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I am trying to make a small board with an RGB LED on it. I would like to power the board with a nice small 12mm coin cell (3V). However the typical forward voltages of the RGB LED (and minimums) are slighly higher (~3.5V).

Would it be kosher to use a non-inverting op amp circuit to bump up the VCC slightly to achieve the proper forward voltage for the LED? Will this damage the battery or cause it to die faster?

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  • \$\begingroup\$ Opamps aren't magic. They can't give a higher output voltage than whatever you put on their supply pins. \$\endgroup\$
    – brhans
    Apr 25, 2017 at 3:04
  • \$\begingroup\$ @brhans So boost converters are magic? \$\endgroup\$
    – The Photon
    Apr 25, 2017 at 14:35
  • \$\begingroup\$ @ThePhoton - No, and op-amps aren't boost converters. Read the question - the OP's assumption is obvious. \$\endgroup\$
    – brhans
    Apr 25, 2017 at 14:59
  • \$\begingroup\$ @brhans Boost converters aren't op-amps, but your comments implied a device would have to be magic to output a higher voltage than it has available as input. The reason op-amps can't do that isn't because they aren't magic, it's because they don't have any significant energy storage devices (inductors or capacitors) configured to do it. \$\endgroup\$
    – The Photon
    Apr 25, 2017 at 15:54
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    \$\begingroup\$ @brhans, consider a learner doesn't know what an op-amp is or isn't. They ask a question about it. You tell them it would have to be magic to produce an output above its power supply voltage. Then three months later they find out about boost converters --- should they think boost converters or magic or should they think you were not informing them accurately about what is and isn't magic? \$\endgroup\$
    – The Photon
    Apr 25, 2017 at 16:47

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Op amps can't increase their output voltage higher than their supply voltage, so you'd have to have a separate higher voltage supply as well, which defeats the purpose. Look into a buck/boost regulator or Ćuk converter instead.

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  • \$\begingroup\$ +1 for suggesting an inductive SMPS, but I think I'd suggest a simple buck converter circuit. he only needs step-up capability here, so no reason to use the more complex topologies. \$\endgroup\$
    – Robherc KV5ROB
    Apr 25, 2017 at 3:18
  • \$\begingroup\$ A buck converter can't do step-up! And with a 3V battery driving LEDs... you'll need both step-up and step-down depending on the LED being driven and the amount of charge used from the battery. \$\endgroup\$
    – Hearth
    Apr 25, 2017 at 3:28
  • \$\begingroup\$ ahhh crap, thanks. I typed buck while thinking boost. Sorry about that. however, I think boost would work so long as the led "color" voltages aren't very far below the coin cell's 3V. However, I can also see where a cuk could be made more efficient by "switching off" between bursts in some setups. \$\endgroup\$
    – Robherc KV5ROB
    Apr 25, 2017 at 4:00
  • \$\begingroup\$ Honestly, I just have a thing for Ćuk converters. I love the way all their magnetics interact and cancel out some of the ripple. You could do it easily with a buck/boost or just a boost converter, probably. \$\endgroup\$
    – Hearth
    Apr 25, 2017 at 4:11

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