Methods for isolating a circuit (without optocoupler)

isolate or not?

I have a circuit that contains 5v, 24v and 48VDC. I don't want to use optocoupler, because i want to keep the cost low and the circuit simple. What do you suggest me about this? Must i use or not? What problems may i encounter? Or what can i do instead of using opto to prevent problems?

Re: isolate or not?

seyyah said:

I have a circuit that contains 5v, 24v and 48VDC. I don't want to use optocoupler, because i want to keep the cost low and the circuit simple. What do you suggest me about this? Must i use or not? What problems may i encounter? Or what can i do instead of using opto to prevent problems?

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what kind of circuit do u have ?

Hi seyyah

Your question is a little bit confusing. What do you want or do you should do with your optocopuler? Is it a power supply? Is the opto used for regulation? Please give a little bit more information...

Bye

No it isn't a power supply. It is a simple circuit. It controls a motor. But there is no speed control, only on and off. There are small relays on pcb which operates at 24v.
And this relays controls the contactors which turns on and off the motor.
There are some swtihes. When swithes are on, 48v comes to the micro and micro decides whether turn on the relays or not.

Using optocouplers may be the most reliable method or you can use level-shifting transistors. It depends on your application and budget but I can say, optocouplers are cheap and good for such things

The most cost effective mthos is using common emmiter/source for level shifter.
in the case of mosfets for up side it is better to use p-channel ones and limiting its GS voltage with a zener or a simple voltage dividre maked by two resistors.
NOTE: although this method is funtional, if one of power transistors fails or damaged, the whole of the ckt components i.e. micro controller will be damaged so be careful when designing in this manner; certainly optocouplers are used for preventing this kind of failure in control ckts.

See also:
http://www.irf.com/technical-info/appnotes/an-940.pdf

in this raange of voltage (48V) simple level shifters is sufficient and its power dissipation is tolerable but at higer level of voltage it is necessary to use other methods like optocouple or HVIC; of course u can use medium voltage HVICs like those from harris, eg HIP408x. they r 80 volt full bridge mosfet driver with several advanced features.
also u can use integrated swithes available from several manufacturer specially IRF, see www.irf.com

BEST!