On Sun, 25 May 2008 12:42:53 -0400, Jamie
t wrote:

Jim Thompson wrote:

On Sun, 25 May 2008 12:01:25 -0400, Jamie
t wrote:


wrote:


here is the circuits picture.

http://www.flickr.com/photos/26914086@N05/2519852045/

I build a deadbug circuits of it. However, the MOSFET is not fully on
or off, the lower drain waveform is shown on the right bottom. it
should be an inversed gate waveform.

load is a photodiode with voltage drop of 2V / 10A.

Is't caused by some parasitic inductance? I couldn't figure out the
parameters. Here I use these equations to calculate the L

V=L di/dt
dt = D/f
di = current ripple
V = Vcc-Vds_on-Vload

but the original circuits use two inductors, why?
Why here are two anti parallel shottkey diodes? I don't think it's
necessary. one is protection and the other is "free wheeling"? Is this
high-side driven a "buck" configuration? I removed the shottkey and
the waveform doesn't change too much.

Why there are two capacitors? local voltage reservoir? can I pick any
large capacitors? or I need to use equation
i=Cdv/dt
dt=D/f
dv=di*Cesr
i=10A?

from IXDD414, the output is shorted by 1k to ground, I don't think
it's necessary.

I am totally confused by the TVL4112 comparator and two FET current
mirror(?). How does is work? I know the comparator show be high or low
but here it will follow the input voltage until the + and - are equal.
How does the feedback work? on the top the current sensing gain is 20
if I remembered. how to calculate the current here? apparently a LM324
won't work as a comparator.


Thank you guys.

Have a nice holiday.


If my symbols aren't failing me, I would say those are non enhanced
MosFets, which means they are on and need to be reversed biased to
be off. In this case, pulling it common I don't think is going to cut it.
Are we using the correct components? Maybe an Enhanced NMOS is what you
want?


Where do you get "non-enhanced" mode MOSFET's in the discrete world?
They are even rare in my integrated circuit world.

...Jim Thompson
well, that's the common symbol used late time I checked.

http://www.rocw.raifoundation.org/co...lecture-10.pdf

and after looking, I would say if this information is correct, he's
using a P-channel which also could be an issue here.

But then again, maybe incorrect footprints are being used.

http://webpages.charter.net/jamie_5"

The common symbol for a depletion mode MOSFET is attached.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

America: Land of the Free, Because of the Brave