JP3127787B2 - Power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plus / minus power supply circuit used for electronic equipment, and more particularly to a power supply circuit capable of ON / OFF control by a microcomputer output signal with a simple circuit configuration.

[0002]

2. Description of the Related Art O / O is controlled by the output of a microcomputer.
FIG. 2 shows an example of the configuration of a power supply circuit that performs N / OFF. In FIG. 2, the Zener diodes D1 and D2 and the Zener diodes D1 and D2 indicated by dotted lines in FIG. Constant voltage circuits 1 and 2 including switching transistors Tr3 and Tr2 connected in parallel, two operation amplifiers Q1 and Q2 operating as comparators, also shown by dotted lines, and Zener diodes D3 and D4. D5, a transistor Tr11 that receives an input from the microcomputer, and an ON / OFF command control circuit 5 including resistors 11, 12, 13, and 14. Incidentally, the capacitor C0 and the resistor R0 are a smoothing circuit for further stabilizing the output voltage of the power supply circuit. Also, in this figure, the power transformer and the rectifier circuit, which are connected to the right end and in front of the plus and minus input terminals 6a and 6b and have a known structure, are omitted.

The operation of the conventional example will be briefly described with reference to FIG. 2. An ON / OFF command signal from a microcomputer is input to the base of a transistor Tr11.
When the microcomputer signal is low voltage (0V),
The transistor Tr11 is in the ON state and the resistor R12
Operational amplifier Q connected via
The negative input of 1 becomes a low voltage (0 V). At this time, assuming that the Zener diode D3 is, for example, 2.5 V, the operation amplifier Q1 becomes minus input (0 V) <plus input (2.5 V) by the resistors R12 and R11. In this state, since the operation amplifier Q1 outputs a positive power supply voltage, the transistor Tr3 is turned on, the base of the transistor Tr5 becomes 0 V, and the transistor Tr5 is turned off. Therefore, the + B power supply is turned off (comparator operation of the operation amplifier). On the other hand, the operation amplifier Q2 is connected to the resistor R1.
4 and minus input (2.5V) by resistor R13
In this state, since the operation amplifier Q2 outputs a negative power supply voltage, the transistor Tr2 is turned on, the transistor Tr4 is turned off, and the -B power supply is turned off.

Next, when the command signal of the microcomputer is at a high voltage, the transistor Tr11 is in the OFF state, and the minus input of the operation amplifier Q1 via the resistor R12 is equal to the collector voltage of the transistor Tr11 (+ 5V). )Become. At this time, assuming that the Zener diode D3 is, for example, 2.5V, the minus input (5V) of the operation amplifier Q1>
It becomes plus input (2.5V). In this state, since the operation amplifier Q1 outputs a negative power supply voltage, the transistor Tr3 is turned off and the transistor Tr5 is turned on. Therefore, + B power supply is ON
(Comparator operation of the operation amplifier). On the other hand, operation amplifier Q2
In this state, the operation amplifier Q2 outputs a positive power supply voltage, so that the transistor Tr2 is turned off, the transistor Tr4 is turned on, and the minus input (2.5V) <the positive input (5V). The B power supply is turned on.

[0005]

In the above-mentioned conventional power supply circuit controlled by a microcomputer, since the operation amplifier is used as a comparator, there are disadvantages that the number of parts is large and the parts cost is large.
There is a problem to be solved, that is, the installation area of a large number of components increases. In order to solve the above-mentioned drawbacks of the conventional example, the present invention devises the connection of the input circuit of the microcomputer control output, two operation amplifiers and a plurality of attached zener diodes,
An object of the present invention is to provide a power supply circuit that eliminates an increase in the number of components and a space for installing components by eliminating resistors and capacitors.

[0006]

A power supply circuit according to the present invention for achieving the above object will be described with reference to FIG. 1 showing an embodiment. A Zener diode D1 for setting a constant voltage will be described.
D2 and the switching transistors Tr3, T connected in parallel with the Zener diodes D1, D2.
A constant voltage circuit (1), (2) on each of the plus side and the minus side including r2, and a transistor connected to the base of the transistor Tr3 and setting the transistor Tr3 to an OFF or ON state by a command signal of a microcomputer. A command circuit (3) including Tr1 is connected in series between a positive terminal (point A) and a negative input terminal 6b (point C) of the Zener diode D1 (A
The voltage between points (points) and (point C) is divided and the transistor T
a control circuit (4) including voltage dividing resistors R1 and R2 for setting the voltage of the base (point B) of r2 to turn the transistor Tr2 OFF or ON, and to control the voltage of the Zener diode D1. If VD1, the absolute value of the voltage of the negative input terminal 6b (point C) is V (-), and the resistance values of the voltage dividing resistors R1 and R2 are R1 and R2, respectively, [R1] / [R2] ≦ [VD1] / [V (-)] When the absolute value of the conduction start voltage of Tr2 is VBE, [R1]. [V (-)] / (R1 + R2)> VBE is set. Power supply circuit.

[0007]

The operation of the power supply circuit having the above configuration will be described below. 1. When ± B power supply is off. When the signal from the microcomputer input to the base of the transistor Tr1 is a low voltage (0 V), the transistor Tr1 is in the OFF state, the collector voltage V1 of the transistor Tr1 is applied to the base of the transistor Tr3, and the transistor Tr3 is turned on. The voltage at the point A in the figure becomes 0V, the base of the transistor Tr5 also becomes 0V, and the transistor is turned off. Therefore, the + B power supply is turned off.

On the other hand, when the transistor Tr3 is turned on, the voltage at the point A in the figure is 0 V, and the absolute value of the voltage at the point C in the figure is the same as the absolute value of the negative input terminal 6b. V (-), the voltage dividing resistors R1, R connected across the points A and C
VB = [R1] · [V (−)] / (R1 + R2) where the point B, which is the connection point of No. 2 and the base of the transistor Tr2, is VB = [R1] · [V (−)] / (R1 + R2) Therefore, VB is the conduction start voltage of the transistor (generally 0.
(Approximately 6 V), the transistor Tr2 is turned on, the base of the transistor Tr4 becomes 0 V, and the transistor Tr4 is turned off. Therefore, the -B power supply is turned off.

[0009] 2. When ± B power supply is ON. When the signal from the microcomputer input to the base of the transistor Tr1 is a high voltage,
1 is ON, and the base of the transistor Tr3 is 0
V and the transistor Tr3 is turned off. Therefore, the voltage at point A in FIG.
Is ON, and the + B power supply is ON.

On the other hand, when the transistor Tr3 is turned off, the voltage at the point A in the figure is VD1 and the absolute value of the voltage at the point C in the figure is the absolute value V (-) of the negative power supply voltage. Is between [VD1] + [V
(−)], And the point B at which the voltage dividing resistors R1 and R2 connected across the points A and C are coupled, that is, the base voltage V2 of the transistor Tr2 is bleeder. Based on the setting conditions of the resistors R1 and R2, [R1] / [R2] ≦ [VD1] / [V (−)], it becomes 0 V or more . Therefore, the transistor Tr2
Becomes OFF, and the transistor Tr4 turns ON.
The B power supply is also turned on.

As is apparent from the above description, the circuit of the present invention is replaced with two operation amplifiers, four resistors, three zener diodes, and one capacitor, which are required in the conventional example. Since only two resistors are required, a power supply circuit having the same function can greatly reduce parts cost and installation space.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of an embodiment of a power supply circuit according to the present invention is as follows.
More specifically, referring to FIG.
Is a Zener diode D1 for setting the constant voltage with the transistors Tr5 and Tr6, and a switching transistor T connected in parallel with the Zener diode D1.
This is a positive side constant voltage circuit including r3. Reference numeral 2 denotes a negative constant voltage circuit including a transistor Tr4, a Zener diode D2 for setting a constant voltage, and a switching transistor Tr2 connected in parallel to the Zener diode D2. FIG. 1 does not show a power transformer and a rectifier circuit to be connected to the plus / minus input terminals 6a and 6b at the right end of the drawing. or,
+ B and -B at the left end of the drawing are output terminals of the plus and minus power supplies, respectively. In this embodiment, the voltages of the plus / minus input terminals 6a and 6b are + 14V and -14V, respectively. The rated voltage of each of the Zener diodes D1 and D2 is 7V.

The transistor Tr1 included in the command circuit 3
Is a transistor provided at an input portion receiving an ON / OFF command signal from the microcomputer, and has a collector connected to the base of the switching transistor Tr3 of the positive side constant voltage circuit 1. A positive voltage V1 is applied to the transistor Tr1 via a load resistor, and this V1 is a switching transistor T1.
In this embodiment, V1 is 5 V because a voltage that can turn on and off r3 is sufficient.

When the signal from the microcomputer is at a low voltage (0 V), the transistor Tr1 is in the OFF state, and the base of the transistor Tr3 is connected to the transistor Tr3.
1 is applied to the transistor Tr3.
Becomes ON, and the base voltage of the transistor Tr5 becomes 0
V, the transistor Tr5 is turned off, and the + B power supply is turned off. Conversely, when the signal from the microcomputer is a high voltage, the transistor Tr1 is turned on,
The base of the transistor Tr3 becomes 0 V and the transistor Tr3 is turned off.
r5 is turned on, and the + B power supply is turned on.

Point A in FIG. 1, that is, the base of the transistor Tr5 of the constant voltage circuit 1 (or the plus side of the switching transistor Tr3 or the plus side of the Zener diode D1) and the minus input terminal 6b, ie, the point C In order to set the base voltage of the transistor Tr2 of the constant voltage circuit 2 by dividing the voltage between the points A and C2, the control circuit 4 includes a resistor R1 and a resistor R2 for voltage division in series. The point B of the connection between the two resistors is connected to the base of the switching transistor Tr2 of the constant voltage circuit 2. The values of these resistors R1 and R2 are
According to the setting conditions [R1] / [R2] ≦ [VD1] / [V (−)], in this embodiment, the voltage VD1 at point A = 7V and the voltage V (−) at point C = 14V (absolute value). From the resistor R
1 is set to 10K ohm and resistor R2 is set to 20K ohm.

When the signal from the microcomputer becomes low voltage (0 V) and the transistor Tr3 is turned on, A
Since the voltage at the point is 0 V and the voltage at the point C is -14 V, the voltage at the point B is about -4.7 V, and the switching transistor Tr2 is turned on. Therefore, the base voltage of the transistor Tr4 becomes 0 V,
r4 is turned off, and the -B power supply is turned off. Conversely, when the signal from the microcomputer is a high voltage, the voltage at the point A is 7V, and the voltage at the point C is -14V, which is a total of 21V, which is [R1] / [R2] ≦ [VD1] / [V ( −)], The voltage at point B is zero.
V, and the transistor Tr2 is turned off. Therefore, the base voltage of the transistor Tr4 becomes 7 V, the transistor Tr4 turns on, and the -B power supply turns on.

As described above, the power supply circuit according to the present invention has been described in detail based on the embodiment considered to be representative. However, the configuration of the power supply circuit according to the present invention is not limited to the structure of the above embodiment. The present invention can be appropriately modified and implemented as long as it has the components described in the above-described claims, exhibits the function of the present invention, and has the effects described below.

[0018]

The power supply circuit according to the present invention has the following effects. Instead of two operation amplifiers, four resistors, three zener diodes, and one capacitor required in the conventional example, the circuit of the present invention requires only two resistors. Therefore, it is possible to save the parts cost and the installation space even though the power supply circuits have the same function.

Further, since a small number of parts means a reduction in the number of assembling steps, it is possible to greatly reduce the manufacturing cost of electronic equipment in conjunction with the reduction in the number of parts.

As apparent from the above description, the power supply circuit of the present invention can reduce the manufacturing cost with a simplified configuration while completely retaining the electrical functions of the microcomputer-controlled plus / minus power supply circuit. Can be expected.

[Brief description of the drawings]

FIG. 1 is a wiring diagram showing a configuration of an embodiment of a power supply circuit of the present invention.

FIG. 2 is a wiring diagram showing a configuration of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Constant voltage circuit on the positive side 2 Constant voltage circuit on the negative side 3 Command circuit 4 Control circuit 5 Command control circuit of conventional example 6a, 6b Positive and negative input terminals

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G05F 1 / 445,1 / 56 G05F 1 / 613,1 / 618

Claims (1)

(57) [Claims] 1. A Zener diode D1 for setting a constant voltage.
And connected in parallel with the Zener diode D1.
Switching transistor Tr3 and the positive input
Connected between the power terminal 6a and the positive output terminal 7a.
Plus-side constant voltage circuit having a transistor Tr5
(1) and a Zener diode D2 for setting a constant voltage.
A switch connected in parallel with the nuclear Zener diode D2
Switching transistor Tr2 and a negative input terminal
6b and the negative side output terminal 7b.
Negative side constant voltage circuit having a transistor Tr4 (2)
Connected to the base of the transistor Tr3 and
The transistor according to the command signal of the microcomputer
Transistor that sets Tr3 to OFF or ON state
A command circuit (3) including Tr1, a Zener diode D1
Cathode terminal (point A) and negative input terminal 6b
(Point C) connected in series between (Point C) and (Point C)
And the voltage at the base (point B) of the transistor Tr2 is set, and the transistor Tr2 is turned off.
Voltage dividing resistors R1 and R2 to be turned on or off
And a control circuit (4) including: a voltage of the zener diode D1 at VD1, and a negative input terminal 6b (C
The absolute value of the voltage at point (dot) is V (-), and the voltage dividing resistor R
[R1] / [R2] ≦ [VD1] / [V (−)] When the absolute value of the conduction start voltage of Tr2 is VBE, [R1] A power supply circuit, wherein [V (−)] / (R1 + R2)> VBE is set.