Power supplies have too high voltage - why? + Introduction

[SampleGrinder]

Hi Guys,

this is my first post - my Name is Simon - I am from Germany, I make electronic music / beats and love to use bent toys for this. I do simple bends myself but also buy circuitbenders stuff. I own a "S01 SamoleGrinder" (you can see it on this page - it is the custom made "flipswitch version") also a re-clocked Fostex DE1 and some toys....


My first question for you is ablot power supplies:

I need 9V DC 500mA - should not be a problem, but measuring the ones I have always results in much higher voltage that the should have by spec. One case I have is a power supply which is supposed to have 9V - but my voltmeter says 13,8V. I snitched that one from a NetGear Router - assuming that the NetGrar router is switched on permanently it would be the case that it would end up having 5V too much constantly.

I had the same thing with a universal power supply which is switchable from 4-12V - to get it to output 9V I had to set it to 4,5V  - setting it to 9V also resulted in much too high voltage.

Because this happens all the time I´d like to know:

- Is this a normal phenomena in power supplies (assuming my voltmeter is correct :-)
It might be so that the initial voltage is better to be higher calculating loss on the way to the circuit.

- Is it advisable to use 13,8V for a 9V unit over time?
Your opinions please.

- What are your general recomendations on this topic?


Thank you!

[Circuitbenders]

The things you want to be looking at are the differences between regulated and unregulated power supplies, and their outputs 'under load'.

As long as whatever you are powering utilizes less than the rated maximum milliamps, a regulated 9v linear power supply or a switched mode psu will always output 9v. The purpose of the extra regulation circuitry inside the supply is to keep the output voltage steady regardless of the current draw. It will just get hotter the more current you use.

If you have an unregulated linear power supply, the voltage it provides will drop under load. As you've discovered, if you measure the output of a 9v unregulated supply while its not powering anything, it'll probably be outputting around 12-13v. Thats because theres no load on the supply.
As soon as you use it to power something, the output voltage will drop in inverse proportion to the current draw. Some unregulated supplies will only be outputting their rated voltage when whatever they are powering is pulling their maximum rated milliamps, although in reality there will be a certain safety margin.

Realistically its perfectly safe to use an unregulated supply with most devices, as most modern kit will have internal power regulation circuitry anyway. In this case you don't really need a regulated PSU as variations on input voltage don't really matter that much. A device thats supposed to run on 9v with internal regulation, will probably be quite happy running on 12v or probably a little more. The internal regulation will be taking it down to a steady 5v or so anyway regardless of the input voltage. It'll just get a little warm at higher voltages.

You only really need a regulated power supply with devices that have no internal regulation, or are very sensitive to the noise that some unregulated supplies produce.

[SampleGrinder]

that summs it up :-)

thank you !