The simplistic Salas low voltage shunt regulator

[Salas]

It eats up >6Vin that is the thing.

[Salas]

Originally Posted by pidesd

ok. i might just not venture into paralleling shunt devices yet.

what do you think about those?

fqp4n20l
http://media.digikey.com/pdf/Data%20...s/FQP4N20L.pdf
zvn0124a
http://www.diodes.com/datasheets/ZVN0124A.pdf
IRLU024Z
http://www.irf.com/product-info/data...rlr024zpbf.pdf

Look how the capacitances enlarge the lower the Vds. Best is the 3rd one for low output voltages for instance. The middle depletion one is out of the question in any case with 0.1S gfs and no sinking ability.

[mns80]

Is it possible to get -3.5V out without modifying the second picture in post 3200?

[pidesd]

Originally Posted by mns80

Is it possible to get -3.5V out without modifying the second picture in post 3200?

no. because of the mosfet Vgs. maybe you could get -4V or so. But if you choose a lower Vgs mosfet, maybe you could, just like i m trying to do with the V1.1. i dont know anyone who has tried yet. (the reg you are talking about is attached)

[pidesd]

Originally Posted by Salas

Look how the capacitances enlarge the lower the Vds. Best is the 3rd one for low output voltages for instance. The middle depletion one is out of the question in any case with 0.1S gfs and no sinking ability.

yes the third one could be nice at high current, albeit being t0-251.

the little depletion one is rated 160 mA max continuous Id. But looking at the curves, i thought that a characteristic 0.4S and around 5pF Crss at 3.3V could be interesting to test, if only to know what benefit low capacitance can bring. Or maybe this is a bad idea altogether...? Moreover, a shunt device battle Bc560c vs little mosfet could be cool

for comparison, irf610 has around 50pF Crss at 5V and 0.4S at around 150mA and a better 0.8S at 500mA.

[pedefede]

Originally Posted by Salas

It eats up >6Vin that is the thing.

Quick test with DC in before rectifier diodes:

bib v1.1 has Vin = Vout + 4,3V
disco has Vin = Vout +4,0V

before Vout starts dropping.

So they burn approx the same on input ?!?

[Salas]

Gets more to be mains drop odds away. The disco can be made some less if you don't have enough Tx VAC installed. Let me know to see in to it.

[AndrewT]

check the voltage drop across the CCS resistor.

That suffers first when mains voltage drops.

If the CCS starts to lose Vdrop then it is no longer a CCS and the attributes of the CCS are lost.

The Shunt part attempts to compensate for the lost CCS current flow by reducing it's own bypass current in trying to maintain output voltage. The reduced current shunt is now not operating at optimum.

Checking output voltage vs input voltage is not the correct way to determine if the CCS + Shunt has sufficient supply voltage.

Check the CCS resistor voltage. It should be substantially constant over the full range of mains supply voltage.

[50AE]

Excuse me for this annoying and maybe repeated question, but can the transistors from the original schematics (like 2SCK170 or IRFP9240) be substituted with others - how critical is it? I plan using these shuns for the 3.3 and 5V rails for my DAC.

[Salas]

It changes the OLG etc. V1.1 uses K117 and TO-220s 9610/9530 and is quite proven. Make that.