EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: FullBridgeRectumfire on May 08, 2017, 05:44:27 pm
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Hi all!
I've been comparing various lab PSUs circuit diagrams and I came across this schematic from Agilent. Main principals of operation are more or less the same as in any other standard PSU, but I'm confused about the current sensing circuit. My question is how does the opamp (U26A) knows the voltage drop across a shunt resistor R66?
+25V_I_MON goes also to ADC, but i think that it's just for displaying current.
Full service manual (http://engineering.case.edu/lab/circuitslab/sites/engineering.case.edu.lab.circuitslab/files/docs/Agilent_E3631_Power_Supply_Service_Guide.pdf)
(http://x3.wykop.pl/cdn/c3201142/comment_07PKC0Lo3DieQRTXEhUA4yhOKwULzFEZ.jpg)
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Resistor R66 (and R67 likewise) is connected on one end to the common terminal.
This terminal also is the analog 'ground'.
So R66 provides a voltage relative to 'ground' proportional to the current.
This voltage is sensed by the current ADC for the display.
The CC opamp compares it to the CC reference (provided by the DAC) and will attempt to keep both the same.