Design and operation information
This page provides an understanding of the supply's design and operation.
TODO: Describe how the low voltage outputs are produced.
The high voltage output is by far the most interesting aspect of this supply. The low voltage sections are fairly standard switchmode designs, however the high voltage section is a little more bespoke.
The HV converts the mains input into a ~60vDC intermediate voltage using a standard switchmode design. This 60vDC is then used to drive the primary of a custom Flyback transformer which steps this up to around 11kV. A voltage doubler potted into the flyback assembly boosts this to around 22kV to reach the starting voltage of the laser tube.
Each section is detailed further below.
The author has not put a lot into working out the design of this section. It's purpose seems to be purely for driving the primary of the HV converter.
The 60v primary voltage is driven into the primary of the flyback transformer using a half-bridge resonant topology. An L6599AT based driver drives two (Infineon IPD082N10N3) Mosfets alternately at around 30KHz into the primary, coupled by two 1uF capacitors in series with the primary. This results in a sine wave in the primary of around 120v peak to peak.
Three parallel 0.18 ohm resistors on the low side of the primary are used for current sense.
The flyback transformer assembly appears to be a custom part, though the electrical design is fairly standard. It's soldered directly to the PCB with four connections.
The primary consists of 16 turns of 12 gauge litz wire. This is then soldered directly to the PCB. A fairly decent iron is needed to melt the solder holding it in. The former on which the primary is wound seems to be adhered to the ferrite core, but with what adhesive is unknown.
The secondary consists of what might be 30 gauge wire. Based on the input and output voltages (120v - 11kv), it's likely to be around 1500 turns.
Adjacent to the secondary is a voltage doubler assembly. This is a well known design which boosts the ~11kV from the transformer up to ~22kV. It consists of two 100pf/15kV capacitors, and two CRVT300 (30kV/25mA) diodes. The positive output is connected to the red wire, and the return is to a smaller gauge wire which is soldered into the PCB.
There is also a long high voltage 100M resistor connecting from the positive output to another wire into the PCB. This is likely a bleed resistor to drain off power when the HV output is turned off.
The entire flyback assembly is potted to prevent arcing, corona discharge, and other losses. The good news is that the compound is a type of clear silicone which makes it easy to see whats inside, and it's soft enough to cut into for potential repairs. However for easy access, the white (nylon?) side would need to be cut away.
This potting compound from Aliexpress seems to be almost identical to the original compound - I bought some and after curing both seem to have identical properties.
The cathode of the tube returns to the power supply via a relatively thin white wire. This passes through a 25k ballast resistor mounted on the left rail. Once in the supply, the return is split by two resistors with one to ground and the other into a circuit used for current sensing.
This is a (reverse engineered) schematic of the high voltage section. Note a number of components are potted within the flyback assembly.
