JP3005316B2 - Power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit of a self-excited switching regulator, and more particularly to a power supply circuit having an automatic voltage switching circuit for making an output current substantially constant for different power supply voltages.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG.
A self-excited switching regulator that outputs a current to the storage battery 5 or the like by connecting an oscillation series circuit including the base winding L3, the resistor R3, and the capacitor C1 to the base of the switching transistor Q1 and switching the switching transistor Q1. Power supply circuits are known.

The power supply circuit extracts a voltage proportional to the input voltage so that the output current is substantially constant when the input voltage from the AC power supply 2 is 100 V or 240 V, and the extracted voltage is It has an automatic voltage switching circuit (hereinafter, referred to as an automatic circuit) that guides the voltage to the base of the switching transistor Q1 to change the switching time of the switching transistor Q1.

[0004]

However, in the power supply circuit of FIG. 4, since one end of the base winding L3 is connected to the connection point between the emitter of the switching transistor Q1 and the emitter resistor R7, the switching transistor Q1
Is not affected by the emitter resistance R7. Therefore, it is not possible to change the inflection point D of the input voltage-output current characteristic curves shown in FIGS. 6 and 7 by changing the resistance value of the emitter resistance R7. Although possible, the slope of the characteristic curve cannot be changed.

On the other hand, in the power supply circuit shown in FIG.
3 is connected to the circuit ground, the base current of the switching transistor Q1 flows through the emitter resistor R8.
Although it is possible to adjust the slope of the above-described input voltage-output current characteristic curve by changing the resistance value, it is difficult to obtain a proper output current because the output current changes.

As described above, in the conventional power supply circuit shown in FIG. 4 or FIG.
It was difficult to make the output current with respect to the case of 0 V substantially constant.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a power supply circuit capable of easily making output current substantially constant with respect to different power supply voltages.

[0008]

To achieve the above object, the present invention provides a power supply circuit for a self-excited switching regulator using a switching transistor for generating a predetermined output current from an input power supply. An automatic voltage switching circuit that extracts a voltage proportional to the input voltage so as to make the output current substantially constant, guides the extracted voltage to a feedback circuit, and changes the switching time of the switching transistor, and is connected in series to the emitter of the switching transistor. And an emitter resistor circuit including a first resistor and a second resistor. The feedback circuit is configured to also use the first resistor as a feedback resistor.

[0009]

According to the power supply circuit having the above structure, a voltage proportional to the input voltage is extracted by the automatic voltage switching circuit, and the extracted voltage is guided to the feedback circuit which also uses the first resistor as a feedback resistor to perform switching. The switching time of the transistor is changed.

[0010]

FIG. 1 is a circuit diagram showing an example of a power supply circuit of a self-excited switching regulator according to the present invention. The AC power supply 2 is connected to the rectifier bridge 3 via a terminal. The AC power supply 2 includes, for example, one that supplies 100 V as a power supply voltage and one that supplies 240 V as a power supply voltage. The rectifying bridge 3 rectifies the input voltage from the AC power supply 2 and outputs the rectified voltage to the primary winding L1 of the transformer 4. The transformer 4 has a primary winding L1 and a secondary winding L2.
And the base winding L3, the current flowing into the primary winding L1 is switched by turning on and off the switching transistor Q1, whereby a voltage is induced in the secondary winding L2 and the base winding L3. I have.

A diode D2 and a storage battery 5 are connected in series to the secondary winding L2. The power induced in the secondary winding L2 is rectified by the diode D2 and supplied to the storage battery 5 for charging. is there. The base of the switching transistor Q1 is connected to the base winding L3 and the resistor R3.
And a series circuit for oscillation composed of a capacitor C1 and a switching transistor Q1 is supplied with a base current by an induced voltage of a base winding L3 to be turned on. Further, the emitter of the switching transistor Q1 is connected to an emitter resistor 1 composed of divided resistors R1 and R2 connected in series. The split resistor R1 also serves as a feedback resistor of an auto circuit described later. The starting resistor R5 supplies a current to the base of the switching transistor Q1 to start the switching transistor Q1.

The base winding L3, the voltage dividing resistor R
4, R5, Zener diode D1, transistor Q2, and split resistor R1 form an auto circuit. That is, the auto circuit extracts a voltage proportional to the input voltage by the base winding L3, and guides the extracted voltage to the voltage dividing resistors R4 and R5, the Zener diode D1 and the transistor Q2, which are feedback circuits, to switch the switching transistor Q1. The on time is controlled to change the switching time of the switching transistor Q1.

That is, the induced voltage of the base winding L3 is
A divided voltage divided by a series circuit including the dividing resistor R4, the dividing resistor R5, and the dividing resistor R1, a voltage generated in the dividing resistor R1 by a current flowing through the base of the switching transistor Q1 via the dividing resistor R1, The split resistors R1 and R2 are provided by the collector current of the switching transistor Q1.
Is higher than the Zener voltage of the Zener diode D1, the Zener diode D1 turns on and the transistor Q2 turns on. When the transistor Q2 is turned on, the switching transistor Q2
1 is turned off. Then, the ON period of the switching transistor Q1 is determined by the automatic circuit.

Next, the operation of the above circuit configuration will be described. When the 100 V AC power supply 2 is connected, the starting resistance R
A current flows to the base of the switching transistor Q1 through 5, and the switching transistor Q1 starts to turn on. For this reason, a current flows through the primary winding L1, and a feedback voltage is induced in the base winding L3.
3, rises at a time constant determined by the resistor R3 and the capacitor C1, the base current of the switching transistor Q1 increases, and the collector current further increases.

On the other hand, the rise of the induced voltage of the base winding L3 and the increase of the base current and the collector current of the switching transistor Q1 cause the voltage dividing resistor R5 and the dividing resistor R5.
When the sum of these voltages rises above the Zener voltage of Zener diode D1, Zener diode D1 turns on and transistor Q2 turns on, so that switching transistor Q1 turns off rapidly. Become.

Thereafter, a current flows again to the base of the switching transistor Q1 through the starting resistor R5, and the switching transistor Q1 turns on. That is, switching transistor Q1 repeats switching, and the switching induces electric power in secondary winding L2 to cause an output current to flow, thereby charging storage battery 5.

Next, when the 240 V AC power supply 2 is connected, the voltage of the base winding L3 increases and the base current and the collector current of the switching transistor Q1 increase, so that the voltage dividing resistor R5 and the dividing resistor R1, The period until the sum of the voltages generated in R2 becomes equal to or higher than the Zener voltage of the Zener diode D1 is shortened, and the period from when the switching transistor Q1 turns on to when the transistor Q2 turns on, that is, when the switching transistor Q1 turns off. Be shorter. Therefore, a change in the output current with respect to the change in the power supply voltage is suppressed.

With the above circuit configuration, the base current of the switching transistor Q1 flows through the dividing resistor R1, so that the gradient of the input voltage-output current characteristic curve can be changed by the dividing resistor R1. On the other hand, since only the collector current of the switching transistor Q1 flows through the dividing resistor R2, the inflection point of the input voltage-output current characteristic curve can be changed by the dividing resistor R2. Therefore, the division resistance R
By appropriately setting the ratio of the resistance value of 1 to the divided resistance R2, as shown by the solid line A, the dashed line B or the dotted line C in FIG. The output current can be made substantially constant when the input voltage from the AC power supply 2 is, for example, 100 V and 240 V. The output current value can be adjusted by changing the combined resistance value of the divisional resistors R1 and R2.

Further, as shown in FIG.
By configuring the emitter resistor with the variable resistor 10 instead of R2, the slope and the inflection point of the input voltage-output current characteristic curve may be adjusted. That is, by using the variable resistor 10, the slope and the inflection point of the input voltage-output current characteristic curve can be adjusted as needed.

[0020]

According to the present invention, since the first resistance of the emitter resistance circuit of the switching transistor is also used as the feedback resistance of the automatic voltage switching circuit, it is possible to change the gradient and the inflection point of the input voltage-output current characteristic curve. Thus, the input voltage-output current characteristic curve can be easily and reliably adjusted to a desired characteristic. That is, for example, when the input voltage is 100 V
The output current can be easily and reliably made substantially constant between the case of (1) and the case of 240V.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a power supply circuit according to the present invention.

FIG. 2 is a circuit diagram showing another example of the power supply circuit according to the present invention.

FIG. 3 is a characteristic diagram showing a change in an input voltage-output current characteristic of the power supply circuit according to the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional power supply circuit.

FIG. 5 is a circuit diagram showing another example of a conventional power supply circuit.

FIG. 6 is a characteristic diagram showing an input voltage-output current characteristic of a conventional power supply circuit.

FIG. 7 is a characteristic diagram showing an input voltage-output current characteristic of a conventional power supply circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Emitter resistance 2 AC power supply 3 Rectifier bridge 4 Transformer 5 Storage battery C1 Capacitor D1 Zener diode R1, R2 Dividing resistance (emitter resistance) R3 Resistance R4, R5 Dividing resistance Q2 transistor Q1 Switching transistor L3 Base winding

Claims (1)

(57) [Claims] In a power supply circuit of a self-excited switching regulator using a switching transistor for generating a predetermined output current from an input power supply, a voltage proportional to the input voltage is extracted to make the output current substantially constant with respect to the input voltage. An automatic voltage switching circuit for guiding the extracted voltage to a feedback circuit to change the switching time of the switching transistor; and an emitter resistor comprising a first resistor and a second resistor connected in series to the emitter of the switching transistor. And a power supply circuit, wherein the feedback circuit is configured to also use the first resistor as a feedback resistor.