[scalesr1]

(09.09.2025, 05:04 PM)kahlo schrieb: Your schematic looks good.

Th NCH6300HV delivers 230V max. Assuming this number, some calculations:

R8 33k: U=230-68=162V | I=162/33000=0.0049A | P=0.8W
R15 36k display OFF: I=230/(36000+24000)=0.00383A | U=36000*0.00383=138V | P=0.53W
R15 36k display ON: U=230-70(assumed glow voltage)=160V | I=160/36000=0.00444A |  P=0.71W

If your resistors have to handle this without help of something like a copper area or heat sink, they dissipate the energy by heating up. This is fine, as long as they are specified correctly and the temperature remains far below the melting point of the solder   .

Hello and many thanks for your speedy reply.

I have tweaked the NCH6300HV to deliver the required 245V (with the assistance of Yan from Omnixie) so I re-calculate:

R8 33k: U=245-68=177V | I=177/33000=0.0053A | P=0.949W
R15 36k display OFF: I=245/(36000+24000)=0.00408A | U=36000*0.00408=147V | P=0.59W
R15 36k display ON: U=245-70(assumed glow voltage)=175V | I=175/36000=0.00486A |  P=0.85W

It just seems all a bit archaic making up all that heat just to generate 68V and I wonder if it might not be more efficient to add a simple 68V boost converter, even as something as simple as the NE555 based circuit - or an MC34063ased design. No, wait, I'm just looking at this https://ww1.microchip.com/downloads/aemD...05399B.pdf
Simple Voltage Regulator ....

What do you think?
 - Richard