JPH05316645A - Multi-input power source circuit - Google Patents

Abstract

PURPOSE:To reduce the influence of the variation of an input voltage on an output voltage by making a control circuit to automatically perform control in accordance with the input voltage so that at least one transistor can be turned on. CONSTITUTION:An AC voltage generated across both ends of a secondary winding 16 is rectified by means of a rectifier circuit 24 and converted into a DC voltage by means of first and second smoothing circuits 28 and 29. Nearly equal voltages are generated across a first output terminal 20 and a first intersection 26 and across a first intersection 26 and a second output terminal 22 A control circuit 42 inputs the voltages at the terminal 20, intersection 26, and terminal 22 and discriminates the level of the AC voltage generated across both ends of the winding 16. When the voltage is high, the circuit 42 connects a first switching element 38 and disconnects a second switching element 40. As a result, the voltage across third and fourth output terminals 34 and 36 drops. When the voltage is low, the circuit 42 disconnects the element 38 and connects the element 44 so as to boost the voltage across the terminals 34 and 36.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a multi-input power supply circuit.

[0002]

2. Description of the Related Art In various countries around the world, voltage standards are different and commercial AC voltage values delivered to ordinary households are different. Therefore, if a product from one country is used incorrectly in another country where the voltage is different, it may fail to operate or even cause a fire, and a multi-input power supply circuit that can handle a wide range of input voltage is required. Has been done. In the conventional multi-input power supply circuit, the secondary winding is generally fixed,
Using an input transformer with several types of primary windings, a person manually switches the primary winding to be used according to the input voltage value.
The output voltage value from the secondary winding is kept within a certain range. Also, in a multi-input power supply circuit that automatically responds to changes in the input voltage, the AC voltage is once rectified and smoothed on the primary side, and the smoothed DC voltage is reconverted into a high frequency AC voltage by a switching element. A DC voltage having a predetermined voltage was converted and generated through an output transformer.

[0003]

However, the above-mentioned conventional multi-input power supply circuit has the following problems. First, when using an input transformer provided with several kinds of primary windings, it is necessary for a person to manually switch the primary windings according to the AC voltage supplied, which is troublesome. Also, 1
When the AC voltage is once converted to the DC voltage on the secondary side and then converted to the AC voltage again, the primary side has a high voltage, so that the parts used, such as the switch element, need to have high withstand voltage,
The number of parts that can be used is small and the price is high. Furthermore, when acquiring a foreign safety standard, the safety of the primary side becomes a problem, but since there are many parts on the primary side, there is a problem that it takes time to acquire and the cost also increases. Therefore,
The present invention has been made to solve the above problems, and an object of the present invention is to provide a multi-input power supply circuit capable of automatically responding to a wide range of input voltages.

[0004]

The present invention has the following constitution in order to achieve the above object. That is, a transformer in which a secondary winding having a center tap terminal is formed,
Input terminals are respectively connected to both ends of the next winding,
A rectifier circuit having a first output terminal that outputs a positive pulsating voltage to the center tap terminal and a second output terminal that outputs a negative pulsating voltage to the center tap terminal; and the first output terminal A first smoothing circuit provided between the center tap terminal and a first intersection, and a second smoothing circuit provided between the second output terminal and the first intersection. And a third output terminal for connecting one end of a load circuit to the first output terminal, a first output node and the second output terminal, and a load circuit. A fourth output terminal for connecting the other end of the first switch element, a first switch element interposed between the first intersection and the fourth output terminal, the second output terminal and the The second, which is interposed between the fourth output terminal and
And a voltage of the first output terminal, the first intersection, and the second output terminal are input to connect either one of the first switch element or the second switch element. And a control circuit that performs disconnection control to bring the state into a state.

[0005]

The AC voltage generated across the secondary winding of the transformer is rectified by the rectifier circuit and further converted into the DC voltage by the first smoothing circuit and the second smoothing circuit. As a result, substantially equal DC voltages are generated between the first output terminal and the first intersection and between the first intersection and the second output terminal.
The control circuit includes a first output terminal, a first intersection, and a second
The voltage of the output terminal is input to determine whether the AC voltage generated in the secondary winding of the transformer is high or low. If the voltage is high, the first switch element is connected and the second switch element is disconnected. And This lowers the voltage generated between the third output terminal and the fourth output terminal. When the AC voltage generated in the secondary winding of the transformer is low, the first switch element is turned off and the second switch element is turned on so that the third output terminal and the fourth output terminal are connected. The voltage generated between the terminals becomes high.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a connection diagram of the multi-input power supply circuit of this embodiment. First, the configuration will be described. The multi-input power supply circuit 10 includes a transformer 18 having a primary winding 12 to which a commercial AC voltage is input and a secondary winding 16 having a center tap terminal 14, and an input terminal at each end of the secondary winding 16. Rectifier circuit 2 having first output terminal 20 connected to each other and outputting a positive pulsating voltage to center tap terminal 14 and second output terminal 22 outputting a negative pulsating voltage to center tap terminal 14.
4, a first smoothing circuit 28 provided between the first output terminal 20 and the first intersection 26 connected to the center tap terminal 14, and a second output terminal 22 and the first intersection 26. A second smoothing circuit 30 provided between the first output terminal 20 and a third output terminal 34 for connecting one end of the load circuit 32, and a first intersection point 26. And the load circuit 3 as well as being connected to the second output terminal 22.
A fourth output terminal 36 for connecting the other end of
Of the second switching element 38 interposed between the second output terminal 22 and the fourth output terminal 36. Switch element 4
0 and the voltage of the first output terminal 20, the first intersection 26, and the second output terminal 22 are input, and either the first switch element 38 or the second switch element 40 is connected. And a control circuit 42 for performing disconnection control.

More specifically, the rectifier circuit 24 is provided with a filter circuit 44 and has a function of reducing high frequency noise of the AC voltage output from the secondary winding 16 of the transformer 18. The first smoothing circuit 28 and the second smoothing circuit 30 reduce high-frequency noise based on the large-capacity capacitor 46 for smoothing the pulsating voltage output from the rectifying circuit 24 and the center tap terminal 14. And a small-capacity capacitor 48. The load circuit 32 includes a stabilized power supply 50 and a load 52, and the stabilized power supply 50 has a third output terminal 34 and a fourth output terminal 3.
It has a function of further stabilizing the DC voltage output between the six and supplying it to the load 52. The first switch element 38 is P
Fourth transistor (TR4) which is an NP transistor
And a diode (D1) whose cathode is connected to the emitter of TR4. Here, the forward voltage of D1 is Vd1. The second switch element 40 is a third transistor (TR3) which is an NPN transistor.

The control circuit 42 includes a first resistor (R1), a second resistor (R2), a third resistor (R3), a fourth resistor (R4), a fifth resistor (R5), and a sixth resistor. Resistance (R6),
Seventh resistor (R7), Zener diode (ZD), P
The first transistor (TR, which is an NP transistor)
1) and a second transistor (TR2) which is an NPN transistor. One end of R1 is connected to the first output terminal 20, and the other end is connected to the cathode terminal of ZD. The anode terminal of ZD is connected to the fourth output terminal 36. Here, the Zener voltage of ZD is Vz. The emitter terminal of TR1 is the cathode terminal of ZD, the base terminal of TR1 is at the first intersection point 26 via R2, and the collector terminal of TR1 is at the fourth output terminal via R3 and R4 connected in series. It is connected to 36. The emitter terminal of TR2 is the base terminal of TR3,
The base terminal of TR2 is connected to the connection point of R3 and R4, and the collector terminal of TR2 is connected to the first intersection point 26 via R5. R6 connects between the base terminal of TR4 and the fourth output terminal 36, and R7 connects between the base terminal of TR4 and the emitter terminal.

Next, the operation will be described. Commercial power supply voltage in each country is roughly divided into high voltage system (commercial power supply voltage V
1: 200V to 240V) and a low voltage system (commercial power supply voltage V2: 100V to 120V).
In this embodiment, the operation in these two cases will be described.
Here, when the commercial power supply voltage V1 and the commercial power supply voltage V2 are applied to the primary winding 12 of the transformer 18, the first smoothing circuit 28 and the second smoothing circuit 28 are passed through the secondary winding 16 of the transformer 18. A substantially equal voltage is generated between both ends of the smoothing circuit 30, and the voltages are respectively E1 and E2 (≈E1 / 2). The forward voltage between the emitter and base terminals of TR1 is V
eb1. The saturation voltage between the collector and emitter terminals of TR3 is Vce3, and the saturation voltage between the emitter and collector terminals of TR4 is Vec4. Further, the Zener voltage Vz of ZD is lower than E1 when the commercial power supply voltage V1 is 200V, and the voltage (E2 when the commercial power supply voltage V2 is 120V (E2
It is set to be slightly higher than + Veb1).

First, the primary winding 12 of the transformer 18
A case in which the commercial power supply voltage V1 is applied to will be described. Between both ends of the second smoothing circuit 30, that is, the first intersection 2
6 and the voltage E1 generated between the second output terminal 22 are V
Since it is higher than z, the voltage applied to the base terminal of TR1 is higher than the voltage applied to the emitter terminal of TR1. As a result, TR1 is turned off. Therefore, no current flows through R3 and R4, TR2 is also turned off, and no current flows into TR3, so that TR3 is also turned off. At this time, the first output terminal 20, the third output terminal 34, the load circuit 32, the fourth output terminal 36, and D are provided between the first output terminal 20 and the second output terminal 22.
A current flows through the paths of 1, R7, R6 and the second output terminal 22. This current causes a voltage drop in R7, a forward voltage is applied between the base terminal and the emitter terminal of TR4, and TR4 is in a saturated ON state.
Therefore, the voltage Vo1 (= E1-Vd1-Vec4) is output between the third output terminal 34 and the fourth output terminal 36.

Second, the case where the commercial power supply voltage V2 is applied to the primary winding 12 of the transformer 18 will be described. Since the voltage E2 generated between both ends of the second smoothing circuit 30, that is, between the first intersection 26 and the second output terminal 22 is lower than Vz, the voltage applied to the base terminal of TR1 is TR1. It is lower than the voltage applied to the emitter terminal of the. As a result, TR1 is turned on. Therefore, R
A current flows through 3 and R4, a current is supplied to the base terminal of TR2, and TR2 is also turned on.
A current flows to the emitter terminal via 5. Along with this, current is also supplied to the base terminal of TR3, and TR3 is saturated and turned on. By saturating TR3 in this way, the voltage difference between the base terminal of TR4 and the anode terminal of D1 becomes Vce3. As a result, TR4 is turned off. Further, D1 prevents current from flowing from R7 to the fourth output terminal through the collector terminal of TR4 and the base terminal. Therefore, the third output terminal 34
And the fourth output terminal 36 between the voltage Vo2 (= 2 * E
2-Vec3) is output.

As described above, when the input voltage to the primary winding 12 of the transformer 18 is V1, the third output terminal 34
And the fourth output terminal 36, Vo1 (= E1-Vd
1-Vec4) is output and the input voltage is V2,
Vo2 (= 2 * E2-Vec3) is output. Here, since E2≈E1 / 2, Vo2≈ (E1-Ve
c3), Vec4≈Vec3, and Vd1 is negligible as compared with E1, so Vo1≈Vo2. As described above, since the control circuit 42 automatically controls TR3 and TR4 so that at least one of them is turned on in accordance with the input voltage, the third output terminal 34 and the fourth output terminal 36 are connected between the third output terminal 34 and the fourth output terminal 36. The influence of the fluctuation of the input voltage on the output voltage can be reduced, and the loss in the stabilized power supply 50 provided in the load circuit 32 can be reduced.

When the commercial power supply voltage applied to the primary winding 12 of the transformer 18 is V1, the power is consumed between the first intersection 26 and the second output terminal 22 (between the second smoothing circuits 30). The generated current is ZD Zener current and D1 to TR4.
It is a light load because it is only the current that flows through the base terminal and R6 through the emitter terminal of. Next, when the commercial power supply voltage applied to the primary winding 12 of the transformer 18 becomes V2 and the voltage between the first intersection 26 and the second output terminal 22 decreases, as described above. TR1 enters the ON state and TR3 also enters the ON state. Therefore, since the current flowing to the load circuit 32 is added to the current consumed between the first intersection 26 and the second output terminal 22, the first intersection 26
The voltage between the second output terminal 22 and the second output terminal 22 is further lowered, though slightly, whereby the ON state of TR1 is promoted and TR1 can be surely shifted to the saturated ON state.

Although various preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and many modifications can be made without departing from the spirit of the invention. Of course.

[0015]

By using the multi-input power supply circuit according to the present invention, substantially equal DC voltages are generated between the first output terminal and the first intersection and between the first intersection and the second output terminal. The control circuit, to which the voltages of the first output terminal, the first crossing point, and the second output terminal that are generated are input, determines whether the AC voltage generated in the secondary winding of the transformer is high or low, and In this case, the first switch element may be connected and the second switch element may be disconnected to reduce the voltage generated between the third output terminal and the fourth output terminal.
When the AC voltage generated in the next winding is low, the voltage generated between the third output terminal and the fourth output terminal is set by disconnecting the first switch element and connecting the second switch element. Can be higher Therefore, even if the commercial AC voltage input to the transformer changes over a wide range, it is possible to automatically suppress the fluctuation of the output voltage to the load circuit.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of a multi-input power supply circuit according to the present invention.

[Explanation of symbols]

 10 multi-input power supply circuit 14 center tap terminal 16 secondary winding 18 transformer 20 first output terminal 22 second output terminal 24 rectifier circuit 26 first crossing point 28 first smoothing circuit 30 second smoothing circuit 32 load Circuit 34 Third output terminal 36 Fourth output terminal 38 First switch element 40 Second switch element 42 Control circuit

Claims (1)

[Claims] 1. A transformer in which a secondary winding having a center tap terminal is formed, input terminals are connected to both ends of the secondary winding, and a positive pulsating voltage is output to the center tap terminal. A first output terminal and a second output terminal that outputs a negative pulsating voltage to the center tap terminal, and a first intersection point connected to the first output terminal and the center tap terminal. Connected to the first output circuit, a second smoothing circuit provided between the second output terminal and the first intersection, and a first smoothing circuit connected to the first output terminal. A third output terminal for connecting one end of the load circuit, and a fourth output for connecting the other end of the load circuit while being connected to the first intersection and the second output terminal A terminal, the first intersection and the A first switch element interposed between a fourth output terminal and the second output terminal; a second switch element interposed between the second output terminal and the fourth output terminal; 1 output terminal, the first intersection, and the second
A multi-input power supply, comprising a control circuit for inputting a voltage at an output terminal of the control circuit and performing connection / disconnection control to bring one of the first switch element and the second switch element into a connected state. circuit.