Page 1 of 1

A few PSU questions

Posted: Sun Dec 28, 2014 4:50 am
by SystemLoc
Got my Nixie clock kit today, and piecing together how it works by reviewing the PIC code and tracings.

I've got a few questions on the HV PSU circuit:

The 5V supply comes across the 470uF filter cap. There is then a boost circuit formed from the 20nH coil and NTD5865NL. The MOSFET switch is driven by pin 10 of the PIC (RB3, P1A, CCP1) through a 100 ohm resistor, R10. The 100n C6 cap is the HV filter cap.

I have some trouble reading PIC assembler, but it looks like the PWM runs open loop, and has no feedback loop to control output?

The NTD5865NL is rated for 60V. The HV should be 170-180V. Seems to me the MOSFET is woefully underspecc'd for voltage.

Re: A few PSU questions

Posted: Sun Dec 28, 2014 3:12 pm
by Tony
The output from T12 is fed into the 3x multiplier formed by D11-15 and C9-13 to produce the HV. Direct conversion of 5V-180V in a single inductor would not be efficient.

Did you receive a kit with a C6? - they haven't been included for nearly 2 years and L1 has been 33uH for about 1 year.

Re: A few PSU questions

Posted: Sun Dec 28, 2014 5:21 pm
by SystemLoc
Brilliant! That makes much more sense. I couldn't simulate a boost convertor to get that much increase worth crud; the duty cycle is too high. I just hit upon this app note ... N-1126.pdf

I took the info about the C6 and the L1 in the 'Kit contents' thread, which has the old components. I was at a loss to find where C6 was installed in the assembly instructions, and as such, there is none included. :)