MOSFET Connection

blakrapter

Hello everyone,

I plan to use·a BS2 to drive a fairly large motor (12Vdc, 20 AMP) via a MOSFET using the BS2 PWM feature.· My problem is, I know only the basics and I know this can be done and I know what main components I need, but I am worried about how to hook it all up.· From my experience with electronics, I am pretty sure I won't be able to hook the MOSFET gate lead to the chosen output pin without putting something in the middle to protect both the stamp and the MOSFET.· The same goes for·the lead·between the MOSFET and the motor...· I talked to several of you about voltage regulators to step the 12V signals down to 5 volts, which requires more than just a regulator. That is why I assume there will need to be some resistors, capacitors, or something between all of my "main" components.

I would really like to know a good resource for looking this kind of stuff up.· I have purchased some starter books on electronics that I am working my way through, but I haven't finished them.· I hope MOSFETs and connecting them will be covered eventually, but I thought I would ask all of you because I learn better from you all than I do from a book.

Thanks!

bennettdan

Hey look at the links below they will help you get started.

http://forums.parallax.com/attachment.php?attachmentid=41944

Also check out this other forum

http://forums.parallax.com/showthread.php?p=590196

I have a small test PWM example that I use to run motors at 50% in one of the replys.

·

Post Edited (bennettdan) : 6/14/2006 2:24:15 AM GMT

T Chap

To get 12 volts to 5 you can easily use an optocoupler with 12 volts on the transistor side, when the stamp turns on the led on the opto)5 volts from stamp), the phototransistor turns on the voltage on and lets it pass through like a switch. To make it easy, theses chips usually have 4 usable pins only. One is the LED input (from your stamp for example) the second is the LED GND connection. Just use a resistor before the LED, maybe 470ohm or 680ohm is fine for 5 volts in from thr stamp volts. Then on the other side of the chip is the 12 volts in to the collector on the transistor, next is the the emitter (output). Think of it as a switch that turns on when the LED is on. This is excellent isoltation from the stamp, no matter what gets shorted on the transistor side, the stamp is protected, since there is no physical connection.

The other easy method to switch 12 volts to 5 is with a 5 volt Zener. You can find them at Radio Shack or anywhere. You need a very simple circuit to do it, but think of it as a regulator that only allows 5 volts out, no matter what goes in, but Zeners come in a lot of ratings, so it is a cheap simple regultor. You may have to consider switching times on both optos and Zeners after you get the basics down.

Here is the simplest version of a zener in a regulating circuit, it uses on one zener and and one resistor, it couldn't be easier. Just buy the zener with a larger voltage rating that you need.


http://www.allaboutcircuits.com/vol_6/chpt_5/7.html

bennettdan

I agree with originator99 I use optoisolators to convert 12v signal down to 5v logic levels myself a 4N25 from jameco or digikey are like 36 cents each. You can use a 1k resistor in series with your 12v signal to turn on the led inside the optoisolator and then use a 470 ohm resistor in series with the 5v and phototransistor to your stamp pin. I will upload you a picture when I get home tonight.

blakrapter

Thanks for the info guys. I think its time for me to start ordering stuff and trying it...

bennettdan

Hey correction on the cost of the 4N25 optos they are 22 cents each.

RinksCustoms

I agree with what everyone said above, Google "discover circuits"and you'll have acces to over 10,000 circuits you can (with alittle knowledge of electronics and digital pots) can interface with your basic stamp projects