JPH02170212A - Stabilizing dc power circuit - Google Patents

Abstract

PURPOSE:To prevent the destruction of a 1st transistor TR by so securing a constitution that the output voltage drops when a short circuit state is pro duced between a DC output terminal and a common terminal and at the same time the current of the 1st TR is reduced. CONSTITUTION:In an overcurrent state, the base current of a 1st TR Q1 increases and a 2nd resistance R2 has its increased voltage drop together with a 5-th TR Q5 turned on respectively. Thus the base current of a 2nd TR Q2 is limited and a load current is also limited. When the output voltage is dropped for limit of the load current, a 4th TR Q4 is turned on and the base currents of the TR Q2 and a 3rd TR Q3 are reduced. At the same time, the base current and the collector current (load current) of the TR Q1 is also reduced. Thus it is possible to protect the drop and draw-in type overcurrents without detecting directly the load current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transistor stabilized DC power supply circuit equipped with a current limiting circuit of the bottom and current drawing type.

BACKGROUND ART As a method for limiting overcurrent when a load is short-circuited in a transistor-stabilized DC power supply circuit called a series regulator, there is a method of suppressing the load current using drooping characteristics or fold-back characteristics.

[Problem to be solved by the invention]

However, since the current detection resistor connected in series with the load current path is configured to cause drooping or fold-back operation when an overcurrent is detected, this does not result in large power loss. , the circuit configuration became complicated.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a stabilized DC power supply circuit that can perform drooping and pull-in type overcurrent protection without directly detecting the load current.

[Means for Solving the Problems] To achieve the above object, the present invention includes a first transistor whose emitter is connected to a DC input terminal and whose collector is connected to a DC output terminal, and a terminal common to the output terminal. a voltage detection circuit that detects a voltage between the reference voltage source and the reference voltage source; a reference voltage source; , a base connected to the output terminal of the error amplifier,
a second transistor having a collector connected to the input terminal; a first resistor connected between the emitter of the second transistor and the common terminal; and a first resistor having a base connected to the second transistor.
a third transistor connected to the emitter of the transistor and having a collector connected to the base of the first transistor; a second resistor connected between the emitter of the third transistor and the common terminal; , a fourth transistor whose collector or emitter is connected to the base of the second transistor, and whose base is connected to the emitter of the second transistor, and the emitter of the fourth transistor is connected to the collector and the DC output terminal. a fifth resistor, the collector of which is connected to the base of the second transistor, the emitter of which is connected to the common terminal, and the base of which is connected to the emitter of the third transistor; The first transistor is configured such that when a short circuit occurs between the DC output terminal and the common terminal, the output voltage drops and the current of the first transistor decreases. This is related to a stabilized DC power supply circuit featuring characteristics.

[For production]

In the stabilized DC power supply circuit of the present invention, when an overcurrent condition occurs, the base Na of the first transistor increases and the second
The voltage drop across the resistor increases, and the fifth transistor is driven on. This limits the base current of the second transistor and also limits the load current. When the output voltage is drooped to limit the load current, the fourth transistor is driven on, the base currents of the second and third transistors decrease, and the base current and collector current of the first transistor (load current ) will also decrease.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS A transistor stabilized DC power supply circuit according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

A DC power supply 1 is connected between a power supply input terminal 2 and an input side common terminal (ground terminal) 3, and a load 4 is connected to a DC output terminal 5.
and the output side common terminal (ground terminal) 6. The first transistor Q+ for main control is connected in series to the power supply line 7 between the input terminal 2 and the output terminal 5. Note that the first transistor Q1 is of a pnp type, and its emitter is connected to the input terminal 2.

f? is connected between the output terminal 5 and the common terminal 6. :, voltage division point IC1i"l of voltage detection resistor 8.9: error amplifier 1
It is connected to one input terminal of 1. error amplifier 11
The other input terminal of is connected to the cathode of a Zener diode 130 for a reference voltage source connected between the input terminal 2 and the common terminal 6 via the constant current source 2. The output terminal of the error amplifier 11 is connected to the base of the second transistor Q2 of npnffil. The collector of the second transistor Q2 is connected to the power supply line 7, and the emitter is connected to the ground line 14 via the first resistor R1, as well as to the base of the third npn transistor Q3. . The collector of the third transistor Q is connected to the base of the first transistor Q1, and the emitter is connected to the ground line 1 through a second resistor R2.
Connected to 4.

The base of a fourth transistor Q4 of npn type is connected to the base of the third transistor Qs, and the collector is connected to the base of the second transistor Q! The emitter is connected to the base of the third
It is connected to the output terminal 5 via the resistor R3. A constant current source 15 is connected between the power supply line 7 and the base of the second transistor Q2. The base of the fifth npn transistor Q5 is connected to the emitter of the third transistor Q3, the collector is connected to the base of the second transistor (h), and the emitter is connected to the ground line 16.

[Made by Kin]

In the circuit of FIG. 1, when the load 4 is normal, the fourth and fifth transistors Q4 and Q5//'i are in an off state. The error amplifier 11 compares the voltage detected by the output voltage detection resistor 8.9 with the voltage applied based on the Zener diode 13, and outputs a voltage corresponding to the difference. The current l of the constant current source 15 flows into the error amplifier 11 and the base of the second transistor Q2. When the output voltage of the error amplifier 11 increases due to a decrease in the output voltage, the base current and collector current of the second transistor Q2 also increase, and the base current R and collector current of the third transistor Q3 also increase. As a result, the base current IB of the first transistor Q10 also becomes large and the output voltage is stopped. When the output voltage becomes higher than the predetermined value, the operation is opposite to that when the output voltage becomes lower.

When load 4 is short-circuited, the output voltage decreases and error amplifier 1
The output of 1 is loud. Therefore, the pace current of the first transistor Q1 increases and the voltage drop across the second resistor R2 becomes large, turning on the fifth transistor Q5. Accordingly, the second and third transistors Q2, Q3
base current is limited. If the base current of the first transistor Ql at this time is IB t -IX and the base-emitter voltage of the transistor Qs of 5 is vBKs, then the following equation holds true.

IB1=VBES/r2 Note that the value is obtained by multiplying the collector current of the first transistor Q1 by the current amplification factor hFK. When the output voltage drops to Vl in FIG. 3, the fourth transistor Q4 turns on and the fifth transistor Q5 turns off. This voltage v1 is applied to the third and fourth transistors Q3.
, Q4's base-emitter voltages are VY1 and vBE4, it can be expressed by the following equation.

■I = vBEj +"B15-VBE4 When the fourth transistor Q4 is turned on due to a load short circuit, the equivalent circuit shown in Fig. 2 is established. As a result, the second transistor Q
The second base current bypasses the fourth transistor Q4, resulting in a decrease in the first transistor Q10 pace current supplied by the third transistor Q3, resulting in the pull-in operation shown in section B of FIG. The base current 'B2 after the pull-in operation in FIG. 3 can be expressed by the following equation.

vBEj +”X R3”” “BI3 +”B2R2
"B2 = "B14- vBza"'XR3)/
``As described above, according to the circuit of FIG. 1, overcurrent protection can be achieved by detecting the base current 3 of the first transistor Q+ instead of detecting the load current.At this time, Since not only the droop but also the load current is reduced, destruction of the first transistor Q1 can be reliably prevented.

[Modified example]

The present invention is not limited to the embodiments described above, but may be modified. For example, connecting the emitter of the fourth transistor Q4 to the base of the second transistor Q2,
The collector may be connected to resistor R3. In this way, since the collector and base of the fourth transistor Q4 are arranged in parallel with the output terminals 5 and 6, the withstand voltages of the fourth transistor Q4 are equivalently equalized.
It becomes possible to obtain a high output voltage.

Further, part or all of the resistor 8 may be used in place of the third resistor R3.

Further, the present invention can also be applied to a system in which the constant current source 15 is not provided.

Further, the reference voltage source does not need to be composed only of the Zener diode 13, and a voltage regulating circuit may be further added to obtain the reference voltage.

〔Effect of the invention〕

As described above, according to the present invention, the current at the time of short circuit can be significantly reduced with a relatively simple circuit configuration, and destruction of the first transistor can be prevented.

[Brief explanation of the drawing]

The first part is a circuit diagram showing a transistor stabilized DC power supply circuit according to an embodiment of the present invention, the second part is an equivalent circuit diagram when the load in Fig. 1 is short-circuited, and the third part is the circuit diagram in Fig. 1. FIG. 3 is a characteristic diagram showing the relationship between the base current and the output voltage when the load is short-circuited. 2.6...Input terminal, 4...Load, 5, 6...
・Output terminal, 17...Error amplifier, 15...Constant II
I flow source, Ql - Q: t + Ql + Q4 + Qs・
...Transistor. Agent Hajime Takano-I B

Claims (1)

[Scope of Claims] [1] A first transistor whose emitter is connected to a DC input terminal and whose collector is connected to a DC output terminal, and a voltage detection circuit that detects a voltage between the output terminal and a common terminal. a reference voltage source; an error amplifier that outputs a voltage corresponding to the difference between the detected voltage obtained from the voltage detection circuit and the reference voltage of the reference voltage source; a base connected to the output terminal of the error amplifier; a second transistor having a collector connected to the input terminal; a first resistor connected between the emitter of the second transistor and the common terminal; and a base connected to the emitter of the second transistor. a third transistor having a collector connected to the base of the first transistor; a second resistor connected between the emitter of the third transistor and the common terminal; a fourth transistor connected to the base of the second transistor, the base of which is connected to the emitter of the second transistor; and a fourth transistor connected between the emitter or collector of the fourth transistor and the DC output terminal. a fifth transistor, the collector of which is connected to the base of the second transistor, the emitter of which is connected to the common terminal, and the base of which is connected to the emitter of the third transistor; A stabilized DC power supply characterized in that the output voltage drops and the current of the first transistor decreases when a short circuit occurs between the DC output terminal and the common terminal. circuit.