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Current mirror: real-life examples?

Current mirror: real-life examples?

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I’m looking for examples of how current mirror is used in real life.

Most tutorials cover the circuit itself but don’t go into examples. Therefore, I’m still struggling to understand how it’s used and what the benefits of it are.transistorscircuit-analysiscurrent-sourceShareEditFollowFlagasked 1 hour agoRodion Degtyar35977 bronze badges

  • 1Look into the inside circuit diagram of any analog chip. For example that one of an operational amplifier. They use plenty of those. You can find them in datasheets. – Janka 1 hour ago

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3 Answers

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Current mirrors are quite common in audio power amplifiers as well:

enter image description here

TR10-TR11 pair in the schematic above (bottom-left) form a current mirror to make the collector currents of TR2-TR3 differential pair equal.

Fun fact: A class-AB power amp is a bigger (more powerful) version of a transistor-operational-amplifier.ShareEditFollowFlagedited 47 mins agoanswered 1 hour agoRohat Kılıç9,71033 gold badges1515 silver badges3535 bronze badges

  • OMG, your real life example is so complicated. Can you give a two transistor circuit for me too newbie? Thanks and cheers. – tlfong01 1 hour ago   
  • @tlfong01 Sorry. My intention is just to show the current mirror usage in a real-life example hoping you to see the tiny subcircuit to the left. Anyway, just look at the input stage (the current source at the top, the diff. pair formed by TR2-TR3, and the current mirror at the bottom) and ignore the rest. – Rohat Kılıç 1 hour ago 
  • Ah thanks a lot for your quick reply. I must apologize that I did not read the OP’s question too carefully. I misunderstood that he was asking for a circuit design, not a usage example. By chance I am using a current sensing amplifier chip using a current mirror amplifier. So perhaps I can also give an example later. Cheers. – tlfong01 57 mins ago   

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Current mirrors are frequently used in linear integrated circuits such as op amps. They are used to provide a stable current for biasing transistors and transistor pairs such as differential pairs.ShareEditFollowFlaganswered 1 hour agoMath Keeps Me Busy2,52211 gold badge44 silver badges1919 bronze badgesadd a comment0

Question

Are there are real life examples of using a current mirror?


Answer

I am using the following current sensing amplifier chip, which is using a current mirror.

mxx4172 1

My real life project still in progress is to plot the I-V curve of a tunnel diode. Because the current I am measuring is very small, in the range of uV to a couple of mV, so I need a current sense amplifier to convert the tiny current to 0 ~ 5V, and I also use a 12-bit ADC to read the digital value which will be read and stored by a Raspberry Pi.

The photo below shows my calibration hardware setup.

max4172 calibration

Wiring the tiny MAX4172 is a bit tricky. There is no assembled module available, so I need to do the point to point wiring, luckily only 8 pins, to a breakout board. I have about 100 hours of SMD hand soldering experience, so it took me only 15 minutes to do the first chip, and then 10 minutes in average for the later ones. The photo below shows my craftmanship. 🙂

max4172 soldering

The software part is not that difficult. I skimmed the datasheet, and found that there is actually no programming required. I only need to find out the a bit complicated amplification gain factor table, and choose the gain resistor to fit my current range. My datasheet summary is show below.

max4172 datasheet summary

The picture below shows my working on the current sense and output resister values.

resistor value

My quick and dirty conclusion is that the hardware soldering is a bit tricky, but there is no software need, just simple calculation.

So all in all, a damn cheap newbie friendly toy to learn new stuff.


References

(1) MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier Product Sheet – Maxim

(2) MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier Datasheet -Maxim

(3) Current Mirror – Wikipedia


ShareEditDeleteFlagedited 35 secs agoanswered 52 mins agotlfong011,43011 gold badge55 silver badges99 bronze badgesadd a comment

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