12v DC to 5v DC - without a Buck Converter?

Thread Starter


Joined Mar 1, 2017
I have a triple socket car cigarette adapter for powering multiple 12v devices from a single cigarette lighter outlet.

What's odd is that there is a USB port built in and it works BUT....

I opened it and the circuit board is unbelievably simple....only a led power indicator, what looks like a transistor and a resistor. That's it.
All the other USB cigarette power devices I have that have a USB port have a 34063A chip and much more components like capacitors and more diodes and resistors etc.

How can this ONE be so simple and still work?


Joined Apr 2, 2009
Possibility is that it could be a simple series regulator.

More components will lead to strict regulation, short circuit protection and current limiting


Joined Jan 28, 2017
I don't know the year and make of car, However my guess would be that it is coming from a different part of the car. Infact if you had the ability to probe the wiring going to this area I would assume that it is going to be 5v in already and could be coming from the BCM or different module altogether. In most cases the ones that plug into a cars normal Aux socket has the ability to have a higher input then 12v. Infact I have one that will take a 24v in put and still give out constant 5 volts without fail.

So as stated if it is working then you should be good plugging things in. It has to be able to do more then just regulate 12v. so my guess is it is coming from somewhere already protected and regulated.

What is the year make and model of car?


Joined Nov 4, 2013
I've ran into a number of extremely cheap 12 volt to USB port adapters that used nothing but a LM7805 or similar linear regulator and a way undersized heat sink, if any, to do the job. They would work for a while until the regulator IC would overheat and shutdown or just burn out.

Easy money maker for gas stations where the vast majority f the customers who bought one will never come back to get a replacement when their burns out 5 miles down the road.

They get them for 25 - 50 cents each and sell them for $4 - $5 each knowing full well that maybe 1 in a 100at best will ever come back for warranty replacement or a refund.

ian field

Joined Oct 27, 2012
If it is working, it won't.
Series pass linears dump the full voltage when they fail SC - but then so does the buck.

I'd go for a flyback regulator driving a step down transformer. Failure blows the fuse and everything stops.

A crowbar SCR is good insurance either way.