For learning purposes you could make a simple transistor regulator.

not that advanced yet, how do I calculate Rv, I'm guessing that will determine voltage, cause its connected to base. What will this do? (or rather how will this do?)

 

Hello,

The regulator will try to keep the voltage between the output and the reference pin at 1.25 Volts.
The output voltage will be about ( (220+750) / 220 ) X 1.25 Volts = 5.51 Volts.

Bertus

 

R1=1,25^2/220=7mW
R2=(5-1,25)^2/750=18.75mW

For transistor regulator read this article,I can't really explain you how it works while I'm writing from the phone: http://www.bristolwatch.com/ele/zener_power_supply.htm

 

I'd just like to add one problem, the LM350T I can only get at mantech.co.za, don't have transport there, at Yebo (www.fort777.co.za) I can get LM7805. Now total all my penalties if I have to go for the LM7805 please. (I can get a lift to Mantech, but that'll be only on Friday, and my Dad won't be happy), that's why I'm saying: what are the penalties for going with the LM7805 vs LM350T

 

For transistor regulator read this article,I can't really explain you how it works while I'm writing from the phone: http://www.bristolwatch.com/ele/zener_power_supply.htm

won't expect of you to do!

 

7805 and 350 are basically the same thing.Difference is that 7805 has internal resistors that sets it to 5V output which means you can get 5-30V adjustable regulator by using some external components.

 

Here are some quick notes on trimming fixed 5 volt regulators, then I will do the emitter follower dividers.

 

Here are some quick notes on trimming fixed 5 volt regulators, then I will do the emitter follower dividers.



View attachment 75776

cant't really read everything, contrast a problem, but I do have to thank you

(and 7805?)

 

Those are the same thing as 7805 just from different manufacturer's

 

(and 7805?)

I can only get the 7805 at yebo electronics, but even that requires a trimmer(?), cause it says 5, 6, 8, 9, 10, 12, 15, 18, 24V regulated. with its (reference? -- no trimmer) voltage of 5v, what sort of tolerances can I expect, low enough for reference 5v digital electronics. whats the cons of not using LM350? lower Amperage on the LM7805, heat, which will be worse... you said the're esentially the same except for internal resistance, so heat should be the same? what else am I losing if not going with the LM350?

 

I can only get the 7805 at yebo electronics, but even that requires a trimmer(?), cause it says 5, 6, 8, 9, 10, 12, 15, 18, 24V regulated. with its (reference? -- no trimmer) voltage of 5v, what sort of tolerances can I expect, low enough for reference 5v digital electronics. whats the cons of not using LM350? lower Amperage on the LM7805, heat, which will be worse... you said the're esentially the same except for internal resistance, so heat should be the same? what else am I losing if not going with the LM350?

You haven't completely answered my question about the difference between MJ and MJE, cause if I have to have the MJE, I have 2 components to get at mantech.co.za, more reason for the drive.

 

Lm7805 and lm350 generate same amount of heat.Difference is 7805 has pre set voltages(7805,7812,7815) while Lm350 uses pot to change the voltage,7805 can be used as adjustable regulator but it can't go under 5V.So buy regulator which is closer to you.

 

Lm7805 and lm350 generate same amount of heat.Difference is 7805 has pre set voltages(7805,7812,7815) while Lm350 uses pot to change the voltage,7805 can be used as adjustable regulator but it can't go under 5V.So buy regulator which is closer to you.

And amperage, LM350 is 3A while 7805 is 1A, but were we ever aiming for more than 1A? But Now *drumm roll* what about an old cellphone charger 5v~800mA/700mA and 400mA The 3 I've got, if I would have (and this remains an educational endeavor) massive heatsink problem if operating at 800mA practically this would be the best solution? The 800mA (switching) measures 7.5V on the multimeter, now I know that switching supplies rate higher without load than with load, how much load do I need to get it to 5V? 700mA ~ 5.16V (no load) multimeter, 400mA ~ 5.13V (no load) multimeter. These aren't USB supplies though, but how much tolerance can I expect if the rating on the label says 5v?

I have upto 10Mohm 0.5W, how would I go about making it load, short the wires with it and then still measure both polarities

 

We would need to know inductor value to get min load .

 

Cellphone (and other) chargers are not usually suitable without modification as they are not true DC.

Have you tried downloading my attachment and viewing it full size? The underlying pic is quite large and easier to see that way.

 

We would need to know inductor value to get min load .

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

 

Cellphone (and other) chargers are not usually suitable without modification as they are not true DC.

Have you tried downloading my attachment and viewing it full size? The underlying pic is quite large and easier to see that way.

Are you referring to the calculations, I still have problem reading it. But surely the USB flavours of cellphone chargers will be stable.

 

Here are some quick notes on trimming fixed 5 volt regulators, then I will do the emitter follower dividers.



View attachment 75776

LM350:
where's R2? and I can't read R2's value

 

is VR1 trimmer to replace R2?

 

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