electronic parts question

[icantsee]

I'm seeking some guidance. I've read several threads that talk about using a mosfet as a relay for switching 10 amp+ loads in hotwires. I believe that I understand the wiring and concept and have found a schematic that gives values for the resisters and cap. I've seen a few recommendations of a specific transistor. My problem is that the mosfets mentioned don't seem to be in stock anywhere when I Google them and the sales places that I'm finding are expecting orders of 1000 pieces. Can anyone tell me a good online vendor that will sell small quantities of parts? I can solder and have made "breadboard" projects before, but I do not know how to substitute parts by spec. if the actual specified part is not available. I found this one at Radio Shack, http://www.radioshack.com/product/index.jsp?productId=2062618&cp=&sr=1&origkw=mosfet&kw=mosfet&parentPage=search



It says that it is 3 amps, so I'm assuming that it won't be up to the task at hand. Please forgive my ignorance, and thanks in advance to anyone that can set me straight.
John

 

[Curious_character]

Digi-Key and Mouser Electronics are two good sources for small quantities of parts.

c_c

 

[icantsee]

Thanks for the info. I went to the mouser site and looked for a IRF1704. Nereus had recommended that one on this thread, http://www.candlepowerforums.com/vb/showthread.php?t=151155

The one mentioned wasn't in stock, but I found this one that seems similar, http://www.mouser.com/search/ProductDetail.aspx?R=STP100NF04virtualkey51120000virtualkey511-STP100NF04

Would this one be close enough? Thanks again.
John

 

[Curious_character]

A glance at the data sheets show only one significant difference -- the 1704 is rated for a maximum junction temperature of 200C and the substitute is rated at 175C. It might be more a difference in testing or process control rather than any fundamental structure difference, though, so I'd consider them to be equivalent for hobby purposes, even in a hot environment. The substitute should work fine.

c_c

 

[icantsee]

Got some on the way. Thanks much for taking the time to help me out.
John

 

[MrAl]

Hi there,

I just thought i would add a few important notes...

This device is a hefty MOSFET and should easily handle 10 amps.
The max voltage is 40 volts.
This is not considered a "logic level" mosfet, so you should drive the gate to
at least 10 volts to turn it on... 7 or 8 volts might work, but 5 volts isnt enough.
In order to keep power dissipation low, make sure the mosfet is turned either
fully on or fully off...that is, either drive the gate with +10 volts or use either
zero or minus something to turn it off.
To keep the transistion switching time low, use a low enough gate drive source
impedance. If the device has to switch on and off a lot of times this is more
important, if the device only has to swich on and off once in a while this is
not as important.
Always check for overheating by either measuring the case temperature while
running and switching or use a finger but be careful as electrical parts can get
hot enough to burn skin very badly. It's better to use a thermometer.

 

[icantsee]

Thanks very much for your advice. I was planning to use this device on a 14.4 light and also got a couple extras for when I do a 5761 on a 6 volt pack. It sounds like I need to search out another device for the 6v application. The 5761 is a 30 watt 6 volt bulb, so it's 5amps, coorect? Thanks again.

John