Ramp and pedestal control circuit

A control circuit for providing a threshold voltage to enable the supply of electrical energy from an alternating current source to a load comprising:

• a first pair of electrical circuit elements connected in series;
• a second pair of electrical circuit elements connected in series, said first and second electrical circuit element pairs being connected in parallel to a source of alternating current;
• and
• means for interconnecting the series junction of said first electrical circuit element pair and the series junction of said second electrical circuit element pair to conduct current from one of the series junctions to the other thereof, said interconnecting means comprising a pair of oppositely poled series connected zener diodes and a pair of balancing resistors each connected in parallel with a corresponding zener diode and having a resistance value selected to compensate for variations between the zener diodes for minimizing the net direct current component of electrical energy supplied to the load.

A ramp and pedestal phase control circuit for controlling electrical energy supplied from an alternating current source to a load comprising:

• a controllable alternating current switching device;
• an electrical energy storage device;
• means for clipping both positive and negative peaks from the alternating current voltage to provide a clipped alternating current voltage as an output;
• threshold means coupled to said switching device for enabling it when a voltage applied to said threshold means exceeds a predetermined value;
• means coupled to the output of said clipping means for rapidly increasing the voltage applied to said threshold means to a first value less than the predetermined value and including a pair of circuit elements connected in series;
• means coupled to the output of said clippings means for more slowly further increasing the voltage applied to said threshold means to at least the predetermined value so as to enable said switching device and including another pair of circuit elements connected in series;
• means for respectively interconnecting the series junction of said first named circuit element pair and said another circuit element pair so as to conduct current only when a potential difference therebetween exceeds a predetermined value greater than zero, said first name circuit element pair and said another circuit element pair being connected in parallel to the output of said clipping means, and said interconnecting means comprising a pair of oppositely poled series connected zener diodes;
• and
• at least one balancing resistor connected in parallel with a corresponding zener diode and having a resistance value selected to compensate for variations between the zener diodes for minimizing the direct current component of the electrical energy supplied to the load.