Electronics > Beginners
High side current sensing circuit gives wrong voltage.
Grzegorz2121:
Welcome!
After years of thinking I finally managed to make a voltage regulator section of my homebrew lab power supply that doesn't oscillate.
Now I'm tying on adding the current regulator section.
Schematic is attached bellow.
My thinking path went like that:
I need a current sensing resistor before the load to not influence it.
I have bought OP07 for this job but it cant survive 30 volts to the input.
So I created two ~5 ratio voltage dividers to lower the max voltage on the op amp input.
Then I created a 5x gain differential amplifier to compensate for those voltage regulators.
The output couldn't go to 0 so i decided to add a negative power supply.
Then i realized that the output voltage is negative... (In the real circuit)
So to debug it I created a simulation and... this simulation doesn't work neither...
I would ideally want 50x gain to compensate for that 0.1 resistor. But i don't think i can achieve it without
using stupid values like 1Meg (I might try but it doesnt work for 5x neither)
Can somebody explain me why doesnt this circuit behave like i designed it to work?
David Hess:
It looks like it should work but in real life, the tolerance of the resistors limits performance. Better is to use a singled ended high side current sense circuit. The only restriction is that the common mode input range of the operational amplifier needs to include the positive supply.
http://www.circuitdiagramworld.com/monitor_circuit_diagram/Current_Monitor_CIRCUIT__LM301A__457.html
jmelson:
You might look at the LTC2057 (or LTC2057HV) high voltage op amps. The HV version is rated up to 60 V supply voltage. I used these in a high-side sense setup and it worked well.
Jon
Grzegorz2121:
I have few trimmers so the resistor accuracy isnt a problem. I will check the board again and post some pic to make sure everything is connected properly.
The most interesting thing is that the output works but it is negative...
The simulation that i made gave me 6V... on the output. Do anybody have any idea why it is so?
edit:
I would like to stay with that amp. I dont have means to get a different amp.
StillTrying:
On that pic of the simulation the -5V is wrong, a double negative!
Navigation
[0] Message Index
[#] Next page
Go to full version