Author Topic: bipolar voltage / current source with current / voltage limit  (Read 1554 times)

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Offline wergorTopic starter

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bipolar voltage / current source with current / voltage limit
« on: August 16, 2020, 10:03:41 pm »
I'm designing a source measure unit which can output positive and negative voltages and currents. This is the circuit (simplified):
1048400-0
Here, V1 controls the voltage or current supplied to R_Load. VV and VC are voltages that represent the voltage and current at R_Load, respectively, and are both measured by an ADC. If VV is passed as feedback to U1 (via R4) the circuit operates in controlled voltage mode, if VC is 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:
1048404-1
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 pulling control towards 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?
« Last Edit: August 16, 2020, 10:31:33 pm by wergor »
 

Offline wergorTopic starter

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Re: bipolar voltage / current source with current / voltage limit
« Reply #1 on: August 21, 2020, 04:59:15 pm »
*push*
any ideas? The diodes D1 and D2 are not necessary, I accidentally left them in the schematic.
 

Offline Vovk_Z

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Re: bipolar voltage / current source with current / voltage limit
« Reply #2 on: August 22, 2020, 05:19:43 am »
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?
 

Offline wergorTopic starter

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Re: bipolar voltage / current source with current / voltage limit
« Reply #3 on: August 23, 2020, 07:43:09 pm »
It seems a bit sophisticated, but not too much.
what do you mean, exactly?
It'll give about +-10 V DC and no more then 0.1-1 A DC as I can see?
about +-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.
 

Offline Vovk_Z

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Re: bipolar voltage / current source with current / voltage limit
« Reply #4 on: August 24, 2020, 01:12:27 am »
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#msg3202124
about +-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.
What 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.
« Last Edit: August 24, 2020, 01:24:31 am by Vovk_Z »
 

Offline wergorTopic starter

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Re: bipolar voltage / current source with current / voltage limit
« Reply #5 on: August 24, 2020, 06:36:01 am »
What opamp do you plan to use to have 26 V DC output? Have you simulated this circuit?
LTC2057HV. I have and simulation suggests it works, but I'm always open for suggestions :)
R12 = 1R seems to much for a 3 A max current.
that's because it is ;) my planned design has selectable current ranges, where different value shunts are used in place of R12.
 

Offline Vovk_Z

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Re: bipolar voltage / current source with current / voltage limit
« Reply #6 on: August 24, 2020, 11:08:05 am »
60V power supply range, ultralow offset and comparably low price - good one, I haven't known about it.
 


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