micro-controller driving isolated output - Page 1
Forum section: electronics / beginners

author: Mad Professor
author_rank: Regular Contributor
timestamp: May 07, 2015, 10:42:48 am
content: Hi AllI am not sure if this topic would be best suited listed under Beginners or Projects section of the forum so please move as needed.I am trying to work out the best way to drive two solenoid valves from a micro-controller, but both the micro-controller and the solenoid valves are on there own isolated power supplies and I can not share the power or ground rails.The simplest way I can thing about doing this is by using optocouplers and mosfets.Here is what I am thinking about using, I have not yet decided on the components to use, that is why there are no part numbers and or values listed.Before I think about things to much, will the above work, or is there a better way?Thanks for your time.Best Regards.

author: Zero999
author_rank: Super Contributor
timestamp: May 07, 2015, 11:05:25 am
content: Yes, it'll work but don't expect it to be fast.

author: Psi
author_rank: Super Contributor
timestamp: May 07, 2015, 11:12:42 am
content: How big are the solenoids? You can get optoisolators with build in drivers that can do 500mA - 2A directly. It would cut down the amount of parts you need.you could also use solid state relays.

author: Andy Watson
author_rank: Super Contributor
timestamp: May 07, 2015, 11:18:30 am
content: You might want to check the polarity of V01 and V02.

author: TopLoser
author_rank: Unknown
timestamp: May 07, 2015, 11:28:35 am
content: I use a lot of these for isolation, simple and easy.http://uk.farnell.com/panasonic-electric-works/aqy212s/relay-photomos-60v-0-5a/dp/2095723

author: Mad Professor
author_rank: Regular Contributor
timestamp: May 07, 2015, 03:52:00 pm
content: Thank you for your replies.I should not need to use any PWM switching with the solenoids, I am simply looking at on/off, and quite low cycle times something like 5 to 10sec on time. The off time varies.I will need to re-check the current draw of the intended solenoids but from memory we are looking around 600ma at 14volts.Thanks again for your time.Best Regards.

author: Zero999
author_rank: Super Contributor
timestamp: May 07, 2015, 07:47:16 pm
content: Quote from: Andy Watson on May 07, 2015, 11:18:30 amOh yes, the phototransitors are upside down.

author: mushroom
author_rank: Regular Contributor
timestamp: May 07, 2015, 09:35:24 pm
content: Solid state relays are designed for that usage.They are opto isolated. Get a DC solid state relay.http://www.crydom.com/en/tech/tips/dc%20relays-technical%20guidelines.pdf

author: Delta
author_rank: Super Contributor
timestamp: May 07, 2015, 11:29:11 pm
content: Fuck all this opto shit and just use some oldskool relays with cheeky low side NPN switches. KISSFFS :-)Easy.

author: TopLoser
author_rank: Unknown
timestamp: May 07, 2015, 11:41:16 pm
content: Quote from: Delta on May 07, 2015, 11:29:11 pmClick click click click 2 years later mechanical failure bits falling off...More tea vicar?

author: Delta
author_rank: Super Contributor
timestamp: May 08, 2015, 12:25:16 am
content: Nah, but I'll take another ale, please.Probably shouldn't be posting whilst I'm on the piss watching the election results roll in...

author: TopLoser
author_rank: Unknown
timestamp: May 08, 2015, 12:32:06 am
content: Your round mate, a cheeky half pint of vodka for me if you don't mind

author: SL4P
author_rank: Super Contributor
timestamp: May 08, 2015, 06:18:23 am
content: Quote from: Mad Professor on May 07, 2015, 03:52:00 pmYou may not 'want' to use PWM, but your solenoids and power supply may like you more if you do.100% fast pull in, then 20% (approx) to hold the position.

author: Jeroen3
author_rank: Super Contributor
timestamp: May 08, 2015, 08:11:26 am
content: What voltage are the solenoids?You can get DC high side drivers, and use opto's or digital isolaters to control them.Such as ITS 4142N with Si8620. (total <$5)You can use those profets, un-isolated, to control some larger (DIN rail) relays if your solenoids are AC or high voltage DC. Some are designed to switch inductive stuff, such as relays.