JPH0561654B2 - - Google Patents

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 ₁ , Q ₂ , Q ₃ ,
Q ₄ , Q ₅ , Q ₆ , Q ₇ , Q ₈ are transistors, R ₁ , R ₂ ,
R ₃ , R ₄ , R ₅ , R ₆ are resistors, D ₁ is a constant voltage Zener diode, a is an input terminal, b is an output terminal, c is a ground terminal, V _CC is an input voltage, and R _L is a load resistance. .
In such a constant voltage circuit, the reference voltage circuit consists of transistors Q ₁ , Q ₂ , Q ₃ , Q ₄ and resistors R ₁ , R ₂ , R ₃ , and the starting circuit consists of a constant voltage Zener diode.
The constant current circuit is made up of transistors _{Q5 and Q6} , _and the output circuit is made up of transistor _Q8 and resistors _{R4 and R5} .

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

When input voltage V _CC is applied to input terminal a, constant voltage Zener diode D ₁ becomes operational via resistor R ₆ . When the constant voltage Zener diode D ₁ becomes operational, the transistors Q ₁ , Q ₅ , Q ₇
and current flows through resistor _R1 . The current flowing through these transistors Q ₁ , Q ₅ , Q ₇ and resistor R ₁ supplies the base current of transistor Q ₈ and the collector current of transistor Q ₃ by a constant current circuit consisting of transistors Q ₅ and Q ₆ . . By supplying the base current to the transistor Q ₈ , current flows through the transistor Q ₈ , the resistors R ₄ and R ₅ , and the load resistor R _L. Transistor Q ₈ and resistors R ₄ , R ₅ and load resistance
The base potential of the transistor Q ₄ rises due to the current flowing through R _L , and when the base potential of the transistor Q ₄ becomes higher than the base potential of the transistor Q ₇ , the transistor Q ₇ is turned off. However, since current is passed through transistors Q ₁ , Q ₂ , and Q ₃ by transistor Q ₄ , the output terminal b
The output voltage V _OUT at is the base potential of the transistor Q ₄ which is the output of the reference voltage circuit and the resistors R ₄ and R ₅
It becomes stable at a potential determined by . The base potential of this transistor _Q4 is determined by the base-emitter voltage of transistors _Q3 and _Q4 and the voltage drop across resistor _R2 .

Therefore, the stable output voltage V _OUT at the output terminal b is expressed by the following equation (1).

V _OUT = R ₄ + R ₅ / R ₄ × (V _BE3 + V _BE4 + V _R2 ) ...(1) where, V _BE3 : Base-emitter voltage of transistor Q ₃ V _BE4 : Base-emitter voltage of transistor Q ₄ V _R2 : Voltage across resistor R ₂ Also, the output current I _OUT flowing through load resistor R _L is expressed by the following equation (2).

I _OUT = V _OUT / R _L ...(2) Here, from equation (2), the allowable load resistance at the allowable output current I _OUTMAX is R _LMIN , and the output current I ₀ flowing from output terminal b at the instant of startup is: transistor
When Q ₅ and Q ₆ have the same characteristics and the base current is ignored, it is expressed by the following equation (3).

I ₀ = I _C7 × h _FE8 ...(3) where I _C7 : Collector current of transistor Q ₇ h _FE8 : Current amplification factor of transistor Q ₈ In addition, the collector current I _C7 of transistor Q ₇ is calculated using the following formula (4) It is expressed as

I _C7 = V _D1 −V _BE7 −V _BE1 /R ₁ +V _D1 −V _BE7 −V _BE3 /R ₂ ...(4) However, V _D1 : Cathode potential of constant voltage Zener diode _D1 V _BE7 : Voltage of transistor _Q7 Base-emitter voltage V _BE1 : Base-emitter voltage of transistor Q ₁ Here, since the current amplification factor of a transistor generally has a positive temperature coefficient, at low temperatures the current amplification factor of transistor Q ₈ h _FE8 decreases, and according to equation (3), the output current I ₀ flowing out from output terminal b at the instant of startup decreases. Output current I ₀ decreases to allowable output current I _OUTMAX
, the base potential of transistor Q ₄ will not become higher than the base potential of transistor Q ₇ and transistor Q ₇ will not be turned off.
The output voltage V _OUT at output terminal b does not become stable as expressed by equation (1). Therefore, it will not work properly.

In order to prevent the output current I ₀ at low temperatures from falling below the allowable current I _OUTMAX , the collector current I _C7 of the transistor Q ₇ should be increased to compensate for the decrease in the current amplification factor h _FE8 of the transistor Q ₈ . however,
In order to increase the collector current I _C7 of the transistor Q ₇ , it is sufficient to reduce the resistors R ₁ and R ₂ since V _D1 , V _BE1 , V _BE3 , and V _BE7 are approximately constant values according to equation (4). A problem arises in that the output voltage V _OUT at the output terminal b, which becomes stable as 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 obtain 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, After the voltage control section is started, it includes a transistor that turns off the startup section, and the transistor added for this differential switching circuit is a constant voltage transistor that is different from the transistor that constitutes the voltage control section. Get the circuit.

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

FIG. 2 shows an embodiment of the present invention. Q ₁ , Q ₂ ,
Q ₃ , Q ₄ , Q ₅ , Q ₆ , Q ₇ , Q ₈ , Q ₉ are transistors,
R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ are resistors, D ₁ is a constant voltage Zener diode, a is an input terminal, b is an output terminal, c is a ground terminal, V _CC is an input voltage, R _L is the load resistance. In this embodiment, the reference voltage circuit, _constant current circuit _, and output circuit have _the same configuration as in _{FIG .} It is made up of. 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 V _CC is applied to input terminal a, a constant voltage Zener diode is applied via resistor _R6 .
_D1 becomes operational. When the constant voltage Zener diode _D1 is activated, current flows through the transistor _Q7 and the resistor _R7 . transistor
The current flowing through Q ₇ and resistor R ₁ is the transistor Q ₅ ,
A constant current circuit consisting of Q ₆ allows transistor Q ₈
and the collector current of transistor _Q3 . By supplying base current to transistor _Q8 , transistor _Q8 and resistor
Current flows through R ₄ , R ₅ and the load resistance R _L. The base potential of the transistor Q _{4 rises due to the current flowing through the transistor Q 8} , the resistors R ₄ and R ₅ , and the load resistor R _L , and a base current is supplied to the transistor _{Q 4 .} By supplying the base current to transistor Q ₄ , current flows through transistors Q ₁ , Q ₂ , Q ₃ and resistors R ₁ , R ₂ , R ₃ . transistor
The base potential of transistor Q ₉ rises due to the current flowing through Q ₁ , Q ₂ , Q ₄ and resistors R ₁ , R ₂ , R ₃ . When the base potential of transistor Q ₉ becomes higher than the base potential of transistor Q ₇ , the transistor
Q ₇ is gradually cut off, and the output voltage V _OUT at output terminal b becomes stable at a potential determined by the base potential of transistor Q ₄ , which is the output of the reference voltage circuit, and resistors R ₄ and R ₅ . This stable output voltage V _OUT at output terminal b is expressed by the following equation (5).

V _OUT = R ₄ + R ₅ / R ₅ × (V _BE3 + V _BE4 + V _R2 ) ...(5) Also, the output current I _OUT flowing through the load resistor R _L is calculated by the following formula:
It is expressed as (6).

I _OUT = V _OUT / R _L ...(6) Here, from equation (6), let the allowable load resistance R _LMIN at the allowable output current I _OUTMAX , and the output terminal b at the moment of startup.
The output current I ₀ flowing out is expressed by the following equation (7).

I ₀ = I _C7 ×h _FE8 (7) In addition, the collector current I _C7 of the transistor Q ₇ is expressed by the following equation (8).

I _C7 = V _D1 −V _BE7 /R ₇ ...(8) From this, the collector current of transistor Q ₇ I _C7
is determined by the transistor _Q7 , the resistor _R7 , and the constant voltage Zener diode _D1 , and can be set independently of the reference voltage circuit.

Therefore, even if the h _FE of transistor Q ₈ decreases at low temperatures, the collector current of transistor Q ₇
By setting I _C7 to an appropriate value, the output current I ₀ flowing out from the output terminal b at the instant of startup can be arbitrarily set, and normal operation can be achieved even when the device is started at an 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 the drawing]

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. _R1 to _R7 and R _L ...Resistor, _Q1 to _Q9 ...Transistor, _D1 ... Constant voltage Zener diode, a...
...Input terminal, b...Output terminal, c...Ground terminal.

Claims (1)

[Claims] 1 first and second terminals to which an input voltage is applied, a first transistor, and a first transistor connected between the base of this transistor and the first terminal.
a constant voltage diode connected between the base of the first transistor and the second terminal; a constant current circuit having an input connected to the collector of the first transistor; an output circuit that is driven by the output of the circuit to generate a predetermined output voltage at an output terminal; a base that receives a resistor-divided voltage of the output voltage; a collector that is connected to the input of the constant current circuit; and an emitter that is connected to a reference voltage circuit. in a constant voltage circuit including a second transistor connected to the second terminal via the base, the base is connected to the emitter of the second transistor, the collector is connected to the first terminal, and the emitter is connected to the second terminal. A third transistor connected to the first transistor is provided, and a connection point between the emitters of the first and third transistors is connected to the second terminal via a second resistor. Constant voltage circuit.