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| Is OPA277 a good op amp for an electronic DC Load? |
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| Paul Rose:
Is this this http://www.scullcom.uk/category/projects/dc-load/ the project your are using for inspiration? It is using an AD8630 in its driver with a positive supply of 5 volts and a negative supply at ground. The AD8630 is rated for "5 V single-supply operation". But the OPA277 requires inputs to be 2 volts inside the supply voltages ( 2v below v+ and 2v above v- ). If you try to run OPA277 from single supply 5 volts, your input would have to be in the range +2 to +3 volts. I think the final version of that project did use OPA277 in its volage sense amplifier, but it generated a -5v rail for its negative supply. |
| Prithul0218:
--- Quote from: Paul Rose on January 17, 2019, 02:43:06 pm ---Is this this http://www.scullcom.uk/category/projects/dc-load/ the project your are using for inspiration? It is using an AD8630 in its driver with a positive supply of 5 volts and a negative supply at ground. The AD8630 is rated for "5 V single-supply operation". But the OPA277 requires inputs to be 2 volts inside the supply voltages ( 2v below v+ and 2v above v- ). If you try to run OPA277 from single supply 5 volts, your input would have to be in the range +2 to +3 volts. I think the final version of that project did use OPA277 in its volage sense amplifier, but it generated a -5v rail for its negative supply. --- End quote --- Yes! I'm using that as inspiration. I will use higher voltage since OPA277 can handle it. I will be using a transformer to generate 12V,5V,-5V rails. and 4.096V, -2.5V reference. for current nulling. Same way Louis Scully did. |
| Kleinstein:
The suitable OPs depend on the supply and the use in the circuit. The OPA277, OP07 and OP27 all need a negative supply. The buffer for the cheap DAC is not that critical - here it's more the question if one needs one at all. So the OP0 would be well good enough here. The critical OP usually is the one amplifying the low voltage signal from the shunt. This could be the same OP driving the MOSFET, but could also be an amplifier stage first. The OPA277 normally is rather expensive, usually more than the OP27 and way more than an OP07. The OP27 is rather fast and could thus tend a little more towards oscillation. With no scope, it would be a good idea to first simulate the circuit. One might also use a simple AC detector to at least get an idea of the amplitude of possible AC signals. |
| Prithul0218:
--- Quote from: Kleinstein on January 17, 2019, 03:02:36 pm ---The suitable OPs depend on the supply and the use in the circuit. The OPA277, OP07 and OP27 all need a negative supply. The buffer for the cheap DAC is not that critical - here it's more the question if one needs one at all. So the OP0 would be well good enough here. The critical OP usually is the one amplifying the low voltage signal from the shunt. This could be the same OP driving the MOSFET, but could also be an amplifier stage first. The OPA277 normally is rather expensive, usually more than the OP27 and way more than an OP07. The OP27 is rather fast and could thus tend a little more towards oscillation. With no scope, it would be a good idea to first simulate the circuit. One might also use a simple AC detector to at least get an idea of the amplitude of possible AC signals. --- End quote --- Since I already have a few OPA277, it's actually less costly for me to use that then buying OP07 (and also waiting for the slow China posts). So, maybe I should go with OPA277? |
| exe:
I'd start with requirements. Chances are, a cheap opamp like tl072 or lm358 will do the job (the latter one can go quite close to negative rail). |
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