I also can't read R1's value, and please teach me how power calculations work with the LM350, will try myself just now.

P=V^2/R R= R1(1k2?) + R2 (4k7) = 5.9 P=25/5.9=4.2mW but thats across both resistor is the rest just algebra?
(AM I correct?)

 

just add 2 capacitors and your good to go!

INPUT: AC 100-240
50-60Hz, 180mA
OUTPUT: DC 5.0V, 800mA
only other info I have is Nokia and serial numbers

would ripple capacitor suffice to make it pure enough DC? I bought 2 * 1000uF 50V the other day just for this reason (yebo have 2200uF and 4700uF aswell, which I'll buy if it would solve the problem)

 

It is pure DC,cheap chargers which use big electrolytic cap and Zener diode aren't good for powering anything current hungry.
Your chargers will work fine since they got switching regulator inside.

 

It is pure DC,cheap chargers which use big electrolytic cap and Zener diode aren't good for powering anything current hungry.
Your chargers will work fine since they got switching regulator inside.

Nothing on it except their size makes me think that they're switching, Is that an error in deduction?

[from the right is 800mA, 700mA and leftmost is 400mA]

 

They probably are switching even cheap Chinese clones are switching.

R1=4.7K
R2=470R

I=V/R
I=5/5170
I=0,9615384621 ~ 1mA

P=Iˇ2/R1
P=1mA X 4700= 4.7 mW

P=Iˇ2/VR2
P=1mA X 470=0.47 mW

 

They probably are switching even cheap Chinese clones are switching.

R1=4.7K
R2=470R

I=V/R
I=5/5170
I=0,9615384621 ~ 1mA

P=Iˇ2/R1
P=1mA X 4700= 4.7 mW

P=Iˇ2/VR2
P=1mA X 470=0.47 mW

Thats for LM309

LM350 then
R1=1k2
VR2=4k7
I=V/R
I=5/5900
I=0.8474mA
P=I^2/VR2=0.718184429762/4.7=0.152805197822mW
P=I^2/R1=0.718184429762/1.2=0.598487024802mW

Check me plz

 

But surely the USB flavours of cellphone chargers will be stable.

Stable, yes, but they are chargers and battery chargers are not true DC, which you want. They are deliberately left as pulsed because that charges the battery better.
In other words they are not smoothed. You have to add your own smoothing and then they will not be so stable and the voltage will not be 5volts.

LM350:
where's R2? and I can't read R2's value
is VR1 trimmer to replace R2?
please teach me how power calculations work with the LM350,

The manufacturer (Fairchild) gives the circuit I showed, but uses R2, sorry I have called it VR1.

They state that the voltage across R1 is held at 1.25 volts and give the following equation for the output voltage

Vo = 1.25*(1 + R2/R1) + Iadjust *R2

Now I observe that the adjustment current is very small compared to the current in R1 and VR1

so Iadjust*R2 is approximately = to zero

Since I want 5 volts output Vo = 5 = 1.25(1+R2/R1)

Here is a very useful note in semiconductor electronics

Volts = milliamps * kiloOhms

So I choose R1 as 1k2 (1200) ohms.

thus 5 = 1.25(1+R2/1.2)

thus (5-1.25) = 3.75 = 1.25 *R2/1.2

R2 = 3.75*1.2/1/25 = 3.5 kiloOhms.

choose next highest pot = 4.7k.

Note that we do not know the voltage across R1 in the other trimmer circuits, but we do know the total output voltage instead.

 

R1=220
R2=750

I=V2/R1
I=1.25/220
I=5mA

I=(V1-V2)/R2
I=(5-1.25)/750
I=5mA

P=I^2/R1
P=25/220
P=110 mW

P=I^2/R2
P=25/750
P=33 mW

 

Stable, yes, but they are chargers and battery chargers are not true DC, which you want. They are deliberately left as pulsed because that charges the battery better.
In other words they are not smoothed. You have to add your own smoothing and then they will not be so stable and the voltage will not be 5volts.
.

But the Raspberry Pi runs on USB cellphone charger (750mA+), but I guess that's cause it's got its own regulator?

 

So what to do if you ordered 5* 2A USB chargers off DX.com to be used in digital electronics, lost cause or is there still a use for them?

 

It has built in regulator.

You can use them to power DC motors or circuits which are not sensitive to small oscillations.
You can use them to power Voltmeter display in case you decide to build one in PSU.

 

You may be lucky with some digital electronics and some chargers, but you should never assume compatibility.

All you need is a storage or filter capacitor, but it will charge up to the peak value of the pulsed supply.

Some electronics doesn't care if the supply switches on and off rapidly.
Some do care.

 

R1=220
R2=750

I=V2/R1
I=1.25/220
I=5mA

I=(V1-V2)/R2
I=(5-1.25)/750
I=5mA

P=I^2/R1
P=25/220
P=110 mW

P=I^2/R2
P=25/750
P=33 mW

thrimmers I can get @ 0.1W, thats 100mW so 33mW would do fine! (1000mW=1W -> 1W/10=0.1; 1000mW/10=100mW)

 

You need a potentiometer a linear one.Trim pots are used for calibration and quick prototypes.

 

You may be lucky with some digital electronics and some chargers, but you should never assume compatibility.

All you need is a storage or filter capacitor, but it will charge up to the peak value of the pulsed supply.

Some electronics doesn't care if the supply switches on and off rapidly.
Some do care.

Biggest Electrolytic: Electrolytic Radial 4700uF 25V (ELS478) or 35V, 25V will do? I'm sure it will.

 

This one:
http://www.fort777.co.za/index.php?main_page=product_info&cPath=269_456_552_582_585&products_id=3059
or this
http://www.fort777.co.za/index.php?main_page=product_info&cPath=269_456_552_582_585&products_id=3064
It will do,buy 2x caps in case one fails.

 

Trim pots are used for calibration and quick prototypes.

Isn't calibration the goal, getting 5.5V down to 5V and then its set? Please tell me reason for potentiometer?

 

I was thinking the 1k, cause 680 was lower than 750 5.1 vs 5.5, do U want to be able to run higher voltages aswell, might be a good idea, more versatile.

 

This one:
http://www.fort777.co.za/index.php?main_page=product_info&cPath=269_456_552_582_585&products_id=3059
or this
http://www.fort777.co.za/index.php?main_page=product_info&cPath=269_456_552_582_585&products_id=3064
It will do,buy 2x caps in case one fails.

usually when I buy components I'm always thinking of my ever growing LAB, so yeah I'll buy a couple more than I need, next time I've already got it in my own stock!

 

You can use trimmer pot since you are building just 5V regulator if you wanted more voltage i'd use pot.