Amen to that last statement. (My emphasis added.)
So true. Keep up the good posts carbon
Cheers,
TV Tech
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Amen to that last statement. (My emphasis added.)
OK, never mind, I got my answer. Thanks for your input guys.
I did it without zener got 111-130vdc 43ma, with zener 18vdc 17ma.
OK, never mind, I got my answer. Thanks for your input guys.
I did it without zener got 111-130vdc 43ma, with zener 18vdc 17ma.
Is the cap X2 rated? If so, it should be ok.I just wanted to know if this HV 2100VAC .90uf can handle being C1 without issues
Is the cap X2 rated? If so, it should be ok.
I assume the X2 rating takes factors other than voltage into account (can anyone confirm that??), e.g. flammability of the dielectric and cap coating, self-healing properties of the dielectric. If your cap is not X2 rated it may, therefore, be unsafe to use even if its voltage rating is adequate.
Hello Guys,
Sorry but I got a question while I was reading this thread.
Is the below circuit isolated from the mains? Can we use it as a supplier in low current application while it has 2 incoming caps?
Thanks
hi,
No its not isolated
Thanks, But whats the reason?!
We all know that both plates of a capacitor are separated to each others and there is a gap (air or anything else) between them. So I am not able to see any reason why the said circuit is not isolated from the mains!
If you touch the output side the cap connected to the "hot" side of the power line, and then touch neutral, ground, or the output side of the cap connected to neutral you will pass a lot of current through you body, limited only by the impedance of the cap and the impedance of your body. If you touch either the + side or the - side of the rectifier circuit (or anything attached to it), then touch "neutral" or ground you will pass current through your body. With an isolating transformer you can touch either side of the secondary winding and then "hot", neutral, or ground on the primary site and not get shocked.Thanks, But whats the reason?!
We all know that both plates of a capacitor are separated to each others and there is a gap (air or anything else) between them. So I am not able to see any reason why the said circuit is not isolated from the mains!
Thanks, But whats the reason?!
We all know that both plates of a capacitor are separated to each others and there is a gap (air or anything else) between them. So I am not able to see any reason why the said circuit is not isolated from the mains!
carbonzit;1009279...capacitors and transformers isolate the downwind part of the power supply from line voltage; in one case said:No, capacitors isolate DC with the dielectric...but they "pass" AC. That's why they are not considered to provide "isolation" in a line powered AC circuit. A capacitive circuit like the one shown merely puts the load in series with the capacitive impedance, across the line. In a transformer isolated circuit the only potential difference at the secondary is between the two ends of the secondary. There is no potential difference between the secondary and the line-feed primary.
However, in the real world, with some poorly designed transformers, there can be a small amount of inter-winding capacitive coupling between the wire in the primary and the wire in the secondary that can cause a measurable AC "leakage current". https://en.wikipedia.org/wiki/Isolation_transformer
Ken
No, capacitors isolate DC with the dielectric...but they "pass" AC. That's why they are not considered to provide "isolation" in a line powered AC circuit. A capacitive circuit like the one shown merely puts the load in series with the capacitive impedance, across the line. In a transformer isolated circuit the only potential difference at the secondary is between the two ends of the secondary. There is no potential difference between the secondary and the line-feed primary.
However, in the real world, with some poorly designed transformers, there can be a small amount of inter-winding capacitive coupling between the wire in the primary and the wire in the secondary that can cause a measurable AC "leakage current". https://en.wikipedia.org/wiki/Isolation_transformer
Ken
Ok to be honest, I did the math for an input capacitor of say 1uF, a body resistance of say 10KHz, and with a mains of say 220V, 50Hz.
The voltage across the said body resistance as I calculated was 166V, which is yet dangerous.
There's no better person to convince you of something than yourself.
Hi OP,
The circuit in question is quite common and used in lots of stuff like lamp dimmers. The key is to make sure there is no way that the user can ever come into contact with any part of the circuit. This means it is definitely possible, plausible, doable, and has been done, used, and reused countless times in circuits.
If on the other hand you have the idea that the circuit is "isolated", then you could find yourself in series trouble. It's indeed isolated, but only for DC not AC, and certainly not for transients.
For example, call one side of the line 'live' and the other side 'ground', connect a small capacitor (rated for AC voltage usage) that hasnt been used in a week and connect it to the power line 'live' side. Connect a 100 ohm resistor to the cap. Using a switch, switch the open end of the cap to ground. As the switch is closed, there could be more than 1 amp peak in the cap and resistor for the time it takes to charge up to some DC level. Some time after that the circuit will function like an AC circuit, but still wont be isolated.
The voltage from the zener to ground is only say 12v, so touching that and ground may not give you a shock. But if the AC input connections are reversed (as they often do become) then the live side is 'ground' and touching the top of the zener and earth ground (wet grass, damp floor, cold pipe, etc.) and you get more than a 100v shock.
So yes, this circuit is doable and usable and has been used for a long time and is still being recommended by lots of big companies, but only for people who know how to deal with the isolation problem and know for sure that there definitely is no isolation that could be taken as pure isolation like that you get from using a transformer with an isolated secondary.
That said, you can use the circuit once you understand how and why it is NOT truely isolated, but until then you really should not do it. Best bet is to purchase a wall wart. If you insist on using the cap, it may give you the proper current level or it may not depending on the load and cap value, but you should be aware that there is definitely a concern for safety with this kind of circuit.
From your opening statement you seem to be aware of the *possible* problem, but you should really be taking this as a *definitive* problem that needs very strict attention to detail.