JPS5816207B2 - Power supply voltage stabilization circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply voltage stabilizing circuit using a switching method, and in particular, the present invention is provided with a circuit means for preventing abnormal voltage from being output to the secondary side circuit and causing damage to the circuit. It is in the power supply voltage stabilization circuit.

In addition, the present invention uses a circuit means for the above prevention to detect an overvoltage number and control the oscillation circuit of the Y roller that performs the switch operation, thereby definitely preventing the occurrence of abnormality. It is famous for its unique characteristics.

Further, the present invention is characterized in that the overvoltage detection circuit is configured using an auxiliary power supply circuit that is proportional to the voltage of the secondary winding.

Furthermore, the present invention is characterized in that the voltage after rectifying the commercial AC power supply is supplied to the overvoltage detection circuit as the power supply voltage, and overvoltage is detected by comparing the reference voltage of this circuit with the auxiliary power supply circuit voltage.

By the way, a power supply voltage stabilizing circuit using a switching method is, for example, an oscillation circuit O8C provided on the primary side of a transformer T with respect to a commercial power supply V applied as shown in FIG.
A predetermined voltage is output to the secondary side via the secondary side.

In the figure, commercial power source (2) is rectified through a rectifier circuit E and applied to a capacitor C1.

The + side terminal of the capacitor C1 is connected to the collector side of a transistor Q5 serving as a switching element via a first winding N1 of a transformer T, with respect to one side terminal which is grounded.

An oscillation circuit O8C is connected to the base of the transistor Q5, and operates in oscillation with a voltage of a predetermined level applied to the oscillation circuit O8C, giving an on/off command to the transistor Q5 to switch the first winding, The power supply voltage converted into DC by the rectifier circuit E is transmitted to the second winding N2 and the third auxiliary winding N3 of the transformer T, respectively.

The third auxiliary winding N3 of the transformer is connected in parallel with the capacitor C3 via a diode D1.

The + side terminal of the capacitor C3 is connected to the oscillation circuit O8C to supply the operating voltage Vc3, and the one side terminal is connected to the emitter terminal of the transistor Q5 and grounded.

□ Also, a capacitor C2 is connected between the + side terminal of the capacitor C5 and the first winding N1 via a diode D2 to stabilize the oscillation circuit O8C at the time of initial start.

The second winding N2, which is the secondary side of the transformer T, constitutes an output section and derives a constant voltage Vo when the commercial power is turned on. A smoothing capacitor Co is connected via a diode Do, and a smoothing capacitor Co is connected through a diode Do. A light emitting diode Di is connected in parallel to the capacitor Co via a resistor Ro.

The light emitting diode Di is designed so that its emitted light is incident on the phototransistor Q8 provided in the oscillation circuit O8C.

The light emitting diode Di and the foot transistor Q8 are configured using a photocoupled semiconductor device mounted in the same package as a photocoupler, for example.

The light emitting diode Di emits light in an amount corresponding to an increase or decrease in the output voltage Vo derived to the output part of the second winding N2, and the light emitted is incident on the phototransistor Q8.

The phototransistor Q8 exhibits an impedance that corresponds to an increase or decrease in the amount of incident light, and the oscillation frequency of the oscillation circuit O8C is controlled by the increase or decrease in the impedance.
The output voltage Vo is controlled on and off, and as a result, the output voltage Vo is controlled to supply a stable voltage.

The above-mentioned power supply voltage stabilization circuit was filed in a patent application filed in 1973 by the same applicant.
It is proposed as No. 71868.

In such a stabilizing circuit, in order to stabilize switching, a return loop circuit is provided from the secondary circuit to the primary circuit (oscillator circuit 0SC), and the primary and secondary sides are made floating. For example, an isolator such as a photocoupler is provided to stabilize the oscillation.

However, if this stabilization circuit loses control due to a failure of the oscillation circuit O8C or the isolator itself, an abnormal voltage is output to the secondary side and auxiliary power supply section, leading to destruction of the secondary side circuit.

For example, this may cause the capacitor to explode or the resistor to burn out.

In other words, the oscillation frequency of the oscillation circuit is controlled by detecting increases and decreases in the secondary voltage in order to stabilize the voltage according to load fluctuations on the secondary side.Usually, the inherent constants of the oscillation circuit have a maximum value depending on the secondary voltage. The oscillation frequency is set so that it can supply sufficient energy when a load is applied, and if control becomes impossible due to a failure of the oscillation circuit or the isolator itself, the oscillation frequency at maximum load will change even when the load is not very high. As a result, the voltage on the secondary side becomes abnormally high.

The present invention has been proposed in order to solve the above-mentioned inconvenient problems incidental to the power supply voltage stabilizing circuit, and the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a circuit diagram showing the configuration of a power supply voltage stabilizing circuit according to the present invention.

In the figure, a commercial AC power supply V is rectified through a rectifier circuit E and applied to a capacitor C1.

The + side terminal of capacitor C1 is connected to the first winding N1 of transformer T.
is connected to the collector side of a transistor Q, which serves as a switching element in the driver circuit 1.

The transformer T also has an auxiliary winding N3, and the auxiliary winding N3 is connected in parallel with the capacitor C3 via the diode D1. The + side terminal of the capacitor C3 is connected to the driver circuit 1 and the oscillation circuit O8C. This constitutes an auxiliary power supply circuit that supplies operating voltage.

The base of the transistor Q of the driver circuit 1 described above is connected to the output terminal of the oscillation circuit O8C, and operates in oscillation when a voltage of a predetermined level is applied to the oscillation circuit O8C, and issues an on/off command to the transistor Q5. Give first
The winding N1 is switched, and the power supply voltage converted into DC by the rectifier circuit E is transmitted to the second winding N2 and the auxiliary winding N3 of the transformer T, respectively.

A capacitor C2 is connected between the auxiliary power supply circuit and the first winding N1 through a diode D2, and a resistor R2 is connected in parallel with the capacitor C2 to stabilize the oscillation circuit O8C at the initial start. .

The second winding N2, which is the secondary side of the transformer T described above, constitutes an output section and derives a constant voltage when the commercial AC power is turned on.

A detection means 2 for detecting an increase/decrease in the output voltage led out to the output section via the detector is connected, and in response to the detection value of the detection means 2, the oscillation frequency of the oscillation circuit O8C is controlled to control the oscillation frequency of the transistor Q5. It controls on and off, and as a result controls the output voltage and supplies a stable voltage.

Specifically, the control structure of the detection means 2 and the oscillation circuit O8C consists of a light emitting diode and a phototransistor as in FIG.

On the other hand, in the above-mentioned auxiliary power supply circuit, the auxiliary winding N3 is wound with the same polarity as the second winding N2, and the winding N3 is wound with the same polarity as the second winding N2.
The voltage is proportional to the winding N3.

That is, the voltage of the auxiliary power supply circuit is proportional to the output voltage of the secondary side.

Therefore, an overvoltage detection circuit means 3 is provided which uses the auxiliary power supply circuit to detect overvoltage in the auxiliary power supply circuit and control the operation of the oscillation circuit O8C to stop.

The circuit means 3 is supplied with the voltage converted into direct current by the rectifier circuit E (voltage at point a) as a power supply voltage, and the voltage of the auxiliary power supply circuit (voltage at point b) is supplied as a comparison voltage, When the voltage at the point exceeds the reference voltage, the oscillation circuit O8
Stop the oscillation operation of C.

A specific configuration of the overvoltage detection circuit means 3 is shown in FIG.

In Figure 3, points a and b are respectively the points a and b in Figure 2.
Corresponding to point A, it is connected to ground through resistors R3 and R4 from point a, and connected to the resistor R from point b through diode D3.
3 and R4.

A Zener diode Z1 is connected to the ground through resistors R5 and R6 from the midpoint between the resistors R3 and R4.

The anode of the programmable unijunction transistor P1 is connected to the midpoint of resistors R3 and R4, its gate is connected to the midpoint of resistors R5 and R6, and its cathode is connected to the oscillation circuit O8C.

Therefore, when the voltage at point b exceeds the reference voltage Z1, Pl turns on and provides a control signal to the oscillation circuit O8C to stop the oscillation operation.

That is, an abnormal voltage is output to the secondary side due to a failure of the oscillation circuit O8C or the detection means 2 on the secondary side, and in response, the voltage of the auxiliary power supply circuit also increases, and this voltage, that is, the voltage at point b, becomes the reference voltage. When the voltage reaches VZ1 or higher, the operation of the oscillation circuit O8C is stopped to prevent overvoltage in the secondary circuit and the auxiliary power supply circuit.

In this case, the reason for supplying the voltage at point a as the electric trout voltage of the overvoltage detection circuit means 3 is to remove the voltage at point a after Pl detects an abnormal voltage and turns on. On the circuit, Pl is prevented from turning off except by opening the power switch and removing the voltage at point a, and is designed to return only after this operation is performed.

This is to prevent the oscillation circuit O8C from returning to operation due to P being turned off unnecessarily while the abnormal voltage is not removed after the oscillation circuit O8C is stopped due to the occurrence of an abnormal voltage.

Note that although the programmable unijunction transistor P1 has been exemplified above, other elements having a latching effect (negative resistance element) and circuits can be used.

As shown in FIG. 4, the above-mentioned oscillation circuit O8C includes transistors Ql, Q2 . In the astable multi-by-break composed of Q3, etc., the voltage across the capacitor C3 of the auxiliary power supply circuit is applied, and when this operating voltage reaches a predetermined level, it self-oscillates and adjusts the frequency based on the circuit conditions. form the output signal.

The output signal is further introduced from the oscillation circuit O8C to the base of the transistor Q5 of the driver circuit 1 through the output terminal consisting of the transistor Q4, etc., and controls the transistor Q5 to be turned on and off at the corresponding frequency, and is connected to the first winding of the transformer. N
Switch 1.

Further, an output signal from the overvoltage detection circuit means 3 is introduced into the base of the transistor Q9, which connects the collector and emitter between the base and ground of the transistor Q3, and turns on the transistor Q9 when overvoltage is detected.
Turn off and stop oscillation.

The oscillation operation of the oscillation circuit O8C shown in FIG. 4 will be briefly explained.

Now, if the voltage across the capacitor C3 of the auxiliary power supply circuit is Vc3, then the voltage V at the initial start when the power is turned on is Vc3.
The temporal change of c3 exhibits the change of curve X shown in FIG.

When the voltage Vc3 reaches a predetermined level set in advance in the oscillation circuit O8C, the astable multivib break circuit bypassed by the resistor starts oscillating.

To explain the order of the oscillations, the capacitor C4 having a relatively low impedance is connected to the base of one transistor Q1 of the astable multi-by-break, so the transistor Q1 turns on first.

(In this state, the other transistor Q2 is off.

) When the transistor Q1 is on, the capacitor C4 is gradually charged through the resistor R4, and the base voltage of the transistor Q1 increases accordingly.

The increase in base voltage also increases the emitter voltage of transistor Q1, causing the other transistor Q2 to turn on.

When transistor Q2 turns on, transistor Q3
also transitions to on.

As a result, transistor Q is bypassed by resistor R1.
The base voltage of transistor Q2 becomes low, and transistor Q2 enters a stable on state.

Note that in this state, the transistor Q1 is turned off.

When the transistor Q3 turns on, the transistor Q4 whose base is connected to the collector terminal of the transistor Q3 also turns on, and the on-state signal is output from the oscillation circuit and introduced into the base of the transistor Q5. to transition to the on state.

Next, the operation of switching the transistor Q5 on and off will be explained.

When transistor Q3 is turned on by the above operation,
The electric charge already stored in the capacitor C4 is gradually discharged through the circuit indicated by the arrow in the figure, and the base voltage of the transistor Q1 also decreases accordingly.

When the voltage drops to a predetermined level, transistor Q1 turns on, and along with this change, each transistor Q2. Q3. Q
4 are all turned off.

As a result, transistor Q5 turns off.

The OFF operation of the transistor Q5 contributes to the switching of the transformer T together with the above-mentioned ON operation, and induces an output voltage on the secondary side of the transformer.

The oscillation circuit that has been initially started starts to turn on the auxiliary winding N as the switching of the transformer T starts.
3, the operating voltage Vc3 is supplied, the voltage shown by the curve Y in FIG. 5 is maintained, and the oscillation operation continues.

In the above oscillation circuit, a phototransistor Q8 is connected to the discharge path of the charge accumulated in the capacitor C4, and a discharging operation is performed for a discharging time corresponding to the impedance of the phototransistor Q8.

That is, the phototransistor Q8 is optically coupled to a light emitting diode serving as a detection means provided at the output section, and exhibits an impedance corresponding to the amount of incident light.

The impedance of phototransistor Q8 changes the discharge time of capacitor C4, thereby changing the on and off times of transistor Q1.

That is, the oscillation frequency of the oscillation circuit O8C is increased or decreased.

As described above, in the present invention, in a power supply voltage stabilization circuit using a switching method, if control becomes impossible due to a failure of the oscillation circuit or isolator itself, abnormal voltage is output to the secondary side and auxiliary power supply circuit. Although this may cause a risk of overvoltage, the overvoltage detection means that detects overvoltage in the auxiliary power supply circuit stops the operation of the oscillation circuit, which prevents circuit damage due to abnormal voltage and provides a highly reliable power supply voltage stabilization circuit. can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a power supply voltage stabilizing circuit according to the invention of the prior application, FIG. 2 is a block diagram showing a power supply voltage stabilizing circuit according to the present invention, and FIG. 3 is an overvoltage detection circuit means according to the present invention. FIG. 4 is an electric circuit diagram showing a specific configuration of the oscillation circuit according to the present invention, and FIG. 5 is a voltage waveform diagram for explaining the operation of FIG. 4. E: Rectifier circuit, T Nidorance, N1. N2 and N3: Winding, 1 driver circuit, Q5: Transistor, OSC
: oscillation circuit, 2: detection means, 3: overvoltage detection circuit means,
Pl: programmable unijunction transistor, Z: Zener diode.

Claims (1)

[Scope of Claims] 1. An oscillation circuit that oscillates when a voltage at a predetermined level is energized, a switching element that is turned on and off by the output of the oscillation circuit, and an output of the switching element that is derived via a transformer. A power supply voltage stabilizing circuit comprising an output section and a detection means provided on the output side for varying the oscillation frequency of the oscillation circuit in response to voltage fluctuation detection on the output side, the power supply voltage stabilizing circuit comprising: A power supply voltage stabilizing circuit having an overvoltage detection means for detecting an overvoltage of an auxiliary power supply circuit that energizes a level voltage and stopping the operation of an oscillation circuit.゛