JPS60243714A - Constant voltage circuit - Google Patents

Abstract

PURPOSE:To hold the normal operation of a constant voltage circuit even if the peripheral temperature is low by forming a transistor (Tr) for interrupting a starting part after the start of a voltage control part independently of a Tr for a differential switching circuit. CONSTITUTION:In the constant voltage circuit, a reference voltage circuit consists of Trs Q1-Q4 and resistors R1-R3, a constant current circuit consists of Trs Q5-Q6 and an output circuit consists of a TrQ8 and resistors R4-R5. In this case, a starting circuit is constituted of a constant voltage Zener diode D1, the Trs Q7-Q8 and the resistors R6-R7. Consequently, the collector current IC7 of the TrQ7 is determined by the TrQ7, the resistor R7 and the constant voltage Zener diode D1 independently of said reference voltage circuit. At an instantaneous time of a starting, output current I0 from an output terminal (b) can be optionally set up, and even if the constant voltage circuit is started by allowable current at a low temperature time, the circuit can be normally operated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a constant voltage circuit that can operate normally even at low temperature and allowable current.

(Conventional Example) An example of a conventional circuit is shown in FIG. Q + + Qz t
Q3 +Q4, Qs, Qe, Q7, Qs are transistors, 1W 2. 3. R4, R, 6 are resistors, Dl is a constant voltage Zener diode, a is an input terminal, b
is the output terminal, C is the ground terminal, VCC is the input voltage sRL
is the load resistance. In such a constant voltage circuit, the reference voltage circuit includes transistors QI, Q2 . Q3. The starting circuit consists of a constant voltage Zener diode D, a transistor Q7 and a resistor R, the constant current circuit consists of a transistor Qs + Q6, and the output circuit consists of a transistor Q8 and a resistor R. 4. It consists of R8.

Next, the operation of the conventional circuit shown in FIG. 1 at startup will be briefly described.

When input voltage VCC is applied to input terminal a, constant voltage Zener diode DI becomes operational via resistor R6. When the constant voltage Zener diode l)1 is activated, a current flows through the transistor Ql+Qs+Q7 and the resistor R1. These transistors Ql, Q5 . The current flowing through Q7 and resistor R1 supplies the base current of transistor QB and the collector current of transistor Q3 by a constant current circuit consisting of transistors Qs and Q6. By supplying the base current to the transistor Qs, a current flows through the transistor Q8, the resistor R41, and the load resistor RL. The base potential of the transistor Q4 rises due to the current flowing through the transistor Qs, the resistor R4°R5, and the load resistor FLL, and when the base potential of the transistor Q4 becomes higher than the base potential of the transistor Q7, the transistor Q7 becomes in an interrupted state. However, since the transistor Q4 causes current to flow through the transistor Q+rQ2+Q3, the output voltage Eh-VOUT at the output terminal is equal to the base potential of the transistor Q4, which is the output of the reference voltage circuit, and the resistance. , R6 becomes stable. The base potential of this transistor Q4 is determined by the base-emitter voltage of the transistors Qs and Q4 and the voltage drop across the resistor fL.

Therefore, the stable output voltage v at the output terminal
ou'r is expressed by the following equation (1).

However, the pace of transistor Qs
Emitter voltage VDl4: Base Φ emitter voltage of transistor Q4 ■R□: Voltage across the resistor R, or output current IOUT flowing through the load resistor RL, is expressed by the following equation (2).

Here, from equation (2), the allowable load resistance at the allowable output current IOUTMAX is set as RLMIN, and on the other hand, the output current IO flowing out from the output terminal at the instant of startup is the transistor Q
When s and Qa have the same characteristics and the base current is ignored, it is expressed by the following equation (3).

I o = IC7 be done.

・・・・・・(4) However, VDl: Cathode potential of constant voltage Zener diode Dl VDl7: Voltage between base and emitter of transistor Q7 VBEI: Voltage between base and emitter of transistor Q1 Here, generally the current of the transistor Since the amplification factor has a positive temperature coefficient of .degree. C., the current amplification factor hrgs of the transistor Q8 decreases at low temperatures, and according to equation (3), the output current flowing out from the output terminal at the instant of startup decreases by 1.degree. When the output current ■o decreases and falls below the allowable output current IOUTMAX, the base potential of the transistor Q4 becomes the transistor Q?
, and the transistor Q7 is not cut off, so the output voltage VOUT at the output terminal does not become stable as expressed by equation (1).

"C It will not work properly.

To ensure that the output current IO at low temperature does not fall below the allowable current IOUTMAX k, the current amplification factor of transistor Q8 h F
In order to compensate for the decrease in EI, the collector current c7 of the transistor Q7 can be increased. However, the collector current IC of transistor Qγ? In order to increase VDl + VBEI + VBE from equation (4)
Since S +VBEt is a nearly constant value, the resistance “I+
Although it is possible to reduce the voltage 2, a problem arises in that the output voltage V OUT at the stable blade terminal expressed by equation (1) changes.

As described above, the conventional circuit configuration has the disadvantage that it does not operate normally when started at an allowable current at low temperatures.

(Problems to be Solved by the Invention) An object of the present invention is to provide a voltage circuit that can ensure normal operation even when the ambient temperature is low.

(Means for Solving Problems) According to the present invention, a voltage control section, a starting section that starts the voltage control section when a voltage is applied, a transistor constituting this starting section, and a differential switching circuit are configured, The voltage control section includes a transistor that cuts off the startup section after startup, and the transistor added for the differential switching circuit with the voltage control section is a constant voltage circuit that is a different transistor from the transistor that constitutes the voltage control section. get.

(Example) Next, the present invention will be explained in more detail with reference to the drawings.

FIG. 2 shows an embodiment of the present invention. Q++Qz+Q3.
Q4. Q5. Q6. Q7. Q8. Q9 is a transistor,
几, , R, , R3, R4, R5, R6 are resistances, D.

is a constant voltage Zener diode, a is an input terminal, b is an output terminal, C is a ground terminal, Vcc is an input voltage s, and RL is a load resistance. In this embodiment, the reference voltage circuit, constant current circuit, and output circuit have the same configuration as in FIG. 1, but the startup circuit includes a constant voltage diode DI and a transistor Q? ,Q
S and resistance ratio6. It is composed of 几7. Note that elements having the same symbols and numbers as in FIG. 1 above indicate the same elements.

Next, the operation of the constant voltage circuit shown in FIG. 2 at startup will be explained. When input voltage VCC is applied to input terminal a, resistor R6
The constant voltage Zener diode D1 is brought into operation via the . When the constant voltage Zener diode D is activated, a current flows through the transistor Q7 and the resistor R7. The current flowing through the transistor Q7 and the resistor R1 supplies the base current of the transistor Qs and the collector current of the transistor Q3 by a constant current circuit consisting of the transistors Qs and Qa. By supplying base current to transistor Q@, transistor Q8 and resistance ratio 4+R
5 and the load resistance R, current flows through it.

Transistor Q8 and resistor FL4. The base potential of the transistor Q4 rises due to the current flowing in proportion to R and the load resistance ratio, and a base current is supplied to the transistor Q4. By supplying the base current to the transistor Q4, the transistor Q r +Qz +Q3 and the resistor R
,,A current flows through R2 and 几3. Transistor Qs,
(h, Q4 and resistance ratio, , R, , , The base potential of transistor Q9 rises due to the current flowing through R3.

When the base potential of transistor Q9 becomes higher than the base potential of transistor Q7, transistor Q7 becomes disconnected, and the output voltage V OUT at the output terminal becomes equal to the base potential of transistor Q4, which is the output of the reference voltage circuit, and resistor R4 + 几. Therefore, it becomes stable at a potential determined by °C. This stable output voltage V OUT at the output terminal is expressed by the following equation (5).

-0几A+R8, -------++ , , - Also, the output current I OUT flowing through the load resistor RL is expressed by the following equation (6).

0UT I OUT ”” −””・°(6) Here, from equation (6), let the allowable load resistance RLMIN at the allowable output current I OUTMAX, and the output current flowing out from the output terminal at the moment of startup is as follows. It is expressed by formula (7).

IO=IC? X hvvs (7)
Further, the collector current ①C7 of the transistor Q1 is expressed by the following equation (8).

'l' DI −VBEl 1c = □ ・・・・・・(8) 7 From this, the collector current Ic7 of the transistor Q7 is
It is determined by the transistor Q7, the resistance ratio 7, and the constant voltage Zener diode D, and can be set independently of the reference voltage circuit.

Therefore, even if the hFE of the transistor Q8 decreases at low temperatures, by setting the collector current Ic7 of the transistor Q7 to an appropriate value, the output current I flows out from the output terminal at the instant of startup. can be set arbitrarily, and normal operation can be achieved even when started at the allowable current at low temperatures.

As described above, according to the present invention, it is possible to realize a constant voltage circuit that can operate normally even when started at an allowable current at low temperatures.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional constant voltage circuit, and FIG. 2 is a circuit diagram of a constant voltage circuit according to an embodiment of the present invention.几, ~R7 and RL...Resistance, Qt~Q,...
...Transistor, DI """ Constant voltage Zener diode, a...Input terminal, b...Output terminal, C...Ground terminal. Agent: Patent attorney Hara Shinimo 2 v α (input terminal),!

Claims (1)

[Claims] An input terminal is connected to the cathode of the constant voltage Zener diode via a first resistor, an anode of the constant voltage Zener diode is connected to a reference potential terminal, and a base of the first transistor is connected to the cathode of the constant voltage Zener diode. the collector of the first transistor is connected to the input of a constant current circuit; the emitter of the first transistor is connected to a ground terminal via a second resistor; the emitters of two transistors are connected, the collectors of the second transistors are connected to the input terminals, the paces of the second transistors are connected to the first output of the reference voltage circuit; 2 is connected to the input of the constant current circuit, the output of the constant current circuit is also connected to the input of the output circuit, and the input of the reference voltage circuit is connected to the first output of the output circuit (-1 A constant voltage circuit characterized in that a second output of the output circuit is used as an output terminal.