JPS6373312A - Variable output type constant voltage power source circuit - Google Patents

Abstract

PURPOSE:To expand the range of an input voltage, and to reduce power consumption in a voltage controlled circuit, by providing voltage sources having different reference voltages in a power source circuit, and switching reference voltage sources corresponding to the change of the input voltage. CONSTITUTION:A variable output type voltage power source circuit consists of a control circuit 1, a voltage-division circuit 2, reference voltage sources 3 and 6 which generate different voltages, an error amplifier 4, a voltage detector 5, a change-over switch 7 which switches the voltage sources 3 and 6, and a load 8. In a state that a circuit is constituted in such way, and the switch circuit 7 is connected to the reference voltage source 3, a voltage V1 is set so as to guarantee the stable operation of a constant voltage circuit, and the logic of the voltage detector 5 is selected so as to select the voltage source 3 first by the switch circuit 7, when the input voltage Ei is higher than the voltage V1. Thus, if it is Ei>V1, the voltage source 3 is used, and it is Ei<V1, the voltage source 6 is operated, thus, a difference between the input voltage and an output voltage can be maintained at a constant level.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a closed circuit type constant voltage power supply circuit.

In particular, it relates to a constant voltage power supply circuit having a reference voltage source.

[Conventional technology]

A closed circuit type constant voltage power supply circuit has a configuration as shown in FIG. A concrete example of the circuit is shown in Fig. 4.

The voltage stabilization principle of this circuit will be explained. The current due to the input voltage E1 is sent to the load resistor 66 through the control transistor 60. Voltage divider circuit 2 with resistors 31 and 62
The output voltage is divided by 6 and this voltage is compared with a reference voltage provided by a reference voltage source 24 by a constant voltage diode 66. The fluctuation of the output voltage is handled by transistor 3.
4 and its load resistor 65, and is amplified by the error amplifier 25 and sent to the input, that is, the base, of the control transistor 50.

Now, if the output voltage EO drops due to fluctuations on the power supply side or the load side, this change in output voltage is sent to the base of the transistor 34 of the error amplifier 25 through the voltage dividing circuit 26.

At this time, since the voltage of the reference voltage source 24 is constant,
The base-emitter voltage of transistor 34 decreases and its collector current decreases. As a result, the collector voltage of the transistor 64, that is, the control transistor 30
Since the base potential of the control transistor 30 rises and the emitter potential of the control transistor 30 also rises, the previous drop in the output voltage is canceled out. From the above, even if the power supply and load fluctuate,
The output voltage EO is kept at a constant value.

The output voltage EO of this circuit is.

EO=--C-・VZ + VBIE 2R++R2 Here, R1 is the resistance value of the resistor 61, R2 is the resistance value of the resistor 32, VZ is the Zener voltage of the constant voltage diode 33, and the base of the vsE all-run star 34. -emitter voltage.

[Problem that the invention seeks to solve]

In the conventional constant voltage power supply circuit described above, when the input voltage decreases to Ei (VZ + VBE2), the transistor 64 no longer functions as an amplifier, and therefore the circuit shown in FIG. 4 no longer operates as a constant voltage power supply. .

This may occur if, for example, you are using a battery as an input power source and its capacity is decreasing, or if the current consumption of other devices connected to the same power source becomes extremely large. .

In such a case, the output of the constant voltage power supply changes directly depending on the load or fluctuations on the power supply side, which has the disadvantage that, for example, the noise of the equipment increases and the operation becomes unstable.

For this reason, if the Zener voltage VZ is chosen low.

The difference between input voltage E1 and output voltage EoO should not be large.

Therefore, the power consumption of the control transistor 30 increases, and a control transistor 30 for high power must be selected, and in extreme cases, a heat sink becomes necessary.

[Means for solving problems]

The present invention relates to a control circuit that controls output current.

A voltage divider circuit that divides an output voltage, a first reference voltage source for obtaining a constant voltage, and an error amplifier that amplifies the difference between the output of the voltage divider circuit and the output of the first reference voltage source. a closed circuit type constant voltage power supply circuit that controls the control circuit with the output of the error amplifier, a voltage detector that detects that the input voltage has decreased below a certain value; a second reference voltage source for obtaining a low reference voltage, and a switch circuit for connecting either the first reference voltage source or the second reference voltage source to the error amplifier, Connect the output to a control terminal of the switch circuit.

-I's- When the input voltage is higher than the judgment value of the voltage detector, the switch circuit is controlled to connect the output of the first reference voltage source to the error amplifier.

The switching circuit is characterized in that the switch circuit is controlled to connect the output of the second reference voltage source to the error amplifier when the input voltage becomes lower than the determination value of the voltage detector.

〔Example〕

Next, nine aspects of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. The control circuit 1 corresponds to the control circuit 22 in FIG. 3, the voltage divider circuit 2 corresponds to the voltage divider circuit 23 in FIG. 6, and the error amplifier 4 corresponds to the error amplifier 25 in FIG. The output of the switch circuit 7 is 21 in FIG. 2 and is connected to the error amplifier 4.

Let the Zener voltages of the constant voltage diodes 19 and 20 in FIG. 2 be n, Vz+, and vZ2, respectively.

Let Vzl>VZ2. The detection voltage of voltage detector 5 is Vz
The voltage v1 is set to a voltage slightly higher than l + VBE, that is, the voltage v1 that guarantees stable operation of the constant voltage circuit when the switch circuit 7 is connected to the first reference voltage source B. The logic of the voltage detector 5 is selected so that the switch circuit 7 selects the first reference voltage source 6 when the input voltage E1 is higher. Therefore, if Pi)V+, the first reference voltage source B operates as a constant voltage power supply. On the other hand, F! 1 (Vl), it operates as a constant voltage power supply using the second reference voltage source B.

Compared to a constant voltage power supply that only has the first reference voltage source, Vzl-V
The output is stabilized by Z2 and the input voltage range is expanded.

In other words, by switching the reference voltage source as soon as the input voltage changes KE.

The difference between the input voltage and the output voltage can be maintained constant.

Next, the voltage detector 5 and switch circuit 7 shown in FIG. 2 will be explained. In the figure, the Zener voltage of the constant voltage diode 11 is set as Vz51, the pace-emitter voltage of the transistor 14 is set as VBE5, and the voltage drop across the resistor 65 is set to a value that can be ignored.

Now, if the input voltage Ei is gl) VZ5 + VBE3, the transistor 14 will be turned on, and accordingly the transistor 15 will be turned off. As a result, the transistor 17 is turned on, the transistor 18 is turned off, and the constant voltage diode 19 is connected to the switch circuit output 21.
That means that. That is, the first reference voltage source 3 is selected. Ei (If Vz3 + VBE3, the on/off of each transistor is reversed, and as a result, a constant voltage diode 20 is connected to the switch circuit output 21.
is connected. In other words, the second reference voltage source 6 has been selected.

Note that when the input voltage is high, the first reference voltage source 3 is selected and the output voltage becomes high, so the power consumed by the control circuit 1 in FIG. 1 can be reduced compared to a circuit using only a low reference voltage. .

〔Effect of the invention〕

As explained above, the present invention has different reference voltage sources,
By switching the reference voltage source according to changes in the input voltage, the input voltage range over which the constant voltage power supply is stable can be expanded.

At the same time, it has the effect of reducing power consumption of the voltage control circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram for explaining the main parts of FIG. 1, and FIG. 6 is a block diagram of an example of a conventional constant voltage power supply. FIG. 4 is an example of the circuit shown in FIG. 3. DESCRIPTION OF SYMBOLS 1... Voltage control circuit, 2... Voltage divider circuit, 6... First reference voltage source, 4... Error amplifier, 5... Voltage detector, 6... Second reference Voltage source, 7... switch circuit.

Claims (1)

[Claims] 1. A control circuit that controls the output current, a circuit that divides the output voltage, and a first reference voltage source that obtains a constant voltage.
A closed-circuit constant voltage power supply circuit comprising an error amplifier that amplifies the difference between the output of the voltage dividing circuit and the output of the first reference voltage source, and controlling the control circuit with the output of the error amplifier, a voltage detector for detecting that the input voltage has decreased below a certain value; a second reference voltage source for obtaining a reference voltage lower than the first reference voltage source; a switch circuit that connects one of the two reference voltage sources to the error amplifier, the output of the voltage detector is connected to a control terminal of the switch circuit, and the input voltage is higher than the determination value of the voltage detector. In this case, the switch circuit is controlled to connect the output of the first reference voltage source to the error amplifier, and when the input voltage becomes lower than the judgment value of the voltage detector, the output of the second reference voltage source is connected to the error amplifier. A variable output constant voltage power supply circuit, characterized in that the switch circuit is controlled to be connected to the error amplifier.