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Transformer heating

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catcat said:
the inductors are correct, they are to smooth the ripple voltage from the capacitor.
The 2200uF filter cap and the LM317 voltage regulator will reduce the ripple voltage so low that it cannot be measured, if a 10uF cap is connected to the ADJ pin of the LM317 to ground.
Sure beats using huge inductors.
 
audio guru wrote:
"I would use a well-made Hammond 12.6VAC center-tapped 500mA transformer, two rectifiers and a main filter capacitor to give an unregulated voltage of 8.1VDC. Then the 5.1V regulator at 200mA would regulate perfectly and heat with only 0.6W and the transformer would barely get warm."

i don't get two rectifier and 8.1V dc how can u get it 12.6Vac transfomer
 
one more thing i have used 330 ohm as R1 instead of 240 ohm i think this wont be a problem
 
nikhil arora said:
one more thing i have used 330 ohm as R1 instead of 240 ohm i think this wont be a problem
Then when the load is disconnected the regulated output voltage will rise.

An expensive LM117 can use 240 ohms or less for R1. An inexpensive LM317 is supposed to use 120 ohms or less for R1.
 
Nigel Goodwin said:
At 50/60Hz the inductors would need to be huge to do anything, so it's extremely rare to have inductors like that. Where you do get them is in switch-mode supplies, where the high frequency used makes them worthwhile.
Or at very high currents and then there's also voltage drop as they smooth out the current ripple, not to mention the voltage spike they produce when you remove the load.
 
nikhil arora said:
so what is the overall effect in using 330ohm instead of 240ohm
The output voltage from the regulator will rise when there isn't a load.
The setting of the pot will also need to be higher.
An LM317 needs 120 ohms, not 220 and not 330 ohms. An LM117 (more expensive) can work with 240 ohms.
 
Lots of circuits on the web have the same mistake.
On the very 1st page of the datasheet for the LM317 is a circuit with a 240 ohm resistor and an LM117.
The LM117 costs more than the LM317 because its operating current (that goes to its output) is half as much, therefore the resistor can have double the value.
 

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That's what is so confusing. You say one thing, the data sheets say another. Who do we believe?
 
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AllVol said:
Who do we believe?
Even ON Semi and Texas Instruments got it wrong on their copy of National Semi's LM317. I believe in National Semi because they invented the LM317.
 
i got it guru so we will use 120 ohms from now cause i am using lm317 from ST.
i belive more in forum then in datasheet
 
nikhil arora said:
i got it guru so we will use 120 ohms from now cause i am using lm317 from ST.
i belive more in forum then in datasheet
You still need to calculate the value of the other resistor which is about half of its value when using 240 ohms.
 
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