This is a multipart series on how to design an efficient and modern high voltage nixie power supply, from the idea to shipping it to customers worldwide.
Summary
- Part 1: Idea
- Part 2: Design & Simulation
- Part 3: Making a prototype
- Part 4: More prototypes!
- Part 5: Sending for Assembly
- Part 6: Efficiency
- Part 6: Production Run
- Part 7: Selling & Conclusion
PCB Prototyping
Thanks to lots Shenzhen-based companies, producing PCBs is cheaper than it has ever been. Coupled with extremely aggressive pricing on shipping and you can basically get yourself professionally made PCBs delivered to your doorstep in about a week for less than US$30. Isn’t it a beautiful thing? Some people are still sad you can’t simply prototype on a breadboard with all these pesky SMD components. I say it’s a trade-off I am more than willing to accept! So the next logical step was to design a PCB.
This is the first design (Rev. A) I came up with:
Looking back, I see now straight away issues: the input voltage going through vias, ground and high voltage pins being way too close to each others; and this high frequency signal coming out of the transformer being dragged all around the board to the diode. As they say hindsight is 20/20.
First results
First of all it’s amazing to see this thing work for the first time. In order to work with 0603 components and the tiny 0.5mm pitch regulator you absolutely need a microscope. It’s almost impossible to see solder bridges with the naked eye.
The other key ingredient to make this work is a stencil. Nowadays the PCB fab will ship you a stencil together with the board for a few more dollars. It’s just not practical to use solder paste with a syringe when you have pads so small. Everything will bridge and you will spend a ton of time fixing the board. Stencils are 100% worth their money.
The thing is, even with a stencil some 0.5mm pads will bridge up, because it’s applied by hand over the PCB stencils holes the amount of paste left will never be as good or as precise as a machine perfectly aligned with it. As with everything: practice makes perfect.
Reading 170V on the multimeter at the output is really reassuring and a good sign!
However, I could only see an efficiency of about 75%. It’s not awful considering the boost ratio we are dealing with, but it’s still miles away from what LTSpice had predicted. I found two culprits:
- The Vishay double diode: it’s a wasted voltage drop party in here, I’m sure we can do better.
- The Snubber network: I purposedly chose a higher voltage MOSFET so I can also get rid of this waster power.
For the 2nd case, I simply unsoldered the 22 Ohm resistor part of the snubber network and efficiency immediately rose up to 80%+. For the diode, that will unfortunately need a revised prototype. It’s ok, I can improve the layout at the same time!
2 thoughts on “High Voltage Nixie Power Supply: from idea to production Part 3: Making a prototype”
Hi Tony, just receive your nixie PSU module – by the way it is looks awesome. Could you actually explain how you imagine one would stack that psu on on nixie tube adapter board, i mean how to organise board to board connections? What came to my mind either to use PLS style connectors soldered to that 5 reserved holes on PCB that requires additionsl wiring and nylon stands. Or using brass stands as a electrical connector – cleaner designs, but that looks add lots of HV open surfaces around one of stands, and what is more important concern is how current will flow thru thread, nuts, etc, should I use copper paste to avoid brass contacts from corrosion. Thanks, Eugene.
Hello Eugene,
I think the best way is to create a surface mount pattern on your main PCB, then solder the screw holes onto your PCB. It’s safe and you do not need to use any sort of stand.
Alternatively, you could screw the board in by matching the hole; again without stands. Since one screw will carry high voltage, make sure it is coated with some sort of insulation though.