JPH0827658B2 - Electronic device power supply circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a power supply circuit of an electronic device that obtains a stabilized output of an unstabilized rectified voltage obtained from an AC power source through a rectifier circuit by a constant voltage circuit. .

(B) Conventional technology Generally, a power supply circuit of an electronic device rectifies and smooths an AC voltage from an AC power supply, and then loads a constant voltage stabilized by a constant voltage circuit, for example, to a DC power supply terminal of various ICs. It is configured to be added.

As an example of this constant voltage circuit, Japanese Examined Patent Publication (Kokoku) No. 48-23701 is cited and a configuration for obtaining a plurality of stabilizing voltages is shown.

Further, when a plurality of first and second constant voltage circuits (1) and (2) are simply provided, each of them is separately provided as shown in FIG. 5 from an AC power source (3) to a power transformer (4) to a rectifier circuit (5). ) Through the constant voltage circuits (1) and (2) and operate each independently to supply the stabilized DC voltage from the output terminals (6) and (7) to a desired load.

(C) Problems to be solved by the invention Regarding the above-mentioned conventional Japanese Patent Publication No. 48-23701, if the underlying constant voltage circuit changes from a normal operating state to an abnormal operating state, another Not only is there a drawback that even one voltage is not a constant voltage, but the setting of circuit constants is also extremely critical, so it is not very suitable as a power supply circuit for electrical equipment.

On the other hand, in the power supply circuit shown in FIG. 5, it is assumed that the first output terminal voltage is V ₀₁ , the input voltage V _i1 , the second output voltage is V ₀₂ , the input voltage V _i2 , the output terminal voltage and the AC voltage reduction guarantee. -A%,
Assuming the saturation voltage Vsat in the constant voltage circuit (2), V _{i2 at the} rated AC voltage is Must be set to.

As an example, if V ₀₁ = 5 V, Vsat = 1.5 V, and A = 35 (%), then V _i2 ≧ 10 V, and (V _i2 −V ₀₂ ) × I is consumed by the constant voltage circuit (2). Therefore, in the above embodiment, at the AC rated voltage, 1/2 of the power supplied to the constant voltage circuit (2) is wasted. Here, I represents a current flowing through the constant voltage circuit (2).

(D) Means for Solving the Problems The present invention relates to a power supply circuit including a plurality of constant voltage circuits having high and low voltages different from each other, and connecting the first and second constant voltage circuits to the output side of the rectifier circuit. Then, switching means is connected to the input side of the first and second constant voltage circuits, and the output terminal of the second constant voltage circuit is connected to the control terminal of the switching means, and the second constant voltage circuit is connected. When the output voltage of the second constant voltage circuit decreases, the switching means is turned on, the first rectified voltage appearing at the input terminal of the first constant voltage circuit is added as the input voltage of the second constant voltage circuit, and a constant AC rated voltage is applied. This is a configuration for reducing the power consumption of the voltage circuit.

(E) Action The second constant voltage circuit can be driven by the first rectified voltage by turning on the switching means at the time of voltage drop of the input terminal of the second constant voltage circuit in the present invention. At the time of guarantee, power consumption in the second constant voltage circuit can be reduced.

(F) Embodiments A power supply circuit for electronic equipment of the present invention will be described with reference to the drawings. FIG. 1 is a basic configuration diagram showing the same circuit of the present invention.
FIG. 2 is an implementation circuit diagram of the same circuit, FIG. 3 is a waveform diagram of each part in FIG. 2, and FIG. 4 is a characteristic diagram of FIG.

In the drawing, the same elements as those in FIG. 5 are designated by the same reference numerals, (8) is an electronic switch as a switching means, (9) is a comparator as a control circuit, and (10) is a backflow prevention. Switching diodes, (11) and (12) are first and second rectified output terminals, (13) and (14) are potential difference detection transistors forming a comparator (9), and (15) is a switching transistor as switching means, (20) (2
1) shows a smoothing capacitor.

Next, the operation of the present invention will be described. First, in FIG. 1, when 100V as a commercial power source is applied from the AC power source (3) to the power source transformer (4), the power source transformer (4) outputs a predetermined voltage. Step down. From the secondary side of the power transformer (4), through the bridge-connected rectification circuit (5) for double-wave rectification, from the first rectification output terminal (11) to V _i1 , the second rectification output terminal ( The rectified voltage of V _i2 appears from 12). (It is assumed that V _i1 > V _i2 .) Here, during normal operation, the first rectified output terminal (11) and the second rectified output terminal (12) have reached a predetermined voltage, and
The constant voltage circuit (1) and the second constant voltage circuit (2) perform a predetermined constant voltage operation. (Switching diode (10)
Is on. ) Therefore, at this time, the second rectified output voltage V _i2 and the second constant voltage output V _i2 are respectively _supplied to the comparator (9) as the control circuit.
₀₂ is added, the ON voltage is not applied to the output, that is, the control terminal (16), the electronic switch (8) is kept off, and the first constant voltage terminal (6) and the second constant voltage terminal (7) are connected. The respective predetermined voltages V ₀₁ and V ₀₂ appear, and the constant voltage is supplied to various ICs as loads connected to the next stage.

On the other hand, if the voltage on the secondary side of the power transformer (4) drops for some reason, a control signal from the comparator (9) is applied to the control terminal (16), and the electronic switch (8) is turned on. The first rectified output voltage (V _i1 ) is applied as an input to the second constant voltage circuit (2), which is driven by the first rectified voltage.
Here, when the electronic switch (8) is turned on, the diode (10) changes the first rectified output V _i1 to the second rectified output V _i2.
Is a switching diode that blocks the reverse flow to the.

Here, a case where the AC power supply in FIG. 2 has a rated voltage and a case where the AC power supply has dropped will be described.

First V _i2 of the AC power supply is satisfied when the rated voltage _{V i2 = V 02 + υ sat} + υ d ...... (2) is applied to the second constant voltage circuit (2). The voltage difference detection transistor (13) as the comparator monitors the potential difference between the voltages V _i2 and V ₀₂ .

Next, when the voltage of the AC power source (3) drops and V _i2 enters the region shown in the following formula (3), the potential difference detection transistors (13) and (14) are turned on and off respectively, and the switching transistor (15) is turned on.

V _i2 ≤ (V ₀₂ + υ _sat + υ _d ) (3) In equations (2) and (3), υ _sat is the voltage drop in the second constant voltage circuit (2), and υ _d is the switching diode (10). Indicates the forward rising voltage.

The second rectified voltage V _i2 is the second constant voltage circuit (2)
At the AC undervoltage guarantee limit point (-A%), set so that V _i2 ≧ (V ₀₂ + υ _sat ) ... (4).

As a result, the power consumption P of the second constant voltage circuit (2) at the AC rated voltage becomes P = υ _sat × I (5). (I indicates the current flowing through the second constant voltage circuit (2).) In the above configuration, if V ₀₂ = 5 V and υ _sat = 1.5 V, the voltage applied to the second constant voltage circuit (2) The power supply is 6.
The power consumption in the second constant voltage circuit (2) is 5 × I.

 Therefore, with respect to the supplied power of 6.5 × I, 1.5 × I / 6.5 × I = 0.23, that is, 23% of the power is wasted.

In the embodiment shown in FIG. 2, the voltage dividing resistors (17) (18)
The values R ₁ and R _{2 of} are set to turn on when the potential difference detection transistor (13) satisfies the equation (3), and the value R ₃ of the resistor (19) is set to the transistors (13) (14) (15). ) Is set to a large loop gain, and the ON / OFF operation of the transistor (13) has a hysteresis characteristic.
The switching operation of the transistor (15) is speeded up to suppress the switching transient power consumption of the transistor (15). These values are shown below.

R ₁ = 4.7KΩ, R ₂ = 10KΩ, R ₃ = 180KΩ Fig. 3 shows the waveform of each part in Fig. 2, and the rectifier circuit (5)
Since the potential of the second rectified output terminal (12) of the above includes a ripple component peculiar to the rectified output obtained from the AC power source (3), the potential difference detection transistor is below the ripple component as the AC voltage decreases. (13) is on, (14) is off,
The potential at the point A is raised to V _i1 only at that moment, and the generation of ripples at V ₀₂ is suppressed. When the AC voltage further decreases, a ripple component appears in V _01, but no ripple component appears in V ₀₂ as long as Expression (4) is satisfied. Therefore, the base voltage of the potential difference detection transistor (13) is V _B (third component).
As shown in the figure (a)) and the collector voltage V _C1 (FIG. 3 (b)), the sawtooth wave voltage and the pulse waveform are obtained.

On the other hand, the collector voltage V of the potential difference detection transistor (14)
_C2 has an inverted waveform of the collector voltage V _C1 of the potential difference detection transistor (13) (FIG. 3C).

When the AC voltage further decreases, the conduction angle of the switching transistor (15) gradually increases, and the upper end of the ripple of the first current output terminal (11) becomes (V ₀₂ + υ _sat + υ _d ).
When it becomes lower than that, the switching transistor (15) is always turned on, and the input voltage of the second constant voltage circuit (2) is always V _i1 , and when the alternating voltage becomes further lower, the first constant voltage circuit (1) is turned on. Although the ripple component appears, the ripple component does not appear in the constant voltage output of the second constant voltage circuit (2) as long as Expression (4) is satisfied. FIG. 3D shows the waveform at the input terminal (point A) of the second constant voltage circuit (2). FIG. 4 shows the characteristics of the output voltage (V ₀₁ and V ₀₂ ) of each constant voltage circuit (1) and (2) with respect to the AC voltage of the AC power source (3), the input voltage and the power consumption characteristics.

(G) Effect of the Invention According to the present invention, in a power supply circuit having a constant voltage circuit for deriving a plurality of constant voltages (high and low constant voltages), an input terminal on the high voltage side when the voltage of the AC power supply is lower than that of the conventional one. The rectified output is supplied to the input terminal on the lower voltage side, and the power consumption in the constant voltage circuit on the lower voltage side can be reduced to 1/2 or less as compared with the conventional power supply circuit. Further, since the output voltage of the constant voltage circuit is used as the reference potential for the voltage drop monitoring, the voltage drop monitoring range is automatically corrected by the variation of the output voltage of the constant voltage circuit itself, so that an extremely stable operation can be guaranteed. Since the single rectifier circuit is configured to supply the rectified voltage to the plurality of constant voltage circuits, the number of parts and the number of steps can be reduced, which results in cost reduction.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a power supply circuit of an electronic apparatus according to the present invention, FIG. 2 is a circuit diagram showing an embodiment of the same circuit, FIG. 3 is a waveform diagram of each part in FIG. 2, and FIG. FIG. 5 is a characteristic diagram and FIG. 5 is a basic configuration diagram of the conventional circuit. Description of main figure numbers (1) …… First constant voltage circuit, (2) …… Second constant voltage circuit, (3) …… AC power supply, (4) …… Power transformer,
(5) ... rectifier circuit, (6) ... first constant voltage terminal,
(7) …… Second constant voltage terminal, (9) …… Comparator, (1
0) ... switching diode, (11) ... first rectified output terminal, (12) ... second rectified output terminal, (13)
(14) …… Potential difference detection transistor, (15) …… Switching transistor, (16) …… Control terminal.

Claims (1)

[Claims] 1. A power transformer having a center tap terminal on the secondary side of the transformer, a full-wave rectification circuit bridge-connected to the secondary side of the power transformer, and a rectification output terminal of the full-wave rectification circuit. A first constant voltage circuit; a second constant voltage circuit connected to the center tap terminal via a backflow blocking switching diode; and a switching connected between the input terminals of the first and second constant voltage circuits. Means and a control circuit connected between the center tap terminal and the output terminal of the second constant voltage circuit and having an output side connected to the control terminal of the switching means. When the input terminal voltage drops, the switching means is turned on and the switching diode is turned off, and the rectified output is output to the input terminal of the second constant voltage circuit. Power supply circuit of the electronic apparatus characterized by supplying from the rectified voltage children.