C1=100 uF 20V
C2=300uF 20V
D1=FAST RECOVERY Schottky diode 30V 3A
R2=3K 1W
R1= 1K 1W
L1=100 uH

Heat dissipation:

Pd=5Vx2A=10W
Pd=10W/77%(0.77)
Pd=13W~
Pd=13W-10W= 3W
Junction to case=2C/W
3Wx2C/W=25+6=31C°

Max temp. of the regulator should be 31C° If my calculus is right.

Q1=I'd like to add, how will I know what LM2576 delivers?

Q2=But how do they make them so small?, is my matchbox sized nokia charger got a transformer in it?

Q1=LM2576 will deliver 2A of current incase you draw more the voltage will drop and regulator overheat unless it has overload protection.

Q2=They have small PCB mounted transformers.
This is very small like 2x2cm.

 

Congratulations, ISB123 on doing a good job here.

 

Brilliant ISB123! Thanks Thanks Thanks! I could only buy 2W resistors, and 3kohm isn't a standard value at yebo or mantech, so i'll just use 1k and then 3*1k for the 3k... that'll work shouldn't it?
One problem when I "checked out" my order this morning, I only had one diode to choose from that I think would work, was I correct: http://www.fort777.co.za/index.php?main_page=product_info&cPath=269_456_605_607_611&products_id=3254 ? Its:

BAT85 Fast Recovery Schottky barrier. (
FML33S Ultra Fast Diode 300V/10A (SEQ81H)
R24.49 <--- too expensive, and I hoped the BAT85 (cheap) would do)

Planar Schottky barrier diode with an integrated protection ring against static discharges, DO-34 package.
FEATURES
· Low forward voltage
· Guard ring protected
· Hermetically-sealed leaded glass package.
APPLICATIONS
· Ultra high-speed switching
· Voltage clamping
· Protection circuits
· Blocking diodes.

Datasheet: http://www.fort777.co.za/images/Datasheets/SEQ87H.pdf

VR continuous reverse voltage − 30 V
IFSM non-repetitive peak forward current tp ≤ 10 ms − 5 A

 

Yes you can put them in series and they will require less wattage like 0,5W.Both diodes are fine so buy one which is cheaper.

 

Yes you can put them in series and they will require less wattage like 0,5W.Both diodes are fine so buy one which is cheaper.

I thought only resistors in parallel will require less wattage, why is this? voltage drop over each resistor? I bought 3 in a pack for R5/pack, that's R1.70 per resistor (2W), if I bought 0.5W it would have been R0.60 per resistor (in packs of 10)... I call these errors school fees, cause now I know for next time, alas, deal is done oh and the BAT85, I knew this morning that it could be wrong, and then that that "school fees" I'm willing to pay, I'll put it in my ever growing components wall, and someday have a use for it.

 

I thought only resistors in parallel will require less wattage, why is this? voltage drop over each resistor? I bought 3 in a pack for R5/pack, that's R1.70 per resistor (2W), if I bought 0.5W it would have been R0.60 per resistor (in packs of 10)... I call these errors school fees, cause now I know for next time, alas, deal is done oh and the BAT85, I knew this morning that it could be wrong, and then that that "school fees" I'm willing to pay, I'll put it in my ever growing components wall, and someday have a use for it.

Like I said, component wall: I have one 10 pack 1K 0.5W resistors, I'll use them before I use the 2W ones (can't get 1W)

 

Yeah it's because Voltage drop across the resistors but 2W is better than 0.5W.Its always better to be safe then sorry.

 

cool ;-) I'm only getting to Mantech on Friday (for the switching ic), then I'll put this on breadboard (is that electronically possible? limits on the breadboard, etc?) Then I'll let you know my results. If I can't get it on breadboard, then vero board, but I'd Much prefer breadboard?

 

It needs to be on veroboard because switching regulators are very sensitive devices.C1,C2 and D1 need to have their ground connection as short as possible and close to regulator as possible.

 

It needs to be on veroboard because switching regulators are very sensitive devices.C1,C2 and D1 need to have their ground connection as short as possible and close to regulator as possible.

Damn, I know it's a necessity but I'm paranoid of veroboard, build a buzzzer circuit the 3rd time now (2 times fail, printed the design and keep on finding reasons not to do 3rd try), doesn't work (use auto route on VeeCAD), I guess it's always bridging, although I can't see anything wrong. But your circuit is pretty simple, hopefully it works.

 

I'll just send you the PCB file and then you try to replicate or use mine.

 

Chillum,

You are bouncing all over the place on this thread. You are approaching it like this is going to be the last power supply you will build.

Just build a simple, 1A 7805 regulated power supply and be done with it. This should last you through a lot of experimentation with logic and microcontrollers. If you need something bigger a year from now, you will be more experienced and better able to do it.

Bob

 

7805 sure is simple but its very ineffective and he can't cool it down with any heatsink available in local shops.

 

And 31 'C doesn't require a heatsink?

 

And 31 'C doesn't require a heatsink?

 

It doesn't. In case you notice it getting a bit hot just put a small heatsink that you can make at home with some aluminum sheet.

 

It doesn't. In case you notice it getting a bit hot just put a small heatsink that you can make at home with some aluminum sheet.

http://www.fort777.co.za/index.php?main_page=product_info&cPath=715_1066&products_id=9886 <---- cost R6 thats 1/4 of a 2litre of milk

 

http://www.fort777.co.za/index.php?main_page=product_info&cPath=715_1066&products_id=9889 <---- cost R4.35

 

It doesn't. In case you notice it getting a bit hot just put a small heatsink that you can make at home with some aluminum sheet.

I have NONE machining tools, I have a hand powered drill for vero board, and a paper cutter (those rectangular blades that shift out)

 

That one is fine.Do you use veroboard with holes or the copper board which you have to etch?
Can you design your own PCB?