Safe Handling of AC/DC Power Adapters — Desktop & Wall-Mount, Part 9: "Never Forget to Check the Protection Features!"

We introduce safe handling methods for AC/DC Power Adapters — Desktop & Wall-Mount. Part 9 features "Never forget to check the protection features!" explaining the protection functions of AC/DC Power Adapters — Desktop & Wall-Mount.

AC/DC Power Adapters — Desktop & Wall-Mount “Bekarazu” Series: Don’t Forget to Check Protective Functions

We occasionally receive inquiries from customers such as:

"Even after canceling the over-voltage condition, the adapter's output does not recover."

Before making such inquiries, we ask that you please confirm the contents listed in the "PROTECTION" section of the product's delivery specification. Our product specifications typically include the following three types of protective functions:

  1.  OVER CURRENT PROTECTION (overcurrent protection function)
  2.  SHORT CIRCUIT PROTECTION (short-circuit protection function)
  3. OVER VOLTAGE PROTECTION (over-voltage protection function)

This time, we would like to discuss item III, "OVER VOLTAGE PROTECTION" (hereafter referred to as OVP), which we believe is the most commonly misunderstood.

 

According to the "Switching Power Supply Glossary (JEITA)", OVP is defined as "One of the power supply protection functions where, when the output voltage exceeds a predetermined level, the output is cut off to protect the load." Also, the same glossary defines "Automatic Restart" as "A function where the protective function that activated due to an abnormal condition automatically returns to normal operation once the abnormal condition is resolved." In other words, when customers ask, "Even after canceling the over-voltage condition, the output does not recover...", they are essentially saying, "It does not automatically restart..."

Next, please check the OVP section of the product's delivery specification. Depending on the control IC or circuit method, our products adopt one of the following two types of OVP:

A. AUTO RECOVERY

B. LATCH

“AUTO RECOVERY” in option A refers to "automatic restart", as mentioned in the glossary. Option B, “LATCH,” refers to a latching mechanism. Not sure what that means? Think of “latch” as a gate bar — like in sumo when one opponent controls the other’s arms by locking them at the elbow... Still unclear? Then how about this?

 

“Gate latch”

In other words, if the OVP section states “AUTO RECOVERY”, the OVP will automatically recover once the triggering condition is cleared (in the photo above, "if you remove the latch bar, the gate opens automatically"). However, if it states “LATCH”, the OVP does not automatically recover even after the condition is cleared (in the photo above, "just removing the latch bar will not open the gate").

 

By the way, typical AC/DC Power Adapters — Desktop & Wall-Mount have their circuit boards housed inside a case, so it is not possible to perform OVP operation checks by applying over-voltage to the board after the product is fully assembled and ready for shipment. Therefore, for products with “AUTO RECOVERY” that do not allow external over-voltage testing (such as those requiring structural modifications for OVP testing), we substitute the OVP inspection with the results from reliability evaluation tests conducted during design and development. Additionally, for products that do allow over-voltage inspection but do not specifically require it at shipping per customer request, we similarly use the results of these reliability evaluations as a substitute for actual OVP inspection at shipping.

Based on the above, customers should select an appropriate model based on their usage conditions: if manual restart after device-side safety checks is required following OVP activation, then a model with “LATCH” is recommended; if automatic recovery is required after the OVP condition has cleared, then a model with “AUTO RECOVERY” should be selected. When choosing AC/DC Power Adapters — Desktop & Wall-Mount, please be sure to check the protective functions accordingly.

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