Alw,Jan didden, Guido please help with TL431

[jackinnj]

Konnichiwa,

Using a passively and actively filtered buffered reference is where a good reference is needed is again obvious, however you really need to dig out low noise Op-Amp's to equal simple transistor shunts.

Sayonara

You have to push the dominant pole of the error amplifier control loop to a point at which the whole shebang is nimble and stable -- just like "Goldilock's " porridge -- not too hot and too cool.

 

[kimschips]

Thank you all.

But I think you are going a bit too far now

My questen is to decide how to decouple a digital psu for a new dac psu with:
TL431->ferrite bead//capacitor//capacitor

1. option Digital chips
TL431//220uf Oscon//Ferrite bead->22uF Oscon//0.1uF//0.01uF ceramic multilayer cap.

2.option for Dac (2VD and 2VA dualmono)
Lm337->CCS->TL431//220uF BGNX-HIQ->Ferrite bead->22uF//0.1uF BG nX-HIQ

Datacheet for ferrite bead
http://www.farnell.com/datasheets/65013.pdf


Any source for cheap Oscon (EU country please)???

Kim

 

[kimschips]

Sorry Per-Anders it´s Onsemi that have a TL431 with 48nV
Texas got one with 140nv@100Hz

Anyone know how to read stability curve page 7 here?

http://www.onsemi.com/pub/Collateral/TL431-D.PDF#search='tl431'

Kim

 

[peranders]

Deside which current you plan to use. Then you have capacitance less than a value and higher than a value which you must use. In the middle you have forbidden values of the decoupling capacitors => unstability

More than 10-22 uF is usually safe and nothing at all which works fine if you have a LP-filter and a buffer afterwards like here. Check IC4, R8 and C7, C8

 

[ThorstenL]

Konnichiwa,

My questen is to decide how to decouple a digital psu for a new dac psu with:
TL431->ferrite bead//capacitor//capacitor

Place at least 5-10uF in parallel with the 431.

Consider placing the ferrite beads in series with the CCS, before the 431. Consider using a cascoded CCS to keep the shunt capacitance low.

Then use a bypass combo where the bypass capacitors have values of ESL & ESR that make sure that together with the various capacitances and the inductive equivalent reactance of the 431 you get a supply line impedance without significant resonance effects. Blindly throwing "boutique" parts at the circuit does not help, you need to conciously and deliberatly select the right parts.

An example may be seen here:

An externally hosted image should be here but it was not working when we last tested it.

I designed this circuit to power the TDA1545, but if you change the CCS for more current.

Any source for cheap Oscon (EU country please)???

I get mine from www.cpc.co.uk

Anyone know how to read stability curve page 7 here?

http://www.onsemi.com/pub/Collateral/TL431-D.PDF#search='tl431'

Yes, same way as all the others, the areas where the 431 is stable are marked "stable", as you can see there are multiple curves drawn for different voltages set, curve B applies for 5V, UNLESS you bypass the Vref 2 K resistor with a capacitor in which case curve A applies under all conditions.

Sayonara

 

[kimschips]

Hello Konnichiwa.

That is exactly what I had in my mind!!

It´s also what Pedja have made with his Non os dac

I will just replace the:
4700uF cap with 2200uF BG-FK->22ohm->2200uF BG-FK
100UF bypass + decoupling with BG-N or Oscon
The LM334 with Led+D44H11 (50mA CCS, 2 for each chip)

Top 1K resistor in TL431 with 320ohm to get 3.3V

In the end (VD 3.3V):
LM337->CCS->Wire from prereg pcb to Dac pcb->Ferrite Bead->TL431//22uF Oscon//0.1uF//0.01NF ceramic

Have you simulated your setup with the TL431?


Thanks
Kim

 

[apolon34]

I think 50mA ccs is not enough. Since you output 3.3v, I think you should go up to 75-80mA to ensure good operation of tl431 and make sure you doesn't run out of current for the dac.

just put an heatsink on d44h11, depending on your input voltage and it'll be fine !

remember that d44h11 as low hfe so load your led enough (7-10mA)

 

[kimschips]

I think 50mA ccs is not enough. Since you output 3.3v, I think you should go up to 75-80mA to ensure good operation of tl431 and make sure you doesn't run out of current for the dac.

Thanks for the tip.

That will be one lm337 and 4CCS for the digital chips

At the pre reg board:Could you replace LM337 and the 4 CCS with one super jung reg, just connect the 4 ferrite bead at the dac board with 4 wires-->Nice and cheep solution if people want it more simple??

Now people let´s go on with the psu for the 2*Pcm1798 Dac

Any one with a solution here?

Kim

 

[kimschips]

Hello

Thanks for all your inputs

The schematic for the project can be seen here:

http://www.diyaudio.com/forums/showthread.php?s=&postid=731045#post731045

Later we will start making the pcb!!

Thanks for all

Kim