Design Walkthrough: Tractive System Active light (TSAL) driver – FSAE

Design-walkthroughs are great. You get to peek over somebody’s shoulder as they design their project and soak up all kinds of vicarious experience. I didn’t learn practical electronics at university – I learned practical electronics on YouTube and forums. Now it’s time to add my own walkthrough into the pool! This time around, we’ll be going through an analogue-only circuit from FSAE Electric

In FSAE, the Tractive System Active Light (TSAL) is a device that indicates a dangerous voltage is present in the Tractive System – the system of components including motor drivers and motors. In this video I walk through my design for a TSAL driver. For those unfamiliar with FSAE or the TSAL, to make this walkthrough a little clearer I’ll describe the basic function of the circuit: When the voltage at the HV terminals is less than 60VDC, a green light should be illuminated. When HV rises above 60VDC, the green light should be off, and a red light flashes steadily.

This TSAL is a drop-in design that requires no tuning. It is intended to work up to the maximum allowable 600VDC.

As always, you can find the design files in the repo. The PCB software is KiCad.

There’s a bunch of useful circuit-blocks and tricks to keep in the back pocket for other projects:

  • Practical optocoupler interfacing
  • high-side drive with a P-channel MOSFET
  • using an N-channel MOSFET as an inverter
  • multi-resistor voltage divider for high voltages
  • comparator voltage-threshold switching
  • enabling/disabling a 555 timer

I’d love to hear from you if you find this design helpful. If you have any uncertainties, or any ideas for how it could be improved; let me know!

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