The simplistic Salas low voltage shunt regulator

[Salas]

Edit: It is actually measured at output of the prototype, but I think the noise is just below/on level with my scope... Quite amazing giving the circumstances

Then where's your hum needle at 50Hz on second pic? Maybe you had the probe at a better angle to the toroid?

[judby]

Originally Posted by Salas

So you know you at least hit your test gear floor level apart from a bit of hum pick up (move that toroid a bit). OTOH you don't know if you really are even below. What lab PSU model?

No, I don't, I only have cheap hobby gear
The PSU just says "PS3005" - it gives me max 35V and 5A.

[judby]

Originally Posted by Salas

Then where's your hum needle at 50Hz on second pic? Maybe you had the probe at a better angle to the toroid?

Probably "drowned" in noise b/c we are at the limits of the equipment. It is visible on my "audio range" picture.

[Salas]

Originally Posted by judby

No, I don't, I only have cheap hobby gear
The PSU just says "PS3005" - it gives me max 35V and 5A.

Should be a Mastech or clone. ELFA lists one such linear PSU.

[judby]

Originally Posted by Salas

Should be a Mastech or clone. ELFA lists one such linear PSU.

Its from ELFA It was a bargain of about €100 a couple of years back. My previous lab supply currently serves as psu for my friends B1...
Yes it has taken us a couple of years to get back to this diy project - he's very happy with his B1 (prototype, with black gates, tantalum resistors and all) :-)

[Salas]

Originally Posted by judby

Probably "drowned" in noise b/c we are at the limits of the equipment. It is visible on my "audio range" picture.

Here its visible again slammed against Y axis.

[Salas]

Originally Posted by judby

Its from ELFA It was a bargain of about €100 a couple of years back. My previous lab supply currently serves as psu for my friends B1...
Yes it has taken us a couple of years to get back to this diy project - he's very happy with his B1 (prototype, with black gates, tantalum resistors and all) :-)

Very practical boxes for prototyping work non the less. A TTi (Thurlby Thandar) with remote sensing, digital control & keypad may wait for better days.

Just keep your DC cables to B1 short and your toroid away in the end installation. Have fun.

[judby]

BTW: Have you seen this behaviour before - that the CCS delivers less current with increasing input voltage?
I assume I'm seeing it because of a combination of lower current (100mA) and different FET (IRF9610).

[Salas]

Not in my old tests with resistor divider bias, one Vbe control and bootstrap cap as far as I remember, but that has to do with the voltage level and BJT bias too. Maybe it got a bit hot as you were going up with 4k7 only, or has other Hfe. And it wasn't your Mosfet type or CCS level either, correct.

[judby]

Sorry, I'm not sure I understand.

My FET is IRF9610.
The BJT didn't get hot.

I just saw that the current decreased when input voltage got above some 21-22V and was slightly puzzled.
Only thing I could think of was that the FET (9610) needed less Vgs for the lower I (100mA) and different type (not IRFP9240), then the BJT needs to drive more current through the 2x 4k7. I changed them to 10k and it improved a bit.
Changed them to 47k and it worked, atleast up to 35V