Diode 1N4007
lets current through in one direction only
A "one-way valve" for current. Used for reverse-polarity protection and, most often in our projects, as a "flyback" diode next to motors and relays.
Open the course →How it works
From anode to cathode the current passes (with a drop of ~0.7 V); the other way, it does not. A motor is a coil, and a coil hates sudden changes of current: when the transistor switches it off, the coil produces a short spike of tens of volts. The diode placed reversed (cathode to +5 V) gives that spike a path around through the motor instead of through the transistor.
Pins and wiring
| Pin | What it is | Where it connects / why |
|---|---|---|
| Anode (+) | The end without the stripe | → to the collector / motor −. |
| Cathode (−) | The end with the grey stripe | → to +5 V. |
Specifications
Max current1 A
Max reverse voltage1000 V
Forward drop~0.7–1 V
PackageDO-41
Tips and typical mistakes
- Reversed across a motor = a short circuit of the supply at power-up. The stripe goes to +.
- For very fast circuits (PWM above 20 kHz) a Schottky diode (1N5819) is better.