Circuit drawing mostly constant current

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Discussion Overview

The discussion revolves around methods to smoothen out current pulses drawn by an integrated circuit, specifically addressing the impact of these pulses on nearby magnetic field sensors. The scope includes circuit design considerations and potential filtering solutions.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests using a resistor and capacitor to smoothen the current pulses, while questioning if there are better solutions.
  • Another participant asserts that using a capacitor is the best approach, noting that many chips have capacitors across their power rails.
  • A participant reiterates the need for smoothing and asks for clarification on the necessity of the solution.
  • The reason for needing a smoothing circuit is provided, indicating that sharp current peaks are inducing noise in a magnetic field sensor.
  • Advice is given to install extra filter capacitance close to the IC and to use a variety of capacitors in parallel to minimize parasitics.
  • Another participant agrees on the importance of keeping leads short and suggests twisting them together to reduce external magnetic fields, also proposing the inclusion of a series inductor for improved filtering.
  • A question is raised regarding the source of interference, suggesting it may be coming through the supply to the sensor rather than from external magnetic fields, and recommending a separate regulator for the sensor.

Areas of Agreement / Disagreement

Participants generally agree on the use of capacitors for smoothing current pulses, but there are differing opinions on the best configuration and additional components needed. The discussion remains unresolved regarding the source of interference affecting the magnetic field sensor.

Contextual Notes

There are limitations regarding the assumptions made about the sources of interference and the specific configurations of the proposed circuits, which have not been fully explored or resolved.

daudaudaudau
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Hello. I have an integrated circuit that draws current in pulses. The pulses have a duration of about 0.5 ms and a period of 2 ms. I need to make a circuit to put in front of this IC that will smoothen out these current pulses. One option is just to use a resistor and a capacitor. When the IC needs current it will draw it from the capacitor and the capacitor is then recharged through the resistor. But I was wondering if there are better solutions out there?
 
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No, a capacitor is best, that is why some chips have capacitors across their power rails and physically adjacent on the board. Something about 100μ is usual.
 
daudaudaudau said:
Hello. I have an integrated circuit that draws current in pulses. The pulses have a duration of about 0.5 ms and a period of 2 ms. I need to make a circuit to put in front of this IC that will smoothen out these current pulses.
There are a number of ways to go about it. Please explain why you need to.
 
NascentOxygen said:
There are a number of ways to go about it. Please explain why you need to.

I need it because the sharp current peaks (dI/dt) are creating magnetic fields which are inducing noise in a magnetic field sensor I have.
 
Then follow Studiot's advice on installing extra filter capacitance close to the IC and use short leads. If space allows, use a selection of capacitors in parallel, e.g., 47uF, 0.47uF, and 0.022uF to minimize parasitics.
http://img803.imageshack.us/img803/4666/holly1756.gif
 
Last edited by a moderator:
Agreed; keep any leads which are downstream of your filter really as short as you can and possibly even twist them together to reduce external magnetic fields. The filter could be made better if there's a series inductor included, too.

One question worth asking is whether the interference you are getting is really external magnetic or is it getting down the supply to your sensor? Perhaps a separate regulator for the sensor could help.
 

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