Beginner · Understand how it works
How do you drive and protect a coil?
Separate control and power. Observe coil current and turn-off voltage.
Enable then disable the command. Compare current, energy and turn-off voltage with and without the diode.
Measurements
- Coil current
- —mA
- Switch voltage
- —V
- Turn-off peak
- —V
- Magnetic energy
- —mJ
A and B use the same reading time.
Changing the coil, driver or diode starts a new trial. Switching the command preserves current.
A and B use the same reading time.
Recorded evidence
- Choose an instrument to keep a reading.
Installation, principle and limits
Ideal RL coil, fixed 0.2 V transistor drop and 0.7 V diode. Direct logic drive is limited to 3.3 V / 4 mA and replaces the power supply. Without the diode, a 60 V comparison clamp provides a discharge path; this does not predict GPIO breakdown. Current rises exponentially; at turn-off L dI/dt = −RI − Ureturn, with Ureturn = 0.7 V for the diode or 60 V minus supply voltage for the clamp. Ideal contact picks up at 70% and holds down to 20% of rated 240 Ω coil current. No bounce, mechanical delay or damage simulated.
Texas Instruments · discharging inductive loads ↗