Accumulator Indicator LED (AILED)
Designed the AILED in Altium Designer and brought it up. This is a hardware circuit that turns on an LED whenever there is > 60V outside the FSAE car's HV battery pack. This is to alert team members to when the HV system is charged, even if it should be discharged.
- Fully functional when LV power is off to account for scenarios where car is turned off, but HV system did not discharge
- Includes a 600V to 15V buck converter using the VIPER265K
- Load switching circuit allows power draw from LV system under normal operation, reducing energy loss from HV buck converter
- Comparator circuit has < 1V hysteresis at 60V threshold
Design
The pack voltage is sensed through a long chain of series resistors to avoid arcing. A comparator checks it against the 60V threshold and drives an optocoupler rated for 8200Vrms, which controls the LED on the isolated side of the barrier. The HV buck makes 15V on the HV side, which also supplies the isolated side through a 12V isolated DCDC.
High Voltage Layout
- The FSAE rule needs 9.5mm of clearance through air, so a 10mm slot is used between the two sides
- No ground plane under anything above 60V, including the input stage and the resistor chain, to avoid arcing between planes
Bringup and Validation
- Hysteresis at the 60V threshold measured under 1V on an HV supply
- The LED stays lit with the LV system fully powered down
- Source handover between the LV rail and the HV buck checked in both directions
- Ran for an hour on HV power alone, under a box to match its sealed no airflow enclosure, with no significant temperature rise measured using a FLIR camera