mangavalkandClaude Opus 5.5
dbc1f0041f
- Design docs: 12 V DC power supply, safety and bring-up, ESP32 interface, BOM - PSU schematic (schemdraw) and KiCad 10 carrier-board project with HV net classes - ESP32 PlatformIO firmware skeleton with HV watchdog toggle - Reference schematic of the Stern 520-5138-00 display PSU Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
83 lines
4.7 KiB
Markdown
83 lines
4.7 KiB
Markdown
# Power supply design
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## Goal
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Generate every panel rail from one **12 V DC** input, using cheap modules. Panel voltages are set by
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**zener references** (copied from the original Stern board), not by module trim pots. A
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mis-set or failed module can't push the panel above its rated voltage.
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## The original board (Stern/Sega 520-5138-00)
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See [../reference/stern-520-5138-00-display-psu-schematic.jpg](../reference/stern-520-5138-00-display-psu-schematic.jpg).
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| CN2 pin | Label | How it is produced | Real value |
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|---|---|---|---|
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| 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 |
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| 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 |
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| 2 | −100 V | Q5 (MJE15030) follower from the D6/D7 junction. Collector to GND via R8 2 kΩ 5 W. | about −100 V |
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| 7 | +12 V | Passed through from CN1 | |
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| 6 | +5 V | Passed through from CN1 | |
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| 4, 5 | GND | | |
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- Q1/D3/R2/R4 and Q2/D4/R3/R5: constant-current feeds (about 2 mA) for the zener references.
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- R6/R7 (330 kΩ): bleeder resistors. C3/C4/C7: 0.1 µF 500 V decoupling.
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## New design
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Full schematic: [../hardware/psu-schematic.svg](../hardware/psu-schematic.svg) (PNG alongside).
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It is generated from [../hardware/psu_schematic.py](../hardware/psu_schematic.py):
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```bash
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python -m pip install schemdraw matplotlib
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python hardware/psu_schematic.py
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```
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The schematic's reference designators are new; the notes on the sheet map them to the original board.
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Replace the transformer and AC front end (D1, D2, C1, C2, F1, R1) with DC boost modules. Keep the
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regulator section as it is.
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```
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Mains ─► [Certified 12V 3A brick] ─► F 3A ─┬──────────────► +12V (only if the panel uses it)
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│
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├─► [Mini560 5V buck] ─► +5V ─► panel logic, ESP32, 74HCT245
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│
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└─► [Relay, NO contact] ◄── HV watchdog (see safety.md)
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│
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┌──────────────┴──────────────┐
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▼ F 1A slow ▼ F 1A slow
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[NCH6100HV #1 set 90V] [Isolated 12→12V DC-DC, 6–10W]
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│ │
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│ [NCH6100HV #2 set 130V]
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│ out+ ─► GND
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▼ F 100mA, +90V raw ▼ F 100mA, −130V raw
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┌───────────────────────────────────────────────────┐
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│ Copy of original regulator section: │
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│ Q1/Q3/D3/D5/R2/R4 → +62–67V │
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│ Q2/Q4/D4/D6/D7/R3/R5 → −112V │
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│ Q5/R8/R10 → −100V │
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│ R6/R7 bleeders, C3/C4/C7 500V caps │
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└───────────────────────────────────────────────────┘
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```
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### Why the isolated converter
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A boost module's output negative is shared with its input ground. Powering module #2 through an
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isolated DC-DC lets its output float, so its **+ output is tied to GND** and its − output becomes
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−130 V. A second certified 12 V wall adapter would also work.
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### Changes compared with the original
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- **Removed:** D1, D2, C1, C2, F1, R1 (the boost modules replace the AC front end; the module current
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limit plus a 100 mA fast fuse replaces R1).
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- **Added:** 10–22 µF / 250 V cap and a 330 kΩ bleeder across each raw HV rail.
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- **Added:** HV-present LED (LED + 100 kΩ 1 W) on each raw HV rail.
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- **Headroom:** +90 V raw feeding the 68 V-referenced stage, and −130 V raw feeding the
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113 V-referenced stage, give the followers enough headroom with modest dissipation. Q3/Q4/Q5 get small heatsinks.
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## Open questions
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- [ ] Real HV current draw of the panel, so you can size the isolated DC-DC (6 W vs 10 W)
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- [ ] Panel power connector pinout and whether +12 V is used
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- [ ] Check that NCH6100HV has a usable enable/shutdown pin (otherwise, switch with the relay only, as drawn)
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