JPH0827673B2 - Constant voltage circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a constant voltage circuit, and particularly to a start-up that can always perform a normal operation against fluctuations in the operating current of a constant-voltage Zener diode when the voltage is reduced and when the temperature is high. The present invention relates to a constant voltage circuit including a circuit.

[Conventional technology]

FIG. 2 shows an example of a conventional circuit. Q1, Q2, Q3, Q4, Q5, Q6,
Q7, Q8 are transistors, R1, R2, R3, R4, R5, R6 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 such a constant voltage circuit, the bandgap type reference voltage circuit is composed of transistors Q1, Q2, Q3, Q4 and resistors R1, R2, R3,
The starting circuit is a constant voltage Zener diode D1 and a transistor
The current mirror type constant current circuit is composed of transistors Q5 and Q6, and the emitter / follower type output circuit is composed of transistor Q8 and resistors R4 and R5. Next, the operation of the conventional circuit when an input voltage is applied will be briefly described with reference to FIG. When the input voltage V _CC is applied to the input terminal a, the constant voltage Zener diode D1 is activated via the resistor R6. When the constant voltage Zener diode D1 is activated, current flows through the transistors Q1, Q5, Q7 and the resistor R1. The current flowing in these transistors Q1, Q5, Q7 and the resistor R1 is supplied to the transistor Q8 by the constant current circuit consisting of the transistors Q5, Q6, so that the current flows in the transistor Q8, the resistors R4, R5 and the load resistor R _L. Flows. The base potential of the transistor Q4 rises due to the current flowing through the transistor Q8, the resistors R4, R5 and the load resistor R _L , and the base potential of the transistor Q4 becomes
When it becomes higher than the base potential of Q7, the transistor Q7 is cut off. However, since a current flows through the transistors Q1, Q2, Q3 by the transistor Q4, the output terminal b
The output voltage V _{out at} is stable at the potential determined by the base potential of the transistor Q4 which is the output of the reference voltage circuit and the resistors R4 and R5. The base potential of the transistor Q4 is determined by the base-emitter voltage of the transistors Q3 and Q4 and the voltage drop of the resistor R2. Therefore, the stable output voltage V _{out at} the output terminal b is expressed by the following equation (1).

V _out = (R4 + R5) / R4 x (V _BE3 + V _BE4 + V _R2 ) (1) where V _BE3 ; base-emitter voltage of transistor Q3 V _BE4 ; base-emitter voltage of transistor Q4 V _R2 ; resistor Therefore, the voltage across R2 is the starting circuit that makes this constant-voltage circuit stable as described above, and the constant-voltage Zener diode makes the reference voltage of this starting circuit. . The operating current I _D1 of the constant voltage Zener diode is determined by the input voltage V _CC , the resistor R6 and the constant voltage Zener diode operating voltage V _D1 , which are determined by the following equation (2).

I _D1 = (V _CC −V _D1 ) / R6 (2) Here, the characteristics of the constant voltage Zener diode are ideally the characteristics shown in Fig. 3 (I), but actually As shown in Fig. II, the characteristic is that it is divided into the constant voltage region A and the non-constant voltage region B by the current. Therefore, when the voltage is reduced due to the decrease of the input voltage, the constant voltage Zener diode The operating current I _D1 decreases, and the constant voltage Zener diode operating voltage decreases. Further, even at high temperature, the operating voltage of the resistor and the constant voltage zener diode have positive temperature coefficients, respectively, so that the operating current of the constant voltage zener diode decreases from the previous equation (2), and the operating voltage of the constant voltage zener diode decreases. Will be lower. This is
Since the base potential of the transistor Q7 drops, the constant current circuit for biasing the reference voltage circuit does not reach normal operation, and the reference voltage circuit and the output circuit cannot be normally biased, the transistor Q7 does not enter the cutoff state. The output voltage V _out at the stable output terminal b represented by the equation (1) does not become V _out . Therefore, it will not operate normally.
Therefore, it is necessary to set the operating current to at least I _D1 or more in the steady state in consideration of the decrease in the operating current of the constant voltage Zener diode at the time of low voltage and high temperature. Conventionally, as a method of solving this drawback, by decreasing the value of the resistor connected between the constant voltage zener diode cathode and the input terminal, the constant voltage zener diode operating current is increased and the constant voltage zener diode operating voltage is The constant voltage region A was always operated and the reference voltage circuit was always activated to obtain a stable output voltage. However, in this solution, there arises a problem that the circuit operating current increases and the change of the circuit operating current becomes large when the input voltage V _CC changes.

[Problems to be solved by the invention]

In the case of the conventional constant voltage circuit described above, the operating current of the constant voltage Zener diode decreases at the time of low voltage and high temperature, the operating voltage of the constant voltage Zener diode does not reach the stable region, and the starting circuit operates normally. Since it does not operate, it is not possible to apply a bias to reach a steady state in the band gap type reference voltage circuit. That is, there is a drawback that a stable output voltage cannot be obtained.

An object of the present invention is to provide a constant voltage circuit which solves the above-mentioned drawbacks and can be started even when the voltage is reduced and which can obtain an output voltage with high stability.

[Means for solving problems]

According to the present invention, the voltage control unit, the activation unit that activates the voltage control unit when a voltage is applied, the transistor that configures the activation unit, and the differential switching circuit are configured, and the activation unit is cut off after the activation. A constant voltage circuit composed of a transistor, a constant current circuit for biasing the voltage control unit, and a constant current circuit for supplying a constant current to the transistor forming the starting unit is obtained.

Specifically, a first transistor having an emitter connected to a ground terminal and a base connected to its collector, and a second transistor having a base connected to the base of the first transistor and an emitter connected to the ground terminal via a resistor Transistor of
A third transistor whose base is connected to the collector of the second transistor and whose emitter is connected to the ground terminal, and one terminal is connected to the collector of the first transistor and the other terminal is connected to the emitter of the fourth transistor. A bandgap reference voltage composed of a first resistor connected to the second resistor and a second resistor having one terminal connected to the collector of the second transistor and the other terminal connected to the emitter of the fourth transistor. A fifth transistor having a collector and a base connected to the collector of the fourth transistor and an emitter connected to the input terminal; and a base having a base at the base of the fifth transistor and an emitter at the input terminal with a collector. A rent-mirror circuit comprising sixth transistors connected to the collectors of the third transistors, A constant voltage zener diode whose anode is connected to the ground terminal and whose cathode is connected to the input terminal through a resistor; and a base whose cathode is the cathode of the constant voltage diode and whose collector is the collector of the fourth transistor whose emitter is the first A fourth transistor connected to the emitters of the four transistors, an emitter having the input terminal connected to the input terminal, a collector connected to the cathode of the constant voltage diode and a base connected to the fifth transistor, and a collector connected to the input; An emitter follower output circuit in which a base is connected to a terminal, a collector is connected to the ground terminal via a resistor, and a collector of the third transistor is connected to the ground terminal; and a divided voltage value of an output of the emitter follower circuit is set to that of the fourth transistor. It is what you type into the base.

〔Example〕

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

FIG. 1 shows an embodiment of the present invention. Q1, Q2, Q3, Q4, Q5, Q
6, Q7, Q8, Q9 are transistors, R1, R2, R3, R4, R5, R6 are resistors, D1 is a constant voltage Zener diode, a is an input terminal, b is an output terminal, c is a ground terminal, and V _CC is The input voltage, R _L, is the load resistance. In this embodiment, the bandgap type reference voltage circuit and the emitter follower type output circuit have the same configuration as in FIG. 2, but the starting circuit is a constant voltage zener diode.
It is composed of D1, a first transistor Q7, and a resistor R6. A constant current circuit for biasing the reference voltage circuit is used for the constant voltage zener diode, and a constant current circuit is formed by the transistors Q9 and Q5. Elements having the same symbols and numbers as in FIG. 2 are the same elements.

Next, the operation of the constant voltage circuit shown in FIG. 1 when an input voltage is applied will be described. When the input voltage V _CC is applied to the input terminal a, the operating voltage of the constant voltage Zener diode D1 passes through the resistor R6.
V _D1 rises. Transistor Q1 by V _D1 of the operating voltage of the Zener diode D1 increases, Q5, current flows through the Q7 and the resistor R1. These transistors Q1, Q5, Q7
And current flowing through the resistor R1 supplies the operating current I _D1 of Zener diode D1 by the constant current circuit consisting of the transistors Q5, Q9. By repeating this process, the operating current I _D1 supplied to the constant voltage Zener diode D1 is obtained by the following equation (3).

I _D1 = (V _CC −V _D1 ) / R6 + I _CQ9 (3) Therefore, the operating current I _D1 of the constant voltage Zener diode _D1
Is the sum of the input voltage V _CC , the operating voltage V _{D1 of the} constant voltage zener diode D ₁ and the current R C ₆ and the current I _CQ9 supplied by the current mirror type constant current circuit. By setting I _CQ9 so that the constant voltage Zener diode operates in the constant voltage region A, the starter circuit operates normally and current flows through the transistors Q1, Q5, Q7 and the resistor R1, and the current mirror composed of the transistors Q5, Q6. A constant current circuit causes a current to flow through transistor Q8, resistors R4 and R5, and load resistor _RL . Thereafter, the same operation as in the conventional circuit is performed, and the output voltage V _out at the output terminal b becomes stable at the potential determined by the base potential of the transistor Q4 and the resistors R4 and R5 which is the output of the bandgap reference voltage circuit.

〔The invention's effect〕

As described above, according to the present invention, the constant current can be supplied to the constant voltage Zener diode by adding one transistor by using the current mirror type constant current circuit for biasing the band gap type reference voltage circuit. However, since the current mirror type constant current circuit is provided, the operating current of the constant voltage Zener diode decreases at the time of low voltage and high temperature, unlike the conventional case, and it is always stable without causing a failure that it cannot start. Since the output voltage V _out can be obtained and the resistance value added between the input terminal and the constant voltage Zener diode cathode can be increased, the change of the circuit operating current with respect to the fluctuation of the input voltage V _CC can be small. The output voltage with high stability can be provided, and the effect is great.

[Brief description of drawings]

FIG. 1 is a constant voltage circuit diagram according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of a conventional constant voltage circuit. Also, the third
Figures (I) and (II) show the characteristics of the constant voltage Zener diode. R1 to R6 and R _L …… Resistors, Q1 to Q9 …… Transistors, D1…
… Constant voltage Zener diode, a …… Input terminal, b ……
Output terminal, c ... Grounding terminal.

Claims (1)

[Claims] 1. A first transistor having an emitter connected to a ground terminal and a base connected to its collector, and a second transistor having a base connected to the base of the first transistor and an emitter connected to the ground terminal via a resistor. , A third transistor having a base connected to the collector of the second transistor and an emitter connected to the ground terminal, and one terminal connected to the collector of the first transistor and the other terminal connected to the fourth transistor. A band consisting of a first resistor connected to the emitter of the transistor, and a second resistor having one terminal connected to the collector of the second transistor and the other terminal connected to the emitter of the fourth transistor. Gap-type reference voltage circuit, collector and base of which are connected to collector of the fourth transistor and emitter of which is connected to the input terminal An rent mirror circuit including a fifth transistor formed by: a sixth transistor having a base connected to the base of the fifth transistor, an emitter connected to the input terminal, and a collector connected to the collector of the third transistor; and an anode. Is connected to the ground terminal and the cathode is connected to the input terminal through a resistor, and the base is the cathode of the constant voltage diode, the collector is the collector of the fourth transistor, and the emitter is the fourth transistor. A transistor connected to the emitters of the transistors, a starter circuit having an emitter connected to the input terminal, a collector connected to the cathode of the constant voltage diode and a base connected to the fifth transistor, and a collector connected to the input terminal. The base is connected to the collector of the third transistor. Constant voltage, characterized in that it has an emitter follower output circuit connected to the ground terminal via a resistor, and a divided value of the output of the emitter follower circuit is input to the base of the fourth transistor. circuit.