I'm trying to solve a small problem with my BEANS amplifier: https://www.diyaudio.com/community/threads/b-e-a-n-s-amplifier.423552/ , namely slight 'sticking' when coming out of clipping. It's only very slight but I would like to try and resolve it. One approach that looks promising is to use an opto-coupler, so that when the drive from the VAS nears the power rail, this causes the opto to start to conduct and that in turn can reduce the drive for the VAS. I've done a few experiments in LTSpice and it looks promising, but looking at the specs of standard devices like the 4N25, it seems they are a bit slow.
Any suggestions?
Any suggestions?
See "Analog Applications" Pg 41-47 of
https://docs.broadcom.com/doc/AV02-4387EN
Interesting parts : HCPL-4562
Further reading: https://elsitek.ru/upload/iblock/9bb/HCPL-4562_HCNW4562---avago_broadcom.pdf
https://docs.broadcom.com/doc/AV02-4387EN
Interesting parts : HCPL-4562
Further reading: https://elsitek.ru/upload/iblock/9bb/HCPL-4562_HCNW4562---avago_broadcom.pdf
Hi,
Do you need just peak detection (on/off) or do you need analog behaviour?
There are some logic opto coupler really fast such as the VOH260A where times are around 50ns.
But there are analog ones such as the SFH6326 whose times are around 200ns to 500ns.
On thing to pay attention is that you need to keep resistance low to extract maxmum speed.
See specs for 4N25 - tr and tf 2us but with Rl=100ohms.
Only analog is suitable for this application. I'll take a look at those. Thanks for the info.
Avoid photo-transistor based opto-couplers, they are all slow due to stored-charge effects. Photo-diode opto-couplers can be very fast if used properly, but they have a lot lower gain (a.k.a. current transfer ratio or CTR), so you may need to boost the output. Be aware of the low input reverse-voltage rating of opto-couplers.
