JPH01314319A - Constant voltage circuit - Google Patents

Abstract

PURPOSE:To enter a stationary state in a short time by constituting an electric feeding means which supplies a current to between the input and output terminals of the constant voltage circuit by a reference voltage circuit and a transistor (TR) when the voltage at a constant voltage output terminal is smaller than a reference value when a power source is turned on. CONSTITUTION:Assuming that a capacitor C2 is connected to the output Vcout of the constant voltage circuit, the output Vcout is 0'V' at the moment of the supply of a source voltage Vcc to this constant voltage circuit. The base- emitter voltage VBE of a transistor TR 12 at this time rises enough to make the TR 12 turn on, so while Vcout<=VBE, the TR 12 is on and the capacitor C2 is charged. Then when Vcout>VBE (base-emitter voltage), the TR 12 turns off to output a constant voltage irrelevantly to the voltage comparing circuit composed of diodes D1 and D2, the TR 12, and a constant current source I5. Consequently, the rising time at the time of power-on operation is shortened.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is applicable to constant voltage circuits (voltage stabilization Specifically, the present invention relates to a circuit configuration that improves the startup characteristics of a constant voltage circuit when the power is turned on.

[Prior Art] An example of a conventional configuration of a constant voltage circuit (reference voltage generation circuit) known as this type of power supply will be explained with reference to FIG.

In the circuit of FIG. 2, the transistors T "1° Tr, 2
．． Tr3. Tr4 constitutes a differential amplifier circuit, and transistors Tr5. Tr6 constitutes an output means of the differential amplifier circuit. Further, Tr7 to Trll constitute a current mirror circuit.

Also, R3 to R5 are resistors, C1 and C2 are capacitors, 1.
, I2 are constant current sources, I, , I4 are currents flowing through resistors R, , R2, cc is a power supply voltage, Vcount is an output of a constant voltage circuit, and GND is a grounding circuit.

To explain the operation of each part of the constant voltage circuit shown in FIG.
7+ V B Al, the following formula is obtained.

However, k: Boltzmann constant 1.38X 10-"[J-' to J-'] T: Absolute temperature [°K] q: Electron charge 1.60X 10-" [C] I0: Reverse saturation current CA] (T r7 to T rll are equal values) V! lTr? = V BTr&, T R514 = fn4 Therefore, the output voltage vcout of the constant voltage circuit is (Is
From push I4), V eout” V BTr7+ RII sT is obtained, where the temperature coefficient of □un4 is 0.120 mV/
”C (near T −' 290°), so VlITr
If the temperature coefficient of 7 is about -2mV/'t:V eQ
ut glue temperature coefficient becomes zero.

The output voltage characteristics of the constant voltage circuit configured as above are given as follows. That is, if we consider that a change occurs in the constant voltage circuit such that 13 < I4, the base potential of the transistor Tr2 will rise above the base potential of the transistor Tri, and the collector current of the transistor Tri will be lower than that of the transistor Tr2. is larger than the collector current of the transistor T.
I3. T I4 moves in the direction of turning on. On the other hand, the collector current of transistor Tr2 decreases and flows into transistor Tr4, so the base current of transistor Tr5 decreases, and part of the current of constant current source 2 is transferred to transistor T.
The amount flowing to the base of r6 increases.

Therefore, the current 13+I4 increases, but as described above, the current I3. Even if I4 increases, the increase in the base voltage of the transistor Tri becomes larger than the base voltage of the transistor Tr2 due to the presence of the resistor R5.

As a result of the above, the entire constant voltage circuit has currents I and I4
This means that each operation is made to make the values equal.

In addition, the current I3. Considering the case where both I4 increases, the base voltages of the transistor Tri and the transistor Tr2 decrease by that amount, so the collector currents of the transistor Tri and the transistor Tr2 increase. Therefore, the base current of transistor Tr5 increases, so constant current source ■
The portion of the current flowing into the base of the transistor Tr6 decreases, and the emitter current of the transistor Tr6 decreases.

As explained above, the constant voltage circuit shown in FIG.
The configuration is such that a stable and constant output voltage can be obtained even when affected by temperature changes and load fluctuations.

[Problems to be Solved by the Invention] By the way, when using the above-mentioned conventional constant voltage circuit, an external capacitor is connected to this constant voltage circuit in order to prevent external noise from being added to the constant voltage output vcout. C
2 is sometimes added to reduce the noise, but in this case, the following problems arise.

That is, now the external capacitor C2 is V eou
If we consider the case where the power supply voltage VCC is input while connected to t, initially vo. Since ut≠0 [V], the base potential of transistors Tri and Tr2 is also 0 [V].
]. Therefore, the transistor Tr2 is turned on and supplies the collector current of the transistor Tr4 and the base current of the transistor Tr5. Therefore, the transistor Tr5 is also turned on, and the current I2 flows only to the collector of the transistor Tr5 and is not supplied to the base of the transistor Tr6.

The off state of this transistor Tr8 continues,
As a result, V cout remains O[V] forever.

In order to improve the startup characteristics of such a constant voltage circuit, a circuit as shown in FIG. 3 has already been developed.

In FIG. 3, a pull-up resistor R5 is connected to the output stage of the conventional circuit shown in FIG.

This resistor allows current to be supplied to the capacitor C2 regardless of the voltage value of the constant voltage circuit.

However, the circuit shown in FIG. 3 has a drawback that increasing the current supplied to the capacitor C2 causes an error in the reference voltage.

[Means for Solving the Problems] The present invention has been made for the purpose of improving the above-mentioned problems with the characteristics of a constant voltage circuit at the time of startup. An object of the present invention is to provide a constant voltage circuit that increases a constant voltage output current until .

The feature of the constant voltage circuit according to the present invention for realizing such an object is that in the constant voltage circuit equipped with a differential amplifier circuit, at least 'Fr' to the constant voltage circuit is
The structure is such that an energizing means is provided for flowing a current to the output end of the constant voltage circuit when the L source is immersed.

[Function] By having the above configuration, the present invention makes the startup operation of the constant voltage circuit stable and reliable when the power is turned on, and also allows the constant voltage circuit to shift to a steady state with a short startup time. Become.

[Example] The present invention will be explained below based on the embodiment shown in FIG.

In the figure, transistors Tri, Tr2. Tr3,
Tr4 constitutes a differential amplifier circuit, and transistors Tr5.
Tr6 constitutes an output means of the differential amplifier circuit. Further, Tr7 to Trll constitute a current mirror circuit. Also, R+'=R4 is a resistor, C, , C are capacitors, D , , D are diodes, I, , I are constant current sources, and these configurations are the same as the constant voltage circuit shown in Figure 2. Same as configuration.

In this embodiment, in addition to the above configuration, the transistor Tr12 is turned on and off according to the output voltage of the constant voltage circuit.
, and the diode DI, D2 that determines its base potential.
The feature is that a constant current source I is provided.

In the circuit of this embodiment, the circuit operation for generating constant voltage VC during steady state is the same as that described in FIG. 2 above.

The feature of this embodiment is that the circuit with the above configuration has an external capacitor C.
This is the operation at startup when 2 is connected, and this will be explained below.

Now, the capacitor C2 is the output V cou of the constant voltage circuit.
t, and considering the moment when the power supply voltage VCC is applied to this constant voltage circuit, the above V cout
is 0 [■].

At this time, the base-emitter voltage of the transistor Tr12 becomes large enough to turn on the transistor Tr12. Therefore, when Vcout≦VIE, the transistor Tr12 turns on and charges the capacitor C2.

■ Do as above. . As the capacitor C2 is charged by , the potential increases, and Vcout>■ll! (base-emitter voltage), the transistor T r1
2 is turned off, and the constant voltage circuit operates using diodes D, D2.
and transistor Tr12. A constant voltage is output regardless of the voltage comparison circuit constituted by the constant current source I.

In other words, when Vcaut becomes higher than the voltage between the base and emitter of the transistor, the operation of the constant voltage circuit becomes normal.

[Effects of the Invention] As described above, in the constant voltage circuit according to the present invention, when the constant voltage output voltage is low, the transistor increases the output current of the constant voltage circuit, so the startup characteristics of the constant voltage circuit are improved. As a result, the rise at the time of power-on is ensured, and the rise time is shortened, which is extremely useful.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an outline of the configuration of a constant voltage circuit according to an embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing the configuration of each constant voltage circuit as a conventional example. TrinT r12...Transistor D+, Dz...
・Diode R3 to R6...Resistance C1 to C6...
Capacitors I+, Iz, Is... Constant current source VCC... Power supply voltage V caut... Output constant voltage 1st section Fig. 2

Claims (1)

[Claims] 1. In a constant voltage circuit equipped with a differential amplifier circuit, when the voltage at the constant voltage output terminal is smaller than the reference value, at least when the power is turned on to the constant voltage circuit, a current is applied between the input and output terminals of the constant voltage circuit. A constant voltage circuit characterized in that a means for supplying current is constituted by a reference voltage circuit and a transistor.