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I'm a newbie in electronics and Trying to understand and build this circuit. would somebody tell me the rule of R1 & C2 in this circuit and their magnitude effect on the controlling of process.why didnt feedback start just after the output of opamp?How could i find the transfer function between the voltage output of Hall effect sensor and the voltage output of MOSFET drain?

The schematic is the circuit of a magnetic levitating tool at:


Thanks so much enter image description here


marked as duplicate by JRE, Enric Blanco, Voltage Spike, winny, PeterJ May 31 '17 at 15:23

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migrated from robotics.stackexchange.com May 30 '17 at 11:55

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  • \$\begingroup\$ You take the feedback from whatever you want to control, in this case you probably want to control the position of something sensed with the hall effect sensor. \$\endgroup\$ – PlasmaHH May 30 '17 at 11:59
  • \$\begingroup\$ Look up constant current source. The op amp is controlling current. \$\endgroup\$ – Voltage Spike May 31 '17 at 4:30

You're asking what the role of R1 and C2 is. This circuit is a PI controller.

With just R1 in the feedback path you have a simple amplifier, with a proportional response. With just C2 in the feedback path you have an integrator.

This circuit combines those behaviours. The faster the signal changes, the more C2 looks like a short and you have a simple proportional feedback through R1. The more slowly the signal is changing, the greater the role C2 plays and the circuit is an integrator.

So, with the proportional response dominating at high frequency, the circuit can rush toward the setpoint faster, then when the output is in the right ballpark the integrator takes over to stabilize it.