Need help solving gate problems associated with RFP12N10L MOSFETs

I've been using Arduinos for a little over 8 months and so far my experience with them has been great and I haven't had a reason to post on the forum until now.

I have a project I'm working on that will essentially control a 12V 1W LED using one of the Arduino's PWM pins with an N-Channel MOSFET (RFP12N10L). While this seems simple enough I've managed to break the gate on two MOSFETs attempting this simple setup and I'm at a lost as to why. By break I mean the gate remains on and never shuts off no matter what I do. Hopefully someone here can help me figure out where I'm going wrong so I don't blow the remaining few MOSFETS I have.

Here's a diagram of my target environment.

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My test environment in which the gates became broke was a 5V 1A source with a standard 5v 20mA LED and a 150 ohm resistor connected to the drain from the LED.

RFP12N10L Documentation: https://www.fairchildsemi.com/datasheets/RF/RFP12N10L.pdf

The LED I'll eventually be using will be similar to one of these http://www.ebay.com/itm/121490605226 if that helps.

Any constructive feedback and/or suggestions would be greatly appreciated.

P.S. I'm a very visual learner so if my diagram is wrong please provide me with a altered diagram. That would help me out a lot.

Hi, welcome to the forum.

If you have the mosfet connected wrong, a 20mA led might still turn on. Can you make a photo of your wiring ?

I use a protection resistor from Arduino output pin to gate. For example 1k when the mosfet is switched on and off only now and then, or 220 ohm or 470 ohm when PWM is used. The 10k pulldown resistor at the gate can be before or after the protection diode.

About those 12V light bulb replacement leds. Do you know if PWM is allowed ? What is inside ? Diodes, resistors, leds, and perhaps capacitors.

Peter_n: Can you make a photo of your wiring ?

As requested, my external power supply is being used for something else at the moment so I just tied it into the arduinos 5v and gnd which should be fine. The mosfet in the photo is one of the broken ones. It's actually off...

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Peter_n: About those 12V light bulb replacement leds. Do you know if PWM is allowed ? What is inside ? Diodes, resistors, leds, and perhaps capacitors.

From what I can tell from the photos it has resistors, LED's and diodes not sure about capacitors... I haven't actually purchased the LED yet I need the MOSFET working properly before I make the investment.

Everything is fine in the photo. I can't read the colors on the resistors, but I assume they are okay.

I don't know how the mosfet could break. I understand you want to know how that happened, but I really don't have a clue. Is it possible that the mosfet is still okay ? Perhaps the breadboard has bad contacts ?

Mosfets are ESD sensitive devices. Connecting pins in the wrong order can damage them.

The best way is to connect the source (ground) first, and then the drain. The gate WIRE should be connected to the Arduino pin/220ohm resistor first, BEFORE it's connected to the gate. Simple rule: Connect gate last and disconnect gate first.

Best resistor values are 220ohm between Arduino and gate, and 100k (not 10k) between gate and source.

The picture shows a 20mA LED.

Not wise to run a single 1A LED from a 12volt supply. That would need a ~8.7ohm current limiting resistor that would consume 8.7watt. Three LEDs in series would be better. They would need a 2.2ohm/5watt resistor. (2.2watt heat) Better to use COB (chip-on-board) LEDs with three LEDs in series, usually with multiple strings. Power LEDs are sometimes better driven with a LED driver board. Leo..

Wawa: Not wise to run a single 1A LED from a 12volt supply.

Oops sorry my mistake I mean't 1W not 1A.

Wawa: Better to use COB (chip-on-board) LEDs with three LEDs in series, usually with multiple strings

Just out of curiosity is the LED in the eBay link not a COB LED? It contains a board and 3 LED's per board (front and back). Just wondering.

Thank you both for helping. I've made the suggested resistor changes to my design. While I don't know what I did wrong originally, I'm hopeful these suggestions will help prevent issues with my MOSFETs in the future.

Ahhh, missed the ebay link.

Many 20mA LEDs, with current limiting resistors, stuffed inside a lightbulb-shaped enclosure. The bulb probably draws about 100-150mA, and can be connected directly to a 12volt supply. PWM with a mosfet is not a problem.

This is an example of a COB light. Leo..

Why use a 100V MOSFET for 12V? You can get much lower on-resistances for a 20V or 30V MOSFET. 0.2 ohms is a lot these days, 0.01 ohms is more usual for a general purpose MOSFET.

However here its not the problem - with that small load you shouldn't have any chance of damaging the MOSFET even driving it in the linear range, so I think you have either static electricity or you're not giving the whole story.

Use a 150 ohm gate resistor to protect the Arduino pin if using PWM.

Never wear nylon/synthetics when handling static sensitive components, never sit in a plastic chair - these are extremely likely to generate levels of static fatal to electronics. Nylon carpet is absolutely to be avoided...

I'm lucky to live on a damp island (UK) where the air is seldom dry, so static isn't a great problem, but other parts of the world require full anti-static precautions to be followed - wrist strap, conductive desks, the works.

MOSFETs are particularly likely to be utterly destroyed by static due to the large gate capacitance - once enough voltage is present to cause breakdown there is a lot of stored energy available in the capacitance (10's of microjoules) to punch a hole in the gate oxide, splattered with molten aluminium - device is toast. Typically the max gate voltage allowable is 20 to 30V only.

In my experience, the gate capacitance helps protect power MOSFET's from ESD damage. It takes a lot more charge to get enough voltage to punch the gate.