Low Charge Pump Voltage (LT1054CP)

[franblanc]

I have constructed a Univibe clone pedal which works on 24 volts DC. I am trying to make it work using a 9 volt DC supply and a charge pump using the LT1054CP Integrated Circuit. I was hoping to get 18 volts out of the charge pump (Road Rage 2019) but it supplies less than 17 volts. (It varies rapidly from 16.5 volts to 16.9 volts). I have measured the voltages around the circuit and I have enclosed them in the attached circuit diagram. I have corrected one ground loop already but I cannot get the voltage to stabilise at 18 volts or near it. I believed the problem might be at D3 1N5817 Shottky Diode because that's where the voltage starts to jump around from 13.0 to 13.3 volts. However all three 1N5817 offer 179 approx on the diode setting of my multimeter so that is consistent. All the components were purchased new from Mouser. My question is...is it normal for charge pump out voltages to vary so much? Do I have a bad LT1054CP? (C5 and C6 were omitted.)

[Lani]

Typically yes, you won't get 18v because of the voltage drop from the diodes. Also the voltage will sag when you start to pull current from the charge pump. I believe the 1054 has a max current output of 100mA and the closer you get to that number the lower the voltage will "sag". So in short yeah, it seems to be working properly.
What isn't working properly is the 7815 regulator.
If you remove or just short out D1 then you will gain approx .3 to .4 volts which may help. 7815 regulator need around 18v to work properly which may be the problem here as it seems to be dropping out of regulation. Did you jump the BST (Boost) pads? That will up the frequency of the 1054 but not sure if it will help but worth a try. I would short out D1 and see if that gets you there.
What is the voltage on the output of the 7815?
Edit - just noticed you don't have C5 populated. That needs to be there for the 1054 to work properly!! Unless I'm missing something....