I need to provide isolation between two circuits using an optocoupler. In the datasheet, it states that there is a need to provide two power supplies to create the isolation for the input and output. I am thinking of using only one power supply, is there any methods to achieve the isolation with only one isolation for the ground and Vcc on both sides?

 

This would mean you have no real isolation. A single power supply would have a single ground, which kind of defeats the purpose of an opto coupler. If you do not need full isolation, for instance, if you have a 1000V circuit that needs to interface with a 5v circuit, at the same ground potential, then you could conceivably come up with something like you mentioned.

Perhaps a bit more detail on what you're trying to do would allow us to give better advice.

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You can generate the other supply using ready made DC-DC converter, taking power from the main supply. Most of them also provide high isolation between input and output pins.

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L.Chung

 

I see, so I definite need two power supplies, cause i need one 9V at the input and another of my optocoupler which is HCPL4562 from avago.

I am thinking of using a inductor to insert between the two Vcc. Not very sure whether it will create the necessary isolation.

 

By the way, my project is to see whether the insertion of an optocoupler will decrease the common-mode current in a circuit and how much will the reduction be if it does.

 

I don't know what you want to build but if you want separation between low voltage levels like 12 volts and 5 volts there is no problem using the same powersupply. Also between different IC families like TTL and CMOS you can switch it via an optocoupler like 4N35 or eq.

If you need the isolation for safety like with a low voltage supply controlling a triac at mains potential I certainly would have galvanic separation via a good optocoupler which is rated for at least 2 kV break down voltage.

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An inductor would effectively short circuit your two supplies together making them anything but isolated.

 

You can create a simple non-regulated low current DC-DC converter with a small pulse transformer and an astable 555 timer.

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actually i want to save costs incurred by using only one power supply, so instead of using another one, the 9V needed at the output will be drawn from that of the input through an inductor.

 

hFor what purpose?, that would bypass the isolation - if you're doing that, you may as well just remove the optp-coupler?.

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Another half baked looney tunes thread.

What are you really trying to do?
OK something about common mode current, but where is this current flowing, why do you think there is a common mode current, is the common mode current a problem?

Your question is far too vague and ambiguous to make sense.

JimB

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