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LM2576 output voltage saturation at no load

Bassem Abouzeid
Prodigy 10 points
Other Parts Discussed in Thread: LM2576

Hi all,

 

I have built an adjustable power supply based on an Lm2576. the specifications are as follows:

Vin = 24V

Vout = 1.23-20V @ 1.5A

The inductor value is 220uH, Cout = 1500uF, Cin = 470uF, R1 and R3 are 1K6 and R2 is a 25k pot.

R1 Connects between one terminal of the potentiometer and ground. R3 connects between the inductor and capacitor junction and the other end of the potentiometer. The pot terminal connects to pin 4 of the regulator.

i have commenced testing this circuit at no load, however have'nt been successfull thus far.

The output voltage swings between around 6V and 1.23V as I vary the pot.

The voltage slowly ramps up to 6V and saturates at that level.

I have tried changing over the regulator and have downsized the output capacitor as well, however the issue was not resolved.

Can anyone please offer any insight as to why this might be happening?

  • 0
    TI__Guru 57555 points

    Connecting a pot with long leads to the FB pin is not a good idea.  This will cause noise pick-up and an unstable output.  Even using a trim pot on the board can be a problem, in some cases.  These parts are not meant to by adjustable in this way.

    FD

  • 0 in reply to Frank De Stasi
    Prodigy 20 points

    hi every one ! i have to make power supply for gsm sim 900, and i have tried this with lm2576 regulator, but i failed...i have used the basic power supply design for lm2576 http://e2e.ti.com/support/power_management/simple_switcher/f/858/p/255499/1039477.aspx#1039477 but at the output i dont get 5 volts, i get the output voltage equal to input... i dont have IN 5822, any schottkey diode so i am using simple diode , and inductor of some different value, so i guess becoz of these two i dont get the desired output,, am i ri8??can i use simple diode or zener diode instead of schotkey, plz help me out in this

  • 0 in reply to ash ali
    TI__Genius 15810 points

    Hello,

    It'd be helpful to see a schematic of your implementation. But as such you should use a schottky diode.

    Regards,
    Akshay