• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

LM317 calculator for filament circuit

Status
Not open for further replies.
Jump to Latest
cbj591

cbj591

Member
Joined 2010
#1
Good afternoon all,

I was looking at a couple of LM317 calculators for R1 and R2.

Question. Is the VOut given in these calculators the voltage drop from the input voltage or the actual voltage output.

The Toroid tranny I have has a 17.8v tap so I was a little confused on what the calculator VOut giving.

Any help would be grateful

Cheers
Brian
 
#2
cbj591 said:
Good afternoon all,

I was looking at a couple of LM317 calculators for R1 and R2.

Question. Is the VOut given in these calculators the voltage drop from the input voltage or the actual voltage output.

The Toroid tranny I have has a 17.8v tap so I was a little confused on what the calculator VOut giving.

Any help would be grateful

Cheers
Brian
Click to expand...

If you can give us a link to the calculator it will be easier to comment!🙂
 
#4
Hmm, If I understand you correct the Vout is actual output voltage.
And for exapmle if you need Vo = 15V
Then R2 = ( Vout/1.25V - 1 ) * R1 = 12*R1 = 12 *120 = 1.5K
And input voltage must by at least 3V greater the Vout.
So Vin_min = 18V
 
#6
Then what input voltage is it basing the output on?

You can play with the R! and R2 values and get different output voltages. Example if my input was 17.8?

Not trying to be dim, just not getting the concept on how it knows the output without a given input.

thanks
 
#11
As long as Vin is at last 3V above Uout. Input voltage does not matter.
But (Vin - Vout) and load current determine the power that will be dissipate in IC.
Pdis = (Vin_max - Vout_min) * Iload_max.
And without the heatsink power dissipation in IC can not be greater then 1.2W
 
Status
Not open for further replies.
Top Bottom