JPS63211007A - Constant voltage power circuit - Google Patents

Abstract

PURPOSE:To reduce a stand-by current and an input/output voltage difference by operating a 1st TR in its saturation area and increasing the resistance value between the base of a 2nd TR and a positive power source and the resistance value between the base of a TR and a constant voltage diode. CONSTITUTION:Transistors TR 2 and TR 1 turn on by the application of an input voltage and a capacitor C3 beings to be charged, thereby outputting VOUT. When the charging voltage of the capacitor C3 exceeds the Zener voltage of the constant voltage diode, the TR 3 turns on and TR 2 and TR 1 turn off, so that the capacitor C3 begins to be charged. When the discharging voltage of the capacitor C3 goes to under the Zener voltage, it is returned to the initial state. At this time, the TR is used in its saturation area at all times and the values of the resistances R4 and R6 are made large to reduce the input/output voltage drop and also reduce the stand-by current of the circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a constant voltage power supply circuit, and more particularly to a constant voltage power supply circuit that reduces standby current and voltage difference between input and output.

(Prior Art) As a constant voltage power supply circuit that supplies power at a predetermined voltage to various electronic control devices, for example, as shown in FIG. Smoothing capacitor CI for Via and output voltage Vout,
There is a series type constant voltage power supply circuit including C2 and C3, a noise countermeasure capacitor C4, a current limiting resistor R, a constant voltage diode ZD that defines the output voltage Vout, and a current amplifying transistor Tr.

(Problem to be solved by the invention) The Zener voltage of the constant voltage diode ZD of this constant voltage power supply circuit is v2, and the forward voltage drop of the diode D is V11.
%) The base-emitter voltage of transistor Tr is Vlz
, the current amplification factor is )lfs, the output voltage Vout is expressed as (V z -V 1g), and the output current 1out is expressed as (Vln Vs - Vz ) ·h, a /R. At this time, when the input voltage Vin decreases, if an attempt is made to maintain the output current Iout, since there is a limit to the current amplification factor of 11 fs of the transistor T, the collector-emitter voltage VCt of the transistor Tr increases, and the output voltage Vout will decrease.

In order to stabilize the output voltage Vout against a decrease in the input voltage Vin, it is necessary to reduce the resistance R. However, if the resistance R is made smaller, the standby current when the constant voltage power supply circuit is not in operation becomes larger. Also, no matter how small the resistance R is, the transistor T
The voltage drop at r is only as small as the forward voltage drop of diode D, and the voltage difference between input and output is limited to the forward voltage drop of two diodes, including the voltage drop of diode D. However, there is a problem in that the voltage drop is large and may be insufficient for reducing the input voltage Vin.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a constant voltage power supply circuit that reduces the standby current and the voltage difference between input and output.

(Means for Solving the Problems) According to the present invention, in order to achieve the above object, a diode whose anode is connected to an input terminal, and a smoothing capacitor connected between the cathode of the diode and the ground are provided. ,
a first transistor having an emitter connected to the cathode of the diode, a collector connected to the output terminal, and a base connected to the cathode of the diode via a bias resistor;
a second transistor whose collector is connected to the base of the first transistor via a resistor, whose emitter is grounded, whose base is grounded via a bias resistor, and which is connected to the cathode of the diode via a resistor; , whose collector is connected to the base of the second transistor,
a third transistor whose emitter is grounded and whose base is grounded via a bias resistor; a first voltage regulator diode that is connected between the output terminal and the base of the third transistor and regulates the output voltage; This configuration includes a series circuit with a resistor and a smoothing capacitor connected between the output terminal and ground.

(Function) When the input terminal is applied to the input terminal, the second and first transistors become conductive, and the smoothing capacitor on the output side is charged. When this charging voltage exceeds the Zener voltage of the first voltage regulator diode, The third transistor conducts and the second and first transistors conduct.
transistor is cut off to stop charging the capacitor and start discharging it. When the voltage of the capacitor becomes lower than the Zener voltage, the third transistor is cut off, the second and first transistors are turned on, and charging starts again. By repeating this switching operation of the first to third transistors, the output voltage is stabilized to a voltage determined by the Zener voltage.

Increasing the resistance between the base of the second transistor and the cathode of the diode and the resistance between the base of the third transistor and the constant voltage diode when the first transistor is operated in the saturation region. is made possible,
Accordingly, the standby current of the circuit becomes smaller. In addition, by operating the first transistor in the saturation region, it is possible to make the voltage drop due to the transistor extremely small, and the voltage drop between the input and output is approximately equal to the voltage drop of only the diode, which is extremely small. .

(Example) An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a series type constant voltage power supply circuit to which the present invention is applied, in which one end of each line 2.3 is connected to an input terminal 4.4'', and each other end is connected to an output terminal 5.4''. 5 is connected to &l!3 is grounded. A diode D1 to prevent reverse connection is connected in series to line 2, with the anode on the input side.
The cathode is connected to the output side and connected in the forward direction from the input side to the output side. Smoothing capacitors CI and C2 are connected in parallel between the cathode of the diode Di and &I3,
The amplification PNP transistor Tri has an emitter and a collector! ! 2 is connected in series with the emitter of the diode D.
The collector is connected to the cathode of diode D1, the collector is connected to the output side, and the base is connected to the cathode of diode D1 via bias resistor R1.

The transistor Tr2 has its collector connected to the base of the transistor Tri via a resistor R2, its emitter connected to a line 3, and its base connected to the line 3 via a bias resistor R3 and to the cathode of a diode DI via a resistor R4. be done. The transistor Tr3 has a collector connected to the base of the transistor Tr2, an emitter connected to &113, and a base connected to &I3 via a bias resistor R5. A series circuit of a constant voltage diode ZDI and a resistor R6 for regulating the output voltage Vout is connected between the output terminal 5 side of the line 2 and the base of the transistor Tr3, and the Zener diode ZDI has its cathode connected to the line 2. The anode is connected to resistor R6. Further, a smoothing capacitor C3 is connected between the output terminal 5 side of [2 and the line 3].

The action will be explained below.

When input voltage Vin is applied between input terminals 4 and 4',
First, the transistor Tr2 becomes conductive (hereinafter referred to as on).
Then, transistor Tri is turned on. When the transistor Tri turns on, the output voltage smoothing capacitor C3
Charging is started at , and the voltage Vout is output to the output terminal 5. The charging voltage of this capacitor C3 is the constant voltage diode Z
When the Zener voltage of DI exceeds ■□, transistor Tr3
turns on. When the transistor Tr3 is turned on, the transistor Tr2 is cut off (hereinafter referred to as off), the transistor Tri is turned off, and charging of the capacitor C3 is stopped. At the same time, capacitor C3 starts discharging and the voltage V
Output out.

When the discharge voltage of the capacitor C3 falls below the Zener voltage V21, the transistor Tr3 is turned off, and accordingly, the transistors Tr2 and Tri are turned on, and charging of the capacitor C3 is started again. This operation is repeated, and the transistors Tri, Tr2 and T
The switching operation of r3 stabilizes the output voltage Vout to a value determined by the Zener voltage VZ+.

At this time, the output current 1out is determined by the current amplification factor of the transistor Tri and the value of the resistor R2.
The current flowing through the resistor R4, that is, the base current of the transistor Tr2, is determined by the current amplification factor of the transistor Tr2 and the value of the resistor R4. It is determined by the amplification factor and the value of resistor R6. Therefore, even if the transistor Tri is always used in the saturation region, it is possible to increase the values of the resistors R4 and R6 that define the standby current that turns on the transistor Tri. As a result, standby current can be reduced.

In addition, by constantly operating the transistor Tri in the saturation region, the collector-emitter voltage vcx of the transistor Tri becomes extremely small, and the voltage difference between the input voltage Vin and the output voltage Vout is also equal to that of the diode D1, that is, approximately one diode. There will be a directional voltage drop and it will become smaller.

FIG. 2 shows another embodiment of the present invention, in which a series constant voltage power supply circuit 6 is connected in parallel to the constant voltage power supply circuit l shown in FIG. 1, and a transistor Tr4 of the constant voltage power supply circuit 6 has a collector. to the cathode of the diode DI, and the emitter to &l
The output terminal 5 side of the output terminal 5 of the output terminal 5 is read directly, and its base is connected to the cathode of the diode D1 via a bias resistor R7, and to the line 3 via a constant voltage diode ZD2.

The constant voltage diode ZD2 has a cathode connected to the transistor T.
At the base of r4, the anode is connected to Ii3. Further, a capacitor C4 is connected in parallel to the constant voltage diode DI.

Then, the Zener voltage V of the constant voltage diode ZDI
By setting Z+ lower than the output voltage Vout and higher than the guaranteed voltage of the applied electronic circuit, the constant voltage power supply circuit Is6 is operated during steady state, and the output terminal 5.5 is output from the constant voltage power supply circuit 6. , and only when the input voltage Vin decreases, the constant voltage power supply circuit 1 is activated instead of the constant voltage power supply circuit 6, that is, the transistor Tri-
The Tr3 is operated in the same manner as described above to supply voltage from the constant voltage power supply circuit 1 to the output terminal 5.5°. At this time, the resistor R7 of the constant voltage power supply circuit 6 is connected to the input voltage Vi
There is no need to consider when n decreases, and therefore there is no need to reduce the resistance value.

As a result, the constant voltage power supply circuit can reduce the standby current as described above, and the input voltage V
The voltage difference between in and the output voltage Vout also becomes a forward voltage drop corresponding to one diode, and becomes small.

(Effects of the Invention) As explained above, according to the present invention, a diode whose anode is connected to an input terminal, a smoothing capacitor connected between the cathode of the diode and the ground, and an emitter connected to the cathode of the diode. a first transistor whose collector is connected to an output terminal and whose base is connected to the cathode of the diode through a bias resistor; whose collector is connected to the base of the first transistor through a resistor and whose emitter is grounded; a second transistor whose base is grounded via a bias resistor and connected to the cathode of the diode via a resistor; whose collector is connected to the base of the second transistor, whose emitter is grounded, and whose base is grounded via a bias resistor; a third transistor that is grounded via a bias resistor, and a series circuit of a first voltage regulator diode and a resistor that is connected between the output terminal and the base of the third transistor and regulates the output voltage. , a smoothing capacitor connected between the output terminal and the ground is configured, so that even if the first transistor is always used in the saturation region, a standby current that turns on the transistor is defined. It becomes possible to increase the resistance value, and as a result, the standby current during non-operation can be reduced.

In addition, by constantly operating the first transistor in the saturation region 81, the voltage between the collector and emitter of the transistor becomes extremely small, and the voltage difference between the input voltage and the output voltage is also approximately the forward voltage drop of one diode. It has excellent effects such as being smaller in size.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the constant voltage power supply circuit according to the present invention, Fig. 2 is a circuit diagram showing another embodiment of the constant voltage power supply circuit of the present invention, and Fig. 3 is a circuit diagram showing a conventional constant voltage power supply circuit. FIG. 3 is a circuit diagram of a power supply circuit. 1.6... Constant voltage power supply circuit, 4.4゛... Input terminal, 5.5°... Output terminal, DI-... Diode,
Trl~Tr4...Transistor, 01~C4...
Capacitor, R1-R7...Resistor, ZDI, ZD2...
... Constant voltage diode.

Claims (1)

[Claims] A diode whose anode is connected to an input terminal, a smoothing capacitor connected between the cathode of the diode and the ground, an emitter connected to the cathode of the diode, a collector connected to the output terminal, and a base connected to the above diode through a bias resistor. a first transistor connected to the cathode of each diode, a collector connected to the base of the first transistor via a resistor, an emitter grounded, and a base grounded via a bias resistor, and a base connected to the first transistor via a resistor; a third transistor whose collector is connected to the base of the second transistor, whose emitter is grounded, and whose base is grounded via a bias resistor; a series circuit of a first voltage regulator diode and a resistor connected between the output terminal and the base of the third transistor to regulate the output voltage; and a smoothing capacitor connected between the output terminal and ground. A constant voltage power supply circuit characterized by comprising: