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High Noise Suppressing Power Supply

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Joeisi

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Hello.
I have designed a circuit to operate in a CAT Loader. This is not a modern CAT, but one from the 1980's. These Loaders run on 24V batteries. I was planning on just hooking a LDO linear regulator up to this supply. After a perfectly operating board was installed(Note: 3.3v system), the LDO was overcome by noise and did not output a voltage. After further inspection the loader's battery actually gave me a voltage of about 20V with 4Vpp with spikes about 5 times a second. The LDO operated normally at a smooth 24v

I was wondering if a switching regulator like this LM2574N-5.0/NOPB could suppress the noise due to the switching nature of the supply, or if anyone here would recommend a certain circuit to me to solve this. Batteries, as well as abnormally large capacitors are absolutely out of the question due to cost. I guess another way of asking is whether the above switching mode regulator will operate under the large voltage swings. In theory, the actual switching part of the regulator will operate normally with any voltage swing, but I am worried about the timing circuit not operating. Could someone shine some light on the subject?
 
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I presume that by LDO, you mean low dropout regulator? i would preceed it with a resistor with a decoupling capacitor to earth. Say 10 ohms and 470 MF. As a vehicle battery is extremely low impedance you have huge currents and induced voltages running wild to give such a large voltage spike. I would totally re-evaluate the connection of your kit to this vehicle. P.S. your were lucky that the regulator went O/C and not S/C !! :-(
Frank
 

A vehicle battery can generate large spikes due to varying loads and starting currents. I recommend adding a 30V zener to ground after the resistor and in parallel with the capacitor suggested by chuckey.

If you are generating 3.3V with the regulator you don't need an LDO. A regular linear regulator should work fine. A regulator designed for the automobile environment extremes might be better. Several IC manufacturers make such regulators.

How much current does your load draw? There's no advantage in going to a switching regulator unless you are concerned about power dissipation in the regulator.
 

Thank you so much in both of your replies. I'm not sure why I overlooked a automotive regulator but luckily I found a regulator that will work with my current circuit. I will try one of these regulators and with luck it will solve my issue.
Thank you both for your great replies.
 

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