Electronics > Beginners
150w DC Load project (low cost, med difficulty)
blackdog:
Hi,
I see several problems in his design, the AD8630 is a nice opamp, but like almost all other chopper or auto zero opamps, it is not suitable for driving capacitive loads...
Take the output of U7D, 100 Ohm and then 100nF to mass, you must be kidding ... :-DD
Look in the datasheet on page 10 and figure 25, above 100pF it is inherent instable, 500pF load 90% overshoot TADA!!!
And also the output section 2K2 resistor for a gate input who is 14nF |O
Probably the circuit is stable for DC use, say for testing batteries, but if you have a load that is not constand, the entire output section can not keep up with it.
In the Netherlands we say: as slow as a snail on a tar barrel.
The AC otput impedance of this current source is low, even in the low frequencies, and likely to get easily generated, during error conditions.
Kind regards,
Blackdog
ArdWar:
Can anyone points me to the schematics, please?
Cliff Matthews:
--- Quote from: blackdog on March 02, 2018, 06:50:25 pm ---Hi,
I see several problems in his design, the AD8630 is a nice opamp, but like almost all other chopper or auto zero opamps, it is not suitable for driving capacitive loads...
Take the output of U7D, 100 Ohm and then 100nF to mass, you must be kidding ... :-DD
Look in the datasheet on page 10 and figure 25, above 100pF it is inherent instable, 500pF load 90% overshoot TADA!!!
And also the output section 2K2 resistor for a gate input who is 14nF |O
Probably the circuit is stable for DC use, say for testing batteries, but if you have a load that is not constand, the entire output section can not keep up with it.
In the Netherlands we say: as slow as a snail on a tar barrel.
The AC otput impedance of this current source is low, even in the low frequencies, and likely to get easily generated, during error conditions.
Kind regards,
Blackdog
--- End quote ---
Just measured my 4 IXFK90n20's at 24.5nF.. I think I'd need a costly PA to drive each one!! There's no free ticket is there?
Cliff Matthews:
--- Quote from: ArdWar on March 02, 2018, 07:02:24 pm ---Can anyone points me to the schematics, please?
--- End quote ---
No problem..
Mechatrommer:
--- Quote from: blackdog on March 02, 2018, 06:50:25 pm ---you must be kidding ... :-DD
--- End quote ---
iirc when following his venture with this dc load project sometime ago, with so many days, weeks, months of design iterations and revisions, he never got into assessing his load performance for stability, transient, pulse etc. the best i can see is he's probing the gate driver pulse. he's too busy drawing schematics, playing with keypads and firmware. not to screw him up but his load could work, but may as well it could not.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version