JPS63213474A - Dc power source circuit - Google Patents

Abstract

PURPOSE:To maintain the output of a DC power source circuit within a predetermined range by automatically switching the secondary windings of a transformer to be used when an AC input voltage is altered. CONSTITUTION:The secondary winding 1a of a transformer 1 has a tap 1b at its intermediate, and is connected at both ends to first rectifying means 2 and at the tap 1b to second rectifying means 3. The DC output side of the means 2 is connected through switching means 4 to an output terminal 5. Further, the voltage of the tap 1b is detected by voltage detecting means 6. A smoothing capacitor 7 is connected between the terminal 5 and a GND terminal 8, and the DC output side of the means 3 is connected to the terminal 5. Thus, when a lower AC voltage than the other is applied to the transformer 1, an output is externally produced from the means 2. When a higher AC voltage is applied, the means 4 is operated by the means 6 to externally produce an output from the means 3.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a DC power supply circuit used in, for example, a printer connected to a personal computer, and
The present invention relates to a DC power supply circuit that can automatically maintain a DC output voltage within a certain range even when the AC input voltage switches from a low voltage to a high voltage.

(b) Prior Art In general, the circuit shown in FIG. 6 is well known as a DC power supply circuit that supplies necessary DC power to, for example, a printer or an electronic circuit that serves as a load.

The circuit shown in FIG. 6 includes a transformer 20 that steps down the AC input voltage to a target voltage, a full-wave rectifier diode 21 connected to the secondary winding of the transformer 20, and a full-wave rectifier diode 21 that steps down the AC input voltage to a target voltage. A smoothing capacitor 22 is connected to the smoothing capacitor 22.

Reference numeral 23 denotes a voltage stabilizing circuit, which is of a so-called dropper type for controlling the amount of voltage drop, and is composed of a Zener diode 23a, a transistor 23b, and a resistor 23c, and supplies a constant voltage to the load 24.

(c) Problems to be Solved by the Invention However, in the above configuration, the DC voltage (secondary side voltage, Vout− in the figure) generated across the capacitor 22 is
GND voltage) increases in proportion to the AC voltage (primary side voltage) applied to the primary winding of the transformer 20, so when the AC voltage is high, the power capacity on the primary side of the transformer 20 increases. increases. This increases the power loss consumed in the circuit connected to the secondary side of the transformer 20, causing an increase in heat generation in the components forming the circuit.

That is, when creating the voltage on the load side (the voltage between V and -GND in the figure) with the voltage stabilizing circuit 23 as described above, the AC voltage is 200V when the AC voltage is toov and when it is 200V.
The power loss consumed by the transistor 23b and the Zener diode 23a when 100V was applied was several times as large as that when 100V was applied. Therefore, when two types of input AC voltages are applied, it is necessary to increase the withstand voltage and capacity of those parts, which increases costs and causes problems in terms of heat generation. .

This invention was made in view of the above circumstances, and by automatically switching the secondary winding of the transformer used when the AC input voltage changes, the output DC voltage is always constant. The present invention aims to provide a DC power supply circuit that can operate at a voltage within a range.

(d) Means for Solving the Problems The present invention comprises a transformer having a tap on the secondary winding, and a first rectifying means for rectifying the alternating current output to both ends of the secondary winding. and a second rectifying means for rectifying the alternating current output between the secondary winding and the tap, and a voltage between both ends of the secondary winding or between one end of the secondary winding and the tap. voltage detection means for detecting that one of the voltages between is higher than a preset predetermined voltage; This is a DC power supply circuit characterized by comprising a switch means for cutting off the power.

As the first rectifier, a full-wave rectifier bridge circuit composed of a plurality of diodes or a half-wave rectifier circuit is suitable.

Further, as the voltage detection means, a circuit mainly composed of a Zener diode that sets a predetermined voltage and a transistor that switches when the Zener diode is activated can be used.

Further, as the switch means, a PNP transistor or an NPN transistor having good switching characteristics is suitable.

(e) When an AC voltage lower than the others is applied to the working transformer, the DC voltage from the first rectifier is outputted to the outside. Next, an AC voltage higher than the above AC voltage is applied,
When the voltage detection means detects that the voltage is higher than the predetermined voltage, the voltage detection means outputs a signal to operate the switch means.

As a result, the output of the first rectifier is cut off and is not output to the outside, and instead the DC voltage output by the second rectifier is output to the outside, so the DC voltage output to the outside is changed from the input AC. Even if the voltage is changed, the voltage is maintained within a certain range.

(F) EXAMPLES Hereinafter, examples of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following examples.

FIG. 1A is a block diagram of an embodiment of the present invention, in which 1 is a transformer, the secondary winding 1a of which has a tap lb approximately in the middle of the winding.
Both ends of the secondary winding 1a are connected to the first rectifying means 2, and the tap 1b is connected to the second rectifying means 3.

A switch means 4 is connected to the DC output side of the first rectifier means 2, and an output terminal 5 is connected to the output side of the switch means 4. Reference numeral 6 denotes voltage detection means, which is connected to the tap lb and detects the voltage outputted to the tap 1b. A smoothing capacitor 7 is connected between the output terminal 5 and the GND terminal 8. The DC output side of the second rectifying means 3 is also connected to the output terminal 5.

FIG. 1B is a specific circuit diagram of the above embodiment, in which the first rectifying means 2 is constituted by a single-phase full-wave rectifying bridge circuit consisting of four diodes. The second rectifying means 3 is composed of one diode, and also functions as a backflow prevention diode when the switching means 4 composed of a transistor 4a and resistors 4b and 4c is outputting direct current. Voltage detection means 6
are a diode 6a that rectifies the voltage between the tap 1b and one end 1c of the secondary winding 1λ, a capacitor 6b that smoothes the pulsating current rectified by the diode 6a, and a Zener connected in parallel to the capacitor 6b. Diode 6c and resistor 6
Series circuit with d, Zener diode 6c and resistor 6d
A transistor 6f whose base is connected to the connection point between the diode 6a and the Zener diode 6c via a resistor 6e, a resistor 6g connected between the connection point between the diode 6a and the Zener diode 6c and the collector of the transistor 6f, and a resistor 6g connected to the collector of the transistor 6f The transistor 6h has a base connected to the resistor 4c, a collector connected to the resistor 4c, and an emitter connected to the GND line.

Next, the operation of this embodiment will be explained.

First, when a lower AC voltage, for example A or C, 100V, is applied to the transformer l, the AC voltage is detected by the voltage detection means 6 based on the voltage at the tap 1b. However, in this case, since the predetermined voltage set for the Zener diode 6c is high, the transistor 6c
f is not ONL. Therefore, the transistor 6h and the transistor 4a of the switch means 4 are ONL, and as a result, the first
The DC voltage rectified by the rectifier 2 is output to the output terminal 5.

Next, transformer l is supplied with a higher alternating voltage, e.g. A, C,
When 200V is applied, the AC voltage becomes the above A and C.
, 10QV is detected by the voltage detection means 6. In other words, since the voltage applied from the tap 1b to the Zener diode 6c via the diode 6a becomes higher than the set predetermined voltage, it is applied to the base of the transistor 6f via the Zener diode 6c and the resistor 6e, and the transistor 6fh' is turned on. do. Therefore, contrary to the above, the transistor 6h and the transistor 4a are turned off, and the output of the first rectifying means 2 is cut off. Therefore, the DC voltage that is the output of the second rectifying means 3 is outputted to the output terminal 5. This DC voltage is
Since b is drawn from approximately the middle (center) of the secondary winding 1a, the value is approximately half of the DC voltage obtained by rectifying the voltage output across the secondary winding 1a. Therefore, even if the AC voltage doubles, the voltage appearing at the output terminal 5 will be within a certain range.

What is shown in FIG. 2 is a circuit diagram of another embodiment of the present invention. Note that the same elements as in the above embodiment are given the same reference numerals and the explanation thereof will be omitted.

In other embodiments, the voltage detection means 6 includes a diode 61
a, a smoothing capacitor 61b, and a capacitor 61b
Zener diode 61c and resistor 61 connected in parallel to
Series circuit with d, Zener diode 61c and resistor 6
The transistor 61f has a base connected to the connection point between the diode 61a and the Zener diode 61c through a resistor 61a, and the resistor 61g is connected between the connection point between the diode 61a and the Zener diode 61c and the collector of the transistor 61f.

Further, the switch means 4 is composed of one transistor. 9 is a backflow prevention diode when the switch means 4 is OFF.

The other embodiment differs from the above embodiment in that the voltage detection means 6 is connected to detect changes in the voltage across the secondary winding 1a. However, 2
The voltage across the next winding 1a is the Zener diode 61
When the voltage becomes higher than the predetermined voltage set in c, the transistor 61f turns on, that is, when the voltage detection means 6 operates,
The operation of cutting off the output of the first rectifying means 2 when the transistor of the switching means 4 reaches 0FFI is the same as in the above embodiment.

FIGS. 3A and 3B are diagrams showing voltage waveforms at various parts of the circuit described later in the above embodiment, respectively.

Figure 3 A shows the voltage waveform F between the part PI and the GND line when the input AC voltage is A, C, 1 OOV.
1, a voltage waveform F2 between the portion P2 and the GND line (the portions PI and P2 are shown in FIG. 1A and FIG. 2).

FIG. 3B shows voltage waveforms F11 and F2 corresponding to the voltage waveforms Fl and F2 when the AC voltage is 200V.
21 is shown.

As is clear from the above two figures, the voltage proportional to the AC voltage on the primary side of the transformer 1 is applied to each part PI, P2.
is output to.

FIG. 4 shows the voltage waveforms Fl and Fil and the voltage waveform F3. between the part P3 and the GND line. It is a figure showing F31. The dotted lines in the figure are voltage waveforms PI when the input AC voltages are A, C, and 10QV.

P3, and the solid line is A, C, voltage waveform Fil between part PI-GND line in case of 200V (7) and part P3-
It is a diagram showing a voltage waveform F31 between GND lines.

In FIG. 4, the Zener voltages of the Zener diodes 6c and 61c are set within the range of the voltage difference Vd between the voltage waveform F31 shown by the solid line and the voltage waveform F3 shown by the dotted line.

FIG. 5A is a diagram showing the relationship between the voltage waveforms Fl and F2 and the waveform of the DC voltage V out between the output terminal 5 and the GND line when the input AC voltages are A, C, and 100V.

In addition, in FIG. 5B, the input AC voltages are A and C.

This is a diagram corresponding to FIG. 5A in the case of 200V.

As is clear from FIGS. 5A and 5B, it can be determined that the DC voltage Vout remains within a certain range even when the AC voltage is changed from A, C, LOOV to A, C, 200V.

(G) Effects of the Invention According to the present invention, a DC power supply circuit can be obtained that can always obtain a DC voltage within a certain range even if the input AC voltage is changed. This makes it possible to suppress power loss to approximately the same value as in the case of a single AC input voltage.

[Brief explanation of the drawing]

FIG. 1A is a block diagram of an embodiment of the present invention, FIG. 1B is a circuit diagram of the embodiment, FIG. 2 is a circuit diagram of another embodiment, and FIG. 3A is a block diagram of an embodiment of the present invention. A waveform diagram showing the relationship between voltage waveforms PI and P2 in the case of 100V, and FIG. 3B shows voltage waveforms F11. A waveform diagram showing voltage waveform F1.P21, FIG. F11. F3. F3
FIG. 5A, a waveform diagram showing the relationship between F1.1 and F1.1, shows the voltage waveform F1. A waveform diagram showing the relationship between F2 and the waveform of the DC voltage V out, and FIG. 5B, shows that the input AC voltage is A,
FIG. 6 is a waveform diagram showing the relationship between the voltage waveforms F'll and P21 and the waveform of the DC voltage Vout in the case of C, 200V, and FIG. 6 is a circuit diagram of a conventional example. DESCRIPTION OF SYMBOLS 1... Transformer, la... Secondary winding, lb... Tap, 2... First rectifier means, 3... Second rectifier means, 4... Switch means, 6. ...Voltage detection means. °−7・− Agent Patent Attorney Shintabe Nogawa, -i1::− Figure 1A Figure 1B

Claims (1)

[Claims] 1. A transformer having a tap on a secondary winding, a first rectifier for rectifying alternating current output to both ends of the secondary winding, and an output between the secondary winding and the tap. a second rectifying means for rectifying the alternating current, and a predetermined voltage in which either the voltage across the secondary winding or the voltage between one end of the secondary winding and the tap is set in advance. A direct current comprising a voltage detection means for detecting that the voltage is higher than the voltage, and a switch means that is activated by a signal output when the voltage detection means detects the voltage and cuts off the output of the first rectification means. power circuit.