1. DC Voltage Reduction

I have recently run into an issue that involves electronics that, as a mechanical engineer leaves me clueless.

I have been investigating how to build an auxiliary battery power source for my handheld GPS and the mechanism for doing this using the cable power source connections on a spare UBS computer cable is very straight forward.

I have determined that the UBS power supply voltage is 5v DC but here is where the issue arises that I cannot solve. I have an adapter power cable for connecting the an auxiliary car power socket to the GPS so I wanted to determine the supply voltage from that 12v DC source to the GPS; and when I did so by using my digital voltmeter at the GPS end of the cable it was also 5v DC. So, while I understand the old school method of using a resistor in series in a flowing current circuit to drop the voltage to a series connection in the circuit what I don't know what type of electronics can reduce an input 12v DC voltage to an outlet voltage of 5v in a circuit with essentially zero current as is the case with a volt meter as the only outlet connection in the circuit.

The importance of understanding this, other than the fact that I don't like not understanding things, is that I would prefer to use standard rechargeable batteries in my auxiliary power source and it appears to do this correctly I must condition the output voltage to the GPS to 5v.

Any input on this issue will be appreciated.

2. I can't help with the understanding part but have you thought about buying a cheap in-car charger (thinking £1 shop or dollar store cheap) and taking it apart? I get the feeling that they probably use a heat shielded regulator chip to keep it compact. I hate giving this answer but it might be worth asking Professor Google (or preferred search engine Professor).

Hope you find some part of this helpful though.

3. Cake of Doom:
Actually your input was helpful in that it reminded me to do what I often fault others for not doing. A quick web search provided a design and construction instructions although I am not sure it is what is commomly used for a simple low current GPS connector.

Also, I am going to test my exisitng automobile cable with some lower input voltages to see if a modified version of it might work for the pupose as well. At the same time, unfortunately it may all be a futile chase since, from the information I have found, such IC chip devices are rather inefficient using more input current that output, which is fine if you are using a 12v automobile connection source but may well defeat my purpose when using a small compact rechargeable battery set.

Thanks for the input.

4. Happy to be of service.

I can see how that kind of inefficiency could be a set back, although, similar things exist for mobile phones which are +/- in the same voltage ball park as your GPS. Link to typical iPhone version. Could be good for inspiration.

5. we can use this product to reduce the DC voltage Jtron12V to 5V DC-DC Reduction Voltage Power Supply Converter Module w/ DC Jack - Black

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