Voltage Doubler Problems

[JacobEdward]

This is my attempt at doubling voltage:



I basically replicated the schematic from this EEVBLOG show at 11:07

http://youtu.be/I4ED_8cuVTU?t=11m7s

I'm not really getting a voltage increase, the voltage will pulsate whenever there's a signal, but it's not really doubling. 

Anybody know how to do this properly?

[elgonzo]

What is the frequency and the duty cycle of your PWM signal?
What is the capacitance of the caps?

[JacobEdward]

The duty cycle is 50% and the capacitance is 10uF for all 4 capacitors.

[elgonzo]

Also, consider that the load has an influence on the output voltage (see Dave's video at 16:28 time mark, where he switches from a 10kOhm load to a 1kOhm load). If your load is "too low", you might try upping the PWM frequency...

[JacobEdward]

I thought using an LED as the load would basically mitigate that problem (though I have no idea what the resistance of an LED would be...), I'll try again with a resistor

[elgonzo]

The resistance of an LED is very low, usually far below 100Ohm. The LED on itself is a very low load, allowing the caps to fully discharge in the blink of an eye...

[JacobEdward]

Then I'm not sure what the problem would be... why isn't the voltage being trippled?

[JacobEdward]

Just tried again... same pulsing problem...  if a diode has insignificant resistance, it wouldn't really matter if I swapped a resistor in there... though, given there is a pulse means there is 'something' going through those capacitors... though it's certainly not at a 50% on 50% off...

http://youtu.be/jJZx77MavhI

[JacobEdward]

I've changed the frequency from 2 hertz to 100 hertz and sure, it's not pulsing anymore, but it's not tripled like it should be, it's only doubled (given two lines are feeding to the same output)... the schematic from his video shows one data pulse line connecting to two capacitors... as in he's claiming that you can triple the voltage via capacitors, not just adding two voltages... so someone's going to have to tell me what I'm not doing correctly.  Thanks

[elgonzo]

I've changed the frequency from 2 hertz to 100 hertz and sure, it's not pulsing anymore, but it's not tripled like it should be, it's only doubled (given two lines are feeding to the same output)... the schematic from his video shows one data pulse line connecting to two capacitors... as in he's claiming that you can triple the voltage via capacitors, not just adding two voltages... so someone's going to have to tell me what I'm not doing correctly.  Thanks

Watch Dave's video again and also listen...
Pay attention to what load values, PWM frequency and capacitor values he uses.
Also pay attention to how the behavior of the circuit changes if he changes one of those parameters.

Especially note what happens when he decreases the PWM frequency. Note that he starts with 10kHz, and goes down to 1kHz. Look at the scope when that happens. From this observation, extrapolate what happens when you go down further to 100Hz.

Also pay attention to what Dave says about the problems this circuit has with maintaing a 3x voltage when the load is not high enough and how a higher/lower value of the capacitors affects the behavior of the circuit.

[JacobEdward]

So my microcontroller is very slow... it can only reach 4kHz with the simplest of loops... is that pretty much it for trying to double the voltage?

http://www.espruino.com/Performance

[elgonzo]

So my microcontroller is very slow... it can only reach 4kHz with the simplest of loops... is that pretty much it for trying to double the voltage?

http://www.espruino.com/Performance

Again, please watch Dave's video again. I get the impression that you did not really paid attention... Dave displays the circuit behavior on a scope and he also shows how you can mitigate a lower PWM frequency (1kHz) somewhat by choosing caps with higher capacitance (given a load of a certain value). Dave explicitely mentions the value of the capacitors in his video... Take some time to watch his video again and listen to what he says... All your questions/problems so far are explicitly answered/addressed in Dave's video...