PSU question

Hello everyone

I'm building a 9V DC power supply for my pedal board, supporting at least 7-8 pedals simultaneously (this means at least 1500 mA of total output)

I found the Carlos' snubberized and regulated psu on the net:

[IMGDEAD]http://myweb.tiscali.co.uk/nuukspot/decdun/gc/snub.reg.psu.png[/IMGDEAD]

My questions are:

-Is it safe use this schematic in country with wall voltage of 220v?
-What should be the secondary voltage ratings to get a 9V output?
-What should be the VA rating of the transformer to get at least 1500 mA of output.
-Can I multiply the output in parallels without adding any other components to the circuit?

Thanks very much in advance

PS: Sorry if this is the wrong forum but since it's a gainclone power supply I figured it would be the best place to post this
 

Paswa

Member
2007-08-10 9:24 am
i think this is not the correct sch.

Though it is safe to use with 220v

I'd recommend to use LM7809 IC instead of the LM338. it would simple and cheap. if the total current dosnt run over 1.5A, it would be good

I coudnt understand why you need +-30V ? you wrote u only need 9V?
 
Paswa said:
i think this is not the correct sch.

Though it is safe to use with 220v

I'd recommend to use LM7809 IC instead of the LM338. it would simple and cheap. if the total current dosnt run over 1.5A, it would be good

I coudnt understand why you need +-30V ? you wrote u only need 9V?


Actually I was asking if I could use this schematic to output 9V.
For example if I use 8v secondary transformer, wouldn't this scheme give approx 9v?

All I'm asking is the right values :) Sorry If I wasnt clear enough

thanks again
 
That curcuit would probably work if you just used the Positive section of the Schematic and changed the resistor Values so that the LM317 puts out 9v....

It would be much easier to simply use a LM7809 Regulator as they are easier to implement and don"t use as many parts and are cheaper than the LM317.....

If you look in the LM7809 Datasheet it should show an example of how to use it, I would use maybe 1000uF before the regulator and maybe 10uf-100uf after the regulator and you will need to use a heatsink on the Regulator as it will get hot when drawing a lot of current.....

a 9v 30-50Va Ac Transformer would be a good size to use....

Cheers
 
Minion said:
That curcuit would probably work if you just used the Positive section of the Schematic and changed the resistor Values so that the LM317 puts out 9v....

It would be much easier to simply use a LM7809 Regulator as they are easier to implement and don"t use as many parts and are cheaper than the LM317.....

If you look in the LM7809 Datasheet it should show an example of how to use it, I would use maybe 1000uF before the regulator and maybe 10uf-100uf after the regulator and you will need to use a heatsink on the Regulator as it will get hot when drawing a lot of current.....

a 9v 30-50Va Ac Transformer would be a good size to use....

Cheers


thanks for the info

is it safe to use a 9v tranny? dosn't the rectifier boosts up the voltage a little bit?

also what do you exactly mean by the positive section? I'm willing to use a 2 sec. toroidal transformer to eliminate the noise

thanks
 
http://www.aaroncake.net/circuits/supply6.asp

in order to use a 7809 regulator IC the input voltage must be between 2V - 15V greater then the ouput (9V). so that means you would want approximately 11 - 24 VDC input to the regulator.

to obtain dc from an AC signal we must put a brdige rectifier in the circuit (BR1) and then a capacitor between the outputs of the bridge ( positive and ground)

to obtain what DC out you will get after the bridge you calculate

(transformer secondary voltage X 1.414) - 1.4 (2 diode voltage drop from bridge)

so lets say you use a 9 Vac transformer

( 9 X 1.414 ) - 1.4 = 11.326

this must be 2 VDC greater then your output and it is. there is always line fluctuation to consider (about 6% of 100VAC, 115, 220, or 230 depending on where you live in the world) so you could calculate that in. or just use a slightly larger output voltage if you wanted to be safe.

So in short
get a 9 or 12 vac secondary transformer 30 - 50 VA
7809 regulator,
1000uF cap before the reg
100uF and 0.1uF caps after regulator

this should work for you

Hope that helps you understand a bit better

Dave

P.S. check data sheet for pin out of 7809 most of them are usually
pin 1 in
pin 2 gnd
pin 3 out
 
also what do you exactly mean by the positive section?


The PSU schematic you posted is for a Positive and negitive supply but for Pedals you only need a Positive supply.....

Also if you need more than 1500mA you will have to use 2 regulators because the LM7809 and the LM317 can ouly put out 1amp to 1.5amps, you could modify the PSU to use a Pass Transistors to boost the current output....

Most analogue pedals shouldn"t use more than maybe 50ma Max each so I doubt you will need 2amps of current unless you have 40 pedals in your board...... Most standard Opamps only draw about 10ma max so unless your Pedals use dozzens of opamps each you won"t need very much current .....

You should be good with a single lm7809 regulator on a Heatsink....

Cheers
 
thanks for the info. I'm starting to get it :D

one more question: is using MUR860s an overkill for this supply? If so which other ultra fast diodes can I use to form a 2A/40-50V bridge rectifier?

also a question for dave just for the better understanding of the schematic :)

why did you changed some values? (2200uf to 1000uf etc...)

thanks
 
sorry to confuse you, i just meant 1000uF as a minimum, generally speaking the more capacitance the more filtered the secondary voltage will be.

for diodes just use 1N400X (like minion said)

i just did a quick google search for 7809 (or 78XX) schematic

i would suggest doing some more looking into power supply theory
there is lots on the internet.


Dave