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M Philbrook

In article ,
says...

Fred McKenzie wrote:
Uniden BC-GPSK Serial GPS Receiver plugs into the serial port of my Ham
Radio. It uses a power adapter built into a 12 Volt lighter plug, that
converts 12 Volts DC into 5 Volts DC 1 Ampere. It has a one Ampere fuse.

After 6 months the GPS stopped working, fuse was blown. Replacement
fuse blew immediately. Opened up the adapter and found a shorted
transistor. There is also an unmarked 8 pin IC. Even if the transistor
is replaced, it still might not work. So I built up a tab-mounted 7805
regulator with a couple of capacitors for stability.

Added some heat sinking, expecting the GPS to draw nearly an Ampere.
Guess what? After hooking the GPS back up, the 7805 barely gets warm.
Temperature is about 10 degrees F above ambient. In other words the
original power adapter was greatly over specified for current. I
suspect a 78L05 would have been sufficient.

The designers must have found it expedient to use an off-the-shelf
adapter, even though it has reduced reliability and they did not need
the available current.

Was this a switching regulator? I've ripped apart a bunch of car adapters
for phones and just USB power and they're all essentially the same device.
Some have a pilot LED, some have fuses, some are rated 12-24V in, but
everything else is the same, and also circles a 8 pin chip.

I use those cheap 120 volt to 5 volt charger cubes or supplies, when I
need 5 volts from 120 volts for a board level project. Saves the hell
out of making your own onboard 120v to 5 supply when you can simply
rip it out of the case of those dirt cheap cubes at the local junk
store.