JPH07230328A - Semiconductor switch circuit - Google Patents

Abstract

PURPOSE:To stabilize the output voltage by varying the impedance of a semiconductor switch element of a semiconductor switch circuit. CONSTITUTION:A 3rd transistor TR Q3 is connected to a 2nd TR Q2 which applies the ON/OFF control to a semiconductor switch element Q1. So that the bias voltage of the TR Q2 is varied. Then a Zener diode D1 is connected to the base of the TR Q3 to detect the output voltage. Thus the impedance of the element Q1 is varied and the output voltage is stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a semiconductor switch circuit to be inserted in a secondary side rectifying / smoothing circuit, which is intended to stabilize the output voltage by changing the impedance of a switch element, improve the characteristics, and reduce the circuit configuration cost.

[0002]

2. Description of the Related Art A basic circuit of a semiconductor switch circuit conventionally inserted in a secondary side rectified output of a switching power supply is shown in FIG. The operating principle of FIG. 4 is that when the switch S is turned on, the transistor Q2 is turned on (ON), and the switching element (in this example, the P-channel type FE) is turned on.
T) Q1 is turned on, and the switching element Q1 merely serves as a switch and does not stabilize the output voltage.

[0003]

In the conventional circuit described above, since the impedance of the semiconductor switch element Q1 is constant,
When the rectifying / smoothing circuit in which the semiconductor switch element Q1 is inserted is an unstable circuit, the output of the semiconductor switch element Q1 is also unstable and the output voltage fluctuates greatly.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and enables the bias voltage (base current) of the transistor Q2 for controlling the semiconductor switching device Q1 to be changed as shown in FIG. When the output voltage tries to vary by connecting the transistor Q3 and connecting the Zener diode D1 connected to the output to the base of the transistor Q3, the impedance of the semiconductor switch element Q1 is changed by the Zener diode to stabilize the output voltage. It is a switch circuit that changes.

That is, in the semiconductor switch circuit including the semiconductor switch element Q1 and the second transistor Q2 for controlling the ON / OFF of the semiconductor switch element Q1, the second transistor Q2
The third transistor Q3 is connected so that the bias voltage (base voltage) thereof can be changed, and the Zener diode D1 for detecting the output voltage is connected to the base of the third transistor Q3 to change the impedance of the semiconductor switch element. The semiconductor switch circuit is characterized in that it stabilizes the output voltage.

[0006]

Since the present invention is constructed as described above,
When the semiconductor switch element Q1 is used in an uncontrolled rectifying / smoothing circuit of a switching power supply, the input voltage of the semiconductor switch element Q1 has large voltage fluctuations and is unstable as shown in FIG. It will be described that the output voltage is stabilized in the step of.

For example, when the input voltage fluctuates and the voltage rises, the output voltage also tries to rise, so that the base current of the transistor Q3 increases due to the Zener diode D1, and the collector-emitter voltage Vce of the transistor Q3 decreases. When Vce decreases, the base current of the transistor Q2 decreases, and the collector-emitter voltage Vce 'of the transistor Q2 increases. When Vce 'becomes higher, the gate voltage of the semiconductor switching device Q1 (P-channel FET in FIG. 1) lowers, so that the source-drain voltage Vs of the semiconductor switching device Q1 becomes lower.
d becomes large. By changing Vsd of the semiconductor switch element Q1 as described above, the output voltage Vout can be stabilized by the formula (1) even if the input voltage Vin changes.

[0008]

[Equation 1]

FIG. 8 shows an output current (output power) -output voltage characteristic, that is, a regulation characteristic at an input voltage of 100 VAC using the circuit of FIG. 1 which is a basic circuit of the present invention, and shows stable characteristics as compared with FIG. Can understand. Conventionally, the cost can be reduced as compared with the system in which a stabilizing circuit such as a chopper or a series regulator is connected in series with a semiconductor switch circuit as shown in FIG.

[0010]

FIG. 1 shows a basic circuit of an embodiment of the present invention. As an example of its application, a switch circuit that operates by an external signal is shown in FIG. 2, and a switch circuit that operates in sequence with another output of a power supply is shown in FIG.

In FIG. 1, when the switch S is turned on, a base current flows through the transistor Q2 through the resistors R3 and R4, and the collector-emitter of the transistor is turned on.
Then, the gate voltage of the following formula (2) is applied to the FET Q1 to turn on the source and drain of the FET Q1.

[0012]

[Equation 2]

When the input voltage Vin is lower than the Zener voltage of the Zener diode D1, the output voltage Vout is almost equal to the input voltage Vin. However, when the input voltage Vin exceeds the Zener voltage of the Zener diode D1, the Zener diode D1 receives Current flows, transistor Q
3, a base current flows through the transistor Q3 to lower the collector-emitter impedance of the transistor Q3, so that the bias voltage of the transistor Q2 lowers, the base current decreases, and the collector-emitter voltage Vce of the transistor Q2 increases. , The gate voltage of the FET Q1 becomes the expression (3), the impedance Ron between the source and drain of the FET Q1 increases, and the output voltage Vout is made constant by the expression represented by the expression (4).

[0014]

[Equation 3]

[0015]

[Equation 4]

Where I is the load current.

FIG. 2 shows an embodiment of the present invention, which is an external switch S.
When the switch S is turned off, the base current flows through the transistor Q2, the impedance between the collector and the emitter of the transistor Q2 is lowered, the gate voltage is applied to the FET Q1, and the source of the FET Q1 is turned on.・ Impedance R between drains
on falls, and the voltage Vout represented by the equation (4) is output. As in FIG. 1, the zener diode D1 causes the impedance R between the source and drain of the FET Q1.
on changes to make the output voltage Vout constant.

FIG. 3 shows another embodiment of the present invention, which is a circuit designed so that the output voltage Vout is output later than the other output type Vout ', and the output Vout' is the voltage of the Zener diode D2. When it exceeds, the base current flows through the transistor Q2, the impedance between the collector and emitter of the transistor is lowered, and the gate voltage is applied to the FET Q1, so the impedance Ron between the source and drain of the FET Q1 is lowered, and the equation (4 The voltage Vout represented by () is output later than the other output system Vout ′. As in FIG. 1, the FE is applied by the Zener diode D1.
Source-drain impedance Ron of T Q1
Changes to make the output voltage Vout constant.

The regulation of the output of the non-control system (generally termed "draining circuit") depends on the load capacity of the output of the control system and the load capacity of the other output system. Normally, the regulation of the output of the non-control system is dominated by the load capacity of the output of the control system when the power is large, and varies with the load capacity of the other outputs in addition to the output capacity of the control system when the power is small. Explaining in FIG. 7 of the conventional example, the dotted line shows the regulation when the control system output is maximum and the other output systems are minimum, and the solid line shows the regulation when the control system output is maximum and the other output systems are maximum. Shows the regulation of. The present invention is based on the above-described embodiment.
It has been demonstrated to exhibit stable regulation characteristics such as. Further, FIG. 8 shows that when the output of the control system is maximum, the other output systems described above are stable in both minimum and maximum.

In the above description, the circuit using the FET as the switch element is described for ease of description, but the same applies to the case where the switch element is replaced with a transistor and configured as shown in FIG. The effect was obtained.

[0021]

According to the present invention, the semiconductor switch circuit described above enables the ON / OFF switching control of the circuit and the voltage stabilization control at the same time, which has the effect of improving the characteristics and reducing the cost.

[Brief description of drawings]

FIG. 1 is a basic circuit diagram of an embodiment of a semiconductor switch circuit of the present invention.

FIG. 2 is a semiconductor switch circuit diagram of an embodiment having an external control according to the present invention.

FIG. 3 is a semiconductor switch circuit diagram of an embodiment having sequence control according to the present invention.

FIG. 4 is a conventional semiconductor switch circuit diagram.

FIG. 5 is a circuit diagram in which a conventional stabilizing circuit and a switch circuit are connected in series and used.

FIG. 6 is a basic circuit diagram of an embodiment in which a semiconductor switch element according to the present invention is replaced with a transistor.

FIG. 7 is a regulation characteristic diagram of a non-control system output of a conventional switching power supply.

FIG. 8 is a regulation characteristic diagram of the embodiment of the semiconductor switch circuit according to the present invention.

[Explanation of symbols]

 Q1 Semiconductor switch element (FET or transistor) Q2 transistor Q3 transistor D1 Zener diode D2 Zener diode D3 Rectifier diode D4 Rectifier diode C1 Electrolytic capacitor C2 Electrolytic capacitor R1 resistor R2 resistor R3 resistor R4 resistor R5 resistor R6 resistor R7 Resistor R8 Resistor S Switch Vcc Battery Vin Input terminal of semiconductor switch circuit Von Output terminal of semiconductor switch circuit

Claims (1)

[Claims] 1. A semiconductor switch element Q1 and its switch
In a semiconductor switch circuit including a second transistor Q2 that is turned off, a third transistor Q3 is connected so as to change the bias voltage (base voltage) of the second transistor Q2, and the base of the third transistor Q3 is connected. A semiconductor switch circuit characterized in that a zener diode D1 for detecting an output voltage is connected to the output terminal to change the impedance of the semiconductor switch element to stabilize the output voltage.