JPS6044847B2 - AC switching circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alternating current switching circuit, and more particularly to an alternating current switching circuit suitable for switching alternating current boosted by a transformer based on an on/off command.

For example, facsimile machines employ flash fixing in which developed recording paper being transported is irradiated with flash light one after another in a predetermined width to fix the image.

To perform this flash fixing, it is necessary to boost the voltage of commercial alternating current using a transistor, charge a capacitor through a rectifier, and apply the voltage to the flash lamp at a predetermined timing.

For this purpose, it is necessary to turn on and off at the timing of the alternating current supplied to a load such as a capacitor. In this way, in order to supply the AC boosted by the transformer to the load at a predetermined timing and for a predetermined time, conventionally a switch such as a triax is provided on the secondary side of the transformer, and this switch is operated at the zero cross point based on a command. I was turning it on and off.

For this reason, there were nine colors that required large and expensive switches with high withstand voltage. An object of the present invention is to provide an alternating current switching circuit which can be made smaller and cheaper, and which can quickly respond to on/off commands, by eliminating the nine colors of the prior art described above.

In order to achieve this objective, the present invention provides a switch on the primary side of the transformer, and when turning off this switch,
It is characterized in that it is turned off at a zero-crossing point immediately after an off-command is input, and when it is turned on, it is turned on at a zero-crossing point of the same phase and phase as the phase of the alternating current at the above-mentioned off time after an on-command is input. .

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of an AC switching circuit showing an embodiment of the present invention, in which 1 is a circuit that boosts the primary commercial AC voltage applied between terminals 2 and 3 and is connected between terminals 4 and 5. 6 is a high-voltage transformer that supplies the secondary side load, and 6 turns on the primary side AC.
This is a tri-attack that turns off.

7 is a small transformer for signals, the secondary side of which is connected to a zero-cross pulse generation circuit 8.

This circuit 8 consists of a resistor R1, a small Zener diode, and an OR gate 0R connected as shown in the figure, and generates a zero-cross pulse b that falls near the zero-cross point of AC a, as shown in the signal waveform diagram of FIG. .

This pulse b is applied to D flip-flops 9, 10 and J-
It is used as a clock pulse for the K flip-flop 11. Reference numeral 12 denotes an inverting circuit, and the on/off command signal c is inputted to the flip-flops 9 and 11 through the inverting circuit 12.

The Q outputs E, f of the flip-flops 9, 10, which are set or reset according to the result, are applied to the base of the transistor 14 via the AND gate 13. Reference numeral 15 denotes a gate control circuit for turning on and off the triac in accordance with input signals, and is composed of a photocoupler consisting of a light emitting element 16 and a light receiving element 17, and a gate circuit 18.

This circuit 15 is provided to separate the gate side of the triac 6 and its input side into the circuit 15, and may be constructed using a pulse transformer instead of a photocoupler.

The AC switching circuit of this embodiment is constructed as described above. Therefore, as shown in FIG. 2, a zero-cross pulse b synchronized with alternating current a is constantly applied to the C terminals of flip-flops 9 to 11. Now, when the command signal c changes from on to off, that is, from the RHJ level to the RLJ level, the D and J inputs of flip-flops 9 and 11 become R.
Changes from LJ level to RHJ level.

As a result, the flip-flop 9 is immediately set at the falling edge of the pulse b, and its O output f becomes the RLJ level.

Therefore, the output G75 of the AND gate 13 goes to the LJ level and the transistor 14 is turned off, so that the output h of the gate circuit 18 disappears and the triac 6 is turned off. In Example 1 shown in FIG. 3, the turn-off point at this time is the zero-crossing point E of the phase a where the alternating current a changes from the negative phase to the positive phase.

On the other hand, at this time, flip-flop 11 is also set at the rising edge of pulse b, and its Q output d is brought to the RHJ level.

After that, while the J input is at the RHJ level, this flip-flop 11 inverts its state every time the pulse b is input, and changes the state to AC a.
It returns to its original state every phase β. In response to the Q output d of the flip-flop 11, the flip-flop 10 also inverts its state every time the pulse b is input, but this state change is
It occurs later than flip-flop 11 by one cycle of pulse b, that is, half a cycle of AC a.

That is, the flip-flop 10 returns to its original state every phase a. In other words, the phase a of the alternating current a at the time when the transistor 14 is turned off is memorized. next,
When the command signal c changes from off to on, the D and J inputs of flip-flops 9 and 11 change from the RHJ level to the RL. Change to j level.

As a result, the flip-flop 9 is set at the falling edge of the direct pulse b, and its O output f becomes the RHO level again.

On the other hand, the flip-flop 11 is reset at the falling edge of the pulse b of phase β, and its Q output d is set to RL. j level and maintain that state thereafter.

Furthermore, the flip-flop 10 is reset at the falling edge of the pulse b of phase a, sets its η output e to the RHJ level, and thereafter maintains this state. Therefore, this state does not change even if the point at which the command signal c turns off shifts to the position indicated by the dotted line in the figure. At this point, the output g of the AND gate 13 becomes the RHJ level, turns on the transistor 14, operates the gate control circuit 15, and fires the triac 6.

As a result, the triac 6 only needs to be of low voltage and low current capacity, and the high voltage load on the secondary side of the step-up transformer 1 can be controlled on and off using the triac 6, which is small and inexpensive.

That is, when turning on and off the primary side of the step-up transformer 1,
For example, if the timing of on and off is incorrect,
It turns off at the zero-crossing point where the phase changes from normal phase to negative phase, and then turns on at the zero-crossing point where the phase changes from negative phase to positive phase.
The iron core of the high-voltage transformer 1 becomes saturated, and an inrush current of about 2 @ normally flows into the primary side. However, in the case of this embodiment, as mentioned above, the on/off is always at the zero cross point of the same phase a, so the residual magnetic field stored in the iron core when it is off is canceled by the current flowing when it is on, and the iron core is not saturated, and the step-up transformer 1 always functions normally. As a result, the triax 6 can be small and inexpensive. Incidentally, in the above embodiment, the signal generating circuit, which is composed of the transformer 7, the gate control circuit 15, etc., and is used to turn on and off the triax 6 at a predetermined timing, is provided separately from the triax 6. , by omitting the transformer 7, it is also possible to integrate it with the triax 6. FIG. 3 shows another embodiment of the present invention for this purpose, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts, and 19 is a conventionally well-known zero-volt ignition circuit.

From this zero volt ignition circuit 19, the first
A zero-crossing pulse b corresponding to the pulse b shown in FIG. 1 and FIG. 2 is generated.

Therefore, if this pulse b is input to the clock terminal C of the flip-flops 9 to 11, the signal g shown in FIG.
The ignition signal h is applied at the timing of . When the AC switching circuit is configured in this manner, the signal generation circuit for turning on and off the triax 6 can be integrated with the triax 6, so that an extremely compact AC switching circuit can be obtained.

As described above, according to the present invention, when an off command is given,
Since the primary side of the transformer is turned off at the zero cross point immediately after that, the AC supplied to the load is turned off within half a cycle or less after the command is given, without generating any high-frequency noise. can do.

In addition, the phase of the alternating current when off is memorized, and the next time an on command is given, the zero cross point corresponding to that phase will be 1
Since the next side is turned on, saturation of the transformer core can be prevented and the transformer can always function normally. As a result, a low-voltage, low-current type, inexpensive switch can be used, and a compact, economical, and good AC switching circuit can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing signal waveforms at various parts to explain its operation, and FIG. 3 is a circuit configuration diagram showing another embodiment of the invention. be. 1, 7...Trans, 6...Triack, 8...
・Zero cross pulse generation circuit, 9, 10, 11...Flip-flop, 12...Inverting circuit, 13...And gate, 14...Transistor, 15...Gate control circuit, 16... - Light emitting element, 17... Light receiving element, 18... Gate circuit, 19... Zero volt ignition circuit.

Claims (1)

[Claims] 1 Turn on the AC supplied to the load via the step-up transformer.
In an AC switching circuit that performs switching at a zero cross point based on an off command, a switch is provided on the primary side of the step-up transformer, and a detection circuit that detects the zero cross point of the AC and outputs a zero cross detection signal, and an off command. A first circuit that generates a first signal in synchronization with the zero-cross detection signal immediately after the input of the ON command, and a second signal in synchronization with the zero-cross detection signal immediately after the input of the ON command, and a zero-cross detection immediately after the input of the OFF command. a second circuit that generates a third signal synchronized with every other zero cross detection signal from the signal;
The switch is turned off in synchronization with the first signal, and the switch is turned off in synchronization with the first signal.
and a third circuit that turns on the switch in synchronization with the third signal immediately after the signal is generated.