JPH0226269A - Self-excited switching regulator - Google Patents

Abstract

PURPOSE:To suppress blocking oscillation by inserting a first resitor between the emitter of a switching transistor and the earth of an input power source and by connecting a second resistor between the above emitter and an input power line. CONSTITUTION:A self-excited switching regulator is composed of a diode bridge DB to rectify commercial power supply AC, a smoothing capacitor C1, a transformer T and a switching transistor(Tr) Q connected inseries to the primary winding n1 of the transformer T, etc. The base of the Tr Q is driven by the output of a feedback winding n3. Further, a first resistor R4 is inserted between the emitter of the Tr Q and the earth of the input power source, while a second resistor R5 and a reverse current preventive diode D2 are connected between the emitter of the Tr Q and the input power line. From the secondary winding n2 of the transformer the power is outputted through rectifying diode D1, etc. In this way, when the input supply voltage is raised, the emitter potential of the Tr Q is raised and the base current can be lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a self-excited switching regulator used as a power supply circuit.

(2) Prior Art A self-excited switching regulator is generally used as a relatively small-capacity power supply circuit provided in an electronic device to supply power to a circuit.

FIG. 2 is a circuit diagram of a conventional self-excited switching regulator that constitutes a so-called ringing choke converter. In the figure, DB is a diode bridge,
Rectifies commercial power AC. C1 is a smoothing capacitor that smooths this. T is a transformer whose primary winding nl
A switching transistor Q is connected in series.

Further, the output of the feedback 1''!n3 of the transformer is connected to the base of a switching transistor Q via a resistor R2. A resistor R1 is connected between the base of this switching transistor Q and the input power supply line Vcc. .

A rectifier diode Dl, a smoothing capacitor C2, and a dummy load R3 are connected to the secondary winding n2 of the transformer T.

The self-excited switching regulator configured as described above operates as follows. First, when the commercial power supply AC is input and the input power supply line Vcc rises to a predetermined voltage level, a base current flows into Q through the starting resistor R1, and Q becomes conductive. As a result, the collector current flowing through nl increases, and an electromotive voltage is generated at 03 in the direction of increasing the base current of Q. At this time, energy is stored in the transformer T. After that, when the collector current reaches twice the amplification factor of the base current, Q can no longer maintain its saturated state, the applied voltage of nl decreases, and accordingly, the electromotive force of n3 decreases, and Q suddenly cuts off. do. that moment n2
A reverse voltage is generated at , Dl becomes conductive, and the energy stored in the transformer T is released to supply power to the load. Thereafter, when the current of Dl becomes O, a surge voltage is generated at n2, which is induced in n3, and Q starts conducting again.

Automatic oscillation is performed by repeating the above steps.

(C1 Problem to be Solved by the Invention) By the way, such conventional self-help switching regulators are designed so that the input AC power supply voltage is not constant, but can be used within a certain voltage range.

- In boat fishing, the higher the input power supply voltage, the more energy is stored in the transformer during one ON period of the switching transistor, and the lower the load supply current, the less energy is released from the transformer during the OFF period of the switching transistor. do. Therefore, when the input power supply voltage is high and there is no load, energy remains in the transformer,
Self-help oscillation becomes unstable, causing intermittent oscillation.

If the oscillation operation becomes unstable in this way, the output voltage fluctuates, causing problems such as ripples. Therefore, conventionally, as shown in FIG. 2, a dummy load R3 was connected to the secondary side of the transformer to prevent the no-load state. However, in order to prevent the intermittent oscillation mentioned above, the resistance value of the dummy load must be set to a certain low value, which generates a large amount of heat, and requires the use of a relatively large resistor. Therefore, the efficiency of the power supply circuit was low and the size of the power supply circuit was increased.

An object of the present invention is to provide a self-excited switching regulator that performs stable self-oscillation operation against changes in input power supply voltage without using a special dummy load.

+d) Means for Solving the Problems This invention connects a switching transistor in series to the primary winding of a transformer for intermittent current flowing through the primary winding, and connects the output of the feedback winding of the transformer to the switching transistor. In the self-excited switching regulator connected to the base, a first resistor is inserted between the emitter of the transistor and the ground of the input power supply, and a second resistor is connected between the input power supply line and the emitter of the transistor. It is said that

(e) Operation In the switching regulator of the present invention, a first resistor is inserted between the emitter of the switching transistor and the ground of the input power supply, and a second resistor is connected between the input power supply line and the emitter of the switching transistor. . Therefore, the emitter potential of the transistor is a voltage divided by the input power supply voltage by the first and second resistors'. Therefore, for example, if the input power supply voltage increases, the emitter potential of the switching transistor also increases, so VII!
As the emitter-base voltage decreases and the base current decreases, the apparent ht- (emitter-grounded current amplification factor) decreases. Therefore, the energy stored in the transformer during one ON period of the transistor is reduced,
The balance of energy accumulation and release from the transformer is maintained without increasing the excessive energy stored in the transformer. In this way, the energy accumulated in the transformer during one ON period of the transistor is reduced, so that the energy accumulated in the transformer is not forcibly released by the dummy load (intermittent oscillation is suppressed).

(f) Embodiment FIG. 1 is a circuit diagram of a self-excited switching regulator which is an embodiment of the present invention. In the figure, DB is a diode bridge that rectifies commercial power AC, and CI is a smoothing capacitor that smoothes the rectified voltage. T is a transformer, and a switching transistor Q is connected in series to its primary winding n1. Further, the output of the feedback winding vAn3 is connected to the switching transistor Q via the current limiting resistor R2.
connected to the base of. Furthermore, a starting resistor R1 is connected between the base of Q and the input power supply line Vcc. A first resistor R4 is inserted between the emitter of the switching transistor Q and the input power supply ground (GND), and a second resistor R5 and a backflow prevention diode D2 are connected between the emitter of the switching transistor Q and the input power supply line Vcc. ing. A rectifier diode D1 and a smoothing capacitor C2 are connected to the secondary winding n2 of the transformer T.

The self-excited switching regulator configured as described above operates as follows. First, when the commercial power SAC is turned on and the voltage of the input power line Vcc reaches a predetermined value, a base current begins to flow into the transistor Q through the starting resistor R1. Due to this, an electromotive voltage is generated in the winding n3, and a base current flows into Q through the current limiting resistor R2. Thereafter, the collector current becomes thicker (hf) decreases, and when the base current becomes insufficient, the transistor Q is unable to maintain the saturation state, and the collector current begins to decrease.

As a result, the electromotive voltage of n3 decreases, the base current shortage is further promoted, and Q finally enters the cut-off state. The energy P accumulated in the transformer during the on period of the transistor Q is P=1/2L1·IPI''.

Here, Ll is the self-inductance of the primary winding n1 of the transformer, and rr+ is the peak current value flowing through nl.

When the transistor Q is turned off, a back electromotive force is generated in the secondary winding n2, and the rectifier diode D1 starts conducting.
Supply power to the load. After that, when the current in n2 becomes O, a reverse current flows during the reverse recovery time of diode D1, a surge voltage is generated in n2, this is induced in n3, and Q starts conducting again. Now that the automatic oscillation operation is performed by repeating the above, and considering the case where the voltage of the input power supply Vcc rises, since resistors R4 and R5 constitute a resistive voltage divider circuit, the emitter potential of Q increases as Vcc rises. rises. As a result, the base current rb based on the electromotive voltage of the feedback winding n3 decreases, so that the base current becomes insufficient within a short time after Q starts conducting, and the peak current flowing through nl decreases. In other words, transistor Q
As the apparent hfe decreases, the energy stored in the transformer during its on period decreases.

Therefore, the energy stored in the transformer is completely released from the secondary side during the off period of transistor Q.
The transformer does not reach saturation and maintains normal oscillation operation.

Conversely, when the voltage of the input power supply Vcc decreases, the emitter potential of Q decreases. Therefore, the base current 1b due to the electromotive voltage of n3 increases, and the peak current flowing to nl increases due to the opposite effect to that described above. Therefore, sufficient energy is stored in the transformer during one ON period of Q.

As described above, when there is no load or light load and the input power supply voltage is high, intermittent oscillation is suppressed, and when the input power supply voltage is low, the transformer can be sufficiently excited and the current capacity for the load is limited. There isn't.

(Effects of the Phantom Invention As described above, this invention provides the following effects.

■Even when the input power supply voltage is high with no load or light load,
Since intermittent oscillation can be suppressed without using a dummy load, loss due to the dummy load and an increase in the size of the device can be avoided.

■Since high-hr transistors can be used,
The current capacity supplied to the load can be maintained even when the input power supply voltage is low or at low temperatures.

■Even if the input power supply voltage is high, intermittent oscillation is suppressed, so
It can support a wide range of input power supply voltages.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a self-excited switching regulator according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional self-excited switching regulator. T-) lance, nl-primary winding, R2-secondary winding, R3-feedback winding, Q-switching transistor, R4-first resistor, R5-second resistor.

Claims (1)

[Claims] (1) In a self-excited switching regulator, in which a switching transistor that intermittents the current flowing through the primary winding is connected in series to the primary winding of a transformer, and the output of the feedback winding of the transformer is connected to the base of the switching transistor. , a first one between the emitter of the transistor and the ground of the input power supply.
A self-excited switching regulator characterized in that a second resistor is connected between the input power supply line and the emitter of the transistor.