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OK- I'm looking for a way to switch up to 20 amp's digitally. I have a BasicStampII (16 input's/output's prorammable computer on a chip basically) I am planning on baseing a security system on. I am fairly good with electronic's, but one thing I havn't "Got" yet is switching high current loads.
From what I've read, there's some really smar people here (techman?) that would probably know about this stuff.
One question I had is are MOSFETs Parallelable? what is the difference between mosfet's and hexfet's?
Basically, I would run the Comp chip. to the Gate/base (on mosfet), +12 to the load, then to mosfet, then mosfet to ground, right?
Any help greatly appreciated.
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Posts: 31 | From: buffalo,MN,USA | Registered: Jun 1999
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Your circuit idea will work. Add a small resistor to the output of your basic stamp to the gate of the fet. Main reason is fets often fail shorted Gate Source. I might even considering using a small single transistor stage to buffer between the fet and the stamp. Also, fets can be paralleled. Keep them matched and they all get their own Gate resistor. Go with 47 ohm gate resistors. Heat sink them at that kind of current, they have a turn on Drain Source resistance of like .015 ohm but at 20 amps you can't be too careful. I would recommend International Rectifiers IRFZ44, 50 amps, 90 watts and plentiful because of their popularity in auto amps. HTH's Off the top of my head so sorry for any errors. What is the output of the stamp?
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Thank You Very Much! That will help alot. The stamp output is 5V, I think the max source curr. is like 25ma? 30ma drain?
Oh- yea, just an Idea- Would a relay(DPDT) to switch RCA cables between sources add alot of noise? -- I was thinking stamp could turn on remote leads, activate sound recorder chip, And pump a siren/BOOM/Warning through Whole system if alarm tripped. Would get more attention if set off than the average alarms that everybody pretty much ignores now. (relay would in off state would connect to head, on would be recorder)
One more thing- this is probably a bad Idea, but the Stamp has an onboard Sinewave Gen, just need's A r/c circuit to filter it. might come in handy.-Not perfect, but, but it'll do down to 1hz, also can mix 2 freqs.
ok, I guess I got another yet thing. Would you know off hand anywhere that has a circuit that is good for picking up the beat of music? Beat->-Mosfet's-->High-Beams? I'm thinking messing with RCA's isn't usually good, pick up beat from head unit out's?
All of these are just Idea's Yet, Any suggestions or Comments GREATLY appreciated.
Thank you very much again!
P.S. Where would you get the IRFZ's? I found them in my Mouser Electronic's Catalog, which I usually get my small/cheap goodies from, listed for $2.29. Is this fairly good? (they will ship standard postal for me, so shipping on like 5 of them would be like under a buck)
[This message has been edited by daboom (edited 08-02-99).]
Posts: 31 | From: buffalo,MN,USA | Registered: Jun 1999
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Ok, your first comment was 5 v out. This isn't going to do what you need on the mosfet drive. You will need to have that 5v fully activate a small signal transistor and have that do your mosfet drive for you. Besides, at 25 ma, anything goes wrong with your fet and poof.
A very small DPDT wouldn't add much, if any, noise to the system. I would look into using a 4066 (hope I got that number right) for IC switching of low level signals.
Let me know on the sinewave generator. I'm not very familiar with the basic stamp.
It is possible to go Speaker out> DC isolation> Rectification> 6db low pass (RC)> mild peak hold> comparator> drive circuit> mosfet. And have that pulse whatever you want.
Your price on the fets is decent, just go with them. I use MCM myself. Unless I order big enough, then I go to a manufacture.
Ok- you said 5V isn't enough, how about 12V? The Board I'm going to make for it will Have a 5V reg. on it, could easily add a 12V or 9V or other, so what would be a good Voltage? Also, for a signal transistor, just like a 2n2222? Actaully, one of those quad. trans. DIP/SIP package would work great,But for some reason I couldn't find any (tired? ;-) )any Suggestions on transistor / transistor-4pack? (There's like 9 pages of tran. in small print- I'm lost.-) Thank's Much-- --Tim
Posts: 31 | From: buffalo,MN,USA | Registered: Jun 1999
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What I'm worried about is if you a H of 5 volt switching on the fet then the fet will pass 5 + or - and wasting the other 7 volts as heat. You need to energize a small signal device as a sort of digital switch. This would allow you to turn your 5 volt H output on your basic stamp to a 12 volt H and this could go to your fet. I think I'm going to need to draw up a schematic, I've been very busy with a new job so bear with me. 2n2222 2n3904 2n3906 are all good options. And available at Rat Shak.
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