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Old 23rd February 2013, 09:43 PM   #1
tony Ma is offline tony Ma  United States
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Default Is there any thing wrong with this design

Dear All,

I have a question with this design for PS

The input is 320 V AC and the out put is 400V DC

I am wondering why Resistor #5 (68K 3W) always very hot?

Can some one give me some clue?

tks
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Old 23rd February 2013, 09:58 PM   #2
AJT is offline AJT  Philippines
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what is the dissipation of that Resistor #5 (68K 3W)? in my case, i use that 3 watt to dissipate less than 1 watt...
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Old 23rd February 2013, 10:18 PM   #3
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Does it actually work at all? I really don't see how you could subject an LM317 to these voltages. How could you send AC straight through a 10mH inductor? What happens if you put 100uF straight over AC? Where does the DC come from? Etc.
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Old 23rd February 2013, 10:27 PM   #4
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That was my initial thought, too, vac. But he has a rectifier box there on the AC input. I don't understand the zener bypass, or the pot wiper to nowhere, or...
so best for me to leave it alone.
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Old 23rd February 2013, 10:29 PM   #5
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Sofaspud,thanks, had overlooked it. And you are also right about your last point.
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Old 23rd February 2013, 10:35 PM   #6
AJT is offline AJT  Philippines
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the zener could be a 27volt one, together with the mje13005 ensures that the vin-vout rating of the lm317 is never exceeded....
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Old 23rd February 2013, 10:40 PM   #7
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Sure. I should've realized. Thanks, Tony.
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Old 23rd February 2013, 10:43 PM   #8
AJT is offline AJT  Philippines
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welcome, the circuit reminds me of the maida regulator....21st Century Maida Regulator
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Old 23rd February 2013, 10:49 PM   #9
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Quote:
Originally Posted by Tony View Post
the zener could be a 27volt one, together with the mje13005 ensures that the vin-vout rating of the lm317 is never exceeded....
You are completely right!
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Old 23rd February 2013, 11:41 PM   #10
mirlo is offline mirlo  United States
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LM 317 adjust pin is 1.25 V below output V. R5 dissipates about 2.35 W = (400-1.25)^2/68000.

The 5k pot is much too large. For 400 V out you need about 213 Ohms there, so you will be using only 4% of the pot, voltage adjustment will be way too sensitive.
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