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| Power OP four quadrant bench supply |
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| Amper:
Hi! As usual i hope i didnt overlook some older post disgussing the same topic. Im the fortunate owner of two APEX PA03 Power OPs. These devices can run up to +-75V and 30A, have thermal protection and a nice salting of tasty beryllium oxide ceramics. Since my recent projects require battery simulation and a general high power for quadrant supply/amplifier would be an amazing addition to my lab id like to give them some housing work. My stuff usually only requires OPs in the basic use cases and i never had to come up with some design myself so i failed miserably at finding a solution my self. What i want to do is to use a second low power low voltage OP to measure the current over a shunt to ground like in a usual bench supply. The Voltage should easily be done by just amplifying a +-10V reference using the PA03 directly. But how do i get both at the same time? Since i want the current limit only to kick in at a specific value i suspect i need a diode for non linearity pulling "down" the voltage reference but what will happen in the negative case? I thought about anti parallel zeners but something doesn´t feel right. I hope someone understands my problem by the vague description given. It would be amazing if you could push me in the right direction. cheers |
| Kleinstein:
The cross over from voltage control to current control is indeed nonlinear. Using diodes is kind of a natural way. As far as I see it one would have too possible cases: 1) have a single set voltage and in theory independent positive and negative current limits. 2) have a set current and separate positive and negative voltage limits - this probably not the way it is wanted. So for case 1) it would be 2 separate circuits for the positive and negative current limit with a diode each to pull the voltage down or up. Quite often one might choose a symmetric limit, but would still have the 2 limiters. |
| David Hess:
You have it right; something more than a single diode connected current control loop is required. The examples I quickly found use a class-B or class-AB voltage output stage like your APEX PA03 and enclose it inside *two* diode connected current control loops with one acting on positive current and the other acting on negative current. This forum discussion shows some examples: https://www.eevblog.com/forum/projects/simple-4-quadrant-psu-with-remote-sense-please-recommend-topologyschematic/ The functional diagram of the LT1970 power operational amplifier also shows this configuration. |
| Amper:
Thanks! Yes, i played a bit in lt spice yesterday and when i went to bed i noticed my mistake. Two current setpoints is just not enought even when you want a symmetric output limit. The anti parallel zeners worked but then other quadrants didnt do what they were supposed to. If i find the time ill play around a bit more and give you an update what i will come up with. |
| duak:
Amper, you may also wish to look at the hp 6825A to 6827A bipolar power supply amplifiiers. There is a write up in the hp Journal from July 1974. www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1974-07.pdf Kepco made similar instruments, the BOP - Bipolar Output Power supplies. Most of the manuals available on line show the block diagram and give an idea of how they work. Cheers, |
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