The Siemens IC SLB 0587 permits the design of digital electronic phase controls for operation of incandes-cent lamps, dimmer for low-voltage halogen lamps with in-series connected transformers, and universal as well as split-pole motors.
Dimmer for Halogen Lamps schematic diagram. In normal, resistive operation of a phase control circuit there is alternately part of the positive and negative line-voltage half cycle applied to the load via the triac that has started to conduct because of the trigger pulse. Operation of the circuit with a transformer and low-voltage halogen lamp connected is largely identical to the operation of a normal filament lamp due to the primarily resistive nature of the load. In operation with resistive and inductive portions of load, the zero crossing of the current compared to that of the line voltage line is delayed.
In operation with heavily inductive loads (eg an idling transformer after lamp failure), a highly lossy state (half cycle operation) can occur after a fault, leading to thermal destruction of the transformer. Control mechanisms integrated into the SLB 0587 serve to protect the load from this situation.