JPH11259151A - Auxiliary power supply circuit for power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simplified and inexpensive auxiliary power supply circuit with a reduced packaging space prepared for a power supply circuit. SOLUTION: An auxiliary power supply circuit is provided with an input voltage detection circuit 10 constituted by combining a transistor(TR) and a Zener diode, a voltage level generation circuit 11 connected to the collector side of a controlling TR to be driven by the circuit 10 and having a built-in Zener diode, and a feedback circuit 12 connected to the circuit 10 to obtain a hysteresis characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an auxiliary power supply circuit for a power supply circuit.

[0002]

2. Description of the Related Art When operating a converter power supply, an auxiliary power supply for operating a series regulator power supply or a control circuit for stabilizing the output of the converter power supply is used. FIG. 6 is a diagram showing a conventional auxiliary power supply circuit.
Q1 is a control transistor for receiving the input voltage Vin and outputting the voltage Vo. Reference numeral 1 denotes an input voltage detection circuit that detects an input voltage. Q2 is a transistor controlled by the input voltage detection circuit 1, and is connected between the base of the control transistor Q1 and the common line. A resistor R is connected between the base and the collector of the control transistor Q1.
Is connected. In addition, a Zener diode D _{Z is provided} between the base of the control transistor Q1 and the common line.
Is connected.

In the circuit configured as described above, when the input voltage reaches a certain value, the input voltage detection circuit 1 drives the transistor Q2, a current flows through the resistor R, and turns on the control transistor Q1. As a result, a stable output Vo is obtained.

[0004] However, such a circuit has the following disadvantages. The input voltage detection circuit 1 detects the input voltage, and when the input voltage reaches a predetermined voltage, drives the transistor Q2 to turn on the control transistor Q1 to generate the output voltage Vo. After the start-up, a current flows through the converter circuit, so that the input voltage Vin decreases, falls below the start-up detection voltage, and the power supply stops.

When the power supply stops, no current flows through the circuit, so that the voltage rises to the starting voltage again and the power supply restarts. Hereinafter, a problem of repeating the same operation occurs. In order to improve such a problem, the input voltage detection circuit is usually provided with a hysteresis circuit so that the voltage is not detected again even if the voltage drops after the start.

FIG. 7 is a diagram showing a configuration example of a conventional circuit having a hysteresis characteristic. A resistor R1, a Zener diode D _Z1 , a resistor R2, and a transistor TR1 constitute an input voltage detection circuit. The on-voltage Von of the transistor TR1 is expressed by (The same applies hereinafter).

Von = V _Z1 + (V _BE / R2) × (R1 + R2) (1) Here, V _Z1 is the Zener voltage of the Zener diode D _Z1 , and V _BE is the base-emitter voltage of the transistor TR1.

When the voltage represented by the equation (1) is detected, the transistor TR1 turns on. On the other hand, the transistor TR2 which is turned on by the base current flowing from the resistor R4
Since the transistor TR1 is turned on, the base current of the transistor TR2 is bypassed, and the transistor TR2 is turned off.

Here, when the transistor TR2 is turned off, a current flows through the resistor R6 to the Zener diode _DZ2 and the base of the transistor TR3, so that the transistor TR3 is turned on and the output voltage Vo for the auxiliary power supply rises.

At this time, since the Zener voltage V _Z2 of the Zener diode D _Z2 is fed back to the base of the transistor TR1 by the resistor R3, the difference voltage between the voltage V _Z2 and the base-emitter voltage V _BE of the transistor TR1 is obtained. The current is applied to the resistor R3, and a current flows through the resistor R3.

The ON condition of the transistor TR1 is determined by a resistor R
2, when a voltage of about 0.6 V is generated in the resistor R2 (corresponding to the base-emitter voltage V _BE of the transistor TR1), and the current of the resistor R2 is equal to the input voltage Vi.
The current flowing to the side of the resistor R1 that detects
And the current flowing from the side. Therefore, the resistance R1
Is obtained by subtracting the current flowing from the resistor R3 from the current that causes the voltage drop of the resistor R2 to be about 0.6 V.

Therefore, the voltage (detection voltage) for turning off the transistor TR1 is given by the following equation, and this voltage becomes the off voltage Voff of the circuit.

[0013]

(Equation 1)

[0014]

As described above, even in the conventional circuit, the power supply circuit can be provided with a hysteresis characteristic, and the ON voltage when the circuit is ON and the OFF voltage when the circuit is OFF are made different. This makes it possible to provide the circuit with a hysteresis characteristic and prevent a problem that the auxiliary power supply circuit is repeatedly turned on / off. That is, once the voltage is turned on, it is possible to prevent the voltage drop from being detected again even if the voltage drops.

However, the conventional circuit has a problem that the number of components is large, the mounting space is large, and the cost is high, as is apparent from FIG. The present invention has been made in view of such a problem, and an object of the present invention is to provide an auxiliary power supply circuit for a power supply circuit that can simplify a circuit, reduce a mounting space, and be inexpensive. .

[0016]

FIG. 1 is a block diagram showing the principle of the present invention. In the figure, reference numeral 10 denotes an input voltage detecting circuit composed of a combination of a transistor and a Zener diode, and 11 denotes a voltage level generating circuit in which a Zener diode is inserted on the collector side of a control transistor driven by the input voltage detecting circuit 10. is there. A feedback circuit 12 is provided from the voltage level generation circuit 11 to the input voltage detection circuit 10 so as to have a hysteresis characteristic.

TR is a transistor which receives the output of the input voltage detecting circuit 10 and the voltage level generating circuit 11 and generates an output voltage Vo. RL is a resistor connected between the emitter and the common line. The output voltage Vo is taken out from the emitter of the control transistor TR.

According to the configuration of the present invention, it is possible to provide a hysteresis characteristic having a difference between the voltage at which the auxiliary power supply is turned on and the voltage at which the auxiliary power supply is turned off, thereby simplifying the circuit and reducing the mounting space, and An auxiliary power supply circuit for a power supply circuit that can be reduced in cost can be provided.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a circuit diagram showing an embodiment of the present invention. The same components as those in FIG. 7 are denoted by the same reference numerals. In the figure, R1, zener diode _DZ1 , and resistor R2 are a series circuit connected between input voltages. TR10 is a PNP-type transistor whose base is connected to a connection point between the resistor R1 and the Zener diode _DZ1 . The input voltage detection circuit 1
0 (see FIG. 1).

TR11 is a control transistor of NPN type. The collector of the transistor TR10 is connected to the base of the transistor TR11 via the resistor R8.

D _Z2 is a Zener diode connected between the base and the common line of the transistor TR11, R9 is a resistor connected between the base and the emitter of the transistor TR11, and RL is connected between the emitter and the common line of the transistor TR11. Resistance.

D _Z3 is a Zener diode, and the other end is connected to the collector of the transistor TR11. The zener diode D _Z3 constitutes a voltage level generating circuit 11 (see FIG. 1). Then, feedback is made from the anode side of the Zener diode D _Z3 to one end of the resistor R1 via the resistor R3. That is, the resistor R3 is
Of the feedback circuit 12. The operation of the circuit thus configured will be described as follows.

In this circuit, the input voltage is detected by a PNP transistor and a Zener diode, instead of the conventional configuration including two NPN transistors, and a Zener diode D _Z3 is connected to the collector side of the control transistor TR11 of the auxiliary power supply circuit. The feedback voltage for adding the hysteresis characteristic has been obtained.

Resistances R1, R2, Zener diode D _Z1
Further, the voltage is detected by an input voltage detection circuit including the transistor TR10. The ON voltage Von is expressed by the following equation. Von = _VZ1 + ( _VBE1 / R1) * (R1 + R2) (3) Here, _VBE1 is a base-emitter voltage of the transistor TR10. When the transistor TR10 is turned on at this voltage, the Zener diode D _Z2 is connected via the resistor R8.
Since the current flows to the base of the transistor TR11, the transistor TR11 is turned on, and the output voltage Vo for the auxiliary power supply rises.

When the transistor TR11 is turned on, a current flows through the collector, so that a voltage V _Z3 is generated at the Zener diode D _Z3 . This generated voltage depends on the transistor T
Feedback is fed back to the base side of R10 via a resistor R3. At this time, due to the potential difference generated in the resistor R3, the resistance R
The current also flows through the resistor R1, and the current flowing through the resistor R1 is
Since the 1 side and the R3 side are combined and the current of the difference flows through the resistor R2 side, the off voltage Voff is expressed by the following equation.

[0026]

(Equation 2)

FIG. 3 is an explanatory diagram of the hysteresis characteristic according to the present invention. When the input voltage Vin is gradually increased and reaches the detection voltage Von, the circuit is turned on and the output voltage Vo is output.
Stand up. At this time, a voltage drop occurs in the circuit due to the current flowing in the converter circuit, and the circuit voltage becomes the detection voltage Von
Than the detection voltage Vo of the detection circuit.
Since ff is also reduced, the circuit does not turn off.
When Vin in the figure becomes Von, a voltage is generated, and Vin is generated.
Falls to Voff, no voltage is generated.
The width VH between Von and Voff at this time becomes hysteresis.

As described above, according to the present invention, it is possible to provide an auxiliary power supply circuit for a power supply circuit capable of simplifying a circuit, reducing a mounting space, and reducing the cost. FIG. 4 is a diagram showing a configuration example of a converter circuit using the present invention. In the figure, reference numeral 30 denotes an auxiliary power supply circuit according to the present invention, which supplies an operation voltage to a control circuit 40. The output of the auxiliary power supply circuit 30 is connected to a smoothing capacitor C3.

After the input voltage Vin is smoothed by the smoothing capacitor C1, a voltage is supplied to the conversion transformer T1 and the switching transistor TR12. The switching transistor TR12 is supplied with a switching control signal from the control circuit 40, and controls the ON time of the switching transistor TR12 such that the output voltage Vout is constant.

At this time, a high-frequency alternating current is generated on the secondary side of the conversion transformer T1. This high-frequency AC is connected to a diode D
1. Full-wave rectification by D2 and conversion to DC. This DC voltage becomes the output voltage Vout via the smoothing coil L1. C2 is a smoothing capacitor connected to the output terminal.

The output voltage Vout of the converter circuit is monitored by the control circuit 40. Then, the on-time (conduction time) of the switching transistor TR12 is controlled so that the output voltage Vout becomes constant.

According to the present invention, even if the input voltage Vin of the primary side circuit decreases due to the current flowing to the load, the operation is continued without turning off the auxiliary power supply due to the hysteresis characteristic.

FIG. 5 is a diagram showing a configuration example of a series regulator circuit using the present invention. The same thing as FIG.
The same reference numerals are given. In this embodiment, FIG.
Is used as an output transistor. Reference numeral 10 denotes an input voltage detection circuit for detecting an input voltage, and its configuration is the same as that shown in FIG. When the input voltage detection circuit 10 rises, the voltage from the transistor TR10 is supplied to the base of the control transistor TR11 via the resistor R8.

On the other hand, IC1 is an operational amplifier for generating a control signal, takes in an output voltage as a divided voltage between the resistors R11 and R12, and outputs the reference voltage generated by the resistor R10 and the Zener diode _DZ4. Compare with According to the result of the comparison, the control transistor TR11
Control signal to the base of As a result, the output Vout of the control transistor TR11 is kept constant.

[0035]

As described in detail above, according to the present invention, there is provided an auxiliary power supply circuit for a power supply circuit, comprising: an input voltage detection circuit comprising a combination of a transistor and a Zener diode; On the collector side of the control transistor driven by the circuit, by providing a voltage level generating circuit in which a zener diode is inserted, and a feedback circuit for obtaining a hysteresis characteristic from the voltage level generating circuit to the input voltage detecting circuit, It is possible to provide an auxiliary power supply circuit for a power supply circuit capable of simplifying a circuit, reducing a mounting space, and reducing cost.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a hysteresis characteristic.

FIG. 4 is a diagram showing a configuration example of a converter circuit using the present invention.

FIG. 5 is a diagram showing a configuration example of a series regulator circuit using the present invention.

FIG. 6 is a diagram showing a conventional auxiliary power supply circuit.

FIG. 7 is a diagram showing a configuration example of a conventional circuit having hysteresis.

[Explanation of symbols]

 Reference Signs List 10 input voltage detection circuit 11 voltage level generation circuit 12 feedback circuit

Claims (1)

[Claims] 1. An auxiliary power supply circuit for a power supply circuit, comprising: an input voltage detection circuit including a combination of a transistor and a zener diode; and an input voltage detection circuit provided on a collector side of a control transistor driven by the input voltage detection circuit. An auxiliary power supply circuit for a power supply circuit, comprising: a voltage level generation circuit having a zener diode inserted therein; and a feedback circuit for obtaining hysteresis characteristics from the voltage level generation circuit to the input voltage detection circuit.