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Step Down Bypass

BGT

Oct 22, 2020
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Oct 22, 2020
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Hopefully my little diagram will make sense as to what I would like to do. My question is: would this be a safe way to switch between 12v & 9v (DC) or would this somehow damage the step down converter ?

xED.gif


the convertor is:
XL4015 Constant current/Constant voltage, Adjustable 5A Step Down Buck
 

danadak

Feb 19, 2021
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Feb 19, 2021
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Short answer is no. This would potentially dump current into the output of the
converter. No predicting what it would do.

A Schottky diode in output of converter then tie that to bypass switch output
and load should work. Note consult datasheet for converter, if it needs a minimum
load to stay in regulation. Note diode will drop the converter output when in use by its
forward V drop, so converter should be slightly adjusted, its output V, to
minimize diode V loss.

Note also the Schottky Vf versus T is ~ -1 to -2 mV / C, depending on Schottky
type.....


Regards, Dana.
 
Last edited:

BGT

Oct 22, 2020
15
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Oct 22, 2020
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What sort of size spec of diode should I be looking for ?

Bearing in mind I have access to a large amount of electrical bits and pieces, what am I looking for ?
 

bertus

Moderator
Nov 8, 2019
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Hello,

Try this, as @danadak suggested:
Regulator bypass.png

The SR diode will drop about 0.5 Volts at 5A.

Bertus
 

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Delta Prime

Jul 29, 2020
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Careful now... Zeners and Schottky
Schematic symbols could be rather confusing.
1688842520181.png
 

Delta Prime

Jul 29, 2020
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Even worse! As far as confusing. This is on a data sheet
Explicitly for a Schottky Diode.
Look at the schematic symbol they have chosen.

Screenshot_20230708_121816.jpg
 
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