Re: Split H-Bridge: Will this work?
- From: Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 20 Oct 2007 08:33:29 -0700
Winfield wrote:
On Oct 20, 12:06 am, sdeyo...@xxxxxxxxxxx wrote:I want to use an H bridge to stress diodes. I need to put 1 amp
forward, then 35v reverse, back & forth. I want to use 2 different
supplies for each half of the bridge: when Ahi and Blo are on, the
diode ( and a 1 ohm resistor in series) will be forward biased and
that power supply will be about 2 volts @ 1 amp. When the other half
is on, I'll use a 35v supply on that half to reverse bias the diode.
I want to use all N Channel MOSFETS with a HIP4080 H Bridge driver.
I know I could stress the diodes with a 35v sine wave and a 35 ohm
series resistor, but then the resistor dissipates 35 watts, and I need
to do 30 diodes at once in parallel, so that's a lot of heat to dump.
That's why I want to use an H bridge with 2 supplies, one low voltage-
high current, the other high voltage-low current. I figure using 1 ohm
resistors, 2 volt supply, about 1 volt shows up across the resistor,
dissipating 1 watt, instead of 35.
I have this working at 1 amp, using P & N channel fets with a Basic
stamp & xistors driving the fets. I need to do 30 diodes at a time,
all in parallel, so I need to scale up alot, and want to use N
channels for lower Ron and lower gate drive voltage.
With the HIP408x, all four of your H-bridge MOSFETs should
be N-channel, I think you do realize that, right?
My question is: is anyone familiar with the HIP4080 or HIP4081
H-Bridge driver ICs?
I'm rather fond of those ICs.
Will they work with two different supplies?
No, no, only one supply for the HIP4080, with a diode and
flying capacitor for each high-side's gate driver. That
supply will need to be about 12 volts.
Yes, you can nicely accomplish your goal with a HIP408x -
the two power supplies you're thinking of will be +2V for
one high-side MOSFET drain and 35V for the other high-side
MOSFET drain. Note, the HIP4080 doesn't know anything
about the voltages on the MOSFET drains, until it turns
one of the high-sides on, then it has to be able to handle
the voltage, which it can, for anywhere from 0V to 80V.
You can put the current-limiting resistor in series with
each diode under test - it won't have any effect when the
diodes are seeing the reverse voltage.
If you use a humongous low-Ron type for the high-current-
carrying FETs, you could run all 30 diodes (with their
individual series resistors) in parallel, at about 1A each,
but I might be inclined to use two or three MOSFETs for the
job, each running 15 or 10 amps maximum. You'll be using
individual gate resistors for each MOSFET anyway, so this
means one HIP4080 chip can drive all the MOSFET bridges.
I'd go discrete as well here but all in parallel sounds quite brazen. It might be a good idea to place a blast plate over the FET ;-)
The data sheets seems to indicate so, it uses 2 separate charge
pumps to drive the 2 upper N channels FETs above their source
voltages, which when on will be the supply voltages.
Right.
I have all the parts on order, but won't come till Monday,
so here I sit and wait and wonder.
Make your drawing and analyze each state. BTW, I assume
you ordered one of the HIP408xA types?
I'm curious, what kind of diode would find this test, 1A
and 35V, difficult or stressful? A small-signal type?
Are you going to log the voltages across the diodes under
current by looking at the resistor-diode nodes? I see that
the voltage swing there is only from about 0.0 volts (well,
10A * Rds(on) = under 50mV for a MOSFET with Rds(on) under
5 milliohms) to about 1.3 volts, so you could use 74hc4051
multiplexer ICs (another fav of mine) to scan the voltages.
--
Regards, Joerg
http://www.analogconsultants.com/
.
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