Designing and building a DC to DC high voltage booster for tubes

Alternative to high output voltage transformers

The completed module

I spent quite a bit of time searching for a high voltage booster schematics, I found some discrete examples and a few based on the UC3843 chip popped up. In the end I decided to settle with the UC3843, as I've seen these chips get used in other tube amplifiers.

The design is based on a circuit drawing from 2006, the auther is M. Moorrees, I can't find any other info about this, the schematics appear when searching for UC3843. I believe this site may belong to M. Moorrees: https://threeneurons.wordpress.com/nixie-power-supply/.

The circuit has been modified to deliver 100vdc and enough current for two tubes, additional components have been added to filter the output voltage. C0G capacitors have been used where possible to provide a stable voltage out. The choice of the timing capacitor means the oscillation is at about 75KHz, this is above the human hearing which means it should not have an impact on the audio amplifier section.

If the circuit is modified to output a higher voltage, then some of the components will need to be changed.

The schematic

The circuit has been designed with SMD resistors and capacitors, high accuracy components were chosen to ensure stabilty and accurate output voltage.

It's imporant that E3 is a low ESR type, ideally with an ESR of 68mΩ or less.

The circuit runs on 12V DC and only needs a few milliamps, this board is not suitable for high current loads, but could be used for nixie tubes.

Standalone 100V Booster Module

For my tube amplfier board, I incorporated the 100v booster into the main board using SMD only components and larger output capacitors.

SMD Version

The calculations

Vfb = 2.5V
R10 = Keep this at 2.2K
R3 = Set this using the calculations below to get desired output voltage
Vout = 100V

Vout
R3 = _______ - 1 x R10

Vfb

We can see 85.8KΩ resistor for R3 achieves the desired 100V out, the actual resistor used was 85.6KΩ.

100
R3 = _______ - 1 x 2200 = 85.8KΩ

2.5

As we are keeping R10 at 2.2K we won't be using this formula.

R10 = R3 ÷ ((Vout ÷ Vfb) - 1)

You can use this formula to work out the Vout if you have two known values for R3 and R10.

Vout = (Vfb(R3 + R10)) ÷ R10

The PCB

The PCB has been made as compact as possible, unfortunately the SMD version is not available as a PCB as I made that as part of the tube amp board. Ground planes are used on both sides to reduce noise. Mounting and output/input is done using 2x dual PCB headers.

Top side of PCB

Bottom side of PCB

3D Model

Bill of materials

Components for standalone module:

Name	Designator	Qty	Manufacturer Part	Manufacturer	Supplier	Supplier Part
56K	R12	1	RC0805FR-0756KL	YAGEO	LCSC	C137509
100nF	C4	1	CGA4J2X7R2A104KT0Y0U	TDK	LCSC	C342919
2.2R	R8,R7,R5,R6	4	RC1206FR-072R2L	YAGEO	LCSC	C137327
4.7nF	C2	1	CGA4J3C0G2E472J125AA	TDK	LCSC	C193083
15uF	E2,E1	2	LKMD1152E150MF	Ymin	LCSC	C443246
2.2K	R10	1	RC0805FR-072K2L	YAGEO	LCSC	C114561
470uF	E3	1	UHW1V471MPD	Nichicon	LCSC	C136284
220uH	L1	1	SMRH74-221M(f)	Shenzhen Zhenhua Fu Elec	LCSC	C241217
SR1200	D1	1	MBR1100RLG	ON	LCSC	C65041
100pF	C3	1	CGJ4C2C0G2A101JT000N	TDK	LCSC	C508866
1R	R1,R2	2	RC1206FR-071RL	YAGEO	LCSC	C137355
HDR-M-2.54_1x2	12V_IN,HV_OUT	2			LCSC	C124375
UC3843BVD1R2G	U1	1	UC3843BVD1R2G	ON Semicon	LCSC	C231572
22R	R4	1	RC0805FR-0722RL	YAGEO	LCSC	C107702
470pF	C1	1	CL21C471JBANNNC	SAMSUNG	LCSC	C28256

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