Redundant Power Input Protection

[Sivand12]

A bit of a generic / fundamental question regarding protection redundancy within circuits. Am grateful for your thoughts!

For good product design, is it still valid to rely on the built-in protection and filtering of an external DC wall-pack? For a low-power device (5 V input), hooked up to a quality DC wall adapter with proprietary polarized connectors, is it necessary to ALSO build in redundant power input circuitry onto circuit itself, for dealing with gross transient and reverse polarity conditions?

My circuit is battery powered and only plugged in for short periods of time to charge an internal lithium-ion battery. There's power management that will switch to wall power and charge the battery at the same time. There's some sensitive analogs in there and I’ve incorporated ESD protection, overcurrent protection, and minor overvoltage protection (i.e., Tolerating few volts above nominal by means of Zener). But is it sufficient to assume large overvoltage conditions (transients, etc.) will be filtered by the quality wall pack? In this case, it might open a large can of worms having to deal with thermal considerations during handling of large transients due to the battery aspect.

Thanks very much in advance,

[Paul Price]

IMHO,

No, not necessary, with proprietary connector if good quality of charger p/s components chosen.

[splin]

It looks like this has been comprehensively answered in the previous reply but just a few thoughts:

I'm guessing it partly depends on exactly how 'unique' the power connector is - don't underestimate how determined an uninformed/distracted/forgetful/drunk user may be in attempting to force-mate the connector from the wrong PSU.

Because of the safety risks associated with LI-ion batteries, which in the worst case could lead to a fire causing loss of life, I think you need to be very careful - especially if your product is to be sold in the USA, where product liability lawsuits can bankrupt individuals and companies. I'm no expert in this area and definately not a lawyer though.

What about high voltage transients due to overhead lines shorting together in storm conditions, or lightning strikes which in some areas is very common? Are you going to specify exactly what protection is to be provided by the PSU - 'quality' doesn't mean much in this context. Typical wall-warts that I've opened up (to repair) don't provide much beyond a fuse and sometimes the filtering of an electroytic capacitor (for non-switch mode supplies at least).

Your equipment becoming non-functional due to a mains transient is one thing; damage which could subsequently, perhaps long after the event, cause your circuit to malfuncton and cause a lithium battery to catch fire is another.

Tony H