Help with Opto High Side Driver

[William At MyBlueRoom]

Attached is a schematic for a high side optoisolator. I've not used optos often enough to know if one exists that can take a 10ma input signal (the led) and supply approx 100ma to 200ma at 40vdc max @ 100hz (I've used some SLOW optos before and they are SLOW...)

 

[Papabravo]

Current Transfer Ratio

The specification you are looking for is called the Current Transfer Ratio, or CTR. A typical CTR value for a 4N25 type opto is 30% to 600%. You can specify a CTR range when you buy them and the higher the CTR the more expensive. They won't quite get to a factor of 10 and they degrade with age so you really can't depend on the CTR remaining constant.

When you say they are slow I assume you mean propagation delay. They are in the 3 to 5 microsecond range. If you want low propagation delay try the HCPL 0710 at 40 nanoseconds. Of course you will pay for this feature.

 

[philba]

why high side? isn't that basically an emitter follower?

I'd use a driver transistor but you should figure out the power dissipation, I think you might be pushing it with a small signal transistor.

 

[Mike - K8LH]

Why are you modulating it at 100-Hz Bill?