LM258A: LM258A/LM2904 Pls help to suggestion How to improved current sensing circuit operation range -20C to 80C ?

prarinya Maneechompoo

Intellectual 540 points

Part Number: LM258A

Dear All

Pls help to suggestion How to improved current sensing circuit operation range -20C to 80C ?

Test result is below .

@ 25C set current is 3.958A the output opamp is 2.493V the result is PASS

@ 55C set current is 3.625A the output opamp is 2.493V the result is FAIL because the power supply is not operation at max load(3.791A )

@ -20C set current 4.166A the output opamp is 2.493V the result is FAIL because the power supply is not protection by current limit ( 3.958A current limit )

Remark :

1.The maximum output current of PSU is 3.791A

2.Current limit is 3.958A

Thank you so much&Bestregard

Prarinya

over 5 years ago

0 Ron Michallick over 5 years ago

TI__Guru**** 152256 points

Hello Prarinya,

Using your data I see that the change in current from -20C to 55C was 541mA. This is a 5.41mV difference in sense resistor voltage. That is a big change. The 4.7uF direct capacitance on the output far too much. In general, there should be no direct capacitance on the output at all. Does removing this capacitor help? The feedback R and C has a crossover at 1Hz. Do you only want only the average current and can tolerate lag? Last but just as important, make sure that the 1.21k resistor and the non inverting resistor have a kelvin connection to the sense resistor.

0 prarinya Maneechompoo over 5 years ago in reply to Ron Michallick

Intellectual 540 points

Dear Ronald

Thank you so much for your help .Pls help again

How to adjust R-C network of circuit to meet current limit (3.958A ) in all temperature rang of device ?

Thank you so much&Bestregard

Prarinya

0 Ron Michallick over 5 years ago in reply to prarinya Maneechompoo

TI__Guru**** 152256 points

Prarinya,

Start by removing the 4.7uF capacitor. This may be all that is needed.

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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LM258A: LM258A/LM2904 Pls help to suggestion How to improved current sensing circuit operation range -20C to 80C ?