So how significant are these 'high-ish pulse currents'? The video input current is quoted as 1µA maximum. To supply this current on average, the current during syncs (just taking line syncs for a ball-park figure) will be
Hi David,
congrats to your converter picture.
If you watch a test pattern your calculation is correct.
The problems take place when you have a jump from a black to
a white picture. When the resitance of the driver is too high,
the sync pulses get smaller for a moment.
When the current (the 1uA) is to low or the cap is to big,
the sync tips lift up from the clamp.
When the cap is to low the picture gets dark from left to right.
You must have a pattern generator where you can switch directly
from a black to a white and vise versa picture!
With the 500 ohms in the IC is a big problem.
You'll never be satisfied.
The best is to generate a clamp current only at the sync tips.
You can see this in my first converter at the input of the cxl's.
In my new converter I had that problem with the input resistor
too.
In the M7403 ccd there is a resistor in front of the clamp too.
The only way to solve this problem is to make a seperate
DC restorer in front of it. And I made this
.
Don't forget the cap is made for 625 at 405 you must
take 15nF at pin 9.
Look with the oscilloscope at 100% white
that the "line" does not fall from the beginning to the end of
the line. You first see this on the oscilloscope bevore you notice
it in the picture.
Kind regards
Darius