7 Protection Circuits You Should NEVER Ship a Product Without
If you learned electronics through kits and tutorials, your prototype is probably missing every single protection in this video.
And that’s fine if it’s just for your own use.
But if you want to commercialize it, that changes everything.
You’ve likely never run into these problems, because your prototype is your baby, and you treat it that way.
You always use the right power adapter, and you’d never dare yank it out while the baby is feeding… I mean charging.
And you’d definitely never unplug it in the middle of a firmware update.
Unfortunately, your customers won’t be that gentle.
They’ll plug in whatever adapter fits, zap it with static, and cut the power at the worst possible moment.
There’s a big jump between a prototype that survives you and a product that survives thousands of strangers.
Most of the product designs my engineering team reviews are missing at least one of these critical protections, and odds are yours is too.
Two of these protections are all that stands between your product and an actual fire.
And one of them is completely free and already likely in your design, but almost certainly turned off.
So in this video I’m counting down seven circuit protections you should never ship a product without, and for every single one I’ll tell you exactly what to use instead.
## Protection #7 – Reverse Polarity Protection
A customer plugs in the wrong barrel jack adapter or inserts batteries backward, and one second later the board is dead.
You’d never make that mistake, but put a few thousand units into the market and someone absolutely will.
The typical prototype fix is a series diode, and it works, but it drops 0.3 to 0.7 V across the diode, which wastes power and adds heat in a production product.
The production-ready approach is a P-channel MOSFET wired on the high side of the power input.
The MOSFET has a built-in body diode that conducts under normal polarity, and once that diode forward biases it turns the MOSFET fully on, so instead of a diode drop you get almost no voltage drop at all.
For higher-current designs, an ideal diode controller does the same job even more efficiently.
And just to be clear, a keyed connector isn’t reverse polarity protection.
Customers defeat mechanical safeguards all the time.
Total cost for this protection is just a few cents.
## Protection #6 – ESD Protection
Your product survives all of your testing, then dies in a carpeted office in dry winter air.
Every connector, button, and exposed port that a person can touch is an entry point for electrostatic discharge.
USB ports, headphone jacks, SD card slots, charging connectors, even exposed screw terminals, all of them are vulnerable, and a simple carpet-to-doorknob shock can hit anywhere from 8 to 15 kV.
This isn’t just a reliability concern, it’s a certification problem.
Selling in Europe means passing ESD immunity testing under IEC requirements, and if your product fails at the test lab, that means a board respin while your launch date slips.
You fix this with ESD diodes on every externally accessible line, placed right at the connector with a short, direct return path to ground.
These clamp voltage spikes before they can reach your sensitive components.
For USB and other high-speed data lines, use low-capacitance versions so you don’t degrade signal integrity.
A lot of engineers assume that the ESD protection structures built into their MCU pins are enough.
Those internal structures are designed to survive the assembly line, not your customer’s wool sweater in the middle of winter.
A member of my Hardware Academy had a product working perfectly for a year, then a unit came back with the charger IC physically blown.
His USB shield was grounded, but he had no ESD diode on the USB power pin, and one static discharge through the port killed the charger IC.
Each protected line adds just a few cents.
## Protection #5 – Overcurrent Protection
A damaged cable, a shorted component, or a curious customer poking something where they shouldn’t, any of these can create a short circuit on your board.
Without overcurrent protection, that short becomes smoke, melted PCB traces, and a safety incident with your company’s name attached to it.
This is where product risk turns into legal risk, because safety standards and major retailers expect overcurrent protection, and fire liability has ended small companies.
When I was designing power management chips at TI, we built current limiting into every chip just to protect the silicon itself.
Your board needs that same kind of protection at the system level, because without it one short takes out everything.
For most consumer products, a resettable PTC fuse is the simplest answer, and it only costs a few cents.
PTC stands for positive temperature coefficient, and it’s basically a component that increases its resistance sharply when too much current flows through it, tripping like a breaker and resetting itself once the fault clears and it cools back down.
The one catch is that PTCs are relatively slow compared to active protection, so they won’t catch very fast transients.
If you need faster and more precise current limiting, an eFuse IC handles that along with overvoltage lockout in the same part, and they typically run about a dollar.
For safety-critical power rails, a traditional one-time fuse is your last line of defense because it blows permanently, which is exactly what you want when the alternative is a fire.
## Protection #4 – Overvoltage and Input Transient Protection
You ship your product with a 5 V adapter.
Two years later the customer grabs a 12 V adapter from the junk drawer, and it fits because it’s the same barrel jack connector.
Everything downstream sees more voltage than it can handle.
And a wrong adapter isn’t the only way an overvoltage condition occurs.
Voltage spikes from hot-plugging cables under load, line transients from noisy power sources, and load-dump surges if your product goes anywhere near a vehicle electrical system all cause the same kind of damage.
For short spikes and transients, the fix is a TVS diode, short for transient voltage suppressor.
You put one on the power input, sized so its standoff voltage sits above your maximum normal operating voltage but its clamping voltage stays below the damage threshold of your downstream parts.
But a TVS can only absorb short bursts of energy, so it can’t protect you from a wrong adapter feeding your board 12 V all day long.
For sustained overvoltage like a wrong adapter, you need an eFuse or overvoltage protection IC that shuts the input off entirely.
So the wrong adapter gets ignored instead of killing your board.
If your product accepts power through USB-C, keep in mind that USB Power Delivery can negotiate voltages up to 48 V on the same cable, which means a misbehaving charger or a bug in your PD negotiation can push dangerous voltage right into a 5 V input rail without warning.
All of that protection adds well under a dollar.
## Protection #3 – Inductive Kickback Protection
Anything with a coil in your product fights back when you cut the current.
Relays, motors, and solenoids all store energy in a magnetic field while current flows, and the moment you switch that current off, the collapsing field fires a high-voltage spike backward into your driver circuits and MCU pins.
The sneaky part is that this usually survives short bench tests just fine.
The damage is cumulative, so units start failing in the field one at a time, weeks or even months apart, and it looks like random bad luck until you finally figure out the pattern.
You fix this with a flyback diode across every DC relay coil, solenoid coil, and simple DC motor to give the stored energy a safe path to dissipate.
Place it as close as possible to the coil itself, not back at the driver, because the shorter that path is the less chance the spike has to cause damage along the way.
## Protection #2 – Battery Protection
If your product has lithium batteries and no dedicated protection circuitry, you’re setting yourself up for a recall.
Over-discharging a cell drops its voltage below the point of safe recovery and gradually kills the pack, sometimes without any visible sign until the battery won’t take a charge at all.
Overcharging and short circuits cause swelling, venting, and fire.
You need UN38.3 testing just to legally ship lithium cells, plus additional safety certifications depending on your market, and most large retailers stack their own requirements on top of that.
So this is the second item on this list that can literally burn a house down.
I always recommend starting with protected cells that already have the safety circuit built in.
That gives you overvoltage, undervoltage, overcurrent, and short-circuit protection right at the cell, it reduces your liability, and it keeps you safer during development when your own charging circuit might not be fully working yet.
Then on your board, add a dedicated charger IC with correct charge termination so cells aren’t charged below freezing or above their rated limit.
## Protection #1 – Watchdog and Brownout Protection
The first six protections on this list protect your product from the physical world.
This one protects it from itself, and I saved it for last on purpose, because it’s the only one that’s completely free.
Your product locks up in a customer’s home, and all they can do is file a support ticket and leave a one-star review.
The worst case is even scarier: the power dips during a flash write and your firmware corrupts itself permanently, and now your product is an expensive paperweight.
The fix is already inside the microcontroller you’re using right now, but most development teams disable the watchdog timer during debugging and never turn it back on for production firmware.
Watchdog and brownout protection is the easiest fix on this entire list, but you have to set it up correctly.
So enable the independent watchdog and feed it from your main loop, only after your critical tasks check out, not from an interrupt that fires no matter what.
Set the brownout detector above the minimum voltage required for reliable flash writes, so the processor resets cleanly instead of corrupting firmware during a power dip.
Some engineers will argue that a watchdog just masks bugs, and I get where that comes from, but in the field, a product that recovers itself beats one that stays locked up, every single time.
