Miller Effect

177

02:22:52

Because the gain of the transistor is 100, it multiplies the capacitance of the 1uF capacitor by 100 thereby creating a semi-accurate simulation of a 100uF capacitor.

published 6 years ago

zorgrian

6 years ago

Yea you can do a similar thing with inductance. Gyrator circuits create inductors which are very useful for making filters

zorgrian

6 years ago

But its unlikely that you could make a gyrator using BJTs. You need higher impedance input so MOSFETs or whole op amp chips are used.

eekee

6 years ago

@zorgrian: http://sound.whsites.net/articles/gyrator-filters.htm#s7 -- diagram, notes, graph on 1-bjt gyrator

eekee

6 years ago

Best use the AC version for any actual use whatsoever, I think, except maybe a power-on timer. It's almost funny what happens if the power supply fluctuates: http://everycircuit.com/circuit/4819249028923392

eekee

6 years ago

In anotehr comment thread, @jason9 replied, "try adding a diode in series with the 100uF capacitor such that it lets it only charge but not discharge. The orange and green lines become almost indistinguishable even when it starts clipping once it’s fully charged." I tried a diode in series with the capacitor or with the resistor. Neither helped. Linked circuit updated.

jason9

6 years ago

This is what I had in mind: http://everycircuit.com/circuit/4582052279353344

eekee

6 years ago

Oh! Oops. :) Why would you want that, though?

jason9

6 years ago

To better emulate the properties of the miller-effect circuit. If you want to be extremely exact, you could increase the capacitor from 100uF to 101uF and then the lines are different by no more than a few tens or hundreds of uVs.

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