Help please with this simple transistor circuit

Thread Starter

bryankerr

Joined Apr 1, 2015
15
wow thanks blocco, when I check the voltage across the cap on the oscope I can see the ramp, its small but its there. Thank you for your explanation.
 

Thread Starter

bryankerr

Joined Apr 1, 2015
15
wow thanks blocco, I checked the voltage across the cap on the oscope and can see a tiny ramp frequency. its small but it is there.
 

blocco a spirale

Joined Jun 18, 2008
1,546
I take back everything I said about it being wrong... although, at first glance it does appear to be wrong.... the diode is the key to its operation.

...back-pedaling into the distance...:confused:
 
Last edited:

bertus

Joined Apr 5, 2008
21,263
Hello,

HOW is the 120 VoltsAC dropped to 3.5 VoltsAC?
As you might know we do NOT allow circuits that are DIRECTLY connected to the mains.

Bertus
 

Thread Starter

bryankerr

Joined Apr 1, 2015
15
what do you mean you don't allow it? I believe that part is neither here nor there. The focus of this discussion was the optocoupler.
 

blocco a spirale

Joined Jun 18, 2008
1,546
I'm sure there is a transformer involved as, otherwise, it could be dangerous.

However, this thread is not about connecting anything directly to the mains, it's about the operation of a falling-edge detector that runs on very low voltage AC.
 

Papabravo

Joined Feb 24, 2006
15,560
Thanks blocco, It could be connected to the mains, but it could not be. right bertus?
The owners of this forum have decided not to host any discussion of circuits that could be hooked up directly to the mains. This is non negotiable and not up for discussion. There are other forums that do not have similar restrictions. The concern is for people who don't know better and might injure or kill themselves in an attempt to duplicate circuits displayed on this site. It would help your case immensely if it was edited to show an isolation or stepdown transformer.
 

blocco a spirale

Joined Jun 18, 2008
1,546
Any circuit could be hooked up directly to the mains; people do stupid things. The question is whether the circuit is soley intended or recommended for direct mains connection.

If someone posts a circuit for running an LED from 12VAC should they also show how the AC voltage was derived, in their case?

If you simply state that no circuit discussed on this forum should, under any circumstances, be connected directly to the mains supply, there will be no ambiguity.
 

Papabravo

Joined Feb 24, 2006
15,560
Any circuit could be hooked up directly to the mains; people do stupid things. The question is whether the circuit is soley intended or recommended for direct mains connection.

If someone posts a circuit for running an LED from 12VAC should they also show how the AC voltage was derived, in their case?

If you simply state that no circuit discussed on this forum should, under any circumstances, be connected directly to the mains supply, there will be no ambiguity.
It is simply stated in the TOS.
 

blocco a spirale

Joined Jun 18, 2008
1,546
It is simply stated in the TOS.
But how is that relevant to this thread?

The circuit discussed is not designed, or claimed to be suitable, for direct mains connection and would be destroyed if it were used in that way. Furthermore, it is not even designed for AC operation.

I do not understand the controversy here.
 

Papabravo

Joined Feb 24, 2006
15,560
The TOS are relevant to every discussion on this board.

In the original drawing it shows an AC waveform after either a full wave rectifier or a bridge rectifier. The source was ambiguous. It could be the mains or it could be something else. If it was something else like an isolation transformer or a stepdown transformer, then we agree it's no problem. But look at the OP's initial in your face response. That tells me he is unconcerned with any restrictions that might be placed on him. If it was a direct connection to the mains then further discussion is disallowed. We all know this and we have all agreed to it.
 

WBahn

Joined Mar 31, 2012
26,398
It appears the TS edited the original post a few hours ago and removed it -- which makes the entire thread confusing and meaningless.
 
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