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    DC Power Supply Protection from Unexpected Damage and Inconvenience

    Altium Designer
    |  April 30, 2018

    Uninterrupted power supply input

    When it comes to parenting, I might not be the best role model. This isn’t because I don’t take good care of my only son; it’s because I’m the stereotypical overprotective dad. I fuss over tiny bruises and rush for a digital thermometer at the slightest hint of a fever. Unable to stop worrying about how my son will adapt and get along with other preschoolers, I even become an occasional nuisance at his nursery.

    Over time, I’m starting to realize that being overprotective of children can more harm than good. In your electronics hardware, however, not being protective enough can become your biggest regret. To prepare for unexpected situations like surges and error, the best choice is to implement preliminary measures to diligently protect your hardware’s supply input.

    Why You Need to Protect the Hardware’s DC Supply Input

    Adding components for additional protection on your hardware’s DC supply input requires slightly more design effort and additional material cost. So, why bother? After all, the hardware would still be as functional as it was at the lab, without the extra work. Well, the price you pay for not adding protective components in your incoming DC circuit can haunt you at the worst moment.

    Lighting surges and transient can send enough overvoltage or current to damage your hardware. And sometimes, the main culprit is human error. An unfocused technician wiring up the hardware may mistakenly connect the incoming wire to the reverse polarity, resulting in the loud pop of components blowing up when powered.

    Depending on the specific situation, the capacitor could blow off, the pricey microcontroller could be damaged, or the tracks could be broken from the excessive current. Either way, you will deal with unnecessary inconvenience as applications powered by the hardware cease to function until a replacement PCB arrives.

    How to Protect Your Hardware DC Input

    You can avoid the hassle of replacing a damaged PCB by adding in a protective measure in the first place. After all, protecting your DC input is nothing complicated and simply requires a few key considerations including overcurrent protection, overvoltage protection, and reverse polarity protection.

    Overcurrent Protection

    Overcurrent on a PCB normally occurs when a fault at the load is being driven by the PCB. In some cases, faulty PCB components causing a short between power and ground may also cause overcurrent. When the PCB draws more current than allowed, it can overload and damage the power supply. Besides that, the copper track can get overheated due to excessive current and in some extreme cases, break off.

    You can easily protect the hardware from overcurrent by adding a fuse. However, make sure that the value of the fuse is higher than the maximum current consumed by your hardware. Otherwise, you’ll find the fuse tripping frequently.

    If you do not want the hassle of replacing a blown fuse, you can opt to include a resettable fuse or PTC in your design. A resettable fuse disconnects like a regular fuse in the case of overcurrent and resets itself after a period of time.

    A fuse within a light rod
    A blown fuse is better than a blown PCB.

    Overvoltage Protection

    Overvoltage is during a transient event like lightning surge, or when a wrong value of power supply is used. The damage is almost immediate, especially if you have an array of relay drawing power directly from the incoming supply. The acrid smell of burning semiconductor will confirm that the hardware has to be repaired or replaced.

    A way to protect against overvoltage is by using a zener diode. Instead of placing it like a regular diode, position a zener diode across the incoming positive supply and ground in a reversed manner. When the reverse voltage across a zener diode exceeds its threshold, the zener diode becomes conductive and clamps the voltage at its specified value.

    For example, you can protect a 12V DC input from overvoltage with a 16V zener diode. In the case of a transient, the zener diode will limit the voltage at 16V, preventing it from rising any further. Of course, you have to account for the power rating of the zener diode, so that it can dissipate the excessive current during transient without being damaged.

    Reverse Polarity Protection

    Besides protecting against environmental conditions like surge, reverse polarity protection is also essential in preventing your PCB from going up in smoke due to human error. With a simple diode, you can connect the incoming DC supply cable the opposite way. When the voltage applied across its terminal exceeds its junction voltage, a diode becomes a conductor.

    For reverse polarity protection, simply place a diode across the positive supply and ground in a reverse manner. When the incoming cable is connected correctly, the diode is like an open circuit. However, the diode starts to conduct when the cable is connected the wrong way. It provides an alternative path for the current and prevents other components from getting damaged.

    Assorted wiring bundled together
    Red, black or…? Stay safe with reverse polarity protection.

    Based on the wide variety of negative consequences possible, there’s no excuse for not including protection features for your DC supply input. After all, the required components are easily available from the integrated libraries available in Altium Designer® .

    Are you under-protecting your DC supply input? Talk to an expert at Altium now.

    About Author

    About Author

    PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

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