Electronics > Beginners
TL431 linear power supply
<< < (22/32) > >>
iMo:
In the below schematics:
1. with C2<1n loop oscillates
2. with C1<220n loop oscillates
3. C3 is not critical
With the values as depicted it seems the response is "the best".
Mind it is an simulation only.
Kleinstein:
The values of 1 nF and 220 nF look much more reasonable, maybe a little on the fast side.

For the regulator it could help to have a capacitor with noticeable ESR at the output. So something like 100 µF with 0.1-1 Ohms in series. 
iMo:
Needs more tuning :)
Kleinstein:
For tuning it can help to look at the response in the frequency domain, e.g. with a load as AC current sink (at both a low and high DC current). For the final tuning also C3 would come in. I would expect a smaller value here to be better. Another point to adjust could be the 56 Ohms resistors - they don't have to be the same. A little more at the emitter could be better if C3 is there.
blackdog:
Hi,

Imo, try  this if you want to test.

Remove Q3, R5, C1 and R7.
Use a diode between R1 (make him 100 Ohm) and the anode of the diode on the base of the BD243.
Place a 4K7 resistor between the base and the emittor of the BD243.
Make the currend source I1 10mA.

Make C2 220pF (play with it for good stability)
Make V3 30V
Connect V2 opamp power supply to V3, so remove V2.

Watch your opamp inputs, are they still connected the wright way in this test setup?

The problem with the schematic and many schematic of power supplys.
The average opamp has between 55 and 65 degrees phase margin.

And for a good stable linear power supply, you need at least 45 degrees phase margin, 60 is better.

If one or more transistors are behind the opamp, these transitors slow down the loop in which the opamp in the transistors is placed.
These transistors all eat a bit of the phase margin.
Below the 30 degree phase margin you come into the danger zone.

Please , please, please, do not disregard this information, because it always goes wrong if you do this.
It doesn't matter if you are developing a linear or a switching power supply or an electronic dummy load, this is always the case!
See my previous post with links to info on this topic from the TI website, first class info from TI!


Kind regards,
Blackdog
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod