The current through the display is limited by the resistors R7, R8, R17, R18. These resistors need to be able to handle some heat. They should be rated at least with 2W, better 5W. Please have a look to the photo below - the big light green Resistors are 5W-Pieces:
The 33k resistor (R2) needs to be rated 1W. I have here two 0.6W resistors in parallel.
Hello and thank you very much for your helpful reply - I shall re-work my board to accommodate larger pieces - certainly larger than the 0805 parts I used!!!!
- Richard
09.09.2025, 11:52 AM (Dieser Beitrag wurde zuletzt bearbeitet: 09.09.2025, 11:53 AM von scalesr1.)
Hello, I finally got the 5W resistors and a Zener rated at 2W. Now whilst the zener diode remains cool, the 5W resistor still gets too warm to touch. Is that what i should expect?
I have attached my schematic for comment if you can but I cannot see that I have deviated too far from the published design, I just made it for 5 phases. The design 'works' but I am uncomfortable with the generation of that much heat on something that should (I believe) consume very little current.
I would be grateful for any insight you may be able to provide.
- Richard
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 .
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:
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 ....
(10.09.2025, 04:56 PM)scalesr1 schrieb: 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
You have the choice: archaic and simple (resistor + zener diode) or more parts for a boost converter. NE555 is not bad for that. The MC34063 would be a terrible choice...
The "Simple Voltage Regulator" from your datasheet link is a linear regulator which will produce the same amount of heat as the archaic solution.
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