Patent Research

The patent research was conducted by searching online government patent registries. These included Canada, United States, and Europe. The parameters that were considered during the search were HPS, standard ballast, dimming, and power control. The list of patents  that resulted from each search were then evaluated for to determine if they were applicable to the project scope.

From this short list, approximately 5-10 patents of interest were found. The patent that was chosen used a simple, fixed-firing angle technique. The theory was then modified and implemented using a micro-controller to allow for an adjustable firing angle. Below is an excerpt from the patent of interest.

Patent Number 3925705US

Circuit Design

A Triac is an AC switching device which will block an applied voltage until a gate signal is applied, at which point the device will conduct. The device will continue to conduct even if the gate signal is removed. The device will stop conduction once the current is removed externally. Phase angle firing is a method of AC voltage control where a Triac blocks a portion of  each cycle.   The phase angle is the delay of the blocked voltage with reference to the 120VAC Line zero crossing. By changing the amount of  delay, the applied current to the lamp can be controlled.

 The micro-controller adjusts the phase angle firing of the Triac, thus controlling the output current to the HPS Lamp.

 Circuit Diagram


Software Design

The micro-controller handles the triggering of the Triac. This is done by providing a gate signal to an interface circuit at appropriate time intervals. When power is applied to the circuit, the micro-controller applies a gate signal to the interface circuit by setting an output pin low. The gate signal is continuously applied while the lamp is warming up.

After approximately 5 minutes, the micro-controller reads an input port for the dimming setting. If the setting is 100% then the micro-controller will continue to apply the continuous gating signal. It will then recheck the input port for a dimmer setting.

If the dimmer setting from the input port is not 100%, a timer is loaded with an appropriate phase delay time value. When the input AC waveform passes from negative to positive voltage, a positive "zero crossing" is detected. Once a positive zero crossing is detected, the gate signal is removed, turning off the Triac. The phase delay timer is also started. When the timer reaches zero, a 1ms gate pulse is applied to the interface circuit, turning on the Triac. The phase delay timer is reset to the correct value and the micro-controller waits for a negative zero crossing. Once this occurs, it will start the phase delay timer. When the timer reaches zero, a 1ms gate pulse is applied. The micro-controller will then read the input port for a dimmer setting, repeating the cycle.

Software Flow Chart