JPS581443B2 - Teidenatsudengen Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a constant voltage power supply circuit that enables smooth startup.

As shown in Figure 1, a constant voltage power supply circuit generally includes a reference voltage circuit 1, a voltage dividing circuit 2 that detects the power supply output voltage, and compares the voltages of both circuits 1 and 2 to determine the power supply output voltage. It consists of a circuit 3 that detects an error, and a control circuit 4 that corrects the error and makes the power supply output voltage constant.

As a concrete embodiment of the circuit shown in FIG. 1 above, the output voltage Vo
The circuit shown in FIG. 2, which has excellent temperature characteristics of ut and load fluctuation characteristics of Vout, may have been considered, but like the circuit shown in FIG. If the collector of the transistor Tr4 is connected to the emitter of the transistor Tr4 of the control circuit, the current 11 may flow at the time of startup.

In other words, the current 12 required to turn on the starting transistor Tr1 becomes the current 11 and flows toward the lower potential.

This tends to occur when the value of the load resistance RL is small, and the voltage of the circuit through which the current I2 flows is approximately (R1Xi2+VBE+
i2+VBE), and the voltage generated from the circuit through which the current 11 flows is (RLit+VBE+VBE), so when (R1+R2)i2>RLi1, the current becomes i1 and flows from the power supply output terminal Vout side to the ground terminal GND. In this case, the starting transistor Tr
1 will not turn on.

If this transistor is not turned on, the constant current source ``0'' will not start, and the constant current sources ``1'' and ``I2'' will not be able to enter the operating state, so the entire circuit will not operate.

FIG. 4 is a detailed diagram of the constant current source 10 to I2 in FIG. 2.

D10 is a diode provided in the current-carrying path with constant current ■0;
R10 is a resistor Tr11 is a transistor forming a constant current source I1, R11 is a resistor, Tr12 is a transistor forming a constant current source 2, and R12 is a resistor.

Here, the startup sequence shown in FIG. 2 will be explained.

First, when the power supply input voltage Vin is extremely low at the beginning of startup in FIG.
A current I0'(Io'≪I0) flows through the path of the resistor R1,
A base current of the transistor Tr11 flows.

When Vin increases until it satisfies the starting condition, the collector current 11' of the transistor Tr11 (I1'≪I1
) flows.

However, at this point, all of the collector current 11' of the transistor Tr1H flows through the base of the transistor Tr6 to the emitter of the transistor Tr6, and no current flows through the Zener diode ZD yet.

Next, the transistor Tr1 becomes conductive, and IO'' (collector current of the transistor Tr1) begins to flow.

When Vin further increases, current also flows through the Zener diode ZD, and the base potential of the transistor Tr6 becomes approximately constant.

As a result, the base potential of the transistor Tr1 also becomes substantially constant, and the current 0 becomes substantially constant.

When the current (2) is constant, the currents I1 and I2 are strictly constant values, and when (1) is constant, the current (2)0 is also a strictly constant value (constant current).

As a result, with a constant bias from the diode D10 and the resistor R10, 11 and I2 become completely constant currents.

This constant current (1) makes the Zener diode ZD voltage extremely stable.

Further, the constant current source I2 achieves a load resistance of ~∞ of the differential amplifier constituted by the transistors Tr2 and Tr3.

This makes the voltage amplification factor of the power supply IC extremely large (approximately 9
0 to 120 dB), the amount of negative feedback obtained from the output Vout by the resistors R6 and R7 is extremely large, and a high-performance constant voltage power supply circuit is obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a constant voltage power supply circuit that solves the above startup problem.

An embodiment of the present invention will be described below with reference to FIG.

Note that the same reference numerals are used for parts corresponding to those in FIGS. 1 and 2.

In the reference voltage circuit 1, when the starting transistor Tr1 is driven, it drives the constant current sources (1) and (2), and obtains a constant voltage by the Zener diode ZD.

Voltage dividing circuit 2 detects voltage fluctuations applied to load RL from the midpoint between resistors R6 and R7.

The error detection circuit 3 applies a voltage corresponding to the output voltage to the base of the transistor Tr3 and a reference voltage to the base of the transistor Tr2 for comparison.

The control circuit 4 is a Darlington-connected transistor Tr.
5, Tr5, and the output voltage is made constant according to the result of comparing the reference voltage and the power supply output voltage.

The stray current blocking transistor Tr7 is connected to the collector power supply input terminal Vin, has its emitter connected to the collector of the transistor Tr2, and its base connected to the base of the transistor Tr4.

Thus, in the operation of the above circuit, when the input voltage Vin is applied, a current i3 flows through the starting resistor R3.

Then, a current 12 flows through the constant current source I1 and the base/emitter of the transistor Tr6, and the starting transistor T
r1 turns on and constant current source ■.

Since a specified voltage is applied to the constant current sources I1 and I2, the constant current sources I1 and I2 enter a predetermined operating state, and the entire circuit enters an operating state.

However, since the transistor Tr7 is included in the above circuit, the stray current 11 in the circuit of FIG. When turned on, the constant current sources 1 and 12 enter the operating state, and the entire circuit operates.

In addition, since this circuit connects the base of the transistor Tr7 to a point having the same potential as the base of the output Darlington transistor Tr4, in other words, the collector of the transistor Tr2 constituting the differential amplifier is corrected via the control circuit 4. Since a voltage is applied to the collector of transistor Tr2,
The emitter voltage VCE can be made constant, and therefore the ripple compression ratio of the power supply output voltage can be made very high.

As explained above, according to the present invention, it is possible to provide a constant voltage power supply circuit which can solve the startup problem in the circuit of FIG. 1 and can improve the ripple compression ratio on the power output side.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the basic configuration of a constant voltage power supply circuit.
FIG. 2 is a constant voltage power supply circuit diagram before improvement, FIG. 3 is a circuit diagram of an embodiment of the present invention, and FIG. 4 is a detailed circuit diagram of the constant current source section of FIGS. 2 and 3. 1... Reference voltage circuit, 2... Voltage dividing circuit, 3... Error detection circuit, 4... Control circuit, Tr1... Starting transistor, Tr7... Stray current blocking transistor.

Claims (1)

[Claims] a Zener diode, a first constant current source that supplies a first constant current to the diode, and a Zener diode and a first
a first voltage divider circuit that divides the potential at the connection point of the constant current source; a first transistor whose base receives the first divided potential of the voltage divider circuit as a reference potential; 2
a second transistor which receives a divided voltage potential at its base and obtains a second constant current at its collector; and a third transistor whose collector is connected to a third constant current source and whose emitter is commonly connected to the emitter of the first transistor. a transistor; the first and third transistors;
The fourth transistor connected to the common emitter connection point of the transistor
a constant current source, a control transistor whose base is connected to the collector of the third transistor and which is inserted between the power supply input terminal and the power supply output terminal, a second voltage dividing circuit that divides the voltage of the power supply output, and this circuit. means for supplying a divided voltage potential to the base of the third transistor, an emitter and a collector connected between the collector of the first transistor and the power supply input terminal; a fourth transistor for stray current prevention that receives an output, and wherein the first and third constant current sources are activated in response to activation of the second constant current source. .