Electronics > Projects, Designs, and Technical Stuff
international standard for ac/ac converter ("electronic transformer")
poorchava:
The scenario is that a potential customer is importing some battery powered equipment (dunno exactly, think a hedge trimmer or something like that) that has a charger which is supposed to work ok 110V. Dunno how it's built inside. Redoing the charger as a whole is outa question due to proprietary battery socket and cost.
I know that it will work, it's also easy to get right in terms of not blowing up. I also have a few years of experience in power electronics, but mainly high power (single digits kW range) DC/DC stuff for test equipment market.
I wonder however what would be the point of rectifying splitcapping the supply. The capacitors would have to be significantly large.
Jay_Diddy_B:
Hi,
The schematic is this:
The output waveform is:
The regulation for the values given:
This circuit needs an inrush limiter, NTC or similar.
Jay_Diddy_B
poorchava:
That makes sense. Much easier. I wonder how the power factor on this one is gonna be. It seems that everything non-lighting over 75W is required to have a good power factor. This one will probably have around 0.7 or something.
The chopper solution just chops the input, so should automatically have a good PF.
The chopper will introduce quite a lot of noise and harmonics though.
Jay_Diddy_B:
Hi,
The power factor is really quite low, around 0.4 for resistive loads.
If is already has a bad power factor, for example a SMPS with no PFC, the PF will be approximately the original PF/2.
This is because the current waveform is the same and the input voltage is double.
This is based on the idea that
PF = W/VA for non-sinusoidal load currents.
PF= cos (angle) only works for sinusoidal load currents.
This solution is only suitable for light loads.
The electrolytic capacitors can be chosen based on the load. Start with 20uF per Watt of load dissipation.
Regards,
Jay_Diddy_B
poorchava:
We're talking about 150W here, that would translate to about 2x 3000uf @ 200V caps. Not exactly small not cheap nor light.
IiRC 560uF@400V is something like 35x58mm. So 3000u@200v would be something like 1.5...2 times as big.
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