OPTOCOUPLERS

[prateeksikka]

oh god audioguru!
that means i held a serious misconception that ground and earth are same i.e at zero potential wrt live terminal?
is there a diff b/w the three:
ground ,earth and common point?your comments?
prateek

 

[audioguru2]

Hi Prateek,
I don't know about your country, but in Canada the ground wire is used for safety so that metal-cased appliances have their case grounded. If a live wire inside touched the case then the breaker would blow. The appliance is powered from the live and neutral wires. The neutral wire is separate from the ground wire at each receptacle because current in the neutral wire creates a voltage across its resistance and therefore at an operating appliance is not at earth potential. The neutral wires and ground wires are joined at the breaker box and earthed there.
If an appliance developed some leakage current from its live wire to its ground wire, its ground potential will be low and wouldn't hurt you but its current could be high enough to destroy a grounded computer that it is connected with.

 

[prateeksikka]

hi audioguru!
that means optocouplers are basically high current filters(not exactly!)
which prevent low rating devices from getting damaged by high current.
prateek

 

[audioguru2]

Optocouplers provide isolation. They use a light beam for coupling instead of conductors.

 

[prateeksikka]

hi audioguru!
you rightly said it couples the signals through a beam of light.Actually a phototransistor is switched on.But do you know that why is the transistor not damaged by high current  on motor side.(i take the motor computer example u gave)
reply soon how could an electronic device like a small signal transistor bear such high
current?
prateek

 

[audioguru2]

Oh yeah? Do you think that the tiny phototransistor in an optocoupler switches the entire load all by itself? Duh!  :

Firstly, the LED in a optocoupler has a max current rating of about 60mA.
Secondly, the optocoupling isn't perfect so the phototransistor can conduct only about 40mA when the LED has its max current. The phototransistor has a max voltage rating of about 30V.

The tiny phototransistor turns on a real transistor that turns on a power driver transistor that turns on a bunch of paralleled power transistors. If the paralleled power transistors can't handle the load then they switch a high-power relay that drives the load.  ;D

 

[prateeksikka]

hi audioguru!
that means its a big complicated chain of transistors which are succesively turned on by LEDs? to increase the signal level current?am i right?
prateek

 

[audioguru2]

The optocoupler has a single LED and a single phototransistor. The chain of transistors amplify the current output and voltage rating of the phototransistor.

 

[EHAB_MANSOUR]

hi  ithink that optocuopler is known as (photocoupler) and used to make isolation between low ampere device such as(micocontroller) and its interface circuit .
if you want any thing else about that device send me a mail message ([email protected]).

 

[Faz1]

how about if I want to give a bipolar input which is +-10V dc to the optocoupler? I came across on the product of H11AA1. Does it really suitable for my application to fed the optocoupler to the ADC part which the voltage signal is +-10V also.

Do i need a low pass filter or a buffer circuit by using the op-amp of 741 after the optocoupler to fed the ADC input.

PLLLLZZZzzzzzzzzz....give an idea ;D

 

[prateeksikka]

i guess at such low voltage level at which you are operating ,u do not need an optocoupler...i generally use it when there is a high voltage AC circuit on 1 side and a very low voltage dc ckt on the other...