AILED
safety board
Designed the accumulator's high-voltage indicator board from schematic through PCB layout. Powered straight from the 588 V tractive bus, with no GLV or software dependency, including with the pack disconnected.
Five rules, each answered in hardware.
The AILED is a rules-required safety light: whenever the accumulator's bus is live, it has to say so, even when everything else on the car is off.
Indicate high voltage at the vehicle side of the isolation relays.
A TLV3011 comparator on the bus trips at 57.4 V nominal.
Keep working with the pack disconnected or removed.
Powered from the bus itself: the isolated flyback starts at about 35 V.
HV presence directly powers and controls it, hard-wired, no software.
Analog end to end: divider, comparator, optocoupler. No firmware anywhere.
The isolation relay control signal must not control it.
Nothing on the detection path connects to the relay control signal.
Keep HV and LV apart on the board.
Designed around 12.7 mm creepage and 9.5 mm clearance across the isolation barrier.
Two paths across one barrier.
Flyback up from ~35 V · comparator enables the steady 12 V indicator above 57.4 V · 5 V aux to the BMU timer
The barrier, cut into the board.
- 01
Creepage as a design rule
Altium checks 12.7 mm along the board surface and 9.5 mm through air between the HV_DOMAIN and LV_DOMAIN net classes. Both pass with zero violations.
- 02
A slot under every crossing
Each part that bridges the barrier sits over a 5 mm milled slot: 15 mm under U1, 30 mm under the transformer, 17 mm under U3. Together they cut 62 of the 86 mm along the barrier.
- 03
Clean at handoff
A separate 4 mm rule keeps the tractive bus nets away from HV ground, and all 18 rules, from 0.2 mm trace width to silkscreen clearance, report zero violations.
The isolated flyback.
- 01
Output set by feedback
The 84.5k / 10k divider on the controller's 1.265 V feedback reference sets 11.95 V.
- 02
Current limited on the secondary
About 36 mV across the 0.12 Ω sense resistor trips the limit near 0.3 A.
- 03
Drain spikes clamped
Leakage spikes route through a 1200 V SiC diode into a 150 V TVS above the bus.
Detecting the bus, across the barrier.
- 01
Threshold from the reference
Four 226k resistors over 20k divide the bus by 46.2, so the TLV3011 trips against its internal 1.242 V reference at 57.38 V, leaving margin below 60 V for offset and hysteresis.
- 02
Light holds the indicator off
Below the threshold the comparator keeps a BC857 PNP on, lighting a CNY65 optocoupler that pulls the isolated gate line up to 12 V. Above 57.4 V the light goes out and the indicator turns on.
- 03
Powered from the flyback
A TPS7B87 LDO makes the 5 V HV-side rail from the flyback's auxiliary bias, and a BAV170 diode pair on IN_CLAMP protects the comparator input.
An indicator that fails lit.
- 01
High-side P-FET switch
Q1, a DMP3098L, switches the isolated 12 V rail onto the indicator connector. R22 pulls its gate low, so it conducts unless the optocoupler pulls the gate up.
- 02
Fails toward lit
The HV side has to actively hold the indicator off. Losing the HV-side 5 V rail or the optocoupler's LED leaves it lit, the safe direction for a high-voltage warning.
- 03
5 V for the BMU timer
A TPS7B87 LDO makes 5 V for the BMU's 555 RTML timer from the same isolated rail, and a green LED shows the 12 V rail is up.
From requirements to PCB.
Completed the architecture, all three schematic sheets, and a DRC-clean PCB layout in Altium. The board render shows the finished design, from the HV power path and isolation barrier to the LV indicator circuitry.