switching transistor 5, a rectifying and smoothing circuit 7 having a diode and the like, and an overvoltage detector having a detecting resistor VR and the like. In this case, a base winding 10 is grounded through a capacitor C, and connected through a control transistor 9 to an input rectifying and smoothing circuit. Further, a resistor R and a diode are connected to the base of the transistor 5. Thus, the rise of a voltage across the capacitor C during an OFF period controls the transistor 9 to control the OFF period (since the ON period is constant), thereby substantially controlling an ON duty ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a self-commutated converter with improved means for controlling the drive current and drive voltage of a switching transistor. In particular, the present invention relates to a self-excited converter that can achieve high efficiency and a wide control range with a simple circuit configuration.

[Conventional technology]

FIG. 4 shows a circuit diagram of a conventional self-excited converter. This converter circuit consists of a main transformer 4 having a primary excitation winding 1, a primary reset winding 2, a secondary winding 3, a tertiary winding N3, a fourth winding N4 and a fifth winding N5. and a self-excited oscillation circuit consisting of a switching transistor 5, a starting resistor 6, and a transistor Q2, diodes Di and D2, and a smoothing choke L.
1 and a rectifying and smoothing circuit 7 consisting of a smoothing capacitor C1, a detection resistor VR, an overvoltage detection circuit and a quaternary winding output voltage control transistor Q3, a diode D3. Consists of D4.

This self-excited converter will be explained. When a forward bias current is applied from the primary side input terminal V1 to the base of the switching transistor 5 through the starting resistor 6, the switching transistor 5 starts conducting, and the regeneration effect of the excitation winding 1 and the base winding N4 of the switching transistor 5 is activated. Through this, 5 becomes conductive all at once. After this, main transformer 4
Due to the magnetic saturation of , the collector current of 5 begins to decrease, and again through the regeneration action, the collector current of 5 is cut off at once, and 5 becomes an OFF state. The control transistors Q3 and D3 of the tertiary winding N3 change their impedances by the operation of the overvoltage detection circuit 8, and control the off-period 5 by changing the flyback voltage during the off-period of Ql. During the off period, the transistor Q2 and the fifth winding N5 actively apply a reverse bias base current when the base and emitter of the switching transistor 5 is biased in the reverse direction.

[Problem that the invention seeks to solve]

In this way, in conventional self-commutated converters, a tertiary winding is installed to control the off period and the flyback voltage of the main transformer is controlled, resulting in a narrow control range and a complex circuit configuration. It had drawbacks. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a self-excited converter that solves the above-mentioned conventional drawbacks.

[Means for solving problems]

The present invention includes a self-excited oscillation circuit consisting of a main transformer and a switching transistor having a primary winding, a secondary winding, and a feedback winding, and a secondary rectifying and smoothing circuit that converts the oscillation output of the self-help oscillating circuit into direct current. In a self-commutated converter configured with a primary side input rectifying and smoothing circuit, one end of the feedback winding is grounded via a capacitor, and the same end of the feedback winding and the output end of the primary side input rectifying and smoothing circuit are connected to each other. A control transistor is connected between them, a resistor and a diode are connected between the other end of the feedback winding and the base of the switching transistor, and according to fluctuations in the output voltage of the secondary side rectifying and smoothing circuit, A self-excited converter characterized in that the output voltage is stabilized by controlling the base current and base-emitter voltage of the switching transistor by changing the impedance of the control transistor.

That is, as a means for solving the above-mentioned problems in the conventional self-commutated converter, a method of varying the on period or the off period regardless of the flyback voltage can be considered. In the present invention, the on-period of the switching transistor is kept constant, and the off-period is determined by the charge accumulation time of the control transistor and the capacitor, so that the output current and input voltage can be adjusted independently of the period in which the main transformer is generating flyback voltage. This is a self-excited converter that responds to fluctuations and controls the output voltage to be constant.

〔Example〕

FIG. 1 shows a circuit diagram of an embodiment of the present invention. FIG. 2 shows the operating waveforms of each part in this circuit diagram.

The operating principle of the present invention will be explained.

Initially, the base current of the switching transistor 5 passes through the control transistor 9, the base winding 10, and flows from the resistor R through the base-emitter of the switching transistor 5 as a direct current. At this time, the collector current of the switching transistor 5 begins to flow between the collector and emitter of the switching transistor 5 through the excitation winding 1, and due to positive feedback between the primary side excitation winding 1 and the base winding 10, the switching transistor 5 becomes conductive at once. At this time, a positive electromotive force is generated across the base winding 10, and the switching transistor 5 is forward biased, so the base current 8 further flows through the capacitor C, and as shown in FIG. It gradually decreases with a time constant. ■. is larger than hFE times the base current I, and the switching transistor 5 is operating in the saturation region, but I
It gradually increases from 0 due to the inductance on the secondary side, and as the base current decreases as mentioned above, the IC
=IIlhF! There is a point in time when From this point on, the switching transistor 5 begins to operate in the active region, and I
Since C begins to decrease, the positive feedback effect of the primary excitation winding 1 and the base winding 10 causes the switching transistor 5 to
is cut off (blocked) all at once. The on period is determined in the manner described above. Switching transistor 5 is turned off and power is generated, which reverse biases switching transistor 5 through C. At this time, {circle around (2)} flows as a peak current, and at the same time, a current flows through the control transistor 9 from the input voltage {circle over (}) of the capacitor C, so that the voltage across C gradually rises. The base-emitter voltage ■ of the switching transistor 5 is the voltage across the base winding 10,
Since it is the sum of the voltage across the capacitor C, as shown in FIG. 2, ■■ gradually increases, and when it reaches the threshold voltage between the base and emitter of the switching transistor 5, the switching transistor
is in the on state. The rise in voltage across the capacitor C during the off period is controlled by the collector current of the control transistor 9, so by controlling the base current of the control transistor 9, the off period can be controlled, that is, the on period can be kept constant. It becomes possible to substantially control the on-duty ratio, and the output voltage can be controlled. In the figure,
The output voltage is ■. When the voltage rises further, the overvoltage detection circuit operates and controls the base current of the control transistor 9, so the collector current of the control transistor 9 decreases, increasing the off period of the switching transistor 5 and lowering the output voltage. Let's do it.

FIG. 3 shows a specific example of the overvoltage detection circuit and constant voltage control circuit. VR, C4, R7 and the shunt regulator 11 constitute an overvoltage detection circuit 8, and R2, R3
, R4, R3, and R4 constitute a constant voltage control circuit 12. The coupling between the overvoltage detection circuit and the constant voltage control circuit is
This is done by the optical coupling element 13. Secondary output voltage is ■. When the voltage becomes higher, the shunt regulator 11 detects the overvoltage, and a current flows to the input side of the optical coupling element 13. At this time,
Since the resistance at the output end of the optical coupling element 13 decreases and the voltage across R3 decreases, the collector current of the control transistor 9 decreases, increasing the off period and keeping the output voltage constant. Also, in Figure 3, R2 is controlled by temperature? [This is a feedback resistor to reduce the influence of hFE fluctuation of the II transistor 9.

〔Effect of the invention〕

With this control method, most of the base current of the switching transistor 5 flows through the capacitor C, so there is an advantage that the drive power of the switching transistor 5 is smaller than that of the conventional one. In addition, the circuit system is simpler than conventional self-excited converters, and has the advantage that the on period of the switching transistor 5 is almost constant, and the off period can be set independently of the flyback voltage, so it is easy to control. It has the effect of being able to cover a wide range.

As described above, according to the present invention, compared to conventional self-excited converters, the circuit configuration can be simplified, the base control power of the switching transistor can be reduced, and a highly efficient self-excited converter can be obtained. Also, compared to conventional self-excited converters, a wider control range can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a self-commutated converter according to an embodiment of the present invention, and FIG. 2 is a waveform diagram of the collector current, base current, base-emitter voltage, and collector-emitter voltage of the switching transistor in the circuit of FIG. Figure 3 is
FIG. 1 is a circuit diagram showing an embodiment of the overvoltage detection circuit and constant voltage control circuit, and FIG. 4 is a circuit diagram of a conventional self-excited converter. DESCRIPTION OF SYMBOLS 1... Primary side excitation winding, 2... Primary side reset winding, 3... Secondary winding, 4... Transformer, 5... Switching transistor, 6... Start Resistor, 7... Rectifier and smoothing circuit, 8... Overvoltage detection circuit, 9... Control transistor, 10... Base winding, 11... Shunt regulator, Chu Figure 2

Claims (3)

[Claims] (1) A self-excited oscillation circuit consisting of a main transformer having a primary winding, a secondary winding, and a feedback winding, and a switching transistor, and a secondary side rectifying and smoothing circuit that converts the oscillation output of the self-exciting oscillation circuit into direct current. and a primary side input rectifying and smoothing circuit, one end of the feedback winding is grounded via a capacitor, and the same end of the feedback winding and the first
A control transistor is connected between the output ends of the secondary input rectifying and smoothing circuit, a resistor and a diode are connected between the other end of the feedback winding and the base of the switching transistor, and the secondary rectifying and smoothing circuit A self-commutated converter characterized in that the base current and base-emitter voltage of the switching transistor are controlled by changing the impedance of the control transistor in accordance with fluctuations in the output voltage of the switching transistor, thereby stabilizing the output voltage. (2) A feedback resistor is connected between the emitter of the control transistor and the output terminal of the primary side input rectifying and smoothing circuit to reduce the influence of fluctuations in the DC current amplification factor due to the temperature of the control transistor. Claim 1:
Self-excited converter as described in the item. (3) connecting two resistors in series between the base of the control transistor and the output terminal and ground terminal of the input rectifying and smoothing circuit, and connecting the output terminal of the optical coupling element to both ends of the output terminal side resistor; 2. The self-excited converter according to claim 1, wherein the input end of the optical coupling element is connected to an overvoltage detection circuit connected to an output end of the secondary side rectifying and smoothing circuit.