| Electronics > Projects, Designs, and Technical Stuff |
| Replacing Zener with vreg? |
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| ogden:
--- Quote from: TERRA Operative on November 28, 2018, 06:15:55 am ---I need to make a friend at Mouser/Digikey who can go test a few diodes and just send me the good ones. ;D --- End quote --- You don't need to - because R7 trimpot is already your friend |
| TERRA Operative:
Alrighty, a bit of an update on the schematic. I updated it with a few corrections, which weren't completely clear from a cursory glance at the schematic. Most notably the + and - 6.3v rails from the zener at the top right corner and a few labels here and there. Might help make things clearer maybe. Also, re. the zener and R7, the different voltage (if it isn't 6.3V) isn't going to cause problems with the 'vref' input in U3 (AD7530LN)? |
| ArthurDent:
--- Quote from: ArthurDent on November 27, 2018, 01:59:28 pm --- The actual voltage of the reference zener isn’t that critical and is generally compensated for later in the supply circuitry. --- End quote --- As I said in my previous post, the actual voltage isn't that critical. The LM399 and LTZ1000 references HP has used in their most accurate and stable multimeters have a range of voltages and that isn't a concern because these are compensated for in the circuitry. As pointed out in your schematic, R7 is a gain adjustment to correct for the minor differences in reference voltages. You will gain nothing by trying to select this zener. |
| TERRA Operative:
Cool. I'll get myself a 1N828/829 and stick it in. Sorry if I sound stubborn or something, it's not that (well I am stubborn, but not right now. :D ), just that I am still learning this stuff so I'm still figuring out where I can and can't tweak numbers and values. :) |
| ArthurDent:
Here is a little more info on the circuit you want to recreate as I understand it. First, there is an error on the first 001 option schematic you show. The 100K pot marked R1 should be marked R8. Second, this 001 option only allows you to use an internal bias supply instead of using an external precision supply. This eliminates the need to use a separate supply to bias the DUT with up to +/-40VDC. There are two ranges on the internal bias supply of 0 to +/-10VDC and 0 to +/-40 VDC selected by the U6.2/U6.3 switch and U6.4/U6.5 selects polarity. I also assume R1-1 through R1-6 is a low temperature coefficient precision resistance module. Here is the adjustment procedure that indicates that the actual Zener voltage isn’t too critical because there is an adjustment on the supply to get the exact voltage HP wanted. |
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