Hi, can anyone who had to do with mosfets recommend a specific transistors that would do the job like driving PWM signals etc.
I am working with voltages 5-250V and currents 1-20A - on low power devices it is usually 12V/500mA
and that is driving the coils.
So what are the best mosfets with VGS 3.3V and also 5V (1-50A) but 3.3V is preferred.
Thank you
So far I found IRF530, IRF510 VGS 2.0V
Also IRF840 is quite good (2.0V, 8A, 500V, 85 mOhm)
Very cheap
For 250V I doubt you'l find any MOSFET with 3.3V gate drive - that would be so fragile to dV/dt transients
burning out the gate oxide. At that sort of voltage its worth considering IGBTs too.
For high voltages like this use a MOSFET gate driver chip powered from 12V, that can drive any MOSFET
you want and be controlled from 3V logic. Strong gate drive protects a MOSFET from dV/dt influences
For lower voltages you will find some low gate voltage logic-level MOSFETs, mainly surface mount.
You haven't explained what you mean by "best". That might be some complicated function of cost,
switching speed, gate charge, package type, on resistance and avalanche rating!
Higher voltages are no problem as those mosfets are much easier to control.
I actually am driving 120V mosfets with 40V mosfets but vgs is higher that 3.3v and they just won't switch properly. (signal too weak) I have 3.3v output pwm/sine signals that must properly drive mosfets.
Frequency just like standard pwm 100khz-500Khz is fine.
I'd rather avoid avalanche situations because it is usually a death of mosfet)
For gate charge I guess it is similar to non rf mosfets and should be small
You need a MOSFET driver chip, clearly, made for the purpose, does the job.
I just have interesting question about power mosfet.
Let's say current goes from source(+) to drain(-) in n-channel enhancement mosfet.
With VGS=0V there is a full current flow - but I want to stop it.
So if I apply a negative VGS (G-,S+) - is it gonna stop the current flow between S-D ??
Is it safe or it will damage the gate? Small threshold GS
Normally VGS controls flow from D to S which is a body diode opposite to the flow
Deous:
I just have interesting question about power mosfet.Let's say current goes from source(+) to drain(-) in n-channel enhancement mosfet.
With VGS=0V there is a full current flow - but I want to stop it.
So if I apply a negative VGS (G-,S+) - is it gonna stop the current flow between S-D ??
Is it safe or it will damage the gate? Small threshold GS
Normally VGS controls flow from D to S which is a body diode opposite to the flow
Power MOSFETs have a body diode, part of the structure of the device is a big PN junction diode
so they always conduct backwards, it cant be turned off, but if the gate is forward biased the
on-resistance of the MOSFET is in parallel with the diode and may reduce dissipation.
Biasing the gate negative doesn't do anything.
So are there FET ICs that could allow to completely stop the current with reverse gate charging?
How about IC that allow controlling current in both directions S<=>D, are there such?
High power AC circuits could be controlled like that
Also another question - if I connect two 100V mosfets in series - can they work with 200V ?
You put two MOSFETs back-to-back for bidirectional switching - this is how some SSR's work. Triacs are
also common for AC switching, but they don't switch off till the current drops to zero.
Really high power AC equipment uses thyristors or gate-turn-off thyristors which can handle kilovolts and
megawatts. They don't switch nearly as fast as FETs though, but good enough for mains and PWM of large motors.
MarkT:
You put two MOSFETs back-to-back for bidirectional switching - this is how some SSR's work. Triacs are
also common for AC switching, but they don't switch off till the current drops to zero.Really high power AC equipment uses thyristors or gate-turn-off thyristors which can handle kilovolts and
megawatts. They don't switch nearly as fast as FETs though, but good enough for mains and PWM of large motors.
Back to back you mean parallel or in series?
In series, otherwise it could not work as you'd have two anti-parallel diodes.
I connected back to back like here
however voltage drops half value. Looks like resistance is too high on second mosfet.
note - voltage going forward and backward is AC mains 110V. all dimming and fine but not enough power.
How do I connect them properly?
I used second configuration on picture below
Also transistors I used - FQPF20N60C, IRFB4115, IXTQ100N25P
Deous:
I have 3.3v output pwm/sine signals that must properly drive mosfets.
at 50% pulse duty sine amplitude should be 5V