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Reg. closed loop bi-directional current driver

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umesh49

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Hi,
My intended application is to generate a very small Guass(less than +/-2 Guass, based on inductor polarity with current required is less than 5mA) magnetic field through an inductor. My inductor inductance and resistances are 200uH and 15Ohm and I have 5V power supply. Guass produced by inductor is sensed by Guass meter and should be FED back to a control circuit to control the current in inductor in closed loop. Voltage output produced by Guass meter should be compared to 2.5V reference voltage to control the field.
I had been thinking to use some PI controller based PWM driving scheme, but it has a limitation to control the inductor current only in one direction so can produce the magnetic field in only one direction.
Please suggest me if someone have an idea to implement the same. My response time for closed loop should be less than 500us.

Regards
Umesh
 

leo_o2

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Add a digital circuit to change the current direction from time to time.
 

FvM

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I had been thinking to use some PI controller based PWM driving scheme, but it has a limitation to control the inductor current only in one direction so can produce the magnetic field in only one direction.
I don't see why PWM should be restricted to unidirectional current, but you would need a bridge driver stage. It's however a bad idea to generate a 5 mA current by a PWM circuit. A single OP is sufficient to drive the coil.
 

umesh49

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I don't see why PWM should be restricted to unidirectional current, but you would need a bridge driver stage. It's however a bad idea to generate a 5 mA current by a PWM circuit. A single OP is sufficient to drive the coil.
FMV,
I am agree with you, I was looking to use to current source to implement the same. I dont want to use a bridge driver to achieve biderection current as I am not sure how to control the direction in closed loop. My problem statment as mention before is as;
1. I have a solenoid was placed in magntic field and a have Guass meter to generate voltage output around 2.5V for +/- field. Now I want to control the current in the coil so that its combined effect of current magnetic field and external magentic field should make guass meter output to be 2.5V (0 magnatic field). I want to control it is closed loop as my coil is varying from sample to sample.
 

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