bipolar voltage / current source with current / voltage limit - Page 1
Forum section: electronics / projects

author: wergor
author_rank: Contributor
timestamp: August 16, 2020, 10:03:41 pm
content: I'm designing a source measure unit which can output positive and negative voltages and currents. This is the circuit (simplified):Here,V1controls the voltage or current supplied to R_Load.VVandVCare voltages that represent the voltage and current at R_Load, respectively, and are both measured by an ADC. IfVVis passed as feedback to U1 (via R4) the circuit operates in controlled voltage mode, ifVCis passed as feedback the circuit operates in controlled current mode. The BJT Q2 and Q1 limit the current through M1 and M2 to protect the supply. My circuit has selectable current and voltage ranges, but these are not shown.I want to add a means to limit the current while in controlled voltage mode and the voltage while in controlled current mode. My first idea was this:Here, positive and negative limit voltages are generated and fed into U6 (for the upper limit) and U7. If the voltage associated with the controlled variable (voltage or current) is greater than the upper limit voltage, U6 will output a positve voltage, making Q3 conduct, thereby pullingcontroltowards GND, lowering the output voltage. The lower limit works in a similar way, except that U7 outputs a negative voltage if the controlled variable drops below the lower limit.Simulations show that the circuit works as expected, at least with a resistive load (I haven't simulated with a source yet).Is there a better solution for this?

author: wergor
author_rank: Contributor
timestamp: August 21, 2020, 04:59:15 pm
content: *push*any ideas? The diodes D1 and D2 are not necessary, I accidentally left them in the schematic.

author: Vovk_Z
author_rank: Super Contributor
timestamp: August 22, 2020, 05:19:43 am
content: It may work, why not. It seems a bit sophisticated, but not too much.It'll give about +-10 V DC and no more then 0.1-1 A DC as I can see?

author: wergor
author_rank: Contributor
timestamp: August 23, 2020, 07:43:09 pm
content: Quote from: Vovk_Z on August 22, 2020, 05:19:43 amwhat do you mean, exactly?Quote from: Vovk_Z on August 22, 2020, 05:19:43 amabout +-26 V DC from a 30 V supply, depending on output current. the planned design will be able to deliver up to 3 A, having several push-pull structures in parallel.

author: Vovk_Z
author_rank: Super Contributor
timestamp: August 24, 2020, 01:12:27 am
content: It seemd sophisticated from first sight but then I remember you need bi-polar supply so it looks ok.Quote from: wergor link=topic=250822.msg3202124#msg3202124What opamp do you plan to use to have 26 V DC output? Have you simulated this circuit?R12 = 1R seems to much for a 3 A max current.

author: wergor
author_rank: Contributor
timestamp: August 24, 2020, 06:36:01 am
content: Quote from: Vovk_Z on August 24, 2020, 01:12:27 amLTC2057HV. I have and simulation suggests it works, but I'm always open for suggestionsQuote from: Vovk_Z on August 24, 2020, 01:12:27 amthat's because it ismy planned design has selectable current ranges, where different value shunts are used in place of R12.

author: Vovk_Z
author_rank: Super Contributor
timestamp: August 24, 2020, 11:08:05 am
content: 60V power supply range, ultralow offset and comparably low price - good one, I haven't known about it.