I'll teach you how to fish

Posted by JLH (A) on March 2, 2010 at 05:47:31

In Reply to: PSUD question posted by drlowmu on March 1, 2010 at 19:09:19:

I’ll calculate Vlaw and Vfac for a 5U4 tube with both its sections in parallel at 150mA (75mA per section). Look up the data sheet for the tube you want. You’ll need the data sheet to have the voltage drop versus plate current curve. You need to pick two points that are on either side of your planned current draw. Looking at the 5U4 data sheet:

http://www.mif.pg.gda.pl/homepages/frank/sheets/093/5/5U4GB.pdf

We see that the voltage drop curve is for EACH section. Therefore, we need to pick a point on either side of 75mA because the paralleled sections will be carrying half the current. I picked 50mA (100mA) and 150mA (300mA) as my points. We can see EACH section will drop 16.67V @ 50mA and 33.5V @ 150mA.

Now we need to use the current law equation to solve for both points in a simultaneous equation.

Ia=1000*Vfac*(V^Vlaw)

Where Ia is the current in mA and V is the drop of voltage in volts. Let’s now take the logarithms of that equation. It becomes:

Log(Ia)=Log(1000)+Log(Vfac)+Vlaw*Log(V)

Substituting the values we took from the data sheet on the equation, we will find:

Log(50mA)=Log(1000)+Log(Vfac)+Vlaw*Log(16.67V)

And

Log(150mA)=Log(1000)+Log(Vfac)+Vlaw*Log(33.5V)

Calculating the logarithms of the known amounts and adding them together, we will reach the following system of equations.

Log(Vfac)+Vlaw*Log(16.67)=Log(50/1000)
Log(Vfac)+Vlaw*Log(33.5)=Log(150/1000)

Log(Vfac)+1.2219Vlaw =-1.3010
Log(Vfac)+1.5250Vlaw =-0.8239

-0.3031Vlaw = -0.47709

Vlaw=1.5740

Substituting the value of Vlaw back into one of our equations we can determine Vfac.

Log(Vfac) +1.2219*1.5740 = -1.3010

Log(Vfac) +1.9233 = -1.3010

Log(Vfac) = -3.2243, using the Windows calculator Inv log function we find Vfac

Vfac = 0.0005966, or 5.966E-04

So, in your PSUDII rectifier text file the input parameters for your parallel 5U4 rectifier should be:

*Name Type DRes Vlaw Vfac Vpiv Ipks Ipkr
5U4_parallel, VT, 0.000,1.5740, 0.0005966, 1550, 99, 1.0

Now you should be able to calculate the Vlaw and Vfac for any type of rectifier you want to model.

Rgs, JLH

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Follow Ups Full Thread

Topic - PSUD question - drlowmu 19:09:19 03/01/10 (16)

Thanks to all who responded ! - drlowmu 07:15:32 03/02/10 (0)

I'll teach you how to fish - JLH 05:47:31 03/02/10 (2)

Your cast went way past my fishing hole, but it was a thing of beauty!:-) (nt) - twystd 18:06:45 03/02/10 (0)

Excellent post! - JoshK 07:41:52 03/02/10 (0)

RE: PSUD question - drsx 01:24:57 03/02/10 (1)

Thanks! Great Tip! (nt) - Vinnie 04:26:11 03/02/10 (0)

Whut drsx sez . . . - Poindexter 20:30:43 03/01/10 (2)

Thanks Poinz . . . - drlowmu 21:00:57 03/01/10 (1)

Go over to duncanamps.com - Poindexter 22:07:19 03/01/10 (0)

RE: PSUD question - drsx 20:01:23 03/01/10 (6)

RE: PSUD question - drlowmu 20:30:44 03/01/10 (5)

RE: PSUD question - Ray Moth 21:23:25 03/01/10 (1)

Nice catch, Ray. - Poindexter 09:57:52 03/02/10 (0)

RE: PSUD question Jeff did you see my Capacitors post?? - Minussss3db 20:45:32 03/01/10 (2)

RE: PSUD question Jeff did you see my Capacitors post?? - tweakydee 07:00:46 03/02/10 (0)

RE: PSUD question Jeff did you see my Capacitors post?? - drlowmu 20:59:05 03/01/10 (0)

Follow Ups

I'll teach you how to fish - JLH 05:47:31 03/02/10 (2)

Your cast went way past my fishing hole, but it was a thing of beauty!:-) (nt) - twystd 18:06:45 03/02/10 (0)

Excellent post! - JoshK 07:41:52 03/02/10 (0)

I'll teach you how to fish

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