Re: Was Chopper circuit - Now ver 3.2

Jon,

Couple of good questions, let me address them in order.

MOSFET circuits require RF layout techniques because of their
extremely fast switching times. This means a pair of board layers
dedicated to ground plane and power distribution. That leaves two
circuit interconnect layers for a total of 4 layers. Multi-layer
boards are more expensive than double-sided boards by about 50%. If
the boards are very small, this is not much of a factor.

The IR2104s are rated at 600VDC making them suitable for 440 volts
RMS circuits, so 80VDC is pretty much under-utilizing them. There are
other factors that get in the way for higher voltages though.
Primarily it is the MOSFET drain to source resistance increasing as
the square of the Vds avalanche rating.

The IR540 contains a silicon die that is about as big as you can get
in a TO-220 package. It is rated at 100 volts. A 200 volt rated
device would have to have silicon with 4 times the area to keep the
same on-resistance. It would not fit in a TO-220 package and would
have to go in the much larger and more expensive TO-247 package.

If a 200 volt TO-220 part (IR640 perhaps) was used, current would
have to be scaled back 50% to keep dissipation normalized. Twice the
voltage at half the current still yeilds the same output power.
Nothing would be gained by it.

If someone was so inclined, they could use IR640s instead of IR540s
and run it at 160VDC. I just don't see the point unless someone wants
to kill themselves because they don't want to use a transformer.

Mariss

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> mariss92705 wrote:
>
> > Hi,
> >
> > 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.
>
> 4 layer? Is this really necessary? That drives up the cost quite
a bit.
> I would think you could do it with a 2-layer board for less, even
if it
> took up a little more area.
>
> > This way, those who may want to "roll their own" would not have to
> > deal with the tricky power stage. This would be maybe 10A and 0 to
> > 80VDC.
>
> Why not use the IR2113S or similar device, and be able to go to 160
V
> for some of the larger motors, especially if you are going up to 10
A?
> I used this in my servo amp, and use a pot core transformer for
high-side
> bias.
>
> Jon