JPS58142624A - Phase controlling circuit - Google Patents

Abstract

PURPOSE:To make a pulse transformer small in size, by using an FET as a switching element. CONSTITUTION:To an electric power source 1, a load 2, a rectifying bridge 3 and an FET4 are connected, and between the gate and the source of the FET4, the secondary side winding of a pulse transformer 7 which has connected in series a capacitor 5 and a diode 6 is connected, and to its primary side, a controlling circuit 8 is connected. The controlling circuit 8 detects voltage zero phase of the electric power source 1, and controls phase of the FET4 through the pulse transformer 7. The pulse transformer 7 outputs an intermittent pulse, and turns on the FET4 during this output period. By constituting in this way, the pulse transformer 7 can be made small in size.

Description

[Detailed description of the invention] The present invention relates to a zero-cross-on type phase control circuit.

Switching elements such as trimacs and thyristors are used for power control using the phase control method, and are made conductive in accordance with the controlled phase. Sometimes sudden changes in voltage or current occur, generating large noise. Furthermore, especially when the load is a lamp or motor, a large rush current flows when the power is turned on, and countermeasures are required. In order to reduce this, as shown in the output voltage waveform in Figure 2, the switching element is made conductive at the zero phase of the commercial frequency (point B), and the controlled phase is cut off by R5 (point 0). , both the noise and the rush current become small, and the noise filter becomes fffiM([r+. However, if you want to use a pulse transformer that isolates the control circuit from the main circuit for driving, the transformer size will be large and the price will be high because commercial frequency output pulses are required, and the GTO thyristor is There are many drawbacks, such as the need to control a fairly large current at turn-off and the drive circuit becoming complex.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a zero-cross-on type phase control circuit that requires a simple drive circuit.

The purpose of this is to use a field effect transistor as the switching element of the phase control circuit, connect a capacitor between the gate and source of the field effect transistor, and control the voltage between both poles of the capacitor i in accordance with the phase of the power supply voltage. This is achieved by applying a voltage at the output of a pulse transformer.

Embodiments of the present invention will be described below with reference to the drawings. In Figure 3, power supply 1 has load 2, rectifier block IJ 7
and four field effect transistors (FF:T) are connected. A secondary winding of a pulse transformer 7 having a capacitor 5 and a diode 6 connected in series is connected in parallel between the gate and source of the F E 'I' 4.

A control circuit 8 is connected to the primary side of the pulse transformer 7.
This control circuit 8 detects the zero phase of the voltage of the power supply 1 and drives the FEiT 4 via the pulse transformer 7. The control circuit 8 is insulated from the main circuit by a pulse transformer. In this case, since the gate input resistance of the FICT is large, the voltage across the capacitor 5 is maintained at a value sufficient to keep the FET in the on state even if the output of the pulse transformer is in an intermittent pulse form. Diode 6 prevents the charge on this capacitor from discharging through the secondary winding of the pulse transformer. The pulse transformer 7 only needs to transmit a pulse whose width is extremely narrow compared to the period of the commercial frequency, and the pulse current only needs to compensate for the discharge of the capacitor 5, so that it can be made smaller and simpler. The period of the transmission pulse of the pulse transformer 7 may be selected to be about a fraction of the discharge time constant of the capacitor 5. As shown in the operation waveforms of each part in FIG. 4, the pulse transformer 7 is controlled by the control circuit 8 in response to the zero phase of the commercial frequency, transmits the pulse 11, and makes the FEiT conductive at point B. When transmission of the pulse 11 is stopped by the control circuit 8 in response to the next controlled phase, the charge in the capacitor 5 is discharged through the gate resistor, and the FKT is cut off at the 0 point, resulting in the output waveform 12 in FIG. , and zero-cross-on type phase control is performed. The cutoff time of FET is gate,
It is also possible to adjust by inserting a resistor between the sources.

In order to perform power control in the embodiment shown in FIG.
4, a bipolar transistor 9 is connected in series to the load 2, and a bipolar transistor 9 is connected in series between its base and collector as shown in FIG. 5, in which parts common to those in FIG. If you connect FET4 to
The output of is small.

As described above, the phase control circuit according to the present invention uses an FET as a switching element, and can use a small pulse transformer that only needs to transmit narrow pulses, and can control the FET with a simple drive circuit. Because you can
It can be used extremely effectively as a zero-cross-on type phase control circuit for noise reduction, which has recently been subject to stricter regulations.

[Brief explanation of drawings]

Fig. 1 is an example of the operating waveform of the phase control circuit, Fig. 2 is an example of the operating waveform of the zero-cross-on type phase control circuit, Fig. 3 is a circuit diagram of an embodiment of the present invention, and Fig. 4 is the pulse transformer and An example of the output waveform of the FET, FIG. 5 is a circuit diagram of another embodiment of the present invention. 1: Power supply, 2 = Load, 4: FKT, 5: Capacitor, 6
: Diode, 7: Pulse transformer, 8: Control circuit. 71 fig.

Claims (1)

[Claims] 1) Equipped with a field effect transistor that can cut off the current flowing to the load, a capacitor is connected between the source and gate of the field effect transistor, and a pulse transformer that is controlled according to the phase of the power supply voltage is connected to both poles of the capacitor. A phase control circuit characterized in that an output voltage of is applied via a diode.