HVPS overall design

The design of the high voltage power supply is a little unconventional, but by convention, most are. In order to simplify the transformer design, I'm going with a hybrid structure, with an unregulated H-bridge inverter fed by a regulated buck converter, all powered by the system's 110V supply.

Block diagram

Control circuit

Control circuit

The control circuit is based around a UC3843 PWM controller. This old chip provides a synchronizable oscillator, a voltage reference, error amplifier, current-mode sense comparator, and an output capable of driving a MOSFET directly.

Regulation is taken from the +2kV output, through a voltage divider and into the voltage sense input of the UC3843. An external frequency compensation circuit and slope compensation circuit (latter not shown) keep the control loop stable.

The 50kHz PWM signal from the UC3843 is fed to a 4013 flip-flop configured as a frequency divider, which produces a 25kHz square wave at 50% duty cycle regardless of the pulse width driving the MOSFET. This signal is buffered by a gate driver IC, producing a strong 24Vp-p output that is then isolated and split by a pair of gate drive transformers and sent to the gates of the H-bridge.


Two transformers are used by this circuit:

High voltage transformer

(Detailed posts to come on the transformer construction!)

The high voltage transformer is a fully custom transformer, with a single primary and a single secondary, wound on a pair of Fair-Rite 9277012002 U-shaped cores. It uses a sectioned winding for the secondary, with the full 2000V output split into six 333V sub-windings separated by pieces of insulating material. This reduces the voltage stress seen by the insulation of the magnet wire to no more than 167V across one layer of enamel (remember that there are two layers of enamel between two adjacent wires).

The filament transformer does not produce high voltages, but it needs to be sufficiently spacious to isolate the primary from the secondary to a working voltage of 2000V. The current plan is for this transformer to be a modified Signal HCTI-1000-2.4 toroidal inductor, with a secondary added using high voltage wire. Whether the ferrite material is suitable for this use remains to be seen.

Last modified: Tue Mar 1 20:46:53 MST 2022. Converted from blog/20220301b-hvps-design.md.
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