Author Topic: 13.8v psu  (Read 1661 times)

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Offline GazeddyTopic starter

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13.8v psu
« on: April 13, 2014, 01:41:39 pm »
been looking at building a 13.8v psu for my cb radio in the house. ive been looking at lm317 and using a pair of 2955 pass transistors to boost the output up to around 30a. ive seen various diagrams and schematics. the bit i dont understand is why the pass transistor goes pre reg instead of post reg?
 

Offline Simon

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Re: 13.8v psu
« Reply #1 on: April 13, 2014, 01:43:21 pm »
As far as I know they go in parallel to carry the current the reg can't handle. but the current sensing that keeps them conducting just right does go in front of the reg as far as i know, that way any voltage drops on resistors don't affect the output voltage.
 

Offline GazeddyTopic starter

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Re: 13.8v psu
« Reply #2 on: April 13, 2014, 01:45:25 pm »
ahh ok sort of makes sense now.
 


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