How to reduce the optocoupler delay time?

[seyyah]

I use a fast optocoupler(6n137) to interface two circuits. When ON signal comes to input, the output transistor immediately turns on without a significant delay. But when OFF signal comes to input, the output transistor of the optocoupler doesn't turn off immediately. It takes 6-7us to turn off. How can i reduce this time. The load is an igbt driver and optocoupler has a delay capability of sub microsecond at ON and OFF.

 

[Borber]

optocoupler circuit with delay

All depends on type of load. If load has 200-300pF capacitance then you will have turnoff delay abt. 5-6us. Optocoupler, specified delay time is valid foe 350ohm paralleled with 15pF.

 

[seyyah]

optokoppler delay time

I think driver has the feature of soft turn off. The delay is because of that. Thanks.

 

[vdaniel]

optocoupler delay

The 22k resistor is too large. With the 6N137 you can have more than 16mA output current, so you can reduse the resistor up to 330 Ohm.

Varuzhan

 

[seyyah]

Re: optocoupler delay

It's the recommendation of the igbt gate driver manufacturer so it's not related to the 6n137. On the other hand it can be reduced but not as low as to 330ohm, i think.

 

[petarpav]

optocoupler delay

Hi. If you need smal delay use fast optocoupler wit internal schmidth trigger like HCPL2601 on HP/_Agilent.

Best Regards.

 

[C-Man]

Re: optocoupler delay

seyyah,

try to connect a resistor of 47K to 100K from the base of your optocoupler (pin6) to GND this improves the turn off delay on most optocouplers ...

best regards

 

[IanP]

Re: optocoupler delay

Or you can use circuit similar to that below, where the optocoupler's transistor is Q1..
Ather option without resistors, diodes etc is two transistors NPN at the top and PNP at the bottom, with both bases connected together as input and both emitters connected togeter as output, collector of NPN goes to (+) and collector of PNP goes to GND.
Regards, IanP

 

[seyyah]

Re: optocoupler delay

Hi. If you need smal delay use fast optocoupler wit internal schmidth trigger like HCPL2601 on HP/_Agilent.

Best Regards.

I think 6n137 is as fast as hcpl2601.

Added after 1 minutes:

seyyah,

try to connect a resistor of 47K to 100K from the base of your optocoupler (pin6) to GND this improves the turn off delay on most optocouplers ...

best regards

Don't look at this schematic for 6n137. It has no base connection.