JPS6249718B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phase control device that requires a peak value.

The conventional control system is shown in Figure 1, and the waveforms of each part are shown in Figure 2.
As shown in the figure.

This method synchronizes with the power supply and after a certain time ta,
The gate signal generating circuit outputs the ignition pulse 9 shown in FIG. 2, conducts the triac 2, applies a voltage of 10 to the ballast, and dims the discharge lamp. However, when the firing angle exceeds 90°, the voltage applied to the ballast decreases by ΔV in peak value, as shown in the waveform after 10 tb. Discharge lamps generally require a high lamp restriking voltage, so when the peak voltage value decreases, it becomes impossible to maintain a stable discharge, causing flickering or extinguishing.

If the firing angle is 90° or less, the time from when the lamp current becomes zero until the voltage is applied is short, so
Due to the residual thermoelectrons within the discharge lamp, the restriking voltage can be relatively low, thereby maintaining stable discharge.

An object of the present invention is to perform stable dimming of a discharge lamp.

According to the present invention, even if the effective value of the voltage applied to the ballast that performs dimming decreases, a peak voltage is always added to the discharge lamp to perform stable control.

An embodiment of the present invention is shown in FIG. 3, and waveforms of various parts are shown in FIG. 4.

This control circuit performs phase control using a gate turn-off thyristor 14 that is passed through a full-wave rectifier 13 between an AC power supply 12 and a ballast 16.
Gate turn-off thyristor 14 which is the main control element
The characteristic of the gate is that it becomes conductive when a forward pulse is applied to the gate, and conversely, when a reverse bias pulse is applied to the gate, the conduction current is cut off and the gate becomes non-conductive. The gate signal generation circuit applies a pulse in the forward direction at a phase angle before 90 degrees, and a pulse in the reverse direction at a phase angle after 90 degrees. The circuit operation is
Forward pulse 2 after t ₀ from zero potential of AC power supply 20
1, gate turn-off thyristor 1
4 conducts and passes through the full-wave rectifier 13 to the ballast 16
A voltage is applied to. After conduction, when a reverse gate pulse is applied after a phase angle of 90° and td, the gate turn-off thyristor 14 becomes non-conductive and a voltage of waveform 22 is applied to the ballast 16. To dim the light by lowering the input voltage of the ballast 16, the ignition phase is set to tf, which is longer than tc, and the ignition phase is also set to tg, which is shorter than td. Therefore, the discharge lamp 19 maintains stable discharge by constantly applying the maximum voltage vp of the AC power source 12 with a phase angle of 90 degrees.

Therefore, it has the effect of stabilizing the dimming of the discharge lamp.

[Brief explanation of the drawing]

FIG. 1 is a conventional control circuit diagram, FIG. 2 is a waveform diagram of various parts of the conventional circuit, FIG. 3 is a control circuit diagram of the present invention, and FIG. 4 is a gate pulse waveform diagram. 13...Full-wave rectifier, 14...Gate turn-off thyristor, 15...Gate signal generation circuit, 16
... Ballast, 17... Capacitor, 18... Filament coil, 19... Discharge lamp.

Claims (1)

[Claims] 1. An AC power source, a discharge lamp and a ballast connected to this power source, and a phase control circuit between the ballast and the power source; a gate turn-off thyristor is used as the main control element of the phase control circuit; The signal generation circuit is centered around a phase angle of 90°, outputs a firing pulse between 0 and 90° to conduct, and applies a turn-off gate pulse between 90° and 180° to make it non-conductive. A discharge lamp dimmer characterized by controlling a conduction angle.