Buck converters

I’ve become more aware of buck converters, and started buying a crap ton of different ones for multiple projects where I need to change the voltage. They are super easy to use, Connect Vin, Vout and ground. Often there’s 2 ground pins to help you wire your load and your battery.

Random comparisons of buck converters to other solutions

A buck converter is a lot more efficient (up to 96% efficient) than a linear LM78Lxx voltage regulator (LM13700N, LM78L05…) though the efficiency curve is often unclear: 80% to 96%, with the heat dissipation issue implications when it is not on its efficiency curve. A buck converter basically charges capacitors and switches them  with a clock to the output to dump a lower voltage (340kHz). The output current is smoothed/regulated using a choke and capacitors.

I believe an LM chip burns the watts you don’t use into heat. Wdissipated = (Vdd-Vload) * Iload. If your chip uses more than a few milli amps, it runs your batteries and becomes hot. For reference, a 50mW controller uses 10mA at 5V. With a 12V supply the LM78L05 wastes 70mW. That is the example of an AtTiny85 driving 12V WS2811 LEDs.

An LM voltage controller is still better than using a plain resistor bridge to lower the voltage. Vload = Vdd (R1 / R1 + R2), because that relation holds only if Iload is negligible vs Ibridge, and the current in the bridge is just wasted energy.

Other bad alternatives: Connecting your controller to Vdd directly with a resistor but if the current draw of your chip varies a lot, its voltage would too and could blow the chip if the current drops (because Vload = Vdd – R * Iload). Connecting your controller to Vdd with diodes, since each one drops 0.6V: You’d need 12 diodes in series to connect your 5V controller to a 12V power supply and would waste energy (Vdd – Vload) * Iload.

Cool buck converters

There’s a couple of tiny buck converters that pack a punch:

  • AMS1117
    Perfect to power a micro controller or something low power piggy backed on a high power higher voltage setup.
    Those support up to 1A,  and come either in adjustable voltage (you use a resistor bridge on the outputs knowing Vref is 2.25V), or in multiple voltage, 3.3V and 5V are common, which means you wire the ref pin directly to ground to get that output voltage, which is super convenient, precise and stable. They come pre-wired on mini boards for a dime with the required capacitors (SMD 104 and 106 caps in parallel on each side).
    If you have a 3.3V board, you can use 3 diodes to connect its ground to your main ground to allow it to regulate to 5V if you don’t have a 5V board.
    Vin is limited at 17V. However with the trick above, for 5V regulation that can become 18.8V
  • Mini 360
    It is higher power at 1.8A. It does 3A peak, but heats up real fast and may do a thermal shut down to not melt.
    It is adjustable (1 – 17V) via a tiny rheostat you tweak (so maybe more prone to de-tuning over time).
    The board is about as wide as an AMS117, but is shorter, so it is super tiny (1/2 a postage stamp if that)! It costs about 30cts/piece.

It’s too bad, you can’t wire buck converters in parallel to get more amps. This causes instability. However even 5A buck converter boards are relatively small and cheap still (a couple of dollars).


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