JSR03 @ 43Vout

[raq]

Hi P-A,
Hi everybody,
I am trying to put together some calcs for 43V out w/ the JSR03 and parts I have available in my bin.
- op amp Vref - prob. (2) LT1034 Vrefs @ 2.5V, to make Vref 5V;
- I am not sure about Dz1, which should be half Vout; some low noise Vref? Any ideas?
- R8 ~ 7.6 kohm if R9 is 1kohm; R7 = R8IIR9 etc.;
- T power - D44H11 is fine.
Any thoughts?
Thank you,
Radu.

[raq]

...this might also exceed the ratings of LM317T. Vin max is 37V. Any workout available, P-A?...
Thanks much.
Radu.

[peranders]

LM317 = 35 V ACROSS Vin and Vout but if you use it you must have at least 5-7 Volts more than out.

Which opamp do you use?

[raq]

I am thinking MAX410, though I obviously have to sort out something about its power supplying (which maxes out at 12V). Maybe try a voltage divider @ R12 considering its current draw - 3.3mA). Or maybe altogether replace R12 with an 7810. Having said that, I do need to think well how split supply vs. single supply works in this case. Any indications or thoughts?

I can also use LM49710.

Also - I am considering three 14V LEDs for "DZ1" (half Vout). I like LEDs for low noise (and they look pretty cool too!).

Thank you, Per-Anders.

[raq]

...I think I have 47V Vin.

[raq]

...on the op amp:
- I like LME49710 (which worked for me well on my 7.1V application). MAX410 is not too likely to end up being my choice, due to very low voltage rating for Vs. I am unsure how that will interact with the relatively high Vout requirements of the application. 
- other possible choices: OPA227/228; LT1128; OPA27/37; and so on (134, 604, etc.). I lean towards trying OPA228 out, but OPA134 seems to be favored by you, so I'll give it some serious thought. I'm trying to roughly stick with the lowest noise, highest Vs rating option out there, as I will have to drop down from the 47V or so I have in.

Any specific suggestions or thoughts regarding this?

Thank you,
Radu.

[peranders]

R13 = 33 k
R11 = Adjust for the double current of the opamp supply current
Add a 33 V Zener across C10
DZ1 = 24 V

Reference voltage preferable 21.5 V and gain = 2

[raq]

Thank you for your input. Some more questions below.

> R13 = 33 k

I guess this is adjusted for safe LED operation @ roughly 43V.

> R11 = Adjust for the double current of the opamp supply current

I am not sure I understand this. I'd assume what I want is to drop Vs from the 43V to whatever's safe for the op amp by using a R. R calculated by Ohm to drop required V in relation to current drawn. Correct?

> Add a 33 V Zener across C10

Can you please explain? Would this not force the op amp to be fed with 33V? Which would limit choice of op amps considerably. 

> DZ1 = 24 V

I thought this needs to be half Vout, 21.5V

> Reference voltage preferable 21.5 V and gain = 2

Am I getting DZ1 and IC2 mixed up? On the schematic I'm relying on for this, the V reference for the op amp (LM431, for instance) is "IC2," while "DZ1" can also be an LED, per schematic.

Going back to Vref (IC2) - it could ultimately be almost anything, provided the gain is adjusted accordingly, correct? Is there a reason to keep gain as low as possible? Anything wrong with a gain of 17.2, for instance?

Thank you very much for your continued support!

[peranders]

The led should have approx. 1-2 mA

Check the datasheet of the opamp for supply current and take this times two. 43-33 = 10 volts across R11

DZ1 is a level shifter for the opamp output.

[raq]

The led should have approx. 1-2 mA

Check the datasheet of the opamp for supply current and take this times two.

I'm simply not clear as to where does that "times two" come from. For a moment, I thought it has to do with split vs/ single supply, but that doesn't make much sense

43-33 = 10 volts across R11

DZ1 is a level shifter for the opamp output.

Thank you.

[raq]

P-A,
Also... if you can help clear out something else for me - I am not sure which op amp is best suited for this application between the following four. OPA227 or OPA228? OPA27 or OPA37?
They seem to have some some specific differences which I am unsure how thwy relate with the JSR03.
Thanks!
Radu.

[peranders]

All will work but you must have a gain greater and 5 for OPA228 and OP37.

[raq]

Check the datasheet of the opamp for supply current and take this times two.

This questions still stands. Why would I calculate the power supplying circuits for twice the consumption of the op amp?
Thank you.

[peranders]

Because of the zener you must add. You must have some current through the zener. Notice also that it can be complicated to get this thing working properly so I can only give you hints. I have no time to really verify this change.

[raq]

Per-Anders,
Understood and thank you. I will test this and tweak these values if necessary, certainly. As before, chances are that this will add more proven setups to the library, and this would be pretty far off of ballpark, which is a good thing.
I appreciate you taking time with this.
Radu.