multiple SMPS Voltages

[muhammadali_16]

you mean to say that this is because of the fluctuation in feedback voltage? and by the use of capacitor, it will be smooth?

 

[goldsmith]

No No NO ! of course i'm not meaning that it is due to the instability of feedback loop ! however it can has a little effect on these overshoots . did you get my idea ? my idea is decreasing ESR and ESL . replace that 1000 u capacitor with some low value capacitors in parallel and at last an MKT capacitor ( 100n) in parallel with all of them . you understand ?

 

[muhammadali_16]

ok.... i got your point. i will try it. should i use that feedback loop capacitor also?

 

[goldsmith]

feedback loop capacitor ? are you referring to the capacitor in parallel with R1 ?

 

[muhammadali_16]

yah. on feedback voltage

 

[goldsmith]

We have two voltage divider resistors . the top one called R1 and below one called R2 (if) then use a 10 uF capacitor in parallel with R1 . it will help to reduce fast changes .

 

[muhammadali_16]

thanks so much for your help!

 

[muhammadali_16]

i did what you ask for. but have the same problem after changing the capacitors. i connect 104 and 100uF capacitor (Previous 1000uF) one by one, but the same result

i have attached the waveform of the noise. kindly tell me what should i do

 

[goldsmith]

did you used just a 100 u ? i told that you have to use some capacitors in parallel ! just 100 u ????

 

[muhammadali_16]

i used 104 (100n), 103(10n) and 100uF. how much more should i use

 

[goldsmith]

just a 100 u ? use 5 , 100 u cap in parallel . and tell me the result . if the result was the same , you have to add auxiliary filter in out put .

 

[muhammadali_16]

tell me about that aux filter. tomarrow i will try for capacitors first and then will go for aux filter

 

[goldsmith]

there are two type of filter as auxiliary filter , first one is an LPF with L and C without diode ,( it is after the main filter ) ( by the way , has the core of your main filter any gap space ? )
and second type is kind of differential filter , ( such as filters that we using as EMI filter .)
Good luck
Goldsmith

 

[muhammadali_16]

refer me some type of circuit. i am not at the stage to study it. i have to give my boss the operational PSU. after that i will study. but now i want to know that components which i should use to have the perfect result

 

[goldsmith]

At first test those capacitors , and at second tell me the specifications of your SMPS , ( frequency of operation , arrangement , and value of your out put filter, and voltage before your filter ( square wave ) and after it )

 

[muhammadali_16]

my operational frequency is 100KHz. i have used SG3525. output voltage is 3.5V and 3A. Input is 24V. Mosfet is used irf540. for filteration MUR3020 (using Push-Pull Terminology). inductor of value 22uH. feedback is connected at the output to SG3525. i dont have the exact voltages of transformer input and output

 

[goldsmith]

is your push pull , in current mode or voltage mode ?

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and how much is the voltage after rectification in secondary ( before filtering )

 

[muhammadali_16]

i have not check the voltage independently before filtering. Voltage mode of Push-Pull is used

 

[goldsmith]

What kind of compensation network you have used ? and how you don't know the voltage before your filter ? how you have designed your circuit ? it is pretty important to know the voltage before your filter .
Best Wishes
Goldsmith

 

[muhammadali_16]

SG3525 have opamp in it for comparing the voltages of reference and supply. i just adjust reference voltage and voltage divider on the supply voltage.
i really didnt remember the voltage before the filteration

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SG3525 have opamp in it for comparing the voltages of reference and supply. i just adjust reference voltage and voltage divider on the supply voltage.
i really didnt remember the voltage before the filteration

- - - Updated - - -

SG3525 have opamp in it for comparing the voltages of reference and supply. i just adjust reference voltage and voltage divider on the supply voltage.
i really didnt remember the voltage before the filteration