Dickson charge pump from a microcontroler and current drawn

[Jaunedeau]

Hi,

  I need to send a 9.5-12V constant signal into a SCART connector (apprently 1KOhm min, 10kOhm nominal). Since I have only 5V on the board I tried to simulate a Dickson charge pump using the timer on the microcontroller inspired by Dave's Microcontroller Voltage Doubler video (I4ED_8cuVTU on youtube).

  I made a simulation to find proper capacitors values before testing on breaboard, and though I found that 1 to 10uF and 1k to 1MHz give the proper output after 1 to 10ms, the current drawn on the pin is very high. I set the ESR to 5Ohm (is this a realistic value for lcsc / aliexpress 0603 1 or 10uF ceramic capacitors ?) and it dropped to a couple hundred mA (for about 20ųs only).

  Should I be concerned with the initial current drawn during the first few cycles ? Do I need to add a serie resistor on the clock outputs ?

Thank you,
j.

[jwet]

Most Port pins on uP's can only source about 20 mA.  I cap looks like a short when first charge.  I would add a resistor to reduce the short circuit to about 20 mA- this would be about 250 ohms.  You'd like to run at a high frequency and use moderate sized caps perhaps 1 uF.  What you is a tripler.  If you feed start at 5v and put 5v minus a diode drop above it, you'll get 9V.  You also want a output cap.  You shouldn't have such high droop on each cycle.

There are small parts that do this job for a dollar- the old faithful is the ICL7660.  Its data sheet might give you some tips too.

[Jaunedeau]

I wanted to avoid using a 7660 (for space issue) but it is apparently not the best choice here !