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I have a 12v LiPo battery, arduino mega and two 6v dc motors (which will be powered by a motor shield). Although arduino can be powered using 12v, i don't want to do it because a lot of power will be wasted as heat by the regulator. Is there any way I can provide 6v (or 7v) to the board without using linear regulators? And switched regulator circuits look too complex for me.

Also I'm planning to give 12v to the motors, but use a low maximum value (150 instead of 255) in PWM to keep them from heating. Is this a good idea?

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    \$\begingroup\$ Linear and switching are the only two choices for powering your 6V load. If you PWM your motor at ~ 50% duty cycle, that is very similar to powering it at 6V, and I believe it will work OK. 150/255 is > 50%, though. You might look into a fully built DC-DC converter to add to your design. It is like a little regulator board that you install on your board as if it were a single component. \$\endgroup\$ – mkeith Apr 9 '16 at 17:43
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If you want to use a '12V' (11.1V?) Lipo to supply 6V to the Arduino and motors then you need something to drop the voltage down. Perhaps not a regulator, but at least a device that keeps the output voltage relatively constant at different load currents. If you want efficiency then you must use inductive and/or capacitive components which have minimal loss, not resistors or semiconductors operated in linear mode. That leaves you with 3 choices:-

  1. buck-mode switching regulator: This is not hard to make if you use an IC like the LM2576. One diode, one inductor, 2 resistors to set the voltage, input and output filter caps, done! If this is too hard then just buy a ready-made module.

  2. step-down transformer: Requires a specially wound transformer, transistors on the input to create AC from DC, and a rectifier and filter capacitor on the output to convert the AC back to DC.

  3. Switched Capacitor: Connect a capacitor to the battery and charge it up, then discharge it into a larger capacitor. Repeat until it charges up to 6V. Requires several switching transistors and a complicated driver circuit. IC's that do this are available (eg. LM2771) but most can only handle low voltage and current.

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