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Safe handling of AC/DC Power Adapters — Desktop & Wall-Mount Part 9: "Never forget to check the protection functions!"
We introduce the safe handling of AC/DC Power Adapters — Desktop & Wall-Mount. Episode 9 features "Don't forget to check the protection features!" and explains the protection functions of the AC/DC Power Adapters — Desktop & Wall-Mount.
AC/DC Power Adapters — Desktop & Wall-Mount “Do Not” Series - Always Check Protection Functions
We sometimes receive the following from customers.
"Even after canceling the overvoltage output condition, the adapter's output does not recover."
Before making such , please be sure to check the content described in the protection function (PROTECTION) section of the product specification sheet. In the specification sheet of our Products, the following three types of protection functions are generally defined:
- OVER CURRENT PROTECTION (Overcurrent Protection)
- SHORT CIRCUIT PROTECTION (Short Circuit Protection)
- OVER VOLTAGE PROTECTION (Overvoltage Protection)
This time, I would like to talk about item III, "OVER VOLTAGE PROTECTION" (hereafter OVP), which is, in my opinion, the most commonly misunderstood.
According to the "Switching Power Supply Glossary" by the Japan Electronics and Information Technology Industries Association, OVP is defined as "One of the power supply protection functions, where output is shut off to protect the load when the output voltage exceeds a predefined limit." Also, the glossary defines "Automatic Restart" as "A function where the protection activated by an abnormal condition automatically returns to normal operation when the abnormal state is resolved." In other words, the initial , "Even after canceling the overvoltage output condition, the adapter's output does not recover ..." equates to the protection function "not recovering automatically."
The next thing to check is the OVP description in the delivery specification sheet of the Products. In our Products, we adopt one of the following two OVP types depending on the control IC or circuit configuration:
A. AUTO RECOVERY
B. LATCH
The "AUTO RECOVERY" in A has the same meaning as "Automatic Restart," and B's "LATCH" means latch, as is. You’re not sure what that means? “Latch” is like a bar across a gate—like in sumo wrestling when a wrestler locks the opponent's arm at the elbow—still not clear? How about this?
"Gate Latch"
In short, if the OVP section says "AUTO RECOVERY", it means the device will automatically recover once the cause of OVP is cleared (like removing the gate latch bar automatically opens the gate). If it says "LATCH", even if the OVP cause is cleared, it will not automatically recover (just removing the gate latch bar won’t open the gate).
By the way, since general AC/DC Power Adapters — Desktop & Wall-Mount have a board enclosed within a case, it is not possible to validate OVP by applying overvoltage at the completed product level prior to shipment. Therefore, for Products with "AUTO RECOVERY" which cannot be tested for OVP externally (those requiring overvoltage application or board modifications), we substitute this with reliability test results from the design/development phase. The same applies even to Products that are externally testable, except for those where customers specifically require OVP testing before shipment—these are also substituted with design/development phase reliability evaluations.
Based on the above, depending on your operating conditions, if a manual restart with safety confirmation on the equipment side is necessary after OVP activation, please select a model with "LATCH". If automatic recovery is required after resolving the overvoltage condition, select a model with "AUTO RECOVERY". Therefore, please make sure to check the protection functions when choosing an AC/DC Power Adapters — Desktop & Wall-Mount.