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I designed transmitter and receiver circuitry, with LT1214CN op amps with +-12V rails, and now realized I'm limited to using a 12V external supply (I was asked to use it). I've considered possibly boosting it to 24 volts then making an active rail-splitter supply to get +-12V, or getting a board online that can output +-12V from 12V input.

How can I go about fixing my mishap? See Tx circuit below for more context: enter image description here

Update: I'm going to try the following circuit with a boost converter to boost to 24V, then use an LM7812 and LM7912 to produce +-12V instead of +-10V on the schematic.

enter image description here

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    \$\begingroup\$ What is the current need on +12V and -12V ? What supply impedance do you need on each rail ? (i.e. how large is the allowed ripple) \$\endgroup\$
    – tobalt
    Sep 17, 2021 at 22:01

5 Answers 5

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A quick search on Digikey shows over 500 DC-DC converters that will take 12V and supply + and - 12V output. Without knowing more about your circuit and its requirements, that's about as specific as I can get. They make chassis/DIN mount converters that will do the same thing, in case your boards are already made.

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  • \$\begingroup\$ Search "dc dc converter" and select "power supplies - board mount" or "power supplies - external/internal" according to taste. \$\endgroup\$
    – vir
    Sep 17, 2021 at 22:10
  • \$\begingroup\$ Right, sorry. Looked at the wrong parameters. Kind of feels like Digikey's parametric search got messed up recently somehow. \$\endgroup\$ Sep 17, 2021 at 22:11
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Depending on the current draw on the -12V rail and how strict requirements you may have on the accuracy you may try to search for a switched capacitor converter. This is a class of ICs by various manufacturers that take positive voltage at the input and with only few external components (three capacitors and no magnetics) generate negative voltage at the output. There is a wide selection for voltages up to 5V; for 12V there is a bit slimmer picking. An example may be Linear Tech (now TI): LT1054 data sheet If +/-5V is what you need here is a tested design: enter image description here

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  • \$\begingroup\$ Hi Martin, thanks for the answer. Im quite new to this. From LTSpice simulations it seems I need a max of 55mA at any one point. I have a power bank that supplies 12V or two USB ports (5V). I gather from the LT1214CN datasheet that I indeed could use +-5V rails instead of +-12V. So Im now considered doing this, but that reduces how gain I can give my input signal to be transmitted before it clips. So I need to figure out if I'll go with the USB option and sacrifice transmitted signal power, or get a switched capacitor converter to get +-12V. \$\endgroup\$ Sep 20, 2021 at 19:50
  • \$\begingroup\$ The LT1214 certainly can operate at a single supply. That doesn't seem to be the question (and the chip would work with single +5V or +12V supply). The key question is whether the circuit you are designing needs to operate around 0V. I cannot assess that without schematic. But if you settle on +/-5V or +/-12V you may actually accept the answer. +/-5V opens the selection to many more chips. I have a recent great experience with LM2776 in similar role. \$\endgroup\$ Sep 20, 2021 at 21:08
  • \$\begingroup\$ @IanEdwards Capacitive inverters are more common at low voltage/current. If you can't find one that meets your needs, usually you step up to an inductive inverter, which can handle higher voltage/current. \$\endgroup\$ Sep 20, 2021 at 22:43
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You can use Inverting Charge Pump Generates.LTC3261 is a good choice.Its output current capacity is 100mA.Please see the circuit below.

enter image description here

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I ended up solving my problem by using an LM7812 linear regulator on the output of a 12V battery, then boosting it to 24V with a boost converter, then using an active rail splitter circuit with an LN1214CN op amp, and 2 x 12k resistors to produce +-12V rails with respect to a virtual ground - that being the output of the LN1214CN. See schematic below (excuse the rough drawing). A charge pump could achieve the desired output as well. The issue I encountered was finding a cheap and available charge pump or switched capacitor converter that could take 12V and produce +-12V hence my rail splitter choice.

Basic rail splitter circuit

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  • \$\begingroup\$ Since the lm7812 has a minimum input voltage of 14.5v, you do not want to put that after a 12v battery. \$\endgroup\$ Oct 1, 2021 at 22:03
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You can design one using an IC like the one mentioned here: https://www.analog.com/en/technical-articles/inverting-dc-dc-controller-converts-a-positive-input-to-a-negative-output-with-a-single-inductor.html

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