Protect Against Flyback Spikes
Add a diode so coils don't damage your board.
Protect Against Flyback Spikes is a free Arduino & IoT Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Arduino & IoT Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Coils Store Energy
Motors and relays contain a coil of wire. While current flows, that coil quietly stores energy in a magnetic field around it. 🧲
The Sudden Cutoff
When you switch the coil off, that stored energy has nowhere to go. The collapsing field forces a huge voltage spike in the opposite direction.
Meet the Flyback Spike
This reverse surge is the flyback spike. It can reach hundreds of volts for an instant, far beyond what your transistor or board can shrug off.
Why It Damages Parts
That spike slams into your switching transistor and can punch right through it. Over time it fries drivers and corrupts nearby Arduino pins.
The Fix Is a Diode
The classic cure is a flyback diode placed across the coil. It gives that surge a safe loop to circulate in instead of attacking your circuit.
Diodes Are One-Way
A diode lets current pass in only one direction. During normal operation it blocks; during the spike it suddenly conducts and drains the energy.
Mind the Orientation
Orientation matters. The diode's striped cathode goes to the positive supply so it stays blocked normally and only opens for the reverse spike.
Backwards Means Trouble
Wire the diode the wrong way and it shorts your supply the moment power is on. Always double-check the stripe before you power up. ⚠️
A Common Choice
The 1N4007 diode is a cheap, sturdy pick for relay and small-motor coils. It handles the brief surge without breaking a sweat.
Often Already Built In
Good news: most relay modules already include a flyback diode on board. You only add one yourself when driving a bare coil or raw motor.
A Tiny Part, Big Protection
One cheap diode across every inductive load saves your driver and your board. It is the habit that separates reliable builds from flaky ones.
Quick Check
Where do you place a flyback diode and why?
Recap
Switching a coil off makes a damaging flyback spike. A diode across the coil, cathode to positive, absorbs it. Many modules include one already. 🚀
Frequently asked questions
Is the “Protect Against Flyback Spikes” lesson free?
Yes — the full text of “Protect Against Flyback Spikes” is free to read here on the web, and the Arduino & IoT Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Arduino & IoT Academy course, upgrade to CoddyKit PRO.
What will I learn in “Protect Against Flyback Spikes”?
Add a diode so coils don't damage your board. You practise Arduino & IoT Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Arduino & IoT Academy?
No prior experience is required. Arduino & IoT Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Protect Against Flyback Spikes” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Arduino & IoT Academy lesson?
Yes. Every Arduino & IoT Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Why You Need a Driver
- Speed & Direction with an H-Bridge
- Switch Mains Devices with a Relay
- Protect Against Flyback Spikes