Using PWM for halogen brightness control

[Joel Moore]

Can I use the Triplc's (T100MD888+, specifically) PWM outputs as dimmers for halogen lighting?  Has anyone tried this?

A 24VDC, 50 Watt bulb will draw just over 2A at full on so it falls within the PWM output's capabilities.  

What about the concept of using PWM for halogen dimming?  Is this even a valid technique?  If so, what's the lowest frequency I can run the PWM at without the bulbs flickering or pulsing?  And can I drive the bulbs with the same power supply I use for the Triplc or is that a bad idea?

I know I can probably answer most of these questions experimentally (and I probably will) but I just wanted to be a little confident that I'm not going to fry a plc before I try it.

[support]

2A is the "steady state" current which is the current after the halogen lamp heats up and reaches steady temperature. Have you checked the in rush current for halogen bulb when cold? For normal filament the in rush current can be 6 times that of steady state current. I am not sure about halogen lamp. As long as the peak current does not exceed the maximum specification I don't see a problem using the PWM output to drive the halogen lamp. One way to overcome high in rush current is to ramp up the duty cycle slowly instead of turning it 100% on instantly. That allows the bulb to heat up to steady state temperature and the current drawn will be what you calculate from P/V.

I don't see a problem using the same power supply for the PLC and the halogen lamp unless as mentioned above, the in rush current exceeds the rated current of the P/S and the PLC will be reset because power supply may trip momentarily when that happen.

If you use frequency above 500Hz you shouldn't notice any flickering especially since the hot filament will continue to emit light during the off period.