JPS5999961A - Self-excited switching power source - Google Patents

Abstract

PURPOSE:To eliminate the abnormal rises of an oscillating frequency and an output voltage under no load and light load conditions by providing an output stabilizer at a winding of output side. CONSTITUTION:An output stabilizer 7 is provided at a winding N2 of the output side of a transformer T. This output stabilizer 7 has a detector 71 which detects a DC output voltage V0 and a switching circuit 72 which operates to shortcircuit a winding N2 in response to the detection signal of a detector 71 when the DC output voltage V0 becomes the prescribed level or higher. The detector 71 is composed of a reference voltage source or a comparator, and the switching circuit 72 is composed of switching elements such as transistors or thyristors.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of Industry-1- The present invention relates to a flyback converter type automatic switching power supply.

Conventional switching power supplies have the advantages of being compact, highly efficient, and highly reliable, and have been widely used as DC power supplies for combyoters and their terminal peripherals. There are passive type switching power supply circuits, but
When the main purpose is to downsize the power supply, an automatic circuit configuration is often adopted. In this self-excited switching power supply, when attempting to stabilize the output, conventionally a circuit system is used in which a reference voltage source is provided on the primary side of the transformer to control the switching elements, or a reference voltage source is provided on the secondary side of the transformer. A circuit system was used in which the switching element was controlled through an insulating coupling element (transformer or photocoupler). The control force method for the switching element includes a circuit system in which the flyback voltage generated in the feedback winding of the transformer is compared with the reference voltage source, and a DC output voltage is transmitted from the secondary side of the transformer through an insulated coupling element. A feedback circuit system compares the DC output voltage with the reference voltage source, and a feedback circuit system that compares the DC output voltage with the reference voltage and returns it from the secondary side of the transformer to the primary side through an insulated coupling element. Things etc. are publicly known.

Disadvantages of the conventional technology However, the conventional circuit system operates so that the effective voltage is maximized at maximum load, and the oscillation frequency becomes abnormally high at no load or light load, resulting in low power consumption. However, there are drawbacks such as increased output voltage, resulting in poor efficiency, and abnormally high DC output voltage, resulting in poor output stability. Furthermore, feedback type systems require insulation coupling elements such as isolation transformers and photocouplers.
The circuit configuration becomes complicated, which is disadvantageous to miniaturization, high-density packaging, and cost reduction.

Purpose of the Invention Therefore, the present invention eliminates the above-mentioned drawbacks of the conventional technology, does not cause the oscillation frequency or output voltage to become abnormally -1-'A during no load or light load, has low power consumption and is highly efficient. An object of the present invention is to provide an automatic switching power supply that does not require an insulating coupling means such as an insulating transformer or a photocoupler.

Configuration of the present invention -1- [In order to achieve the first objective, the present invention applies positive feedback from the output side to the input side of the switching element r- through the winding of the transformer to cause self-oscillation operation, In an automatic switching power supply in which the oscillation output is extracted from another winding of the transformer, a circuit for detecting a DC output voltage and a circuit for detecting the DC output voltage are provided on the other winding side of the transformer. The present invention is characterized by comprising an output stabilizing circuit configured with a circuit that operates to short-circuit the other winding in response to a detection output signal of the circuit when the voltage exceeds a level.

Embodiment FIG. 1 is an electrical circuit connection diagram of an automatic switching power supply according to the present invention. In the figure, 2 and 2 are input terminals into which a DC input voltage Vin obtained by rectifying a commercial AC power supply or the like is input, and 3 and 4 are DC output terminals.

T is a transformer, N1. N2 and N3 are respective windings of the transformer T. A transistor Ql serving as a switching element is connected in series to the winding N1. Is there a flyback voltage in winding N2? A diverting diode D1 is connected in series, and a smoothing capacitor C1 is connected in parallel. The winding N3 is a feedback winding that applies positive feedback to the transistor Ql, and has one end connected to the emitter of the transistor Ql, and the other end connected to the base of the transistor Ql through the coupling circuit 5. 6 is an overcurrent protection circuit.

Although the circuit configuration described in 1- is conventionally known, the main feature of the present invention is that the output stabilizing circuit 7 is provided on the output side winding N2.

This output stabilization circuit 7 includes a detection circuit 71 that detects a DC output voltage vO, and a DC output voltage 20 that exceeds a certain level I-
The switching circuit 72 operates to short-circuit the winding N2 in response to the detection output signal of the detection circuit 71 when The detection circuit 71 is
Generally, it is configured to include a reference voltage source, a comparator, etc. for comparing and detecting deviations of the DC output voltage vO from a predetermined value, and the switching circuit 72 is configured to include switching elements such as transistors and thyristors. Ru.

In the circuit configuration shown in No. 42, windings N1 and N of transformer T
3 applies positive feedback from the collector side to the base side of the transistor Q1, causing the transistor Q1 to perform blocking oscillation operation, and direct current power V applied to the input terminals 1 and 2.
in, and the switching output is taken out to the winding N2 side of the transformer T. The switching power supply shown in this example is a flyback converter type.
The voltage induced in the winding N2 when the transistor Q1 is turned on is converted to β by the diode D1, stored as electromagnetic energy in the winding N2, and released as flyback energy when the transistor Q1 is turned off. The flyback voltage generated in the winding N2 is converted into DC by the diode Di and the capacitor Ct, and a DC output voltage vO is supplied from the output terminals 3 and 4 to the load RL. In a range where the DC output voltage vO is lower than a predetermined value, the output stabilizing circuit 7 does not operate, and therefore, the above-mentioned circuit operation continues in this range, and the DC output voltage VO becomes l:I.
I will do it.

However, when the DC output voltage VO exceeds a predetermined level y1, it is detected by the detection circuit 71, and the detection signal is sent from the detection circuit 71 to the switching circuit 72 as Ij-
available. When the transistor Q1 is about to turn on while the detection signal is input to the switching circuit 72, the switching circuit 72 short-circuits the winding N2 by the voltage induced in the winding N2 at that time. When the winding N2 is short-circuited, the transistor Ql cannot be turned on because no voltage is induced in the return winding N3 to cause a base current sufficient to turn on the transistor Ql. As a result, +l'[outflow force cloth pressure Vo decreases. When the DC output voltage vO falls below a predetermined value, the switching circuit 72 is turned off, and the normal operating state returns. By repeating this circuit action, stabilization control is performed so that the DC output voltage vO becomes a constant value.

FIG. 2 shows a further example of the automatic switching power supply according to the present invention.
It is an electric circuit connection diagram in an integrated embodiment. In the figure, the same reference numerals as in FIG. 1 indicate the same components. In this embodiment, the detection circuit 71 includes resistors R1 and R2 that divide the DC output voltage 0, a series circuit consisting of a resistor R3 connected in parallel to both ends of the resistor R1, and a reference voltage Zener diode D2, and a base with the resistor R3. Transistor Q2 and collector resistor R inserted and connected between emitters
4#. The switching circuit 72 also includes a transistor Q3 connected in parallel to the winding N2.
, a reverse blocking diode D3 connected in series to the transistor Q3, a resistor R5 connected between the base and emitter of the I transistor Q3, and the like. Note that Q4 is a transistor that constitutes an overcurrent protection circuit, R6 is a resistor for current detection, D4 is a diode that together with resistor R7 constitutes a DC feedback circuit from the feedback winding N3 to the base of transistor Ql, and C2 is a diode that together with resistor R8 constitutes an AC This is a capacitor that constitutes a coupling circuit. R9 is a resistor.

In the circuit configuration described in 1-, the DC output voltage vO is low;
When the voltage divided by resistors R1 and R2 does not reach a value that makes Zener diode D2 conductive, transistor Q2 and transistor Q3 are turned off, so the output stabilization effect is not performed and the operation is the same as before. .

However, when the DC output voltage VO becomes higher than a predetermined level, the voltage divided by the resistors R1 and R2 makes the Zener diode D2 conductive, causing a voltage drop across the resistor R3, and turning on the transistor Q2. Here, when the switching transistor Q1 is about to shift from off to on, the emitter of the transistor Q3 becomes a negative voltage, turning on the transistor Q3 and shorting the winding N2. Therefore, a voltage sufficient to cause a base current to flow to turn on the transistor Q1 is not induced in the feedback winding N3, and the transistor Q1 cannot be turned on. Therefore, the DC output voltage Vo decreases. DC output voltage VO
When the Zener diode D2 is turned off due to the low voltage, the transistors Q2 and Q3 are also turned off, returning to normal operation. Due to such circuit action, the DC output voltage Vo is stabilized and controlled to a constant value.

FIG. 3 is a waveform diagram showing the voltage stabilizing effect of the self-help switching power supply according to the present invention, where FIG. 3(a) is the collector voltage waveform of the transistor Ql, and FIG. 3(b) is the waveform of the DC output voltage VO. It is a diagram. Now, if the detection level is Vd,
During the time (t2 - tl) from time tl, when transistor Q1 is turned off, to 12:00, when the DC output voltage vO becomes Vd≧■0 due to discharge to the load, transistor Ql cannot be turned on and remains in the off state. hold. Said (t
Since the 2-tB waiting time becomes longer as the load becomes lighter, the time interval during which transistor Q1 is turned on becomes longer for no-load or light-load operation. As a result, power consumption is reduced to about 17% compared to conventional
It decreases to about 10, and the efficiency is significantly improved. Fourth
The figure shows the output-efficiency characteristics of the automatic switching power supply according to the present invention in comparison with the conventional one.
1 shows the characteristics of the automatic switching power supply according to the present invention, and curve L2 shows the characteristics of the conventional one. As shown in the figure, the conventional type has the highest efficiency when the output is maximum, but the 1" single excitation switching power supply according to the present invention has almost no difference in efficiency due to increase or decrease in output, and is extremely high. Reduce efficiency.

Also, when there is no load or light load 4; ■, 41 transistor Q
Since the time (t, 2 - tL) during which transistor 1 is off becomes longer, the switching frequency of transistor Q, 1 becomes lower, eliminating disturbances in the oscillation frequency and also eliminating abnormalities in the output voltage. This will definitely get you 1 defense.

Moreover, despite the secondary side control method, the self-excited switching power supply according to the present invention is different from conventional ones in that it does not require a single stage of insulation coupling such as an isolation transformer or a photocoupler, and is small and compact. , it meets the requirements for high-density packaging and is inexpensive.

Effects of the Present Invention As described above, the present invention causes self-sustaining oscillation by applying positive feedback from the output side of the switching element to the input terminal via the winding of the transformer at +1, and the oscillation output 1 is In a self-excited switching power supply that is taken out from the other winding of the transformer, there is a circuit for detecting a DC output voltage on the other winding side of the transformer, and a circuit that detects the DC output voltage. The present invention is characterized by comprising an output stabilizing circuit constituted by a circuit that operates to short-circuit the other winding in response to a detection output signal of the circuit when the state becomes I-, so that no load and no load can be caused. Provides a self-help switching power supply that does not cause abnormal oscillation frequency or output voltage (- or jt) at light loads, has low power consumption, is highly efficient, and does not require insulation coupling means such as isolation transformers or photocouplers. can do.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit connection diagram of an automatic switching power supply according to the present invention, FIG. 2 is an electric circuit connection diagram of a more detailed embodiment of the automatic switching power supply according to the present invention, and FIG.
Figure (a) shows the collector voltage waveform of transistor Q1,
FIG. 4(b) is a waveform diagram of the DC output voltage 10, and FIG. 4 is a diagram showing the output-efficiency characteristics of the automatic switching power supply according to the present invention in comparison with the conventional one. Ql, Q2, Q3・φ-transistor 'r 1-φ・transformer N 1 , N 2 , N 3 φ - ・
Line wire 7... Output stabilization circuit 71... Detection circuit 72, φ-switching circuit A-L~ System "zt"; Negative f', ? [E
2 SIF lock"d't'Th year 12 /:] 271.1
Male, j/In' Director General Wainu, Special Request No. 88873 of 1988, Supplement 11! Relationship with 1%ji1 Patent applicant

Claims (1)

[Claims] (1) Automatic type in which positive feedback is applied from the output side to the input side of the switching element via the transformer winding to cause self-excited oscillation, and the oscillation output is extracted from the other winding of the transformer. In the switching power supply, a circuit for detecting a DC output voltage is provided on the other winding side of the transformer, and the circuit detects the DC output voltage in response to a detection output signal of the circuit when the DC output voltage exceeds a certain level I-. A self-help switching power supply characterized by comprising an output stabilizing circuit consisting of a circuit that operates to short-circuit other windings.