EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: w3amd on December 28, 2015, 08:12:16 pm
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Hi all,
I'm trying to understand something in the op-amp datasheets. For idle or quiescent current datasheets give a value of typical and maximum current.
For a dual rail supply of +12,-12 does this mean each side of the power rail is using this amount of current?
Should I be dividing this current value by 2 if a dual supply is used?
I'm trying to calculate idle power used of each op-amp
TIA,
John
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The same current flows from the positive supply to the negative supply. The amp has no concept of ground. Also, no dividing by two, if anything, you have to double it to get the absolute value.
The q. current will be dependent on the temperature and the supply voltage, with some spread from part to part.
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The op amp has no idea if it's connected to a dual rail or single supply. Iq flows from Vdd through the op amp and into Vss, so quiescent power dissipated by the op amp will be (Vdd-Vss)*Iq, regardless of whether or not Vss==Gnd. So yes, both the -12V supply *and* the +12V supply need to supply the full quiescent current, but only half of the quiescent power, assuming a symmetrical split supply.
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As stated above, the quiescent current flows from the positive supply terminal through the device to the negative supply terminal.
Any current delivered into the circuit's load (positive or negative) will be in addition to the quiescent current, but will flow from one or the other supply terminal, as required.