82 lines
4.7 KiB
Markdown
82 lines
4.7 KiB
Markdown
 
|
# Power supply design
|
|||
|
|
|
|||
|
|
## Goal
|
|||
|
|
|
|||
|
|
Generate every panel rail from one **12 V DC** input, using cheap modules. Panel voltages are set by
|
|||
|
|
**zener references** (copied from the original Stern board), not by module trim pots. A
|
|||
|
|
mis-set or failed module can't push the panel above its rated voltage.
|
|||
|
|
|
|||
|
|
## The original board (Stern/Sega 520-5138-00)
|
|||
|
|
|
|||
|
|
See [../reference/stern-520-5138-00-display-psu-schematic.jpg](../reference/stern-520-5138-00-display-psu-schematic.jpg).
|
|||
|
|
|
|||
|
|
| CN2 pin | Label | How it is produced | Real value |
|
|||
|
|
|---|---|---|---|
|
|||
|
|
| 8 | +60 V | 88 VAC → D1 → C1 (about +120 V raw) → Q3 (MJE15030) emitter follower, base on D5 68 V zener | about +62–67 V |
|
|||
|
|
| 1 | −120 V | 110 VAC → D2 → C2 (about −150 V raw) → Q4 (MJE15031) follower, base on D6 100 V + D7 13 V zeners | about −112 V |
|
|||
|
|
| 2 | −100 V | Q5 (MJE15030) follower from the D6/D7 junction. Collector to GND via R8 2 kΩ 5 W. | about −100 V |
|
|||
|
|
| 7 | +12 V | Passed through from CN1 | |
|
|||
|
|
| 6 | +5 V | Passed through from CN1 | |
|
|||
|
|
| 4, 5 | GND | | |
|
|||
|
|
|
|||
|
|
- Q1/D3/R2/R4 and Q2/D4/R3/R5: constant-current feeds (about 2 mA) for the zener references.
|
|||
|
|
- R6/R7 (330 kΩ): bleeder resistors. C3/C4/C7: 0.1 µF 500 V decoupling.
|
|||
|
|
|
|||
|
|
## New design
|
|||
|
|
|
|||
|
|
Full schematic: [../hardware/psu-schematic.svg](../hardware/psu-schematic.svg) (PNG alongside).
|
|||
|
|
It is generated from [../hardware/psu_schematic.py](../hardware/psu_schematic.py):
|
|||
|
|
|
|||
|
|
```bash
|
|||
|
|
python -m pip install schemdraw matplotlib
|
|||
|
|
python hardware/psu_schematic.py
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
The schematic's reference designators are new; the notes on the sheet map them to the original board.
|
|||
|
|
|
|||
|
|
Replace the transformer and AC front end (D1, D2, C1, C2, F1, R1) with DC boost modules. Keep the
|
|||
|
|
regulator section as it is.
|
|||
|
|
|
|||
|
|
```
|
|||
|
|
Mains ─► [Certified 12V 3A brick] ─► F 3A ─┬──────────────► +12V (only if the panel uses it)
|
|||
|
|
│
|
|||
|
|
├─► [Mini560 5V buck] ─► +5V ─► panel logic, ESP32, 74HCT245
|
|||
|
|
│
|
|||
|
|
└─► [Relay, NO contact] ◄── HV watchdog (see safety.md)
|
|||
|
|
│
|
|||
|
|
┌──────────────┴──────────────┐
|
|||
|
|
▼ F 1A slow ▼ F 1A slow
|
|||
|
|
[NCH6100HV #1 set 90V] [Isolated 12→12V DC-DC, 6–10W]
|
|||
|
|
│ │
|
|||
|
|
│ [NCH6100HV #2 set 130V]
|
|||
|
|
│ out+ ─► GND
|
|||
|
|
▼ F 100mA, +90V raw ▼ F 100mA, −130V raw
|
|||
|
|
┌───────────────────────────────────────────────────┐
|
|||
|
|
│ Copy of original regulator section: │
|
|||
|
|
│ Q1/Q3/D3/D5/R2/R4 → +62–67V │
|
|||
|
|
│ Q2/Q4/D4/D6/D7/R3/R5 → −112V │
|
|||
|
|
│ Q5/R8/R10 → −100V │
|
|||
|
|
│ R6/R7 bleeders, C3/C4/C7 500V caps │
|
|||
|
|
└───────────────────────────────────────────────────┘
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
### Why the isolated converter
|
|||
|
|
|
|||
|
|
A boost module's output negative is shared with its input ground. Powering module #2 through an
|
|||
|
|
isolated DC-DC lets its output float, so its **+ output is tied to GND** and its − output becomes
|
|||
|
|
−130 V. A second certified 12 V wall adapter would also work.
|
|||
|
|
|
|||
|
|
### Changes compared with the original
|
|||
|
|
|
|||
|
|
- **Removed:** D1, D2, C1, C2, F1, R1 (the boost modules replace the AC front end; the module current
|
|||
|
|
limit plus a 100 mA fast fuse replaces R1).
|
|||
|
|
- **Added:** 10–22 µF / 250 V cap and a 330 kΩ bleeder across each raw HV rail.
|
|||
|
|
- **Added:** HV-present LED (LED + 100 kΩ 1 W) on each raw HV rail.
|
|||
|
|
- **Headroom:** +90 V raw feeding the 68 V-referenced stage, and −130 V raw feeding the
|
|||
|
|
113 V-referenced stage, give the followers enough headroom with modest dissipation. Q3/Q4/Q5 get small heatsinks.
|
|||
|
|
|
|||
|
|
## Open questions
|
|||
|
|
|
|||
|
|
- [ ] Real HV current draw of the panel, so you can size the isolated DC-DC (6 W vs 10 W)
|
|||
|
|
- [ ] Panel power connector pinout and whether +12 V is used
|
|||
|
|
- [ ] Check that NCH6100HV has a usable enable/shutdown pin (otherwise, switch with the relay only, as drawn)
|