Re: Modern myths

From: William Levak (
Date: 1999-04-23 06:43:05

At least that was a coherent description of the circuit.

I don't see where there is a problem.  We have 3 TTL level chips connected
together.  Typically a TTL chip output can drive 10 devices.  There is no
potential for chip failure here.  Remember, these are not unlimited output
drivers.  for instance, a 74LS20 will output 0.4 milliamps, maximum,
whereas it's input current is 0.1 milliamps.  The 6522, on the other hand,
can handle 1.6 milliamps.  If the 6522 is set to input, it will clearly
pull the signal to it's level, whether high or low.  The signal will then
either be close to zero volts or five volts.  This signal is fed to a ramp
generator.  The actual voltage level is not relevant.  all that is
necessary is that it is high enough to trigger the ramp generator.  The
ramp generator controls the output to the deflection yoke by a feedback
network.  You cannot overdrive it.  The only potential problem is to drive
it at a frequency higher that it is intended for, and thus supplying a
higher effective power output to the deflection yoke. But, the feedback
circuit limits this also.  

This is about as much as I know about ramp generators.  All I can do is
repeat what several engineers have said to me.  If you try to run the ramp
generator at too high a frequency, it will simply not trigger and you will
get no output.


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