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vainajala

Switching power supply

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The TL431B can be viewed here: http://www.wb-power.com/bbs/u/20/1093886118.pdf If you f ex change R6 to 15k the output voltage will be 5Volts.

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Hello

I am on the lookout for a 12V 3,33A powersupply (for a TFT monitor), the one on page 54 looks almost simple, and it gives 3,5A 15V but that can probably ber changed easy. But what about the T1, there is no description of that? - or have I just missed it

another question is, if the TFT goes into power save or gets switched off, can the switchmode PSU deal with that?? (or does it need a minimum load?)

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Bikerman,

Got yourself a BOSS! Well, congratulations! ;D ;D ;D

About T1, I think you are right there is no description to be found here. Maybe an e-mail to onsemi will get you the data for the transformer. If you are lucky they might send you some samples of the MC33374 also. Please post the result if you get it the info.

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Guest Alun

Here's a very simple switching power supply I designed a couple of months ago to run 24V appliances of a 12V car battery. It's step-up only so it's probably of little for this application but if another coil was wound on to L1 thus converting it into a transformer it could be a step-up/step-down regulator too, current limiting might be possible as well. Let me know if you're interested.

Switch.pdf

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Hi Alun,

Welcome to this forum.

Nice and simple DC/DC project with good documentation, thanks! With some small changes it might be possible to run a laptop in your car with it. Most laptops run at 16

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Guest Alun

Ante, you could power a laptop as long as it doesn't mind some noise and the the supply voltage going up or down by a volt or so. I believe most laptops these days have a built in voltage regulator to provide separate 12V, +-15, 5V & 3V supplies or whatever modern computers need.

One thing I tried in order to improve the efficiency (but it didn't work) was to substitute Tr2 with a power MOSFET and connect the gate to ground with a reversed diode to prevent it from being destroyed by the negative pulse. The circuit would oscillate at very low voltages (1 to 3V drawing an amp or more) and higher voltages the it would latch on. I tried altering R1 and C1 also replacing L1 and altering the numbers of turns on the driver and feedback all to no avail.

Does anyone know how to make a MOSFET blocking oscillator?

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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?

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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?!

post-7158-14279142119385_thumb.gif

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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.

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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

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Guest 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?

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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)


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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.

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Guest 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.

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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

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Guest 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

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Guest 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

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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)

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