AC/DC Power Adapter Safe Handling Part 9 "Do Not Forget to Check the Protection Functions!"

AC/DC Power Adapter safe handling methods are introduced. The 9th installment features "Do not forget to check the protection functions!" We explain the protection functions of AC/DC Power Adapter.

AC/DC Power Adapter"Must-Not" Series: Do Not Forget to Check the Protection Functions

We sometimes receive the following inquiries from customers.

"Even after clearing the output overvoltage condition, the adapter output does not recover." 

Before making such an inquiry, please check the PROTECTION section in the product specification sheet. In our product specification sheets, the following three types of protection functions are typically specified.

1.  OVER CURRENT PROTECTION (Overcurrent Protection)
2.  SHORT CIRCUIT PROTECTION (Short Circuit Protection)
3. OVER VOLTAGE PROTECTION (Overvoltage Protection)

Among these, we would like to talk about item 3, "OVER VOLTAGE PROTECTION (hereinafter referred to as OVP)," which is the most easily misunderstood (in our opinion).

According to the "Switching Power Supply Glossary (Japan Electronics and Information Technology Industries Association)," OVP is described as "One of the protection functions for power supply equipment that shuts down the output to protect the load when the output voltage exceeds a preset level." In the same glossary, "Automatic Restart" is described as "A function in which a protection feature activated in response to an abnormal condition automatically returns to normal operation once the abnormal condition is cleared." In other words, the inquiry at the beginning, "Even after clearing the output overvoltage condition, the adapter output does not recover...", means "It does not automatically restart..."

Next, please check the OVP section of the product specification sheet. In our products, one of the following two types of OVP is adopted depending on the control IC and circuit configuration.

A. AUTO RECOVERY

B. LATCH

"AUTO RECOVERY" in A has the same meaning as "Automatic Restart" in the glossary above, while B "LATCH" means exactly that - a latch. Not sure what that means? A latch is like a bar used to lock a gate.

"Gate latch"

In other words, if the OVP section states "AUTO RECOVERY," the unit will automatically recover once the cause of the OVP is removed (in the photo above, "the gate opens automatically when the latch bar is removed"). If it states "LATCH," the unit will not automatically recover even after the cause of the OVP is removed (in the photo above, "the gate does not open simply by removing the latch bar").

Incidentally, since a typical AC/DC Power Adapter houses a circuit board inside its case, it is not possible to verify OVP operation by applying overvoltage to the board once the product is fully assembled prior to shipment. Therefore, for our "AUTO RECOVERY" compatible products, except for those that allow OVP testing by applying external overvoltage, we substitute the results of reliability evaluation tests conducted during design and development for OVP inspection (for products that would require applying overvoltage to the board or opening circuit patterns for OVP testing). Furthermore, even for "AUTO RECOVERY" compatible products that allow external overvoltage OVP testing, except for certain products for which customers specifically request OVP testing at the time of shipment, we also substitute the results of reliability evaluation tests conducted during design and development for OVP inspection.

Based on the above, depending on your specific usage conditions, if manual restart after confirming safety on the equipment side is required following OVP activation, you should select a model that supports "LATCH." If automatic recovery is required after clearing the output overvoltage condition following OVP activation, you should select a model that supports "AUTO RECOVERY." Therefore, when selecting an AC/DC Power Adapter, please be sure to check the protection functions.

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