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# How to drive the opto-coupler?

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#### yzou_ua

##### Member level 5
My control signals out from a buffer would go thru. the opto-coupler to drive a inverter module.
Is there any required MINIMUM value for the input current of opto-coupler?? Buz the signals out of buffer is just 6mA... Thx a lot. (The datasheet shows IF vs. VF curve fro IF ranging from 0 to 20mA, so it seems that it does not matter what the input curr. is...)

You would have a resistor in series with the input diode. There will be a minimum "on" voltage requirement (3V) I think 6 mA may be enough.

Well, I think needed driving current depends on the required speed (or rate) of change of the opto-coupler output circuit. If your application is low frequency, you can use the minimum driving current (proved that driven circuit is really turned on /off). Otherwise you need to know the rise / fall delays effectively obtained with a given ammount of driving current.

yzou_ua

### yzou_ua

Points: 2
yzou

Find bellow a circuit I used to drive a wash-machine motor and works fine.
Note that current that drive optocoupler is at same magnitude of 6mA you said : ( 5v-2v ) / ( 680R ) = ~4mA.

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yzou_ua

### yzou_ua

Points: 2
Thx a lot.
I think u r right and my appli. is high speed ... I choose 16mA at last.

Well, I think needed driving current depends on the required speed (or rate) of change of the opto-coupler output circuit. If your application is low frequency, you can use the minimum driving current (proved that driven circuit is really turned on /off). Otherwise you need to know the rise / fall delays effectively obtained with a given ammount of driving current.

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