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I am trying to power my servomotor only for a short period of time (controlled by my MCU). I have seen I could use a switching regulator (3 pins). The thing is that I am working with really low power. The battery provides 3.6V to 4.2V; My MCU works with 3.3V and my motor needs 3.5V to 6.4V.

Do you have a solution to power my motor with this kind of switching regulator?

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  • \$\begingroup\$ I think you are referring to PWM more than switching regulator (as in SMPS) \$\endgroup\$
    – clabacchio
    Jun 14, 2012 at 12:43
  • \$\begingroup\$ IF you mean that the motor can run on any voltage from 3.5 to 6.4 then Vbattery of 3.6 to 4.2 is always in the range and you do not need a regulator. \$\endgroup\$
    – Russell McMahon ♦
    Jun 14, 2012 at 14:32
  • \$\begingroup\$ You must tell us what max motor current is and whether anv voltage from 3.5-6.4 is OK or if you MUST have eg 6.0 on occasions. \$\endgroup\$
    – Russell McMahon ♦
    Jun 14, 2012 at 14:38
  • \$\begingroup\$ I didn't measure the max motor current (I need to learn how to make a PWM before). I want to use the switch in order to stop powering the motor (sleeping mode for few months). \$\endgroup\$
    – Mattew
    Jun 15, 2012 at 0:58
  • \$\begingroup\$ With all due respect to Russell, but why did you accept his answer? It's just a copy of stevenvh's who posted earlier, and Russell doesn't even mention shutdown, which you seem to need. \$\endgroup\$
    – Federico Russo
    Jun 15, 2012 at 7:44

2 Answers 2

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(1) NO regulator needed?

IF you mean that the motor can run on any voltage from 3.5 to 6.4 then Vbattery of 3.6 to 4.2 is always in the range and you do not need a regulator. ie

  • Vbat_min < Vmotor_Min < Vbat_max < Vmotor_max

(2) Buck Boost:

If you mean that you want to be able to set a motor voltage anywhere in the range 3.5V to 6.4V at any time regardless of battery voltage then you need a buck-boost converter. A boost only or buck only converter will not work in all cases.

If maximum efficiency is not crucial (and it may not be for 3 seconds of opoeration) Then the 48 cents MC34063 data sheet here will do your job. See fig 17 for one of several ways to achieve buck boost - efficiency can be better than what they say.

For better efficincy the eg TPS63060 is an example of an IC that uses syncronous rectification data sheet here About $4/1 at Digikey. This can provide over 1A out in buck or boost mode.

Example circuit only:

enter image description here

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  • \$\begingroup\$ Things look like I need to find a DC/DC Converter module all included. I would like to find a module which could provide 3.6V or 0 only when I send a command from my MCU. Do you know where could I find these modules ? \$\endgroup\$
    – Mattew
    Jun 15, 2012 at 7:36
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Your input range is very close to the output voltage and then a buck/boost regulator is useful.

enter image description here

This one has a 95 % efficiency and a 5 \$\mu\$A shutdown mode. You set the output voltage with the resistor divider R1/R2. Note: this comes in a small package, which may or not may be an advantage.

Anyway, there are many buck/boost converters with an enable input. You'll find a list from Linear Technologies here.

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  • \$\begingroup\$ Thank you very much. I am using a LIPO battery, do you think I can use the same system. I also need to be careful to the size (really small device). Thank you. \$\endgroup\$
    – Mattew
    Jun 14, 2012 at 13:31
  • \$\begingroup\$ Your not getting my upvote for anything short of 99% efficiency. Let me know when corrected :)~ \$\endgroup\$
    – Kortuk
    Jun 14, 2012 at 13:32
  • \$\begingroup\$ @Mattew, your comments are signed by you, actually, everything on the site you do will have a signature of some sort from you, there is no need to ever had a signature. If you want to thank him give him an upvote(when you have the rep) or accept his answer if it is the best. \$\endgroup\$
    – Kortuk
    Jun 14, 2012 at 13:33
  • \$\begingroup\$ Wow, that is expensive, as all of the LT parts :) $5 in 100qty! \$\endgroup\$
    – abdullah kahraman
    Jun 14, 2012 at 13:34
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    \$\begingroup\$ @abdullah - You better believe it, 'coz it's true :-). That at least partly explains the higher price; those FAEs have to eat too ;-). (FAEs are a free service by a distributor or manufacturer.) At a professional level good support may save you lots of design problems, and then the higher component price pays itself back. \$\endgroup\$
    – stevenvh
    Jun 14, 2012 at 15:19

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