Problems with a back to back MOSFET dimmer for 230VAC

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Lars Englund

Joined Dec 31, 2016
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I've been trying, unsuccessfully, to dim a 60W indascent lightbulb with two back to back mosfets similar as in this post: http://easy-electronics4u.blogspot.se/2012/02/switch-ac-loads-using-mosfets-as-relay.html

My circuit looks like this:

(there is also a 2A fast blow fuse and a 7D471K MOV on the mains input)

Below is the output from my scope:


C1: Live_230VAC, C2: DIM_GPIO, C3: Drain of Q5, C4: Source of Q5 and Q6

Q6 gets burning hot, Q5 stays cool. The lamp (obviously) flickers as we are only getting every other half wave. Thinking about the circuit I feel that it will be impossible to get a Vgs voltage that is higher than the voltage at the source pin since the source pin will see the peak of the 230VAC? Is there a way (preferably simple & cheap :)) of solving this kind of double mosfet dimmer?
 

ScottWang

Joined Aug 23, 2012
7,414
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