multiple SMPS Voltages

[goldsmith]

Hi again
What do you mean by around 12.8 ? are you referring to the voltage ? or current ?

 

[pol]

bothly

i want the output 13,8 v.i=0,5...

 

[goldsmith]

I completely understood that what you need . can you show me the circuit ? perhaps thus i can find the problem .

 

[muhammadali_16]

hizzzzzzz ....

i want to know sumthing from u. u told me abt the snubber but i hvnt implement tht. im little confused abt the what u told me..


u said me that i should use the oscilloscope to note the noise frequency and then calculate the exact snubber resistor and cap.... i want to at which terminal i should check the noise in the push-pull scenario?

 

[goldsmith]

Dear Muhammad
Hi
Where is the place that you want to use snubber in parallel that ? of course your transformer . right ?
So , you should see the voltage across the transformer .
Best Wishes
Goldsmith

 

[muhammadali_16]

rite...... u mean to say that that i should check the output wave of transformer and then analyze the the noise?

 

[goldsmith]

the voltage across the transformer .

 

[muhammadali_16]

thx so much for ur help.......!

 

[muhammadali_16]

i hv tried now. my noise period is 116ns which make 8.6MHz. im confused how i select th Resistor and Capacitor value. kindly tell me how to calculate it

---------- Post added at 09:47 ---------- Previous post was at 09:45 ----------

i hv tried now. my noise period is 116ns which make 8.6MHz. im confused how i select th Resistor and Capacitor value. kindly tell me how to calculate it

Dear Muhammad
Hi
See below , please :
View attachment 71895
View attachment 71896
Now i show you a wave form with zoom in .
View attachment 71897
So , what is the frequency of those damped oscillations ?
So i have designed an snubber network to improve those oscillations . see below , please :
View attachment 71898
View attachment 71899
Best Wishes
Goldsmith

 

[goldsmith]

Hi muhammad
I have calculated it for you . R=10 ohms and C= 2.2 nF .
Can you tell me that how i calculated it ?
Best Wishes
Goldsmith

 

[muhammadali_16]

how you calculate?????

 

[goldsmith]

Muhammad
I think i told you the way . you can select one of the components randomly and then the equation will give you the other one . but most important think , here is the value of R should be low .
Good luck
Goldsmith

 

[muhammadali_16]

my noise pulse time period is 116ns which make its frequency 8Mhz. how you can say that Fr=1/2 *R*C can be useful.

you mean to say 8MHz=1/2 * 10ohm * 2.2nF ????????

 

[goldsmith]

AT first , 1/2RC isn't correct . 1/2*pi*R*C is correct . i think you misunderstood my meaning . did you read that post that i explained the snubber design in that really ? if you read it , did you understand it ?

 

[AMSA84]

Hello there guys,

I know that goldsmith has suggested me a thread that the topic was about doing some calculations, but even though I can't understand one thing, and this thing is related to the practical way to implement. For example, the "size" of wires, why to choose one determined king, the core, how can we determine which core to use - first we do the math and after that we get the dimensions of the core? But we need more specifications from the core, regarding this, the store where I'll buy the core will provide that kind of information? I read that we need to have in consideration so many aspects to build the core like "spaces" between the sides of the core and the turns, etc.

There is any tutorial that demonstrates how to build a transformer?

BTW, the considerations to build a transformer to a simple direct converter is different to the flyback? Which are the main differences?

 

[goldsmith]

Hi my friend !
I'll attach a table , that you can select your desired core according to that , but if i forgot , recall me please . ( these days i'm pretty busy , hence it is possible that i forget ) .
Best Wishes
Goldsmith

 

[muhammadali_16]

hi goldsmith....
i have a very problem. kindly reply me as soon as possible.

i have designed a power supply of 3.5V. when i connect the oscilloscope at the output voltage, i experience a very horrible noise.
the noise has 40nS period, max voltage is 6V and min voltage is 2V. i am very puzzle of what should i do.

kindly help me out...
i am waiting for ur reply

 

[goldsmith]

Hi muhammad
I know exactly what you saw in your oscilloscope . what is the value of your out put capacitor ? and how is your feedback network ? with tl431 and opto coupler ?

 

[muhammadali_16]

i have used 1000uF. didnt used tl431 n optocoupler (its DC to DC converter). have used sg3525 with direct feedback

 

[goldsmith]

Muhammad , do you know what is TL431 ? it is a variable zener diode , that made for isolated feedback applications . i know you are using SG3526 . but is your feedback isolated ? or just two resistors ?
I have been suspected that you have used just a large value electrolytic capacitor ! use a 100n capacitor in parallel with that and if the problem still be available , replace that 1000u capacitor with some electrolytic capacitors and a 100 n MKT capacitor . thus the problem will solve . the only cause can be the large value of ESR and high value of relaxation !!
Good luck
Goldsmith

- - - Updated - - -

( some electrolytic capacitors in parallel !)