Optocoupler dimmer circuit for high intensity, gaseous discharge lamp

DETAILED DESCRIPTION The present invention employs an optically isolated driver means, preferably in the form of an optocoupler, for providing separated timing and trigger actuation functions to a gated bypass means connected to a reactive portion of a lamp ballast.
The gated bypass means and ballast connections are similar to that shown in the circuits disclosed in U.
S.
Pat.
Nos.
3,816,794 and 3,894,265; however, in the present invention, the gate of the gated bypass means, normally a triac, is connected to the drive element, such as a phototriac, phototransistor, or photoSCR, or an optocoupler.
The receiver element, preferably in the form of a light emitting diode (LED), is actuated by externally applied pulses.
The pulsing determines the duration of conduction of the LED and, hence, the duration of drive voltage through the driver portion to the gated bypass means.
The low voltage applied through the driver portion is derived from the ac distribution line by transformer action, a capacitor divider network, a tap from a reactor ballast, or the like.
Bridge networks and Zener diodes can be used to ensure operation of the gated bypass means only at proper operating times.
The LED can be connected to receive unipolar pulses, or can be connected to a suitable rectifier network for pulse shaping from bipolar pulses to unipolar pulses.
Also, high frequency signals superimposed over the ac distribution line or applied by separate gate leads can be suitably filtered for use as pulses applied to the LED.
The use of high frequency in this connection also permits selective filtering from among different frequencies by timed circuits connected to different lamps so that selective dimming of the different lamps may be chosen.