# Low-side switch

I'm trying to do low-side switch with N-MOSFET.

I don't want to connect something into it. My load should be resistor in order to see how this transistor works (turning on/off, power dissipation). I chose 600V transistor, 11A drain current, 0,3Ω Rdson. I know, it's big, but my goal is, to compare him to SiC transistor, so they need to be almost the same. Max Vdd is 30V. So, from Ohm's law i calculated that my load(resistor) should be 2,7Ω in order to achieve 11A drain current. But then i'll have above 300W power, which none resistor 2,7Ω can hold out. What can i do, to achieve 11A drain current? I heard, that i can connect more resistors in series and parralell and it helps me to spread power on single resistors, but i don't know how to do that. Sorry if there are mistakes in english, but i'm from Poland and my english is not as good, as i want it to be :)

• You want to characterize a MOSFET, but don't know what "put resistors in parallel" means? Sounds unlikely. – Marcus Müller Mar 19 '17 at 19:49
• You could change/replace voltage source instead of building giant bank of power resistors. – Chupacabras Mar 19 '17 at 19:50
• I know what it means, but i don't know how to do it in this circuit to get what i want :) – Junior20 Mar 19 '17 at 19:57
• I assure you it is possible to buy a 2.7 Ohm 300 W resistor. You can also use a smaller one if you don't plan to keep it on for a long time (like 100W for 2 seconds). – mkeith Mar 19 '17 at 20:36
• 27 V x 11 A is going to be near 300 W no matter what kind of load you use (resistor or anything else). So you need to find a load that can handle 300 W. – The Photon Mar 20 '17 at 0:41

What can i do, to achieve 11A drain current?

Lower Vdd.

Use a beefy resistor.

Make a pulsed measurement. Most large power resistors will be able to dissipate a much higher power during 1ms that what they could dissipate continuously.

Examples:

Vishay 1-10W wirewound see page 5, even the 1W model will withstand 1kW during 1ms. You can use resistors with higher dissipation rating if needed.

Of course, remember to keep average power low enough not to melt it! You will need a pretty low pulse repetition rate.

If you want lower inductance, use SMD resistors. For example, this document mentions a 2512 SMD resistor will take repetitive 50W pulses during 1ms. You can solder them in, say, a 5x5 grid on a bit of PCB, which gives you 25*50W, and cool them with a fan. The large surface area should dissipate average power quite well. MELF resistors also have nice pulse power ratings.