HV Nixie DC-DC Switching Power Supply
- Michail Papadimitriou
-
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Nixie tubes need about ~180Vdc to light up and thus on most devices, a DC-DC converter is needed. Here we designed a simple DC-DC switching regulator capable of powering most of Nixie tubes. The board accepts 12Vdc input and gives an output of 150-250Vdc.
Description
The module is based on the MAX1771 Step-Up DC-DC Controller. The controller works up to 300kHz switching frequency and that allows the usage of miniature surface mount components. In the default configuration, it accepts an input voltage from 2V to Vout and outputs 12V, but in this module, the output voltage is selected using the onboard potentiometer and it’s in the range 150-250Vdc. The maximum output current is 50mA @ 180Vdc.
The MAX1771 is driving an external N-channel MOSFET (IRF740) and with the help of the inductor and a fast diode, high voltage is produced.
MOSFET has to be low RDSon, the diode has to be fast Mttr, typically < 50nS, and capacitors have to be low ESR type to have good efficiency.
Schematic
Parts List
| Part | Value | LCSC.com |
|---|---|---|
| R1 | 1.5M - 0805 SMD | C118025 |
| R3 | 10k 0805 | C269724 |
| R4 | 5k trimmer SMD | C132878 |
| Rs | 0.05 Ohm - 0805 SMD | C149662 |
| C1 | 100uF Tantalium SMD | C444810 |
| C2-C3 | 100nF - 0805 SMD | C116832 |
| C4 | 4.7uF / 250V SMD | C88702 |
| C5 | 100nF / 250V SMD 1210 | C76688 |
| IC | MAX1771 SO-8 | C407903 |
| L1 | 100uH / 2.2 A | C429814 |
| Q1 | IRF740 D2PAK | C467558 |
| D2 | ES2F-E3 | C145321 |
| X1-X2 | screw terminal Pitch 3.5mm | C474892 |
Oscilloscope Measurements
Efficiency
The module’s efficiency is calculated for two outputs currents (50mA and 25mA) at 180Vdc voltage output and 12V input. In the first case, the Pout = 8.1W while the Pin=10.96W, so efficiency is calculated at 47.75%. In the second case, the Pout = 4.1W while the Pin=5.52W, so efficiency is calculated at 74.54%. We see that for lower currents efficiency is greater than for the maximum current of 50mA.
Photos
MAX1771 Datasheet
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Hi, what is the nominal and or maximal output current @ 180V ?
And you say that i can be powered from 2, to 16.5V. Is it really 2v or 12V ?
Thank you !
It can be powered from 12V to 16.5V. This is fixed in paragraph.
Poor Layout
where is your design ZF
Design is completely updated. Thanks
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I think it’s better to have more clearance to GND at the HV Output at the bottom side of your PCB. It seems there is a distance of less 1mm to GND. I would let end of the GND polygon about 1cm before the HV Connector and connect the HV-GND Pin with a single strip to the polygon. It feels a bit safer this way.
Thanks for your input. I agree with you and i will take this into consideration for the next version. If you are familiar with EAGLE, you can do this fix and share with us?
Hello, I am not an expert in mosfets but I wanted to know if I can replace the IRF740ASTRLPBF with IRF740STRLPBF (same reference without the “A”). The datasheet is quite similar and I don’t know if the difference matters for this application…
Yes, you can use it, as the basic characteristics are the same.