Here we have both charge UP and charge DOWN action such as we have in
a PLL charge pump.
The transistor will be the trick to get working as intended. I have
had some success however with using transistors in the Integrator
(Charge Pump) section before; so it looks like no sweat.
Sometimes you need as high as a 100uf cap in the Q output to the
charge pump from U2 as a load, and a filter. It will distort the
control voltage wave form sometimes but it might help in that the
waveform is now reshaped and makes for a better kind of pulse so
strictly ramped or square waves are not the Bible here.
What is important is the rate of charge pumped to the Integrator and
so the Integrator has a long time constant to slowly build up the charge
voltage to make slow and smooth corrections. The output form U2 then is
a matter of amplitude and pulse duration or period.
I am using as high as a 20 second time constant in the Integrator
section (charge pump storage section). Actually this makes it so that
the voltage can barely reach the 63.7% average of the output voltage
across the two 1000uF caps.
Dan
