26-08-2026, 05:04 PM
A lamp is poor to abysmal for switch on surge as it can be 1/10th resistance when cold. This is why valve TVs had a thermistor that was highish resistance till it heated as the series valve heaters had a low cold resistance. Some older radios with a barretter (iron wire in a hydrogen atmosphere) to regulate current with varying mains voltage when the C series heater chain was hot also had a regular thermistor to stop cold surge.
A tungsten or halogen lamp limiter is simply a modern replacement for a barretter.
More compact thermistors that look like ceramic disc capacitors are sold to limit inrush surge on a SMPSU as these may have a bridge rectifier feeding 100 uF to 400 uF on the larger PSUs (100W to 600W).
I used to fit those in the light switch feeding 100W and 200W halogen lamps.
The thermistor for the degaussing coils on a colour shadow mask CRT usually has three terminals, because it is is very low resistance to the coils when cold but has a resistive heater to make the thermistor go high resistance, so a sort of turbo barretter and useless to limit in-rush currents.
A tungsten or halogen lamp limiter is simply a modern replacement for a barretter.
More compact thermistors that look like ceramic disc capacitors are sold to limit inrush surge on a SMPSU as these may have a bridge rectifier feeding 100 uF to 400 uF on the larger PSUs (100W to 600W).
I used to fit those in the light switch feeding 100W and 200W halogen lamps.
The thermistor for the degaussing coils on a colour shadow mask CRT usually has three terminals, because it is is very low resistance to the coils when cold but has a resistive heater to make the thermistor go high resistance, so a sort of turbo barretter and useless to limit in-rush currents.
