5V to 12V converter

Arduino applications sometimes require a 12V supply and thus an external 12V power supply. With this 5 to 12V converter an 12V external power supply (and its and extension cord) is not needed anymore. The 5V comes from the USB cable.

This 5 to 12V converter is especially for:

  1. Applications that needs less than 200 mA out of the 12V.
  2. Mobile applications. Only a laptop, USB cable and the Arduino application are needed. An external power supply is unhandy in mobile applications.

I used this (very cheap) MC34063 Based Switching Regulator Adapter for a solar cell curvetracer:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230481402192&ssPageName=ADME:...

Reducing the ripple voltage

The 5 to 12V MC34063 based switching regulator has a ripple voltage at the output and also causes a ripple voltage at the 5V input. For sensitive applications such as the Arduino (with its 10 bit ADC) sometimes this is not allowed. Here I describe how to eliminate the ripple voltages.

The voltage comparator inside the MC34063 turns the switching circuit on and off to regulate the output voltage. The disadvantage of this simple on / off regulation is that it causes an extra low frequency ripple (about 100 Hz) at the 5V supply line. Because of the low frequency it is not possible to use a LC filter to reduce this ripple, the L and C values would become too large. The 45 kHz ripple from the switching circuit can be reduced easily because the frequency is high enough.

Modifications: 1. Remove the three parallel current sense resistors R2, R3 and R4 from 1 ohm. Replace them by one resistor (Rsc), for instance 2.2 ohm (the value depends on the load). This reduces the peak inductor current and thus the 45 kHz ripple. Also it ensures that the output power is just as much as needed so that the switching circuit runs continuously at 45 kHz without being interrupted by the comparator. 2. Turn the potentiometer completely right. This disables the comparator, the negative input is low and the output is continuously high. When the resistor Rsc has the correct value the output voltage should be larger than 15V now. 3. Place a voltage regulator 78L12 at the output, because the MC34063 is not regulated anymore. This also eliminates the output ripple. 4. Place an inductor of 100 uH in series with the 5V input.

If you are in a situation where you need both 12 and 5 v, surely it will almost ALWAYS make the best sense to have a 12v supply, and derive 5 from it, especially in an Arduino context? Especially as Arduononauts are likely to want 12v for power hungry devices... lights, relays, motors, etc?

So why would anyone market the module which gave rise to this thread?

Once upon a time, perhaps, there were devices which mostly worked at 5v, and once in a while a special support chip (an ADC, for instance) might need a few milliamps of something "exotic". Hence the step-up module.

Anyway... it pays to K.I.S.S.

Which is going to be easier, and something that you use again and again? Making 5 from 12, or 12 from 5?

Using a wasteful linear regulator in this scenario is not necessarily an ideal solution, particularly in power-sensitive applications such as battery and/or solar power (or other "alternative" sources). Note that there are other techniques such as physical separation, shielding, bypassing, grounding, etc. to reduce switchmode power supply noise in a project.

This 5 to 12 V converter is especially for application that needs a few milliamps out of the 12V. Here the linear regulator is the easiest way to eliminate the ripple.