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how/where does the current flow??

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subzero349

New Member
hello...
i need help with the circuit below... I would like to know how much current flows through the h11l1 and R1 and R2... and how much voltage the zener diode drops...

I just can't see how the h11l1 doesn't blow up from the 120V mains... please help... does R2 have to be the same voltage as the h11l1 becasue they are in parallel? if so, how much current will go through R2 and the h11l1? please help
 

Roff

Well-Known Member
I can't view your schematic, but if it is the same as in the previous post, the peak current through the H11L1 is about 15ma. The peak voltage across R1 is 120*1.414-V(D5)-V(D1)-V(LED). The current through R2 is negligible. R2 is there to discharge the intrinsic and stray capacitance of the LED so that it will turn off rapidly when D5 ceases to conduct (near each zero crossing of the AC line).
I see a major error in the schematic. The bridge is returned to earth GND ( the bare wire in your house wiring), as is the low side of the line. The bridge should be returned to the low side of the line, and the earth GND wire should ONLY be connected to the ground on the control circuit - pin 1 on the 555, etc. This needs to be done to protect you in case your isolation circuits fail or are wired incorrectly. Do NOT connect the low side of the line to earth GND. You should also be aware that the voltages on the AC side of this circuit are lethal. Be sure to run this from a GFCI outlet, at least during the testing phase.
 

subzero349

New Member
thank you ron...

I got this circuit from an application note datasheet and I realized that the "chasis" ground is seperate from the "earth" ground... and "chasis" ground is just the low/neutral line of ac...
 
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