JPH04295275A - Switching electric power source circuit - Google Patents

Abstract

PURPOSE:To start it easily even if the saturation resistance of a switching transistor is large and the current amplification factor is small by suppressing the starting current flowing in the driving controller for controlling the driving of that switching transistor, concerning the starting property of the ringing choke type switching power source circuit which converts the input DC power into other DC power and outputs it. CONSTITUTION:Switching power source circuit, wherein a diode is so connected in series to a driving controller that the base current of the switching transistor flows forward, unlike conventional ringing choke type switching power source circuits.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit that improves the starting characteristics of a ringing choke type switching power supply circuit that converts an input DC power source into another DC power source and outputs the converted DC power source.

0002

2. Description of the Related Art A conventional ringing choke type switching power supply circuit is shown in FIG. 3(A), and FIG. 3(B) is a waveform diagram of the main points. The basic operation of this switching power supply circuit will be explained below. The input DC power supply V1 is obtained by rectifying the AC power supply E (AC) with diodes X1 to X4 and smoothing it with a capacitor C1. When V1 generated by turning on the power switch SW is applied, the first transistor (switching transistor) TR passes through the starting resistor R1.
A small base current flows through the base of TR1, TR1 becomes conductive, and collector current begins to flow. V1 is transformer T
Since it is also applied to the primary winding N1, a voltage based on the turns ratio of N1 and N3 is generated in the tertiary winding (positive feedback winding) N3 (symbol d), and this voltage is applied to the second transistor. (Drive transistor) Collector current flows to TR2
rapidly enters the conduction region (symbol c), and a current i1 that increases linearly flows through N1 as shown by symbol a. As a result, a voltage indicated by symbol b is generated at N1.

On the other hand, since the base current of TR1 becomes a decreasing current (symbol e) in the waveform shaping circuit (the series circuit of L1 and R4), i1 eventually reaches its peak and begins to decrease. Therefore, the voltages generated at N1 and N3 are also reversed, and TR1 is rapidly turned off (symbols b, c, and d). The energy stored in the transformer T during the ON period of TR1 is released to the load side (N2) during the OFF period of TR1. In other words, a linearly decreasing current i3 flows through the secondary winding N2 during the OFF period of TR1, with the maximum value being the current ip2 determined by the maximum current ip1 of i1 and the winding ratio (N1 and N2) (symbol g). . This i3
tries to continue decreasing, but is not allowed to flow due to D2, and the voltage induced in the winding N2 is reversed due to the current change at this time, and the induced voltages of N1 and N3 are also reversed accordingly (symbols b and d). The off period of TR1 is determined by N2 and the load circuit. When the voltage of N3 is reversed, the base of TR1 is forward biased, so that it becomes i2, which acts to pull TR1 into the on state. Therefore, TR1 returns to the initial operation and continues to repeat the on/off operation by self-excitation. In this way, the voltage e2 (symbol f) generated in the winding N2 during the OFF period of TR1 is rectified and smoothed by D2 and C2, and the output voltage V2 (symbol h
) is supplied to the load. The collector current of TR2 that drives TR1 is indicated by i. Drive control of TR2 to TR1, which has the effect of stabilizing V2 against load fluctuations or fluctuations in V1, is performed by changing the internal forward equivalent resistance of TR2 to control the time t1 (=TR1 ON period) and amplitude of collector current i4. This is achieved by varying both of i4. As a result, the base current i2 of TR1 changes, and TR1
V2 is stabilized by changing the on period and the voltage e2 of N2. Note that the off period of TR1 is constant. The internal forward equivalent resistance of TR2 is determined by the detection output signal from the error detection section 2.
This is done by controlling the base current of. The error detection section 2 compares a DC voltage obtained by rectifying the voltage generated in the quaternary winding N4 with a constant reference voltage, amplifies this comparison difference, and outputs it as a detection output signal. A voltage similar to N2 is generated at N4. For example, when the output voltage V2 increases, a detection output signal that reduces the base current of TR2 is output. As a result, e2, indicated by symbol f, falls to suppress the rise in V2. When the output voltage V2 decreases, a detection output signal that increases the base current of TR2 is output, and the decrease in V2 is suppressed by the opposite effect to the above. The base current of TR1 in the above operation is made up of the sum of the starting current due to R1, the collector current i4 of TR2, and the current i5 of the waveform shaping circuit.

0004

[Problem to be Solved by the Invention] At the moment when the power switch SW is turned on, as explained above, a small starting base current determined by the voltage value V1 of the input DC power supply and the starting resistor R1 flows, so that the switching circuit operates. However, the starting base current fluctuates due to variations in the saturation resistance (collector-emitter, base-emitter) and current amplification factor of the first transistor TR1, and the larger the saturation resistance and the smaller the current amplification factor, It is suppressed and becomes smaller, making it difficult to start. One way to improve this is to reduce the starting resistance R1 to increase the starting current, but this is not preferable because the starting current always flows during the conduction period of TR1, impairing circuit performance and reliability of TR1. On the other hand, the starting base current when subjected to the above suppression is N3
through the second transistor TR2 in the opposite direction to i4.
The inverse HFE of TR2 flows into the TR2, further inhibiting startup. The present invention provides a switching power supply circuit that suppresses the current flowing into the second transistor TR2 and easily starts up even when the saturation resistance of the first transistor TR1 is large and the current amplification factor is small. The purpose is to

[0005]

[Means for Solving the Problems] The present invention provides a first resistor whose one end is connected to the positive electrode side of a DC power source, a primary winding whose one end is connected to the first end, and a rectifier. A transformer consisting of a secondary winding that serves as a DC voltage output, a tertiary winding, and a quaternary winding whose one end is connected to one end of the tertiary winding, and whose collector is the other end of the primary winding. a first transistor whose base is connected to the other end of the first resistor and whose emitter is connected to the negative electrode side of the DC power supply via a second resistor;
an error detection section whose input end is connected to the other end of the quaternary winding;
It is provided in a loop that returns from the other end of the tertiary winding to one end of the tertiary winding via the base and emitter of the first transistor, and the detection output signal from the output end of the error detector is used to detect the first A switching power supply circuit comprising a drive control section for controlling a base current of a transistor, wherein a diode is provided in series with the drive control section so that the base current of the first transistor flows in a forward direction. The present invention provides a switching power supply circuit.

[0006]

[Operation] By providing a diode on the collector side or emitter side of the drive transistor, the flow of the starting base current is suppressed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A switching power supply circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a main part showing an embodiment of a switching power supply circuit according to the present invention. Figure 2
FIG. 2 is a circuit diagram showing a main part of another embodiment of a switching power supply circuit according to the present invention. 1 and 2, E is an AC input power supply, SW is a power switch, X1 to X4 are diodes as a so-called bridge rectifier circuit that rectifies the AC power supply, C1 is a smoothing capacitor, and V1 is an AC input power supply E.
is the input DC power source obtained from the diodes X1 to X4 and the capacitor C1, and T is the primary winding N1 to the fourth winding N4.
TR1 is a first transistor that performs a switching operation, and TR2 is a first transistor TR1.
D1 is a first diode that blocks the starting base current from flowing into the second transistor; D2 is a second diode that rectifies the voltage generated in the secondary winding N2; C2 is a second capacitor that smooths the rectified voltage from the second diode D2 to provide a DC output power source V2, R1 is a starting resistor that causes a starting current to flow through the first transistor TR1 when the power switch SW is turned on, and R2 is a A second resistor for the purpose of limiting the collector current of TR1, R4 is a fourth resistor, L1 and R4 are connected to TR
1 Inductance that shapes the waveform of base current

000
8] The basic operation of the present invention is the same as that described in FIG. 3 except for the action of the first diode D1. The flow of the starting base current into the second transistor TR2, which becomes noticeable when the saturation resistance of the first transistor TR1 is large and the current amplification factor is small, can be avoided by providing a first diode as shown in FIGS. 1 and 2. This can be prevented by FIG. 1 shows the case where it is provided at the emitter of the TR2, and FIG. 2 shows the case where it is provided at the collector. Both have the same blocking effect.

[0009]

As explained above, according to the present invention, it is possible to prevent the starting base current of the switching transistor from flowing into the drive transistor, which becomes noticeable when the saturation resistance of the switching transistor is large or when the current amplification factor is small. This has the effect of improving the startup characteristics when the power switch is turned on, and greatly contributes to improving the performance of the switching power supply circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a main part of an embodiment of a switching power supply circuit according to the present invention.

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

FIG. 3A is a main circuit diagram showing an example of a conventional switching power supply circuit, and FIG. 3B is a waveform diagram.

[Explanation of symbols]

1 Drive control section 2 Error detection section E　AC input power supply SW　Power switch X1 Diode X2 diode X3 Diode X4 diode V1 Input DC power supply T transformer TR1 First transistor TR2 Second transistor D1 First diode D2 Second diode C1 First capacitor C2 Second capacitor R1 First resistance R2 Second resistance R3 Third resistance R4 Fourth resistor L1 inductance

Claims (3)

[Claims] Claim 1: A first resistor with one end connected to the positive electrode side of a DC power source, a primary winding with one end connected to the first end, and a secondary winding that rectifies and provides a DC voltage output. Lines and,
A transformer includes a tertiary winding, a quartic winding having one end connected to one end of the tertiary winding, a collector connected to the other end of the primary winding, and a base connected to the first resistor. a first transistor connected to the other end and having its emitter connected to the negative electrode side of the DC power supply via a second resistor; and an error detection section having an input end connected to the other end of the quaternary winding; from the other end of the tertiary winding to the base and emitter of the first transistor to the third
In the switching power supply circuit, the switching power supply circuit includes a drive control section that is provided in a loop returning to one end of the next winding and controls the base current of the first transistor using a detection output signal from the output terminal of the error detection section. 1. A switching power supply circuit comprising a diode connected in series with the drive control section so that the base current of the first transistor flows in the forward direction. 2. The drive control unit includes a diode having a cathode connected to one end of the tertiary winding, an emitter connected to an anode of the diode, and a collector having a third
2. The switching power supply circuit according to claim 1, further comprising a second transistor connected to the emitter of the first transistor via a resistor and having a base supplied with the detection output signal. 3. The drive control section includes a diode having an anode connected to the emitter of the first transistor via a third resistor, a collector connected to the cathode of the diode, and an emitter connected to the tertiary winding. 2. The switching power supply circuit according to claim 1, further comprising a second transistor connected to one end of the transistor and having a base supplied with the detection output signal.