Switching power supply

[sangj]

this is my first visiting to this forum.your discuss is very particular. I have designed a SMPS with TL494,the out put is 27V/8A,using halfbridge topoligy.But the temperature of transformer is very hot,the transformer is EER42. Who can tell me how to chose the correct transformer?

 

[ante1]

Hi sangj,

Welcome to this forum.
Can you post the schematic?

 

[rplink3r]

I need a simple 9V isolated supply for my multimeter.


I have many coils, from ATX power suppys lying around in my junk staff, but i dont know how to use them. I tryed with ne555 and a power fet,on freq 150kHz,but the fet got too hot, and i had to shut all down :-\.I tryed many things, on the primary, secondary,the result was always the same.

PLZ HELP?!

View attachment 36582

 

[audioguru2]

Hi RP,
Welcome to our forum.
The data for the 2SC4977 recommends 50KHz switching. Its Tr=1us, Tstor=2.5uS and Tf= 1us. Their total time is 4.5us, which is much longer than 1/2 cycle of 150KHz.
No wonder it heats, it is ramping instead of switching.
What is your load current?
What is the value of Rout feeding its base?
What part number are D2 and D5?

Try it at 50KHz or lower.

 

[computron4]

you said it was the board detecting teh extra flow im just a noob but you might try bypassing the sensor if you want more voltage than it will let you have a way you might bypass it is to solder a wire to the connector and solder it to the next componet

 

[Alun]

Hello Guys! how are you?

Well i wna make switched mode power supply would u like to help me please!

Hi Junaid,
Please be more specific
Output voltage and power level?
Input voltage?

 

[ante1]

Hi rplink3r,

How much current does your multimeter need? This circuit seems a bit "overkill" for the purpose.

 

[devilson]

Is there any Schematic on Switch Mode Power Supply using mosfets such as PNP n NPN tat can reach up to 10A? This using a full bridge inverter to control the current of the supply. Thank

 

[ante1]

Hi devilson,

Welcome to our forum,

You have to be more precise, I do not know of any mosfets which are NPN or PNP. Mosfets are usually P-channel or N-channel and bipolar transistors are NPN or PNP. You do not give any data for input and output voltage so it’s not easy to understand what you need. 8)

 

[Alun]

Yes we do, click here to get to the thread, you can also search the forum by clicking on the button at the top of the screen.

Could the moderator please append this to the thread in question.

 

[ante1]

Alun,

Where in this thread “do we” find NPN and PNP mosfets? And did I miss something, like the input and output voltage somewhere in the post?

I didn’t think the question gave enough info to fully give correct advice, but since you apparently do… go ahead.

 

[Alun]

I agree Ante, more information would allow us to help,  but I was just pointing him in the right direction as well as asking the moderator to move it. ;D

I've seen people getting confused about N-channel and NPN transistors too, I'd recommend a MOSFET anyway.

 

[soon1401]

Hi,

Glad I found this forum. I am trying to buld a AC-DC SMPS base on TI chip UCC28221 (see attachment) using the interleaved forward topology. The apps note provided by TI is configured for DC-DC at 36-75VDCwith the output of 12V, 16.67A . I am trying to modify the circuit to AC-DC at 195-265VAC with the output of 24V, 25A. Iam having some problem on the main transformer part. I really do not understand how to design the transformer for the system. Can any of you guys help out?

200-W_Interleaved_Forward_Converter_Design_Review.pdf

 

[Alun]

Here's an interesting simple switching regulator circuit the author says it's over 90% efficient but mine design was only 85% efficient at the most and it's step down (mine is step-up). I wonder if he could tweak my circuit to 90% - shame I couldn't find his email on the website or I would've sent him the design. ;D

 

[SM2GXN]

Amazing that he could get that high efficiency with a ratsnest like that, guess there has been some tweaking. What I've read the layout is rader critical to get those last percent of efficiency out of a circuit. Must say that it was an interesting switcher.
Alun do you have LT,s switchercad? If so, try to simulate the circuit just to see how it match the real one.

Bjorn

 

[ante1]

Hi Guys!

I have built a”converter” once, without any transformer to produce 28Volts from 12Volts. But I never measured its efficiency! I think it was good though becurse it run cool at 2.5A!  8)

 

[Alun]

http://www.romanblack.com/a04.htm
Add an extra transistor and you can have currewnt limiting, in fact if you removed the zener and set RS to the right value for the forward cuurent you want, you'll have a switching constant current source which would be ideal for powering high intensity white LEDs.

 

[ante1]

Hi Alun,

I found it! Maybe you can calculate the efficiency, since you are good with figures? 8)

View attachment 37465

 

[audioguru2]

Hi Ante,
That's a cool charge-pump circuit. ;D
The current through the zeners is about 20mA continuously, and the transistors will drop out of saturation if the total load current exceeds about 200mA for each transistor if they are weak.
Therefore the efficiency is about 95% before adding the 0.5V saturation loss of each transistor. ;D

 

[ante1]

Hi Audioguru,

Thanks for the assessment, what’s the bottom line then? The darlingtons have more than 1000 in gain so there is no problem. The converter put out 2.5A for hours and stayed cool! 8)