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Looking for a homebrew Solid state relay circuit... — Parallax Forums

Looking for a homebrew Solid state relay circuit...

denodeno Posts: 242
edited 2009-06-25 09:26 in General Discussion
Does anyone have or know of a good homebrew circuit for a solid state relay.·

Needs to be DC input, and able to·switch up to 10 amps DC at the output.·

Thanks· DenO

Comments

  • mctriviamctrivia Posts: 3,772
    edited 2009-06-21 16:12
    optoisolater followed by a darlington pair.

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  • Greg LaPollaGreg LaPolla Posts: 324
    edited 2009-06-21 16:34
    I posted about this some time ago here

    Greg
  • denodeno Posts: 242
    edited 2009-06-21 17:17
    Thank Greg for the reply..

    And McTrivia...the opto with the darlington pair doesn't produce a low enough "on" resistance. To much heat would be generated at 10 amps of conduction. Does anyone know what components are used in making a solid state relay?

    DenO
  • LeonLeon Posts: 7,620
    edited 2009-06-21 18:14
    Just buy one, they aren't expensive.

    Leon

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  • PhilldapillPhilldapill Posts: 1,283
    edited 2009-06-21 20:47
    deno, I made a MOSFET board a while back. It's got opto-isolated inputs which turn some high current mosfets on/off. The board I made can accommodate 16 Mosfet switches, but I can expand or contract that amount. Let me know if you want the schematic or board.
  • denodeno Posts: 242
    edited 2009-06-22 11:45
    Philladapill...thank you for the reply, and I would like to see what you put together. I too have breadboarded a mosfet switch, but I wouldn't mind compairing notes. I am using the mosfet switch to turn on and off a solar panel (150 watts..9 amps full sun) when the battery bank is full. Using a mosfet in this fashion dictates that I use a P channel mosfet..meaning the higher voltage is on the panel side of the mosfet which is the source charging the battery bank which is the lower voltage. thanks..I will send you a PM with my email address.

    Leon...actually, a DC to DC 10amp solid state relay costs about $30 to $40 each, and I need 4 of them. To handle that many amps, the SSR's usually come in what they call the PUCK type with screw terminals. PUCK type, meaning Hockey Puck 'looking'. Never the less, thank you for your reply.

    DenO
  • LeonLeon Posts: 7,620
    edited 2009-06-22 13:05
    The price is about right, but small PCB-mounted 10A SSRs are available:

    uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2448993

    Leon

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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2009-06-22 14:58
    There are digital to MOSfet driver chips that do a better job of driving MOSfets than individual components. Nuts & Volts had a discussion of them a few months back. One doesn't always need the opto-isolators and other chips do isolate the CPU from potential damage. And opto-isolation can be slower than direct wire.

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  • LeonLeon Posts: 7,620
    edited 2009-06-23 09:19
    Micrel makes a nice MOSFET driver - the MIC4426. I've got some but haven't tried them yet.

    Leon

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  • PhilldapillPhilldapill Posts: 1,283
    edited 2009-06-23 16:40
    TI Makes some really good MOSFET drivers. One of which is the UCC27322. It's a 9A, low side driver, which is the one I use most of the time. It works VERY well at high freqs.
  • QuattroRS4QuattroRS4 Posts: 916
    edited 2009-06-25 01:17
    How about a High Side switch ... similar to this.
    see attached PDF....I have used these frequently in prop based designs .
    These are used quite a lot in automotive light control modules.

    Regards,
    ··········· John

    EDIT: in fact I am just assembling a few boards as I type . See attached images

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    'Convince a man against his will, he's of the same opinion still.'



    Post Edited (QuattroRS4) : 6/25/2009 1:28:27 AM GMT
    pdf
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    VN920.pdf
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  • mctriviamctrivia Posts: 3,772
    edited 2009-06-25 01:45
    turn down the iso on your camera. can't make anything out. Piece of paper over a flash works well to soften the bright light.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5

    Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.

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  • $WMc%$WMc% Posts: 1,884
    edited 2009-06-25 02:41
    Have you looked into IGBTs. I've justed started looking into them? The reason I brought this up is. I recently took apart a VFD. What I thought was some kind of MOSFET turned out to be a IGBT after a quick goggle search.This little fella (about the size of a computer mouse) is good for 300amps at 1200v. The best thing is its fully ON with just 3vDC and hardly any current. I found the the voltage from My Fluke 87-5 (set on OHMs) would make the junction turn. Fluke clams 14Meg or better impedance on their meters.

    I know not every ones into switching 300amps (I play around with welding machines), But I can see all kinds of uses for a 30amp IGBT vers.

    I often need to switch 120vAC with a 5volt 20ma or less output. I have a bunch of opto 22s 5v That are made to sw/ 120vAC with a 5vDC input, but the input current exceeds the output current of the STAMPs so I'd have to use a driver anyway.




    ___________$WMc%___

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  • PhilldapillPhilldapill Posts: 1,283
    edited 2009-06-25 04:01
    $WMc%, the trouble with IGBTs is they are NOT bipolar. What I mean by that, is they don't allow current to flow in both directions. They are in fact constructed like a hybrid between a MOSFET and a bipolar junction transistor(BJT). They generally have the voltage drop properties of a BJT, but the input is more like a gate of a MOSFET. Picture an NPN BJT - now connect the source of an N-channel mosfet to the base of this BJT, and connect the drain of the MOSFET to the collector of the BJT. Now, to turn the BJT on, all you have to do is supply a tiny bit of current momentarily to the MOSFET, and it goes into saturation. I suppose its kind of like a Darlington pair, but with near infinite gain.

    IGBTs are nice though. GREAT for high-freq applications. I've got some samples from ST Microelectronics that are good for 30A, 600V continuous. I'm thinking about making an inductive heater with them!
  • QuattroRS4QuattroRS4 Posts: 916
    edited 2009-06-25 07:58
    mctrivia said...
    turn down the iso on your camera. can't make anything out. Piece of paper over a flash works well to soften the bright light.

    .. These were taken with a mobile phone (cell phone for those states side) no flash and bad lighting .. and merely as a reference to items mentioned..

    Rgds,
    John

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    'Necessity is the mother of invention'

    'Those who can, do.Those who can’t, teach.'
    'Convince a man against his will, he's of the same opinion still.'

    ·
  • mctriviamctrivia Posts: 3,772
    edited 2009-06-25 09:26
    Well that will do it. Only so much you can do with cell cameras.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5

    Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.

    Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
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