Power supply high voltage

[Fractus]

Why is the power supply has a higher voltage?

 

[bertus]

Hello,

Could it be that the powersupply is unregulated?
If so, the voltage should go down under load.

Bertus

 

[Fractus]

Hello,

Could it be that the powersupply is unregulated?
If so, the voltage should go down under load.

Bertus

The powersupply is regulated.

 

[bertus]

Hello,

How can you tell it is regulated?
It is not noticed on the power supply.

Bertus

 

[Harald Kapp]

The powersupply is regulated.

That is a contradiction. When regulated, the output voltage should be 4.5 V.
From the single 220 V input rating I take it this is a transformer based power supply. This type of wall wart quite often consists of a transformer, rectifier and capacitor only. Put a load to the output, around 220 Ω to draw the rated 20 mA, check the voltage again with load.

 

[bertus]

Hello,

@Harald Kapp , The power supply is rated for 400 mA.
The given 20 mA is for the 220 Volts side.

Bertus

 

[Fractus]

That is a contradiction. When regulated, the output voltage should be 4.5 V.
From the single 220 V input rating I take it this is a transformer based power supply. This type of wall wart quite often consists of a transformer, rectifier and capacitor only. Put a load to the output, around 220 Ω to draw the rated 20 mA, check the voltage again with load.

But if I check the voltage on load does it bust my device?

 

[bertus]

Hello,

As Halrald said, try a resistor (or a small lightbulb from 4.5 or 6 volts torch) as load and see if the voltage goes down.

Bertus

 

[Harald Kapp]

The given 20 mA is for the 220 Volts side.

Oops, I goofed. Thanks for the correction.
Anyway, 220 Ω should suffice to load the output.

 

[Harald Kapp]

But if I check the voltage on load does it bust my device?

Use a bare resistor as load, the risk is very low that it gets damaged, And if so, so what? It's only a resistor.
Do not use an electronic device you want to keep in working order.

 

[ColKlonk]

Those power supplies are rated at the current specified. This is an unregulated power supply.

In the picture you should get 4.5 Volts when drawing 400mA, the voltage climbing as you draw less current, and visa-versa.
It's done this way because of the transformer and secondary winding resistance losses, and what you've measured there is the 'no-load' voltage.
You can now draw a 'straight line' V-I graph to see the voltage-current relationship of the power supply, so if the tranformer can handle a short circuit , you would get around 800mA at around 0 Volts. (Don't do this though - it'll cook the transformer)