JP4811720B2 - Electronic transformer - Google Patents

Description

  The present invention relates to a switching power supply, and more particularly to a power supply that directly switches an alternating current.

The simplest way to create an AC voltage insulated from commercial AC100V is to use an AC transformer. To reduce the size of the transformer, the AC is once converted to DC as shown in FIG. A method is used in which a high frequency current is generated by switching direct current and an insulated voltage is generated through a high frequency transformer. This transformer is called an electronic transformer.
In the conventional electronic transformer, the alternating current is once exchanged into the direct current by the bridge rectifier, but the voltage drop by the bridge rectifier becomes about 2V, which is one of the causes of reducing the efficiency of the electronic transformer.

  An object of the present invention is to eliminate the loss of the bridge rectifier, which has conventionally reduced the efficiency, by directly switching the alternating current without first turning the alternating current into a direct current.

  In the present invention, in order to directly switch alternating current, two bidirectional switches composed of two MOSFETs are used to synthesize a signal obtained by detecting the positive / negative of an alternating sine wave and a high-frequency signal to form a gate of the MOSFET. It is characterized by adding to.

  The electronic transformer of the present invention improves efficiency because the loss of the bridge rectifier can be zero.

  The best mode for carrying out the invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
In the figure, reference numeral 9 denotes an AC phase identification circuit which outputs a pulse from the terminal P when the AC voltage is in the positive phase of the sine wave, and outputs a pulse from the terminal S when it is in the negative phase. Reference numeral 10 denotes a dual oscillation control circuit, which alternately outputs pulses from the terminal U and the terminal V. The width of each pulse is the same. There may be a delay time in which neither U nor V emits a pulse. Reference numerals 11 to 14 denote OR circuits.
The ON / OFF state that each pulse and 4 to 7 MOSFETs can take is assumed to be 1 while the pulse of the AC phase identification circuit and the dual oscillation control circuit is output, and 0 when the pulse is not output. The results are summarized in Table 1.

Table 1 shows the MOSFET on by 1 and off by 0. The output of the AC phase identification circuit is 0 when P is 1 and 1 when P is 0. In the dual oscillation control circuit, if U is 1, V is 0, and if V is 1, U is 0. There is also a state where U is 0 and V is 0.
In the state A of Table 1, current flows from the AC power source through the MOSFETs 4 and 5, the primary winding 8 a of the transformer 8 and the capacitor 3, and power is supplied to the load 15 through the secondary winding 8 b of the transformer 8. When the state B is reached, the current from the AC power supply stops, and the excitation energy accumulated in the transformer 8 is discharged through the body diodes of the MOSFET 7 and MOSFET 6 of the ON-shaped bear and the capacitor 3 and is regenerated as charges in the capacitor 3. When the state C is reached, current flows from the AC power source through the capacitor 2, the primary winding 8 a of the transformer 8, and the MOSFETs 6 and 7, and power is supplied to the load 15 through the secondary winding 8 b of the transformer 8. In the state D, the current from the AC power supply is stopped, and the excitation energy accumulated in the transformer 8 is discharged through the MOSFET 5 and the body diode of the MOSFET 4 and the capacitor 2 and is regenerated as charges in the capacitor 2. In this way, the state is repeated and the current from the AC power source is directly switched and supplied to the load via the transformer 8. The waveforms of the current flowing through the AC power supply and the current flowing through the load are shown in FIG.
Excitation energy, which is excess energy that accumulates in the transformer 8 when the transformer 8 passes power, is regenerated and does not cause a loss.

FIG. 3 is a circuit diagram showing an embodiment of the second aspect of the present invention. The steps from the AC power source 1 to the primary winding 8a of the transformer 8 are the same as those in FIG.
In the figure, reference numerals 16 to 19 denote MOSFETs, and pulses of the AC phase identification circuit 9 and the dual oscillation control circuit 10 are supplied to their gates via AND circuits 20 to 23.
Table 2 shows a summary of the on / off states of the MOSFETs 11 to 14 and the MOSFETs 20 to 23 with respect to the pulses of the AC phase identification circuit 9 and the dual oscillation control circuit 10 in the circuit of FIG.

In the state A of Table 2, as described with reference to FIG. 1 of the embodiment, the current flows through the primary winding 8a of the transformer 8. However, since the MOSFET 16 is in the ON state, the current is supplied from the secondary winding 8b to the MOSFET 17. The power is supplied to the load via the body diode and the MOSFET 16 in the on state. In state B, MOSFETs 16 to 19 are off, so no current is supplied to the load. In state C, a current flows through the primary winding 8a of the transformer 8 in the opposite direction to that in the state A. However, since the MOSFET 18 is on, the current of the secondary winding 8b is connected to the body diode of the MOSFET 19 and the on state. It is supplied to the load via the MOSFET 18. The direction of the current flowing through the load is the same as in the state A.
That is, the current flowing through the load coincides with the AC phase. FIG. 4 shows waveforms of current flowing through the AC power source and current flowing through the load.
By inserting a filter that removes high frequencies before the load, the current flowing through the load becomes a sine wave.
FIG. 5 is a circuit diagram showing an embodiment of the third aspect of the present invention. MOSFETs 4 to 7 and 16 to 19 in FIG. 3 are replaced by combinations of IGBTs and diodes. The operation is the same as the circuit diagram of FIG.

  By directly switching the alternating current, the bridge rectifier can be eliminated and the efficiency is improved because the loss is reduced accordingly. Further, since the current supplied to the load can be easily changed to an alternating current, it can be replaced with a conventional commercial transformer.

  FIG. 2 is a circuit diagram showing an embodiment of the invention as set forth in claim 1;   It is a wave form diagram which shows the current waveform of FIG.   It is a circuit diagram which shows the Example of invention of Claim 2.   It is a wave form diagram which shows the current waveform of FIG.   It is a circuit diagram which shows the Example of invention of Claim 3.   It is a circuit diagram which shows an example of a conventional system.

Explanation of symbols

1 AC power supply 2, 3 capacitor 4 second MOSFET
5 First MOSFET
6 Fourth MOSFET
7 Third MOSFET
8 Transformer 8a Primary winding 8b Secondary winding 9 AC phase identification circuit 10 Dual oscillation control circuit 11, 12, 13, 14 OR circuit 15 Load 16 Fifth MOSFET
17 Sixth MOSFET
18 Seventh MOSFET
19 Eighth MOSFET
20, 21, 22, 23 AND circuit 24, 25, 26, 27, 28, 29, 30, 31 IGBT
32, 33, 34, 35, 36, 37, 38, 39 Diode 101 Bridge rectifier 102, 103 Transistor

Claims (3)

  A series circuit composed of an AC power source and first and second capacitors connected in parallel to the AC power source; a series circuit composed of first and second bidirectional switch circuits connected in parallel to the AC power source; A transformer primary winding connected between a midpoint of the first and second capacitors and a midpoint of the first and second bidirectional switch circuits; and An electronic transformer comprising a coupled secondary winding, a load connected to the secondary winding, and a dual oscillation control circuit for alternately turning on and off the first and second bidirectional switch circuits The first bidirectional switch circuit includes first and second MOSFETs connected in series in opposite directions, and the second bidirectional switch circuit includes third and third MOSFETs connected in series in opposite directions. The AC power source comprising a fourth MOSFET An AC phase identification circuit that detects a positive half wave and a negative half wave of a voltage sine wave and outputs a signal is added to generate a signal that is generated when the AC phase identification circuit detects a positive half wave. The signal of the dual oscillation control circuit is added to the gates of the first MOSFET and the third MOSFET in an OR connection, and a signal generated when the AC phase identification circuit detects a negative half-wave is output to the second MOSFET. An electronic transformer characterized in that an alternating current can be directly switched by applying an OR connection to the signal of the dual oscillation control circuit to the gates of the MOSFET and the fourth MOSFET.   2. The fifth MOSFET according to claim 1, wherein a fifth MOSFET is inserted in series between one terminal of the secondary winding and one terminal of the load, and another terminal of the secondary winding is separated from the load. A sixth MOSFET is inserted in series between one terminal of the second winding, a seventh MOSFET is connected between the other one terminal of the secondary winding and one terminal of the load, and the secondary winding is connected. An eighth MOSFET is connected between one terminal of the line and the other terminal of the load, and two signals applied to the gate of the fifth MOSFET by OR connection to the gate of the first MOSFET are ANDed. In addition, two signals are applied by AND connection to the gate of the sixth MOSFET and ORed to the gate of the second MOSFET to the gate of the sixth MOSFET, and ORed to the gate of the third MOSFET to the gate of the seventh MOSFET Add on connection One of the signals added by an AND connection, electronic transformers, characterized in that the addition of the two signals added in the OR connected to a gate of said fourth MOSFET to the gate of said eighth MOSFET with an AND connection.   3. The electronic transformer according to claim 2, wherein a part or all of the first to eighth MOSFETs are replaced with IGBTs, and diodes are connected in parallel to the IGBTs.

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