JPS5914818Y2 - DC voltage stabilization circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to DC voltage stabilization circuits such as switching regulators or sinose regulators, and in particular proposes a device that can effectively protect the control transistors from destruction due to DC overload current. It is something to do.

Referring to FIG. 1, a reference example of a DC voltage stabilizing circuit that can achieve this purpose will be described below.

The example shown in FIG. 1 is a switching regulator.

1 is an unstable DC power supply, which rectifies the commercial AC voltage from input terminals 4a and 4b with a rectifier circuit 3, smooths it with a smoothing capacitor 4, and outputs it to + and - side output terminals 2.
The structure is such that an unstable DC voltage can be obtained between a and 2b.

35a and 35b are output terminals for the stabilized DC voltage on the + side and the - side.

A control transistor 5 whose collector and emitter are connected in series is provided between one end 2a of the unstable DC power supply 1 and one of the output terminals 35a of the stabilized DC voltage.

The control transistor 5 is a switching transistor, and is composed of a Darlington-connected NPN transistor 6 and a PNP transistor.

The collector of the transistor 6 is connected to the output terminal 2a, and the emitter is connected to the output terminal 35a.

The collector of transistor 7 is connected to the base of transistor 6, and the emitter of transistor 7 is connected to output terminal 2a.

36 is a smoothing circuit, which is composed of a coil (inductor) 33 and a capacitor 26, in which the emitter of the transistor 6 is connected to the output terminal 35a through the coil 33, and the capacitor 26 is connected in parallel between the output terminals 35a and 35b. has been done.

Further, 34 is a diode for emitting energy of the coil 33, and its cathode is connected to the emitter of the transistor 6, and its anode is connected to the output terminal 2b.

8 is a reference voltage element, which in this example is a Zener diode.

A comparison circuit 9 compares the detected voltage related to the stabilized DC voltage with the reference voltage of the reference voltage element 8, and controls the control transistor 5 based on the comparison output.

In this example, the comparison circuit 9 has a differential circuit configuration having PNP type transistors 10 and 11, the emitters of the transistors 10 and 11 are connected to the output terminal 2a through the resistor 12, and the collector of the transistor 10 is connected to the output terminal 2a. 2b, and the collector of the transistor 11 is connected to the output terminal 2b through a load resistor 13.

The cathode of the Zener diode 8 is connected to the base of the transistor 10, and the anode is connected to the output terminal 2b.

Further, the cathode of the Zener diode 8 is connected to the output terminal 2a through a resistor 16.

22 is a resistive voltage divider for dividing the stabilized DC voltage (load voltage), which is disconnected from the series circuit of resistor 23, potentiometer 24, and resistor 25, and connected between output terminals 35a and 35b. ing.

A movable intermediate terminal of the potentiometer 24 is connected to the base of the transistor 11.

The switching of the control transistor 5 is controlled by the comparison output of the comparison circuit 9. In this example, an NPN type transistor 14 is provided, and its emitter is connected to the output terminal 2b. , its collector is connected to the base of transistor 7 via resistor 15, and the base of transistor 14 is connected to the collector of transistor 11.

In this switching regulator, the output terminal 35 is
A detection voltage obtained by dividing the DC voltage between a and 35b by the resistive voltage divider 22 is supplied to the base of the transistor 11 of the comparator circuit 9, and the reference voltage of the Zener diode 8 is supplied to the base of the transistor 10. Voltages are compared.

Then, when the detection voltage becomes higher than the reference voltage, the transistor 11 is turned off, which causes the transistor 14 to turn off.
is also turned off.

Therefore, transistor 7 and transistor 6 are also turned off.

Further, when the detection voltage becomes lower than the reference voltage, the transistor 11 is turned on, which turns on the transistor 14, and both the transistor 7 and the transistor 6 are turned on.

Therefore, in this switching regulator, the control transistor 5 is turned on and off depending on the magnitude of the detected voltage and the reference voltage, and the pulse voltage obtained by turning on and off is smoothed by the smoothing circuit 36 and output to the output terminals 35a and 35. b is output as a stabilized DC voltage.

Further, a self-holding switch circuit 1 is connected in parallel to the reference voltage element 8.
7 is connected, and the output terminals 35 a and 35 b
An overcurrent detection circuit 27 is provided for detecting that the DC load current flowing through the load connected between the two has exceeded a predetermined value.

In this example, the self-holding switch circuit 17 is composed of a PNP transistor 18 and an NPN transistor 19 connected in a thyristor configuration, and a resistor 20.

That is, the emitter of transistor 18 is the same as transistor 10.
A resistor 20 is connected between the base and emitter of the transistor 18, the base of the transistor 18 is connected to the collector of the transistor 19, the collector of the transistor 18 is connected to the base of the transistor 19, and the resistor 20 is connected between the base and emitter of the transistor 18. The emitter is connected to the output terminal 2b.

The overcurrent detection circuit 29 has an output terminal 2b and an output terminal 35b.
A low resistance resistor (0, 2
2Ω) 28 and an integrating circuit 29.

The voltage drop generated across the resistor 28 due to the current flowing through it is applied to the resistor (220Ω) 31 and the capacitor (10Ω).
0 μF) by an integrating circuit 29 consisting of 30,
The voltage is divided by a voltage divider from the series circuit of resistors 32 and 21 and supplied between the base and emitter of transistor 19.

The resistor 21 is a semi-fixed resistor and can be used for sensitivity adjustment, but this resistor 21 may be omitted.

The integrating circuit 29 is provided to prevent the self-holding switch circuit 17 from operating due to inrush.

In this switching regulator, the output terminal 35
When a load is connected between a and 35 b, and the DC load current exceeds a predetermined value, the voltage across the overcurrent detection resistor 28 also exceeds a predetermined voltage, which turns on the transistor 19, which is normally off. Therefore, the transistor 18, which is normally off, is also turned on, and both ends of the Zener diode 8 are substantially shorted by this transistor 19, and the base potential of the transistor 10 is lowered and turned on, so that the transistor 11 is turned off.
As a result, transistor 5 is turned off.

In this case, even if the DC load current flowing through the overcurrent detection resistor 28 falls below a predetermined value, the self-holding switch circuit 1
Since transistor 7 remains on, transistor 5 remains off.

To cancel this problem, simply turn off the unstable DC power supply and then turn it on again.

That is, in this case, it is sufficient to temporarily cut off the supply of commercial AC voltage to the input terminals 4a and 4b.

Therefore, the present invention aims to further simplify the circuit of the reference example shown in Figure 1 and propose a DC voltage stabilizing circuit that can effectively protect the control transistor from destruction due to DC overload current. be.

Next, an embodiment of the present invention will be described with reference to FIG.

The embodiment of FIG. 2 is a partial improvement of the circuit of FIG. 1, and only a portion thereof is shown.

In the example shown in FIG. 2, instead of the self-holding switch circuit 17 consisting of transistors 18, 19 and resistor 20 as shown in FIG.
and a resistor 21.

That is, the collector of transistor 19 is directly connected to the base of transistor 10, and the collector of transistor 10 is connected to the base of transistor 19.

The emitter of the transistor 19 is connected to the output terminal 2b, and a resistor 21 is connected between its base and emitter.

Note that, as in FIG. 1, the comparison output of the comparison circuit 9 is supplied from the collector of the transistor 11 to the base of the transistor 14.

In the circuit shown in FIG. 2 as well, the overcurrent detection resistor 28
When a DC load current of a predetermined value or more flows through transistor 1
9 is turned on, therefore transistor 10 is also turned on, transistor 11 is turned off, and control transistor 5 is turned off.

In this case as well, even if the overcurrent flowing through the overcurrent detection resistor 28 becomes less than a predetermined value, current continues to flow through the transistor 1o, so that a deep bias is applied to the transistor 19 by the voltage across the resistor 21. The transistor 10 still remains on, and therefore the control transistor 5 also remains off.

According to the present invention described above, one transistor 18 of the pair of transistors 18 and 19 of the self-holding switch circuit 17 having a thyristor configuration in the circuit shown in FIG. A self-holding switch circuit having a thyristor configuration in which the second and third transistors 10 and 19 are used also as one of a pair of dynamic transistors (second and first transistors) 10 and 11 (second transistor) 10. 17, the circuit is simplified by one transistor compared to the circuit shown in Figure 1, and even if an excessive DC current attempts to flow into the load, it is immediately detected and the control transistor is switched on. Since the control transistor is turned off, it is possible to obtain a DC voltage stabilizing circuit that can effectively avoid destruction of the control transistor due to overload DC current.

In the above embodiment, the present invention is applied to a switching regulator, but it may also be applied to a series regulator.

In that case, the control transistor operates as a variable impedance element, but the impedance of the control transistor is maximized at the time of overload DC current.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a reference example of a DC voltage stabilizing circuit, and FIG. 2 is a circuit diagram showing a main part of an embodiment of the present invention. 1 is an unstable DC power supply, 2a and 2b are its output terminals, 5 is a control transistor, 8 is a reference voltage element, 9 is a comparator circuit, 10.11 is a differential transistor (second and first transistor), 17 1 is a self-holding switch circuit, 19 is a transistor (third transistor), and 27 is an overcurrent detection circuit.

Claims (1)

[Scope of utility model registration request] A control transistor whose collector and emitter are connected in series between one end of the unstable DC power source and one of the output terminals of the stabilized DC voltage, a reference voltage element, and a detection voltage related to the stabilized DC voltage. and a reference voltage of the reference voltage element, respectively, are supplied to differential first and second transistors for comparison, and the control transistor is controlled based on the comparison output; A self-holding switch circuit connected in parallel to the voltage element, and an overcurrent detection circuit that detects when the DC load current flowing through the load connected between the output terminals exceeds a predetermined value, The self-holding switch circuit includes the second transistor and the third transistor connected to form a thyristor, and turns on the self-holding switch circuit when the DC load current exceeds the predetermined value. A DC voltage stabilizing circuit characterized in that the control transistor is turned off when the control transistor is turned off.