The SL441C is a symmetrical burst control integrated circuit in an 8 pin DIL package. When used with a triac, AC power may be regulated by varying the number of mains cycles applied to the load in a fixed timing period. The device is especially suited to room temperature control applications including panel heaters, fan heaters etc. Zero
Voltage Switching has the advantage of minimising radio frequency interference.

FEATURES
■ Balanced zero voltage point crossing detector, spike filter and pulse generator for reliable triggering of the triac.
■ A period pulse generator and bistable which are arranged to provide symmetrical burst control and eliminate 1/2 wave firing. (EN50.006 BS5406,1976)
■ A ramp generator whose output is used to modify an internal reference voltage which is then compared with the voltage appearing on the thermistor to form a proportional control system. The period of the ramp generator is defined externally and may be chosen to limit 'lamp flicker' in accordance with EN50.006/BS5406, 1976.
■ The comparison amplifier has inbuilt hysteresis to eliminate switching jitter and a spike filter/sampling circuit to provide high immunity to both spikes and coherent 50Hz/60Hz.
■ Thermistor malfunction may be sensed and power automatically removed.
■ A supply voltage sensing circuit which inhibits firing pulses when the supply is inadequate to guarantee proper circuit operation. This eliminates stressing of the triac at switch-on.