indicate the lamp needs replacing is connected to an open collector npn transistor 356 the u201c replace lamp u201d warning is given when the operating voltage across the lamp output terminals 322 and 324 exceed some threshold e g 38vdc as a cermax lamp ages its operating voltage will increase this is always associated with a worn out lamp the base of transistor 356 will become forward biased by a simple voltage divider connected across lamp output terminals 322 and 324 if the lamp connected between output terminals 322 and 324 is on at all a transistor 358 will switch on and drive another external led indicator this one for u201c lamp on u201d a transistor 360 will prevent transistor 358 from switching on as long as the voltage across output terminals 322 and 324 is too high indicating a lamp that is not connected or has not been ignited such led indications can be placed remotely at convenient observation points in the user 39 s application both of these led drivers are primary side isolated the igniting of cermax lamps requires a boost voltage of at least 250v dc be applied together with series induced trigger pulses of 25 30kv.