Pedal power supply with indication and short circuit protection

[Crontox102098]

Hi guys, here Carlos again asking stupid things.
Again, in Google i've been searching a good schematic for a little power supply with a little indication and short circuit protection. But there's nothing i founded.
I would like a little circuit with this features, where i can know if the circuit will deliver max 100mA or 200mA changing a resistor or something like that. Think you know what i mean.

Hope you can help me with some schematic guide or something
Thanks and cheers.

Carlos.

[GibsonGM]

Why not build your own?  First, what voltage do you want this to provide?   And what maximum current?  You said 200mA - that is a lot, but can be built easily.   I don't think you need to worry about 'changing' anything for current output, just build it to be able to give 200mA.  Your load will do the rest. 

So, what you seem to need is a transformer + rectifier or DC supply able to give the voltage you want, plus 3 to 5V more to run a regulator at your desired voltage.     LM78XX or LM317 have short-circuit protection built in!     An indicator LED can easily tap off the regulator output in parallel, or the power supply input TO the regulator.  I prefer one on the output to let me know it's working.

On Page 18 of this document, there are typical applications for the regulator, where you supply the input:  https://www.fairchildsemi.com/datasheets/LM/LM7809.pdf

Searching the internet for "basic regulated power supply" should find you many more tutorials and resources, too! 
Also "LM7808 tutorial" or such thing, and try YouTube.  You will learn a lot that way!

[gjcamann]

I second using a voltage regulator with built in short circuit protection and let that do the work for you.

You could also look into re-settable fuses. http://www.taydaelectronics.com/circuit-protection/varistors.html

As far as an indicator, I think having an LED that it illuminated when working and extinguished when not working would be much easier to implement.

[Seljer]

If you have some time watch this, it'll explain everything about build and adjustable linear power supply with current control, a bit more than you need but it's all informative.

https://www.youtube.com/watch?v=CIGjActDeoM

Personally, for pedals/pedal breadbording I'd just take one of those 78L09 regulators. It's more than quiet enough and the internal overload protections that supposedly kicks in at 100mA is pretty good (I've yet to kill one by shorting the output).

[free electron]

There is also the L200C, which has an adjustable current limiter built in.

[PRR]

In general, you do not want to be setting a current limit for every load.

Look at your house wiring. You can plug in a 3 Watt night-light or a 1,000 Watt toaster. The only current limit is a 2,000W-3,000W limit in case you plug in a lot of toasters at once.

A happy pedal will only pull the current it needs. An unhappy pedal will have to be fixed anyway.

All the standard voltage regulators have overload protection. You can short them all day long and they will pop right back to action when you remove the short.

I do not know what "a little indication" means. If you want a ON light, wire an LED and resistor across the 9V. If you want a "I am delivering power" light, that can be quite difficult. There's always a trace of leakage, and some pedals don't pull much more than that. With wall-power, mostly I would put an LED on each pedal, "I am getting power", which is maybe what you really need to know.

[bloxstompboxes]

I've been using the power supply project from tonepad.com for a while now but rarely have more than 3 pedals at a time on it since I just muck around at home. Most of my power usage is from the LEDs on the pedals, of course.

[Crontox102098]

Why not build your own?  First, what voltage do you want this to provide?   And what maximum current?  You said 200mA - that is a lot, but can be built easily.   I don't think you need to worry about 'changing' anything for current output, just build it to be able to give 200mA.  Your load will do the rest. 

So, what you seem to need is a transformer + rectifier or DC supply able to give the voltage you want, plus 3 to 5V more to run a regulator at your desired voltage.     LM78XX or LM317 have short-circuit protection built in!     An indicator LED can easily tap off the regulator output in parallel, or the power supply input TO the regulator.  I prefer one on the output to let me know it's working.

On Page 18 of this document, there are typical applications for the regulator, where you supply the input:  https://www.fairchildsemi.com/datasheets/LM/LM7809.pdf

Searching the internet for "basic regulated power supply" should find you many more tutorials and resources, too! 
Also "LM7808 tutorial" or such thing, and try YouTube.  You will learn a lot that way!

Last time I designed my own circuit, does not work as well (that's why i need your help), as i want (with a red LED and a short circuit protection... just got 7.9V (i tried with  a pair of 7809 cause i believed the first was broken), when really needed 9V.
Want to provide 9V and 12V, that's easy to do, a simple 7809 and 7812 and a pair of condensers in both can do this as well...

Some digital effects (kinda i love, dunno why) require 500mA to work as well, but some analog stompboxes (Adapser) my own phaser, just need 20mA to work as well. So, i want to build a power supply who can drive different supplies (just as Cioks DC10) with a little LED who gives his shine (LOL) when a stompbox is connected.

Thanks.

[GibsonGM]

I would keep it simple and use the advice given, Carlos.   You can place an LED and its resistor ACROSS the power output terminals, and when the circuit is powered on it will "give his shine"      This way you will not have a VOLTAGE DROP as you would if you place the LED in series, which will also limit your current!   Seems that you were only getting 7.9V because of a diode voltage drop, to me.   

Build a power supply that will give up to 1A output (7809 with suitable transformer in front of it, something like 16 or 18VAC).    If you want an LED for each pedal you are powering, place it IN that pedal instead of somewhere on your power line.    Or just never mind for now - that's the "job" of the circuit, not the power supply.

Keep reading.  On this page, you will probably do what is shown in Fig. 3.  Where it says "Load", is where you would place the regulator.
You will want a fuse and power on/off switch on the mains line!!   And if you are not comfortable with this part, find someone who understands line power to help out!!  Playing with mains power can be fatal....

http://www.bristolwatch.com/ele/basic_ac_rectification.htm

[Crontox102098]

I would keep it simple and use the advice given, Carlos.   You can place an LED and its resistor ACROSS the power output terminals, and when the circuit is powered on it will "give his shine"      This way you will not have a VOLTAGE DROP as you would if you place the LED in series, which will also limit your current!   Seems that you were only getting 7.9V because of a diode voltage drop, to me.   

Build a power supply that will give up to 1A output (7809 with suitable transformer in front of it, something like 16 or 18VAC).    If you want an LED for each pedal you are powering, place it IN that pedal instead of somewhere on your power line.    Or just never mind for now - that's the "job" of the circuit, not the power supply.

Keep reading.  On this page, you will probably do what is shown in Fig. 3.  Where it says "Load", is where you would place the regulator.
You will want a fuse and power on/off switch on the mains line!!   And if you are not comfortable with this part, find someone who understands line power to help out!!  Playing with mains power can be fatal....

http://www.bristolwatch.com/ele/basic_ac_rectification.htm

I understand that final thing as well, I am very careful when i know something like this can kill me. I know about AC, rectification and that things.
After further searching, I found this on this glorious website.



Author says this:
For 1A you have to change the 2 ohms resistor into 1 ohms/3W. You may want to upgrade the capacitors a bit. Especially the 100u. But on the other hand, how much current are you really going to need. What I like about this design that it is really stable and protects the transformers well. My Rebote Delay 2.5 actually works on my supply even though the over current/short circuit LED starts to blink. So it is operating at a voltage below 9 volts but works fine.

But he says this is yet unverified... and i want to deliver 200mA in each circuit... 100uF to 1000uF, 10uF to 100uF and a little 0.1uF condenser but... 3ohms will deliver 250mA? and the most important question... WILL WORK?

Thanks.

[GibsonGM]

Don't know, Carlos.  That's more than what I would do for this.  Just the transformer, rectifier, and regulator with caps is all that's needed here, I think. 

I don't know if the schematic about "will work".  I can see the caps at the regulator aren't what the manufacturer recommends but that may not matter....The transistors, while not a bad thing, seem to me to be overkill for what you need.  The regulator takes care of....regulating... and provides short circuit protection.  And it will allow you up to 1.5A output current if properly heat sinked.   You only need 400mA total?  NO problem!   

You can put an indicator on the output to show when power is on.

Specifications met    In my opinion, the simpler you make something, the more reliable it tends to be. I KNOW the trafo, bridge, caps and regulator will work, so that is what I would do.

[Crontox102098]

Don't know, Carlos.  That's more than what I would do for this.  Just the transformer, rectifier, and regulator with caps is all that's needed here, I think. 

I don't know if the schematic about "will work".  I can see the caps at the regulator aren't what the manufacturer recommends but that may not matter....The transistors, while not a bad thing, seem to me to be overkill for what you need.  The regulator takes care of....regulating... and provides short circuit protection.  And it will allow you up to 1.5A output current if properly heat sinked.   You only need 400mA total?  NO problem!   

You can put an indicator on the output to show when power is on.

Specifications met    In my opinion, the simpler you make something, the more reliable it tends to be. I KNOW the trafo, bridge, caps and regulator will work, so that is what I would do.

Should be better, after a pair of TIP42 burned out 
P.s. Really all i need is just 2A to supply all my chain of stompboxes, commonly digitals.

Thanks for your help guys. 
Cheers!.

[GibsonGM]

2 AMPERES???  That sounds like a HUGE system you have going, bud!!!!  Wow, I'd be surprised if all effects I owned drew more than 800mA.

[antonis]

Really all i need is just 2A to supply all my chain of stompboxes, commonly digitals.

If you're sure about this you need a transformer with secondary winding output of - at least - 3A, a bridge (or rectifier diodes) up to 5A, a transistor with SOA of 5A (with proper cooling), a biasing Zener with 600-700mV higher than the desired output voltage and a BIG filter capacitor (depending on the desired ripple voltage)...

You may also use a LM350 (TO-3) with proper cooling..

P.S.
You better not use a transformer with an output higher than 12V (for power consumption reason..)
A 9V secondary output might work just fine but it depends on your transformer's capability (which shloud be - at minimum - of 30VA)