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LM2576: Problem Peak current

Yannick Yapo
Prodigy 70 points
Part Number: LM2576

Hello !

I have a LM2576 (TO-220) that heats a lot and sometimes disconnects. So, I decided to look the current which comes into the LM2576.

I did the test with a Resistor of 10 ohm as a charge. So the current provided by the LM2576 should have been about 500mA.

VIN = 31,6 V

VOUT = 5 V

Cin : 330uF ,50V , 580 mA

Cout : 680uF ,10V , 660 mA

D1 : 1N5822+

L1 : 150uH Irms 3.4A

Current IN :

How can I reduce these peaks?

  • 0
    TI__Expert 8130 points

    Hello Yannick,

    See comments below:

    1. Please isolate the power supply (disconnect from rest of circuitry) and monitor behavior. The waveform demonstrates an odd behavior as if there is still a load on the output demanding high currents. Plus, the 580mA input current measured is very high for a 500mA output. Provide test results.
    2. What was your output current when tested under the 10Ω? You mentioned "should have been about 500mA"? Did it result 660mA? Please clarify the confusion.
    3. The device sometimes disconnects because it is most likely triggering thermal shutdown. Make sure temperature ranges (ambient, junction, etc.) are within recommended operating range found in the datasheet.

    Thanks,
    Alejandro

  • 0 in reply to iAlejandro
    Prodigy 70 points

    1. Sorry :

    Cin : 330uF ,50V , 580 mA

    Cout : 680uF ,10V , 660 mA

    D1 : 1N5822+

    L1 : 150uH Irms 3.4A

    Was just the characteristics of my components, not the current.

    2.

    Current out : 

    And the Vout :

  • 0 in reply to Yannick Yapo
    TI__Expert 8130 points

    Hi Yannick,

    I would recommend to isolate the device when testing. I noticed there are high voltage spikes on the output. What is the output connected to? The circuit schematic stops at the filter.

    Regards,
    Alejandro

  • 0 in reply to iAlejandro
    Prodigy 70 points

    Hi Alejandro,

    Lately I had few issues with the LM2576 which was working fine. So I decided to do a simple test to simulate a charge.

    This is the test I did :

  • +1 in reply to Yannick Yapo
    TI__Expert 8130 points

    Hi Yannick,

    Thanks for the info provided, it is very helpful. I would recommend to test the following:

    1. Can you please also monitor the SW node, I would like to take a look at the behavior.
    2. I would recommend to place another 470uF in parallel with Cout. The device might be unstable therefore getting the following results.

    Regards,
    Alejandro