insolated PS

[alberto110]

Hi
I want to build a simple switching PS . and before that simulate with proteus .
for transformer i dont know differnces between saturated trans and simple trans . i use an square wave gen with 20Khz by 555 timer .
the only things i want is to isolate between input and output finaly i regulate the voltage with 7805 . commerical PS is expensive .
thanks alot

[pickit2]

what voltage are you using for input ? example 12-24Vdc, 110Vac or 240Vac (where you live might help too)
next what current do you want out. (by using 7805 it must be about 1Amp)

As for proteus you can use a generator to replace transformer, for simulator.

[alberto110]

48 as input
output 9
max 500mA current need .
specially i need to simulate transformer response . then i need to use transformer in simulation .

[sam_des]

Hi,

48 as input
output 9
max 500mA current need .
specially i need to simulate transformer response . then i need to use transformer in simulation .

Is 48 -> 48VDC and 9->9VDC ?
If so why are you using 7805 ? Do you expect a lot of ripple on 9V due to poor regulation ?

You can directly get well regulated 5VDC/500mA from your input. Look for current controlled DC-DC regulators. There are many IC available but, 384x ICs are cheap, reilable and well documented. Circuits are simple and they provide Cycle-Cycle current limit, switching frequencies can be higher leading to smaller transformers, low ripple, high line & load regulation and efficiency.

Subject of Transformer design is certainly not easy.  
Get your hands on,
1) Designing Magnetic Components for High Freq. dc-dc Converters - Col. Wm. T. McLyman
2) Applications Handbook 1985-86 from Unitrode Corp - Has many circuits, but no tranformer details
3) Switching Power Supply Design - Abraham Pressman

Simulations of trasformers won't get you far. Try and build them, use them to check what's good and what's bad. Over the time you will get them right  

regards,
sam_des

[alberto110]

yes , all voltages are DC .

i'm using a 7805 after 9v in order to get regulated 5v .
i want to build very simple and non precision 48 -> 9 .
ripple on 9v is not important because we have 7805 .
the 48-> 9 should be so cheap . efficiency is not so important .
yes i can use ICs for SMPS but the design of that circuit also transformer is not easy .
so i decide to built an unregulated SMPS + 7805  .
thanks a lot

[solutions]

Go to National's website and use their webbench.  It does it all for you.

You're dissipating 2W in that regulator...now you have a thermal problem on your hands and a heatsink to pay for.  

You also need to power the 555....before you get your 5V power (!?) It won't run on 48V for very long, but if you insist, look up the schematic for "smoke generator".

Your economic analysis is one of false self-assurance...I think you talked yourself into your conclusions by hearing what you want to hear instead of approaching the problem unbiased and solving it optimally to its real constraints.

Also, I know everyone is not a native English speaker here, but "insolation" is the amount of sunlight falling on something.

[alberto110]

sure , in my region only part available is UC3842 and TL494 .

[enzine]

You can also see  LinearTechnology web site and try LTspice IV,
it's a free simulation tool and device models to allow even novice designers to quickly and easily evaluate circuits using  switching regulators.
They also have many examples to build circuits similar to your.
Best regards

[solutions]

sure , in my region only part available is UC3842 and TL494 .

All you are interested in is topology and frequency. Pick any part for the simulations (LTSPICE, webbench, whatever) that is similar in architecture to what you can get.

The surrounding parts are clearly what pain you, not the analog PWM controllers. Don't get hung up on part numbers or manufacturers.

[StackPointer]

Why don't you try adjustable LM2576? It's good, simple, step-down switcher. Hook it up with panel voltmeter and potentiometer instead of fixed voltage divider and you can have 1.23 to 37V on output.  You mentioned that 48V would be voltage input, so it would be advisable to take HV (high voltage) version of LM2576.

[enzine]

 If the insulation from the side input is essential, you can not use LM2576 as provided in applications notes.
Flyback topology is the simplest to use for your application (TL494 or UC3842  +  PowerMos), one needs to design the transformer using ferrite cores...

[alberto110]

If the insulation from the side input is essential, you can not use LM2576 as provided in applications notes.
Flyback topology is the simplest to use for your application (TL494 or UC3842  +  PowerMos), one needs to design the transformer using ferrite cores...

yes isolation is the most important  . regulation is done with the 7805 .  i need 9 v unregulated  with SMPS  . because i make voltage like 3.3 and 5v i want to build 9v SMPS then make 3.3 and 5 with 7805 and 3.3v regulator . making multi output SMPS is very complicated for me  .

[pickit2]

why not buy a phone charger and make mods to suit your needs.
Phone charger = 5V and all you need is add 3.3 reg, Cheap and eazy to do.

[metal]

I think you can simply change the zener diode on the output sense, I am not sure, but give it a try.

[alberto110]

phone charger has 240vAC input and i have 48 DC .

[iphone]

BTW, may I know why you need to isolate 48V to 9V and then down to 5V via 7805?

If you just want to convert 48Vdc to 5Vdc, let try like this (I dont have 48V dc supply so cannot try it)  ..  you can drop the voltage through a zener diode ( say 9V zener diode ) and then feed it (39Vdc)  into IC 34063 and set to 5Vdc output.

It's simple and no need for heatsink.
 
34063 can supply 1A ( 1.5A from datasheet).

[solutions]

phone charger has 240vAC input and i have 48 DC .

Almost all switching converters work from DC to DC. If you put 48VDC onto the plug prongs, the internal rectifier will either block your 48VDC supply, or pass it on to the buck converter.  The converter should adjust its duty cycle accordingly. The only problem may be if they got clever and put a low voltage dropout detect in it, but I doubt they would, especially on a CHEAP one.

For the $5 risk (actually almost zero risk because you likely won't toast anything and can take it back for a refund...after testing it on AC to make sure it still works and that you're not screwing the next guy that buys it), it's worth a try.

[alberto110]

building PS with tl494 or UC3842  is better idea . these are only part found in my area .
does anyone has suggestion .

[enzine]

You can find the circuit that you need (48Vdc in -5V dc out) in the Application Note 1272 - UC3842.
"Flyback Regulator with Shunt Regulated 5V Power Supply"
Simply google "uc3842 an1272" .
There's also include the draft of the transformer.
Let me know if you encounter problems

[alberto110]

i want to build (Application Note 1272 PS) and now want to build transformer . what does these  means  LBS (8x #24) Lpri(2x #25) -3T(3x #22)
?

[enzine]

For this core 2V/turn is optimal

Primary voltage = 48V --> 24 turn
Control voltage = 16V --> 8 turn
Secondary voltage = 5V --> 3 turn

...and then:

Lpri= primary winding : 24 turns awg 25 (awg =American Wire Gauge;  awg 25 =0.45mm diameter ); 2x = 2 wires paralleled

LBS = control winding : 8 turns awg 24 (awg 24 = 0.51mm)

Lsec= secondary winding : 3 turns awg 22 (awg 22 = 0.64mm);  3x = 3 wires paralleled

In altre parole:

Lpri = 25 spire di filo di rame smaltato 0.45 diametro AVVOLTO BIFILARE (per diminuire le perdite)
LBS = 8 spire  di filo di rame smaltato 0.50 diametro
Lsec= 3 spire di filo di rame smaltato 0.65 diametro AVVOLTO TRIFILARE (per diminuire le perdite)

Ciao!