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

mariss92705 wrote:

> Jon,
>
> I appreciate your thougtful comments. I would hate to be the poor
> bastard that designed the HIP4080. Probably the most miserable half-
> bridge driver ever built. Probably looking for a job now somewhere.

Well, they push it as a class-D audio power amp, to run from 12 - 15 V
power supplies. It does pretty well at that. The design isn't so bad,
it was what the marketing folks claimed it was good for that was the
problem! Specsmanship is one thing, but this chip has specs that
are bald-faced lies!

> About IGBTs. You have to keep in mind what they are; essentialy a
> Darlignton transistor that uses a MOSFET as the "low current"
> Darlington driver into a bipolar pass transistor.
>
> Where they fit into the scheme of things is for circuits that operate
> at voltages above 440VDC. The advantage goes to bipolar transistors
> in that range due to their lower Vsat versus Rds for MOSFETs. Below
> those rarified voltages MOSFETs rule. Simply their losses are lower.

Using the largest FET die that you can get, mosfets can "rule". But, these
huge chunks of silicon cost a bundle! For your 80 V max drives, I think
you are right, mosfets are best. When you start talking about 160 V
drives, it is not so clear. You need to put 250 V (absolute minimum)
fets in a 160 V drive, and I think 400 V would be safer. Here, you start
to see where the IGBT starts to lead. It may not actually save POWER,
but it may be able to match the FETs on power, with a die HALF the
area! That will save money.

> Four layer boards versus two layer boards. Printed circuit board
> price matrices primarily are based on square inches of board size.
> The number of holes, the number of different hole sizes and to a
> great degree the number of layers are irrelevant. What matters is the
> size of the board.
>
> If you make a big board, it will be expensive; if you design a small
> board, it will be cheap. That's all there is to it. 4 layers or 2, it
> makes no difference.

Once you go past 2 layers, they have to laminate, so it is a jump to a
different process. With the off-shore prices you showed, it really doesn't
matter. I generally pay $100 per board, even ** 2 layer ** in the
quantities I do stuff in! I just got some 6 layer boards back, about
$240 each. But, I only ordered 10 pieces. You design things for MUCH
larger batches.

>
> The market that addresses the 440V range multi-HP motor drives is
> very small relative to sub 200V drives. That market requires IGBT
> devices. MOSFETs are the more efficient choice in the lattter.
>
> I have designed 440V IGBT dives on a contract baisis for major drive
> manufacturers. IGBTs are slow, lossy but rugged. They are not
> economical below 440V, not 100V.

OK, well, I've stated my point, and you've stated yours. I'm still not
convinced that they are only viable above 440 V in all cases.

Jon