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Registered Member #575
Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263
Hi, I am now planning building my first DRSSTC. I am aiming for a little one like Steve Ward's DRSSTC-.5.
Now to the question: I have been looking on a circuit that Dan made: And I think it is interesting. But I am going to use one of Steve's schematics to drive the DRSSTC and I want keep the CT's used to a minimum. Is there anyway I can connect only the LM3914 circuit to fit into Steve's typical LM311 over current circuit and still remain a good accuracy? I remember I saw a circuit that Reaching made, that was very interesting but I didn't manage to find it
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
No.
I'm sure you can easily connect the LM3914, but you won't correct the offset / gain due to the bridge rectifier diodes, etc...
Also, my circuit does require that expensive LT1630 op-amp as its rail-to-rail output unless you are using pos and neg rails.
Also, in my circuit, you can DELETE the U3 op-amp branch. All that is doing is giving you a setpoint display of the current limit. You don't need that. In fact, i don't use that portion either.
Registered Member #575
Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263
Ok, thanks.
In the thread you presents the over current protection you mentions that LM741 can be used instead of LT1630. If so do I need to do any adjustments to the circuit or can I just leave it as it is?
Also, If I decides to use your circuit can I then just connect it to the CT already used in the main driver circuit over current protection?
Registered Member #1024
Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95
Hi Christian, I may be wrong but I think you have answered your own question. You say your goal is to add LM3914 based led display to Steves LM311 based OCD whilst minimising CT count. Well pdf you posted is essentially exactly that. As DG mentioned above, you do not require U3 opamp section. -----------------------------------------
--------------------------------- The U1 section is basically the same as Steves LM311 section. So by adding the U4 branch, which provides the sample/hold required, and LM3914 page, you will have what you are after without having to have another CT. ----------------------------------------------
---------------------------- I have done this in my driver. --==Link==-- I DO NOT reccomend you use the circuit presented in my thread, stick to what is in the pdf you posted (I have since had to undo all my little cheats and corner cuts)
Registered Member #575
Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263
Dylan wrote ...
Hi Christian, I may be wrong but I think you have answered your own question. You say your goal is to add LM3914 based led display to Steves LM311 based OCD whilst minimising CT count. Well pdf you posted is essentially exactly that. As DG mentioned above, you do not require U3 opamp section. -----------------------------------------
--------------------------------- The U1 section is basically the same as Steves LM311 section. So by adding the U4 branch, which provides the sample/hold required, and LM3914 page, you will have what you are after without having to have another CT. ----------------------------------------------
---------------------------- I have done this in my driver. --==Link==-- I DO NOT reccomend you use the circuit presented in my thread, stick to what is in the pdf you posted (I have since had to undo all my little cheats and corner cuts)
Thanks, and I think you are right. The thing is that it wont be calibrated then. And I don't have a clue how I am going to calculate the right components to calibrate it. And I don't have CT to a oscilloscope so I can't measure that high currents.
Registered Member #1024
Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95
Mmm, well, its really not that hard to calibrate everyting. I assume one of your concerns is the accuracy of homemade CT's? If so , that was also one of my concerns, --==Link==-- So , you can pretty much do the math, and all you should need for reasonable accuracy is a multimeter to set the opamp pots.
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Need help: Overcurrent protection in a DRSSTC
