Normally Closed Relay
StarMan
Posts: 306
I have a 12 volt circuit that I would like to temporarily turn off with a Stamp pin while the Stamp does other things, then turn the circuit back on.· The 12V circuit could have a wide range of loads and the current could be anywhere from 200mA to 10 amps.· I am assuming the best way to do this is with a relay switched·by a transistor.· Does anyone have a recommendation for a transistor/NC relay combination for this application?
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Chris Savage
Parallax Tech Support
Do you possibly have a spec for a relay that would fit my needs?· Preferably solid state.· I've been on the Crydom web site, but I really don't know how to spec out a relay.
Chris I.
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Chris Savage
Parallax Tech Support
What would you do differently for an SSR?· I found one at Crydom that will fit my needs initially (it only switches 5 amps).· The part number is DC60S5-B.··· What I am using it for is to temporarily turn off a string of LEDs.
Chris I.
If you are only switching 10 amps at 12VDC then a fet should be all you need and you can drive it directly from the stamp pin.
Since you are driving LED's I assume the current is only one direction. A relay allows you to go both directions while an SSR typically switches AC voltage at the zero crossing point.
I would think you would want to regulate the current though, sounds like a lot of LED's to take 10amps unless it's 5 red/orange luxeon3's with a big heat sink.
Here is a to220 package that takes 15 amps up to 60V. .86 cents qty 1
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=381989&Row=863498&Site=US
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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
Post Edited (metron9) : 6/9/2007 3:53:14 AM GMT
You may want to check out this thread:
http://forums.parallax.com/showthread.php?p=654078
Also, I have a question about the operation.· If I want to run current through the MOSFET, should I pull the gate high with a 10K resistor?· How then would I switch it down?· Through a transistor?· Will I need a heatsink on the MOSFET?
BTW, Yes, I'm running·a lot of·LEDs on this system.
Chris I.
In the specs, you will see data related to Vgs ( Voltage, gate with respect to Source) and corresponding values of Rdson ( resistance, Drain to Source in the ON condition). You want Rdson to be a fraction of an ohm when voltage signal on the gate is 5 volts. Some specs show this as a graph.
The IRL510, IRL 520 mentioned previously are specifically designed for microprocessor signal levels and will conduct fully with 5 volts on the gate.
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Tom Sisk
http://www.siskconsult.com
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Crydom run a nice range of 'DC Load' SSR's in the CMX range...mosfet switching stage...
www.crydom.com/products/productFamily.aspx?id=21
I have attached the Datasheet also ...
Regards,
Quattro
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'Necessity is the mother of invention'
Post Edited (QuattroRS4) : 6/13/2007 3:05:36 AM GMT
Question, Why would someone select a part that is 10 to 20 times higher price given it can perform the same task or is it different than a fet in it's operation or meets some other criteria for safety or something else?
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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
They're called high side switches.
Google search for "Infineon Profet" if you're interested. Incredibly low on resistances for the high-power parts.
Downside? Trying to find a distributor that sells a single quantity of the exact part you need.
Of course, for a hobbyist, just use a relay!
As for using a DC or AC SSR versus a fet, it's all about packaging. An SSR is a conveniently packaged fet. Easier to drop in and replace if it blows up.