Help with Opto High Side Driver - Electronic Circuits Projects Diagrams Free

William At MyBlueRoom · 9th May 2006, 03:57 AM

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 · 9th May 2006, 04:43 AM

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 · 9th May 2006, 07:34 AM

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 · 9th May 2006, 08:24 AM

Why are you modulating it at 100-Hz Bill?

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9th May 2006, 04:43 AM	(permalink)
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.

9th May 2006, 07:34 AM	(permalink)
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.

9th May 2006, 08:24 AM	(permalink)
Mike, K8LH	Why are you modulating it at 100-Hz Bill?