Wednesday, April 23, 2014

Using USB car charger for powering your projects

Most car chargers available sport a MC34063 based DC-DC converter to step down 12 volts to 5 volts.

MC34063 based circuit within USB Car chargers
Such chargers can be used to derive 5 volts from 12 volt power supplies/lead acid batteries while constructing projects.

Using the charger to get 5V from 12V power supplies in projects.

This charger is a bit different from the regular ones.
It can supply upto 2 amperes. Instead of MC34063, it uses the IC CX8509


Greenray said...

This kind of zero-cost units, can be used for another scope.
Currently I'm designing a project powered with 24DC V.
The MCU is very few hungry of power and for this reason I can reduce the voltage from 24 to 12 V or 5 V, without regarding the little energy wasted.
But my project will also display to the user some information with 15 LEDs.
Every LED need a not so high current, the same that flows into the resistors in series to anyone of those LEDs.
If we think that across any LED falls less than 2 V, our mind immediately run to ask how many volts will fall on any series resistor!

Oh, yes, I can drive the LEDS with 5V instead of 24, but this is like transform the small 5V regulator for the MCU, as a big resistor for all the LED!

So I propose to use a Step-Down converter to "pass" from 24DC V, to a smaller voltage, adequate for the LED characteristic and configuration (one LED, two or more LEDs in series).

This solution resolve not only the needed power voltage, but reduce drastically the wasted power, because a Step-Down (Buk converter) transfer just the power needed asking very little energy for itself, meeting a very high efficiency and a very little loss of energy, that traduced means: no heat!.

Be care: some of these circuits are designed for trucks and so, can be supplied at 24 VDC, while some other are designed only for cars and their nominal input voltage is 12.

The absolute maximum input voltage for the MC34063 exceed 24 VDC, but you have to examine the entire circuit to sleep paceful!

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