Re: [CAD_CAM_EDM_DRO] Re: Was Chopper circuit - Now ver 3.2

Larry Edington wrote:

> ----- Original Message -----
> From: "mariss92705" <mariss92705@...>
> > Just an errant thought here. Would anyone be interested if I were to
> > cobble-up a single or dual bridge, all n-channel MOSFET (TO-220,
> > IRF540) power driver? This would be on a 4-layer PCB and include all
> > necessary supply bypassing, TTL input interface and a current sense
> > resistor.
>
> Running the 2104 in standard boost mode with a cap? Then it'll have to be
> run on a chopping drive right? I just don't want someone to end up putting
> a steady state drive signal on an input and their boost cap ends up
> discharging
> below minimum vgs then the high side fet gets unhappy.
>
> An oscillator would fix that but now you are into more complexity and cost.
>
> I assume you intended these to be for standard chopping drives so I thought
> I'd just mention it. I used 2104's to drive IRF540's for a chopping drive
> that
> worked out great. They don't like to be left on too long though.

I had a modulator that would go to 100% duty cycle in extreme cases, so I
couldn't use the bootstrap bias on the high side. I put in a CD4049 hex inverter
with 3 stages paralleled for each side of a differential output, and fed this to
the primary of a small pot-core transformer. I use one secondary to
run the high-side current monitor, which sends overcurrent info to the rest
of the circuit through an optocoupler. Two other secondary windings
power the 2 IR2113S FET drive chips. The only problem I ran into was I
tried to use bifilar wire to make it easy to wind the coil, but the capacitance
between wires was enough to pop the CD4049, due to the very high dV/dT
of the FETs. I changed to separate, layered windings, and it was fine.
This really wasn't much added cost, at all.

Jon