problems with MOSFET

njpatter

hello..... im using the IRF510 mosfet that others have talked about in the forum. I'm pretty sure i have it all hooked up correctly using the following link as a reference:
http://www.awce.com/fetrly.htm

At the moment I am just powering a LED to make sure things work before I plug it into my motor. The circuit works when using Vss as my ground and Vdd as my source (I just have it toggle on and off). When i swap out out Vss and Vdd for the leads of my 7.2v battery pack the circuit stops working. I have tried both orientations of leads just in case the battery was wired backwards but neither orientation works.

any ideas?

FireHopper

you need to make sure the gnd of the battery is connected to circut ground.

Mike Green

The IRF510 will not work well with a logic level input (like from a microcontroller I/O pin).· You want to use a logic level MOSFET (like the IRL510).

njpatter

ya, i was planning on getting the irl510 after i had verified it worked (irf510 was at radioshack for $2)

thanks for the info

Phil Pilgrim (PhiPi)

Don't feel bad. Many fall into this trap due to Radio Shack's insistence on selling a logic-incompatible device. I'm not sure who they think their market is for that transistor, but it has certainly wreaked havoc in this forum over the years when people try to use it. I wish they'd just replace it with the IRL version.

-Phil

Beau Schwabe

One trick is to offset the Ground supply to your microprocessor (Stamp) by a diode drop. (<- typically 0.6V)

Since the VGS of the IRF510 ranges from 2V to 4V (<- temperature and current dependent) and the Stamp's I/O can be 0.6V below VDD when HIGH (4.4V), that only leaves about 400mV of overhead which can cause the IRF510 to heat more than it should, because you are operating it in it's linear region. Unfortunately, as the IRF510 heats up, the situation only gets worse and you can have a nice thermal event.

Use caution though if using the diode trick... A similar thing can now happen at the other end. This time if the I/O pin goes LOW, instead of 0.6V being ground, it could very well be 1.2V ... you have a little bit more headroom here (800mV) before you start to approach the VGS 2V threshold.

The IRL510 on the other hand has a VGS of 1V to 2V and is better suited for microcontroller control.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

lleblanc

I fell into this trap with the IRF510 as well and now I've been searching for the IRL510 and I can't seem to find it anywhere.

Anyone have any suggestions?

Phil Pilgrim (PhiPi)

DigiKey carries them. So does Mouser.

-Phil

lleblanc

I've never ordered from Mouser before but if the item says non-stocked should I just order the IRL510A?

Phil Pilgrim (PhiPi)

Yes. The IRL510A should be fine. Different manufacturers use different suffices to indicate package type, lead-free status, etc. Internally, the parts have the same specs, except maybe power dissipation, which is package-dependent.

-Phil

ElectroHack

I've bought a few IRF510's at Radio Shack.·I had the idea of using a TLC555 PWM arrangment that I built. The stamp would change resistance,·via a digital pot,to the TLC555 and therefore duty cycle.

The gate of the 510 was to receive input from the output pin of a 555 thru an optoisolator.·

I got the·555 PWM part working, and I was able to send a variable duty cycle to the 510, with which, I could control my motor, with a single IRF510. In this configuration, the motor was on the high side, wired to drain, and source went to ground. The gate also had a connection to ground thru a resistor. This ensured turnoff.

Things started not working when I introduced a second 510. I· attempted to build a bridge. Based on every MOSFET brigh diagram I saw, wiring would have to have been

IRF510 #1

High => Drain

Source => motor

Motor => Drain (IRF510#2)

Source => Ground

When it didn't work, I took it· apart, and tried the first half of the circuit by itself. The same components and signals that worked fine when wired

High => Motor

Motor => Drain

Source => Ground·· : did not work when wired as

High => Drain

Source => Motor

Motor => Ground

Are there PNP·and NPN MOSFETs?

I found a ·post elsewhere on this forum and found a layout for a bridge using ·TIP42 and TIP31 (PNP and NPN)·transistors.·That one works, but I have problems with this too. One direction provides lower voltage than the other. I assume this as due to variance in resistors etc.

LoopyByteloose

I suspect that Radio Shack, like many other suppliers just buy and resell what is easily available. Mouser and a few other places are very clear about what is available and what is not. It really is an added value to shop from them rather than off the shelf. All of us have boxes of stuff that just didn't pan out and taught us to be more aware of what the specifications actually are telling us.

We go on line and see things that are in a catalog or PDF and think that they are also in inventory everywhere. They may be list items that require special production runs that must be ordered in quantities of 10,000 or more just to be gotten. Or they may very popular items that go out of stock as soon as production runs are done.

In some case, one can work around the problem by the fact that the manufacture will set aside a few for free sample requests. But don't abuse the courtesy by requesting tons of free samples that you just want to accumlate for a rainy day.

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PLEASE CONSIDER the following:

Do you want a quickly operational black box solution or the knowledge included therein?······

···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Professor Chaos

Speaking of finding what is available, the following site seems to be a good way to find who stocks what at what price:


octopart.com