Can i use unregulated AC/DC adapter on basic circuit

rushtonism · Joined: Oct 11, 2009 Posts: 13 Location: UK

Hi All

I've just acquired a universal AC/DC adapter that plugs into the wall and outputs 3, 4.5, 6, 7.5, 9 and 12V at 500mA. Can I use this directly into a simple circuit like a 40106 oscillator (from Nicolas Collins' book)? I have the oscillator breadboarded, going into a 1W simple amp (little kit I built) and then going into a mixer and finally into a big Yamaha HiFi amp. I've been using a 9V battery and it sounds great. Will the adapter work as well? I checked it with a multimeter and when the dial was on 4.5V the output was 7.8V and when it was on 6V the output was 10V. Should I go by what the meter is telling me or by what the adapter is telling me? Also, if I go by the multimeter is it best to use 7.8V or 10V on a circuit that runs on a 9V? or does it not matter?

Lots of questions...sorry

Thanks

andrewF · Posted: Tue Nov 10, 2009 6:27 pm Post subject:

to E-M

the adapter should work fine and is a 'reasonably' safe way to get power if you are new to electronics.

Probably it is better to measure the output of the ac/dc adapter when it is connected to your circuit and the circuit is turned on. You will find the output voltage drops closer to the expected level when a circuit is drawing current.

To be cautious, start the adapter on 6V, read the output voltage with your multimeter and see how it all works. The 40106 will handle up to 15V easily.

Usually it is better to trust your multi-meter

have fun, make some Noise Very Happy

rushtonism · Joined: Oct 11, 2009 Posts: 13 Location: UK

Awesome! Thanks a lot! I will do as you suggest.

Uncle Krunkus · Posted: Wed Nov 11, 2009 2:39 am Post subject:

An unregulated supply will always be at a higher voltage than quoted when you draw less current than it is rated at.
Your multimeter (as a volt meter) will draw next to no current and will show the biggest discrepancy. Once you have even a small load (like a CMOS chip) across the supply, the voltage will be closer to what you would have expected.
I still wouldn't go above "9V" though, because the CMOS chips won't draw enough to pull it down. "12V" on a CMOS will easily be higher than 15V, and will "fry your chips" so to speak! Laughing