Series Diode Protection
The simplest protection method, which prevents current from flowing on reverse connection by placing a power diode in the direction of current in the supply line. It solves the problem with a single part, but in normal operation it continuously drops 0.4–0.7 V and turns that drop into heat.
The loss is directly proportional to the current. A Schottky diode dropping 0.45 V at 15 A produces about 6.8 W, while a diode dropping 0.6 V at 30 A produces 18 W of heat. These power levels require a heat sink and noticeably enlarge the total heat budget of the module.
There is a second problem on the voltage side: in a 12 V system, 0.6 V is 5 percent of the supply voltage. When the battery weakens, this drop can cause the under-voltage lockout to engage early.
- Where it is suitable: Low-current control and signal supplies, auxiliary circuits that do not exceed a few amps.
- Where it is not suitable: Power lines of 15 A and above; there, protection based on a P-channel MOSFET is preferred.
Using a Schottky diode reduces the drop, but its reverse leakage current and the way its loss grows with temperature must be taken into account. When sizing the diode, choose according to the peak current of the starting pulse, not the continuous current.
Where this term is used: DC Motor Driver Selection Guide