voltage level detector

[p72]

To be honest, my intention was only to detect whether its AC or DC power, nothing else BUT few my friends told me exact same thing that you said regarding switching backup DC supply if AC fails. one of my friends told me that this is one of the applications of this kind of design.

I am not really experienced student in designing circuit so I did wrong wiring.
What are the chances of this circuit that works for the purpose that I am looking for?
Do you think this way I can detect AC vs DC?

Thank you for the input.
Help me.
p72

 

[kam1787]

I think I can tell you with some certainty. The circuit as drawn will not work with any AC or DC input because the supply is shorted out!

and if the polarity of the DC can change, it too needs to be run thru the diode bridge

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[p72]

any help in circuit wiring??

 

[p72]

help with wiring of circuit.
please.

 

[SACHIN C]

"I would like to set Relay in "default mode" for DC supply. That means if I applied AC voltage to the Relay, it should switch Relay position/contacts and goes into further stage.For DC voltage, I am thinking to put diode before relay, which will block DC and will not allow to pass it through the Relay. As a result, Relay will stay in its original (default) position and DC will pass without entering into Relay".


Hi p72,
If you use Diode in place of AC Connection it will pass only single cycle as full wave can not be used it will pass the DC also:?:
As per your connection viz, Normally closed terminal of relay will be always connected to the DC & Normally open terminal connected to the AC:?:
Actually this circuit don't need diode,as when AC supply is present,it will change the Relay state & route for AC path & when there will be no Ac signal it will not change the path as Normally connected terminal will remain activated as a Default state DC path will be activated.:smile:
Pls correct if i am wrong.....:?:

Thanks,:smile:

 

[p72]

"I would like to set Relay in "default mode" for DC supply. That means if I applied AC voltage to the Relay, it should switch Relay position/contacts and goes into further stage.For DC voltage, I am thinking to put diode before relay, which will block DC and will not allow to pass it through the Relay. As a result, Relay will stay in its original (default) position and DC will pass without entering into Relay".


Hi p72,
If you use Diode in place of AC Connection it will pass only single cycle as full wave can not be used it will pass the DC also:?:
As per your connection viz, Normally closed terminal of relay will be always connected to the DC & Normally open terminal connected to the AC:?:
Actually this circuit don't need diode,as when AC supply is present,it will change the Relay state & route for AC path & when there will be no Ac signal it will not change the path as Normally connected terminal will remain activated as a Default state DC path will be activated.:smile:
Pls correct if i am wrong.....:?:

Thanks,:smile:

Hi Sachin,
Can you draw circuit diagram??

 

[p72]

I'm assuming your input can be AC or DC on the same wires, otherwise rectify the AC, scale it with a potential divider and compare it with the DC scaled with a second potential divider. Even if you have two separate inputs, the circuit will work to check for AC presence.

The schematic works by utilizing the reactance of the capacitor to allow AC to reach the opto-coupler and also the capacitor's property of blocking DC. When DC is applied, apart from a very short pulse of current as the capacitor charges, no current flows into the opto-coupler LED so the output side goes to a logic high level.

When AC is applied, the capacitor allows current to flow, the diode conducts on one half cycle and the LED inside the opto-coupler on the other. The output side of the opto-coupler will go low when the LED lights and the capacitor across it will be discharged, taking the output to logic low. It will actually be a low level pulsing signal at the output because the capacitor will try to recharge when the opto-coupler is turned off but with suitable time constant it should stay below logic low level.

The bonus to the circuit is it gives safety isolation between the voltage you are checking and whatever follows it.

Brian.

Hey Brian,
I was looking your suggestion and have a question, on the circuit what is the role of +5V at the output side? What is the functionality of that?

Thank you,
p72

 

[betwixt]

It can be any reasonable voltage that the opto-coupler transistor is happy with. When AC is applied the LED in the opto-coupler lights on positive half cycles and when it lights, the transistor on it's output side conducts and discharges the capacitor so the voltage across it drops very low. The resistor and supply (5V or whatever) pull it high again when the AC is NOT present.

So, given suitable values the output will be say 0.5V when AC is present and it will be 5V or whatever you apply at that point when the AC is missing.

Brian.

 

[p72]

Thanks betwixt.