IRL520 Gate Voltage

Tim-M

I hope some of you more experienced folks can help me read the data sheet for an IRL520 Power MOSFET Transistor, I'm having some trouble. My question is about the gate drive voltage... I understand that it's a logic-level gate drive at 5 volts, but I'm wondering if I can drive it with 12V and not do damage.

The data sheet is here: http://www.vishay.com/docs/91298/91298.pdf

The closest spec. I see is the Gate-Source Voltage, or Vgs, listed at plus/minus 10V. Is this the right spec. to be looking at and how is it interpreted in regards to the 12 volts I'd like to drive it with? Does the 12V fall within that 20V range or is it 2V over the plus 10V side? By the way, the transistor is switching a 12 volt load in case you want relate it to the voltage differences at the other junctions.

Thanks for the help,

Tim

Mike Green

The datasheet is very clear on this. In the Absolute Maximum Ratings section it gives a gate to source voltage of +-10V. There's no way to be any more clear. They're saying that you cannot apply a gate to source voltage of more than 10V, whether positive or negative relative to the source (ground) lead.

What will happen if you exceed any of the values given in the Absolute Maximum Ratings section? They don't say, but you won't be able to complain to them or to whomever sold you the part if it fails to work or explodes taking out all the equipment within 2 feet of the device or the magic smoke escapes or whatever.

Tim-M

Thanks for explaining this Mike, I wasn't sure that I was relating it correctly. This means that the 12 volt drive is too high, so I'll divide it down to half and give 6 volts a try.

Thanks for your help,

Tim

Peter Jakacki

Tim, is there any reason you are trying to use this particular mosfet, it's not a very good one at all. The IRF3708 is an excellent device with a low 12milli-ohm Ron vs your 270milli-ohm and the device is suitable for direct logic drive. Still, the absolute max gate voltage is +/-12V so you would have to reduce or clamp the voltage but why are you driving it at 12V anyway?

Alternatively I have used the IRF3205 in past designs and they have an 8milli-ohm Ron and the absolute max gate voltage is 20V.

*Peter*

Tim-M

Hi Peter,

The mosfet choice and drive voltage details don't add up because I was looking for a quick and dirty solution with the parts I had in the house. A good friend of mine wears a heated vest when motorcycle riding and the thermostat for that vest went out. I had a cheap 12 volt powered 555 pwm kit that I thought would make a pretty good thermostat, but the output transistor would only drive up to 1 amp. The IRL520's are the only power transistors that I have right now, so I thought I'd give one a try as the output transistor replacement. The pwm output from the 555 is nearly 12 volts and it directly drives the transistor. To stick with parts on hand, I used a couple of resistors to divide the 555 drive voltage in half and the IRL520 seems to work OK.

Thank you for the better suited mosfet recommendations, that information is much appreciated. I hope to put a few of these together for other riders and a it would be good to have a better output transistor match that has the lowest On-Resistance possible... this one is just the proof of concept.

Tim

P.S. Perhaps a question for another thread... When using a mosfet as a full on/off switch, which spec. indicates the drive voltage required for saturation?

Post Edited (Tim-M) : 9/25/2009 11:57:14 PM GMT