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Building a symmetrical psu B1 buffer
Building a symmetrical psu B1 buffer
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Old 22nd February 2012, 02:57 PM   #2471
Salas is offline Salas  Greece
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Building a symmetrical psu B1 buffer
CCS current=((3xVf)-Vgs)/Rset. The strings of 5 are going to set the +/- Vo. CCS currents are to be in the same ballpark and Vo polarities near enough. If the DC offset is going to be low in the audio output that is the only important criterion.
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Old 22nd February 2012, 03:00 PM   #2472
KatieandDad is offline KatieandDad  United Kingdom
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So the 5V (3 x LED) are only setting the current through the regs.
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Old 22nd February 2012, 03:05 PM   #2473
KatieandDad is offline KatieandDad  United Kingdom
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I've got approx 5.38V and the series resistors are currently 22R

I'm aiming for about 200mA - I did ask earlier about the voltage across the series resistors but no-one replied.

Using my BJT knowledge. With Vb at 5.38V, Vbe=0.6V so the voltage across the Emitter resistors needs to be about 4.78V.

I=E/R so I would be 217mA with a BJT. If that is still true with a MOSFET, I just don't know.
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Old 22nd February 2012, 03:06 PM   #2474
Salas is offline Salas  Greece
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Building a symmetrical psu B1 buffer
Quote:
Originally Posted by KatieandDad View Post
So the 5V (3 x LED) are only setting the current through the regs.
Those, the particular Mosfet Vgs, and the particular setting resistor. PMOS and NMOS are not having the same Id-Vgs curve in most cases anyway, no same Mosfet is guaranteed to have the same curve, and so it goes. But not crucial at all.
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Old 22nd February 2012, 03:12 PM   #2475
Salas is offline Salas  Greece
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Building a symmetrical psu B1 buffer
IRFP9240 shows about 3.5V Vgs @ 0.2A and Tj 25C. The junction will go hotter, so something like 1.6-2V across Rset is probably expected given the variations. Most use 8R2-10R 5W for circa 200mA CCS.
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Old 22nd February 2012, 03:35 PM   #2476
KatieandDad is offline KatieandDad  United Kingdom
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So my 22R 3Watters may burn up then ???

I'm still not sure about the Nichicom caps. They do test OK.
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Last edited by KatieandDad; 22nd February 2012 at 03:41 PM.
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Old 22nd February 2012, 03:44 PM   #2477
Salas is offline Salas  Greece
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Building a symmetrical psu B1 buffer
They will just give less CCS current than you expected. Around 100mA maybe.
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Old 22nd February 2012, 03:49 PM   #2478
KatieandDad is offline KatieandDad  United Kingdom
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I can play around from that value.

Some guys have tried as much as 600mA.
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Old 23rd February 2012, 06:32 PM   #2479
KatieandDad is offline KatieandDad  United Kingdom
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Well I've finished the PSU part of the DCB1.

I've got +/- 9.58V give or take 10mV or one digit on the DMMs.

Running current with the 22Rs is 63mA - a bit lower than intended but everything is running cool.

The voltage seems to be dropping slowly as warm them up, not much but it started at 9.6V and after a 10 min test they were 9.5V.

The IRFPs have no heatsinking, they are cool to the touch.

Next step is to fit the elusive matched 2SK170BLs and then it's finished.
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Last edited by KatieandDad; 23rd February 2012 at 06:37 PM.
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Old 23rd February 2012, 06:56 PM   #2480
udailey is offline udailey  United States
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Building a symmetrical psu B1 buffer
Remember, they dont have to be matched. AndrewT has covered that multiple times.
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purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.com
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