PSU 1KV
Project
We are building a 1KV, 100mA DC power supply that will be used in open-source semiconducuctor fabrication by university laboratories.
Block diagram
By adjusting the buck's voltage, we directly influence the voltage at the output of the system linearly.
The comparator hotpath detects if any of the two conditions are met, driven by two DAC lines from the MCU:
- Output current is larger than CC setpoint
- Output voltage is larger than CV setpoint
If any of these two conditions happen, the buck is told to lower its voltage by pulling its feedback pin HIGH.
The buck converter must be chosen so that its datasheet directly states the feedback pin can be operated with a logic signal, because most parts expect to be able to read an analog voltage as feedback.
Transformer build
- 4 turns of litz wire, 0.2mm strand with ~200 internal wires.
- 46 turns of 0.2mm standard enamel wire (same usage as in 230v transformers). Repeat 4 times.
- Ferrite core is wrapped in 1mm of kapton take that ensures the core does not arc to any winding.
- Windings are separated by 1mm FR4 PCB that also provides electrical contacts for the wire (at the ends)
- There must be no winding-to-winding isolation path provided by air. All such paths must be filled by epoxy. Example:
- FR4 disc to center core
- FR4 disc to FR4 disc (for the triple disk insulation)
- Exterior of the windings
Parts overview
| Type | PN |
|---|---|
| Reinforced amplifier +- 1V | TI AMC3330 |
| STM32 MCU with minimum 2 DAC + 4 ADC | STM32F303RCT6 |
| Hish-side H bridge isolated PSU | TRACO TBA 2-2423 |
| Mosfet gate driver | Analog ADuM4120 |
| Mosfet | Onsemi FDBL0630N150 |
Warning
Verify gate driver and gate driver supply at switching frequency of 200KHz.
Gate impedance calculator. Driver datasheet calls for 7.5ohm impedance @ 15V.
Mosfet gate resistance: 2.2ohm
Driver output impedance: 1.5ohm
Remaining ~4ohm must be provided with an external resistor (use 1206 or bigger).
A milliohm resistor inline with the coil will be used to tune the deadtime of the h-bridge switcher.
Secondary concern: the isolated PSU can supply about 60mA. The mosfet driver will try to push peak 2A into the mosfet gate. The RC curve needs to be calculated and integrated so that a single charge of the gate does not brownout the gate driver. This is tuned by having big enough bulk caps on the +15_ISO rail.