Is there any reason a reverse phase control dimmer would have less conducted emissions than a forward phase control dimmer if the rise (or fall) times are the same? It seems the conducted EMI spectrum is entirely a function of the speed of the on/off transition.
     I understand that non-triac dimmers have low conducted EMI because of slow transitions in the turn on/off. This slow edge reduces EMI and efficiency. However, chokes used in triac dimmers also have some losses. It'd be interesting to compare efficiencies between choke and non-choke dimmers.
     My (perhaps wrong) understanding of IGBTs is that they are kinda like a BJT with a FET between the base and the collector. This limits the saturation voltage to Vbe, typically about 700mV. A regular BJT would have  a saturation voltage of 300mV or so, and an FET would be even lower.
     Of course the IGBT, BJT, or FET are DC devices. You could add a diode bridge or another device and steering diodes to handle AC. This adds complexity and increases the saturation voltage further.
     Then there's the problem of driving this device. You want to have isolation between the PIC and the power device (like the good ol' MOC3020), but there's no simple way to do it.
     So, it's an interesting problem. For now, I'm using triacs (or SCR pairs).

Harold


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