9V/18V Charge Pump switch question

[lars-musik]

Hello fellows,

I wonder if the switching of this little circuit is good enough. I wanted to layout a very small charge pump that is attached to the switch. In previous versions I used DPDT to also break the line to the charge pump but I like it better this way.

Would you expect any problems here? Is it allright to switch the voltage while the pedal is running or could this be harmful in any way?

Thanks for your input!

[MrStab]

hi Lars,

iirc there was a user a while back who tried this method and had latchup as the Vref took longer to settle down to the new voltage than the power rail itself. i've actually used this method myself, once, without an issue, but not on a circuit i depend on. so maybe certain conditions need to be met.

i think the recommendation was using a voltage divider or regulator to switch between 9V & 18V, from the 18V rail, though this definitely isn't the most efficient route.

[lars-musik]

Ah, that doesn't sound too good, but thanks all the same!
What about using a header and jumper, so that the transistion of the voltage isn't immediate? So the way to change the power would be: Unplug the pedal, un-screw the lid, fiddle with a nasty jumper. That should give enough time.

[Groovenut]

You might try this approach. I would recommend an RC filter between the switch and the bias points in the circuit to firm up the VB2. You'll want to stay with a small time constant though so the new 18V arrives at the same time as VB2. or you could put the RC before the switch and not worry about the time constant as the cap will be charged at power up.
Like this

[MrStab]

i like your thinking, Lawrence - i'll need to remember this if i ever use it.

at first i thought a jumper seemed a bit odd, but then i thought either that or an internal switch would make sense if you never expect to switch the voltage in a hurry. could also save you some room on the panel.