Constant current boost converter problems

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Discussion Overview

The discussion revolves around the challenges faced in designing a constant current driver for a Xenon arc lamp, specifically focusing on issues related to surging, audible noise, and current regulation. Participants explore various technical aspects of the circuit design, including component selection, layout considerations, and the behavior of the boost converter under different load conditions.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes the circuit's operation, noting that it surges and produces audible whines, with current often exceeding the set value.
  • Another participant suggests that intermittent sounds may be due to poor connections forming unintended RC circuits, recommending re-flowing connections to isolate the source of the noise.
  • A different participant introduces the concept of "clumping," which they attribute to poor layout and suggest that it can cause bursts of switching pulses that lead to irregular current behavior.
  • Concerns are raised about the oscillator frequency and its relation to audible sounds, with suggestions to investigate the layout of the switching regulator and proper grounding techniques.
  • Some participants propose adding inductance to stabilize the arc current, indicating that current spikes could damage the output capacitor.
  • One participant notes that moving the output capacitor's negative end after the sense resistor eliminates the whine but does not resolve the issue of current regulation.
  • Another participant discusses rearranging components to improve stability, reporting that the system remains sensitive to various factors that can affect current output.
  • There are mentions of ground loops and the importance of isolation and bypassing in circuit design, with references to external resources for better layout practices.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the causes of the issues and potential solutions. There is no consensus on a single cause or resolution, as various hypotheses are presented and explored.

Contextual Notes

Participants highlight limitations in the current design, including potential ground loops, layout issues, and the need for proper component arrangement. The discussion reflects ongoing experimentation and adjustments without definitive conclusions.

Who May Find This Useful

Individuals interested in circuit design, particularly those working with power electronics and switching regulators, may find the insights and troubleshooting approaches discussed here relevant.

  • #31
I recommend we isolate the lamp with a close resistor load, measure the load on initial lamp start up as it will, I would think drop once its fully on. Then try a potentiometer on the load side and check the signal behavior. If the behavior improves then we can look into a means to regulate it. If it doesn't improve then we know were still configured wrong on the 494
 
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  • #32
jim hardy said:
Are above traces with lamp load or resistor load?
What is the yellow trace now - current through load or voltage across output capacitor?
5Ω resistive load.
The traces are across current feedback output - 20:1 amp of current across 0.01Ω sense resistor, with RC filter of 100Ω and 0.1μF.

jim hardy said:
So - what region of your closed loop has a response time around a half millisecond?
The ignitor transformer?
It's 200μH worth of choke in series with the load.


All in all, I'm likely to give up on this design, and try a CV boost followed by CC buck instead.
So, thanks all for help.
 

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