Calculating current requirements of IC (Begginer)...

• posted

Hi group!, this is the first post I make, and I would be very glad if you orient me.

I am designing an analog I/O card with several step down DC-DC converters (basically to energize the signal conditioning circuitry), and at one moment I got confused with the amount of current I should be able to supply.

To sum up, I am not so sure which parameters I should look for in the datasheets of the chips, to get an estimation of the current that every single IC could consume at maximum. By knowing it, I would be able to design a converter able to provide the right amount of energy. I mean, if I am going to use one instrumentation amplifier, one comparator, etcetera, knowing the voltage required, which current should I supply to them at maximum?

I know this is a very basic question for the designers, but I am just a begginer in design (but in electronics theory).

Franco.

• posted

Not too hard, first look at the datasheets for the amplifiers and whatnot, they'll list typical and maximum idling currents. That;s the current draw of the internals.

Then figure out how much current you're using to bias the inputs (if any). Then add the current being pulled from the outputs, usually quite small, but it doesnt hurt to include these. You should also add up all the AC current being pulled, but unless you're designing a killer car stereo, you can probably calculate this and realize it's just microwatts.

The total will likely be a rather small number, like 110 milliamps. I'd aim at supplying at least 1.5 times that much, as your design might grow.

Regards,

George

• posted

Use a LM78T05 regulator - they are cheap and easier than doing math.

If it gets hot to the touch, put a heatsink on it.

If it shuts off, there is probably something wrong with your circuit.

Luhan

• posted

Vice versa!!! From R&D in aerospace electronics, use bench power supply during development, test your design to any limits. As usual you will add/remove/change components during this time. When done, measure the current drawn and then give it twice as much.

HTH

• posted

Be careful using a DC-DC converter on signal conditioning stuff. Make sure your output is regulated to prevent power supply noise being an issue. If optimal power efficiency is not a requriement then simply use a linear voltage regular, low dropout type if needed, they are cheap, simple, and low noise.

Dave :)

• posted

I was looking at that possibility, but the main limitation was I need to supply with -12V some stage (I also dont like the hitting issues, but I can surivive with that). Do you know If I can use linear voltage regulators to get -12V from a possitive voltage (+24)??

Franco.

David L. Jones ha escrito:

• posted

Nice answer, very helpful. I had values of current in the magnitude you suggested (I was hoping to get lower values :().

Thanks...

Franco.

Ancient_Hacker ha escrito:

• posted

No, you need an inverter (like a ICL7660 type), and then a negative linear regulator on the output.

For signal conditioning stuff that needs +/-12V, you'd typically have say a +15V DC (can be noisy) input supply which gets inverted to give you -15V (even noisier) and then you'd use a positive and negative linear regulators (7812, 7912 etc) to give you a nice clean +/-12V

Also, there are more exotic linear regulators that can give you lower noise than the standard 7812 type if needed.

Dave :)

• posted

Great, I will try that. Thank you very much David.

Regards....

Franco.

David L. Jones ha escrito:

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