| Chris Daly |
Hi
I need help with an interesting question, I am currently examining a AM 1Kw transmitter which currently uses
6 amp fuses for fault /DC protection- 1 per module.
I am assessing whether just fuses are the best answer
for this output stage. I think two LM338 devices acting
as a current regulators will provide another layer of
protection.
Also to consider is that AM modulation is switch mode added at a sine -wave frequency of 125Khz across the DC rail ( where the fuses are ) into a bridge 4 device per module Fet network
Will a LM338 arranged as a current regulator Vref/R
allow this modulation frequency to pass as well. ? or
does a LM338 attempt to block frequency content
preferring to live in a DC environment.
Has anyone had experience with frequency and LM338
LM317 family of devices ?
My other option is to design current regulation within
a DC part of the board before modulation is added.
Thank You :) |
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| Chris Daly |
A few additional points:
The idea is to current limit the circuit to approx 5 amps per module - which should be within the 338's capability
rather than just relying on 6amp fuses.
The fuses will remain to protect the circuitry in case of outright abuse. |
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| AndrewT |
Hi,
125kHz is well beyond the knee in the frequency response of the regulator. It does not work very well at this high a frequency.
That may lead to some serious performance shortfall. |
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| Chris Daly |
Hi Andrew
Thanks very much, it begs the question what is the
frequency response of a fast blow fuse ?
I can design this limiting earlier which should solve
the reliability issues. Many Thanks
Cheers / Chris |
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