Hi all,
I normally use NTE and similar wet sites to locate suitable substitutes when I can’t find a part that a particular project calls for. This time round, though, I thought I’d try and dig a bit deeper. Can anyone tell me what critical ratings I should ensure are met or exceeded when selecting a substitute MOSFET?
In this particular case, I need to find something that’ll work in place of an stp60n06, which’ll be used to pulse current to a airplane Glow engine (12v source, looks like very low duty cycle < 10%). Looks like the NTR2395 'll work for this, but I got to wondering if I maybe have something already that might due as well.
Typically for a power switching application like that I’m looking at Vds_max, Rds_on, Vgs_th, and Vgs_max ratings.
- Vds_max - make sure you're not exceeding the max drain to source voltage.
- Rds_on - the effective resistance of the part at a given Vgs. Lower Rds_on means less power dissipated in the part (less heat) and less voltage drop in the circuit.
- Vgs_th - the threshold voltage where the part turns on. I typically look for pretty low Vgs_th so I can interface to logic gates and processors.
- Vgs_max - max voltage the gate can sustain without damage. Do not exceed.
Of course, another consideration is package. How do you plan to mount it and if you’re switching high currents how do you plan to get heat out of the part (heat sinking).
Some parts have some gate protection circuitry, which is a ‘nice-to-have’ to help you keep from blowing the gate accidentally while handling and such.
Gate capacitance can also be a factor if you’re switching at high speed. Not typically a big issue in load switching unless you’re doing some PWM.
Hadn’t made it back to the forum in a while, just wanted to say much thanks for the info!!