HELP! Combining power supplies

Thread Starter

mhighmark

Joined Jun 21, 2014
6
Hi guys. I'm new to electronics, but I'm really getting to enjoy it. This is my first question.

I'm running a breadboard project on a power supply (AC to 12v DC adapter). My breadboard uses a solenoid valve running on the the full 12volts while some controlling 555 timers and a sound chip run on a stable 3.3v. The 555 chips should control the 12v valve by switching it on and off. All it does now is light an LED when the valve is supposed to be on.

How do I do that right?

I've tried letting the 3.3v part run on its own battery power supply while swithing the other 12v supply - combining two power supplies. No luck.

I've tried branching off a 3.3v stable signal from the 12v supply (using a zener), but I suspect that doesn't leave enough amperage for my chips to run properly.

I've messed around with voltage regulators, zener diodes and NPN transistors, but no luck - all I got was burned, smoke and some weird smells:)

Any input would be greatly appreciated!

Mike
 

crutschow

Joined Mar 14, 2008
25,423
You can run as many supplies as you want. Just connect the (isolated) commons of all the supplies together at the circuit common.
 

Thread Starter

mhighmark

Joined Jun 21, 2014
6
Thanks so much for your replies!:)

My power supply delivers 1A.

As far as I can tell from data sheets etc, the valve is eating up 600mA and the sound chip between 150-200mA. Not sure about the 555 timers, which are NOT CMOS as I understand, but I could be wrong. They are NE555P, but I got them cheap from eBay china.

crutschow, do you have an illustration of this setup somewhere? I don't quite understand the terminology, but maybe I'll understand by seeing it in action:)

NorthGuy, thanks, that unit looks indeed much easier than the stuff I'm messing with:) I might just get a couple of those.

Thanks again guys
 

Alec_t

Joined Sep 17, 2013
11,644
If the 3.3V supply is 200mA, deriving it from 12V would mean nearly 2W wasted power in a linear regulator. It would get hot. Do you have a USB adaptor or spare phone charger available? Deriving 3.3V from 5V would waste less power.
3.3V doesn't leave much headroom for the 555 timers to operate. Perhaps run them from 12V instead?
 

Thread Starter

mhighmark

Joined Jun 21, 2014
6
Thanks guys.

I think your inputs have me drawing the conclusion that I'm looking at combining multiple power supplies at different voltages, rather than deriving from a single source.

Maybe a battery for the 5 and 3.3v, and an AC adapter for the 12v. So does anyone have a sample of this being done?

A 555 timer, on its own power supply, triggering a 12v valve running on another power supply?

Thanks
 

Thread Starter

mhighmark

Joined Jun 21, 2014
6
Why dont you use an old Atx psu as your bench power unit, gives out +3v, 5v, 12v at least 18amps max, easy to convert.
I'm definitely marking this as an option for future projects, so thanks!:) But this one in particular is a water toy for my kids - water, 18Amps and my kids make for a cocktail I'm not at all comfortable with:eek:
 

Thread Starter

mhighmark

Joined Jun 21, 2014
6
Why not run the 555 and valve from the same 12V supply?
You just saved my life! Your idea combined with a DPST switch just proved the missing piece of my puzzle. I'll use the switch to run the two power sources in parallel!

Thank you so much for all your help guys!:)
 
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