Maker Pro
Maker Pro

Hi side MOSFET

B

BrianK

Jan 1, 1970
0
Hi, I have been reading the posts on high side MOSFET drivers, and
still have some questions. I just want to drive 12V, 40amps, using a
PWM signal. I drive 12V, the other end of the load is connected to
ground.

1. Would you use an N-channel mosfet because they are cheaper, better,
etc. If I do, I would need a high side driver and a charge pump to
generate at least 18 volts. I was looking at the IR2117 to drive it
but its current (+200mA/-420mA) seems low to drive a P75NF75 mosfet. I
ran some calcualations for a gate driver and it came up around 6 amps.
I thought MOSFET drivers needed to drive higher currents because of
the gate capacitance. Are there any high side drivers with the charge
pump built in?

2. If I use a P-channel MOSFET, I would still need a high side driver,
what would you recommend? I have seen examples just using a 2N2222.
Again, isn't that current low (500ma). If I use a series resistor to
drive the gate, won't that slow it down even more?

Thanks,
Brian
 
M

maxfoo

Jan 1, 1970
0
Uv, V unir orra ernqvat gur cbfgf ba uvtu fvqr ZBFSRG qeviref, naq
fgvyy unir fbzr dhrfgvbaf. V whfg jnag gb qevir 12I, 40nzcf, hfvat n
CJZ fvtany. V qevir 12I, gur bgure raq bs gur ybnq vf pbaarpgrq gb
tebhaq.

1. Jbhyq lbh hfr na A-punaary zbfsrg orpnhfr gurl ner purncre, orggre,
rgp. Vs V qb, V jbhyq arrq n uvtu fvqr qevire naq n punetr chzc gb
trarengr ng yrnfg 18 ibygf. V jnf ybbxvat ng gur VE2117 gb qevir vg
ohg vgf pheerag (+200zN/-420zN) frrzf ybj gb qevir n C75AS75 zbfsrg. V
ena fbzr pnyphnyngvbaf sbe n tngr qevire naq vg pnzr hc nebhaq 6 nzcf.
V gubhtug ZBFSRG qeviref arrqrq gb qevir uvture pheeragf orpnhfr bs
gur tngr pncnpvgnapr. Ner gurer nal uvtu fvqr qeviref jvgu gur punetr
chzc ohvyg va?

2. Vs V hfr n C-punaary ZBFSRG, V jbhyq fgvyy arrq n uvtu fvqr qevire,
jung jbhyq lbh erpbzzraq? V unir frra rknzcyrf whfg hfvat n 2A2222.
Ntnva, vfa'g gung pheerag ybj (500zn). Vs V hfr n frevrf erfvfgbe gb
qevir gur tngr, jba'g gung fybj vg qbja rira zber?

Gunaxf,
Oevna

Not 40A, but this safely handles 10A using a BUZ11, just search digikey for
higher amps.
http://www.uoguelph.ca/~antoon/circ/pwm555.html
 
M

Mook Johnson

Jan 1, 1970
0
It depends on the swithcing frequency as to how much gate charge current is
neded to switch it fast enough to not dissipate power. You could make an
isolated DC supply and optocouple to the input a 1A or better driver to
drive a large high side N-FET.

A more reasonable solution is to put the N-fet on the low side with the
source referenced to ground. Then you can use the many low side drivers
and drive it as hard as you desire.

The series resistor close to the gate is to prevent undershoot and overshoot
(shic could get as serious as oscillations in some cases) gaused by the gate
capacitance, stray inductance and high Di/dt diring the charging edge. It
usually only takes 10 ohms or so to damp it. Yes it will slightly slow down
you switching but this can be a good thing as a compromise between the
radiated EMI and the MOSFET power dissipation. Fast edges and wires are
good RF tramsmitters.
 
W

Winfield Hill

Jan 1, 1970
0
Brian said:
Hi, I have been reading the posts on high side MOSFET drivers, and
still have some questions. I just want to drive 12V, 40amps, using
a PWM signal. I drive 12V, the other end of the load is connected
to ground.

1. Would you use an N-channel mosfet because they are cheaper, better,
etc. If I do, I would need a high side driver and a charge pump to
generate at least 18 volts.

Most n-channel high-side MOSFET drivers include a provision for a
flying-capacitor gate-driver supply voltage, using the PWM signal
itself for the charge-pump action. You have to add the capacitor,
and sometimes a diode as well. Some include a low-voltage disable.
I was looking at the IR2117 to drive it but its current (+200mA/-420mA) seems low to drive a P75NF75 mosfet.

The IR2117 is meant for high-voltage offline use. There are lots
of good choices for low-voltage high-side drivers, and most have
much higher current capability. Check out TI, MicroChip, LTC, etc.
I ran some calcualations for a gate driver and it came up around
6 amps. I thought MOSFET drivers needed to drive higher currents
because of the gate capacitance.

ST's 75nf75 is a modestly-serious MOSFET, and 400mA gate-drive
current would be a bit on the weak side, but 6A will likely be
more than you need. Anyway, there are drivers to 12A and beyond.
Are there any high side drivers with the charge pump built in?

There are a few that have internal self-oscillating charge pumps,
so they can be used at DC, but they're rarely used for PWM.
 
Hi, I have been reading the posts on high side MOSFET drivers, and
still have some questions. I just want to drive 12V, 40amps, using a
PWM signal. I drive 12V, the other end of the load is connected to
ground.

1. Would you use an N-channel mosfet because they are cheaper, better,
etc. If I do, I would need a high side driver and a charge pump to
generate at least 18 volts. I was looking at the IR2117 to drive it
but its current (+200mA/-420mA) seems low to drive a P75NF75 mosfet. I
ran some calcualations for a gate driver and it came up around 6 amps.
I thought MOSFET drivers needed to drive higher currents because of
the gate capacitance. Are there any high side drivers with the charge
pump built in?

2. If I use a P-channel MOSFET, I would still need a high side driver,
what would you recommend? I have seen examples just using a 2N2222.
Again, isn't that current low (500ma). If I use a series resistor to
drive the gate, won't that slow it down even more?

Thanks,
Brian

I would recommend you use an IX6R11S3 -- high side/low side gate
driver with 6Amps peak output current. You can get info off the IXYS
web site -- www.ixys.net

Sam
 
J

John Fields

Jan 1, 1970
0
Hi, I have been reading the posts on high side MOSFET drivers, and
still have some questions. I just want to drive 12V, 40amps, using a
PWM signal. I drive 12V, the other end of the load is connected to
ground.
 
Top