AC adapter working on DC Input

We have an ac adapter that has input voltage range from from 180~240 VAC and gives output rated at 24 Vdc. But one of my colleague has used the adapter with 24v DC input voltage and is getting around 24 Vdc at the output. Will this setup work?

adnan_hayat88 said:

one of my colleague has used the adapter with 24v DC input voltage and is getting around 24 Vdc at the output.

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If 24Vdc is available, why would you use an adapter?

I may be able to shed some light on this
First it does not surprise me that you can run the converter on 24DC input and get 24VDC out, if the load was light.
This has to do with the type of converter in this case as with most modern power supplies they are called switching power supplies. They are cheap to build and very small. There is no transformer.
If you look at the circuit . The front end is usually a full wave bridge rectifier with the DC out of the rectifier connected to a filter cap. As you know a full wave bridge rectifier will pass DC current through it, so a DC input will work. The voltage on the first filter cap will be the peak of the AC or DC input voltage (RMS voltage X 1.414). The rectified DC on the first filter cap is then passes through a high frequency switching transistor (usually a FET ) this switching transistor’s on time is varied to allow enough current to pass through to charge the 2nd filter cap or output cap to rated output voltage in this case 24VDC.
The more current on the output the higher the on time for the switched transistor.
This transistor is usually switched as 10K hertz. It’s the ratio of on time to off time that controls the amount of current it lets through this controls the charge voltage on the output.
So if the load is light, then 24VDC in can supply an output of 24 VDC the switching transistor would be on most of the time. On the other side with 220VAC in and 24VDC out the switching transistor would be off most of the time. It only turns on to bring the output voltage to required level.

Most of the newer power supplies have a protection circuit built in to the output. If the output voltage rises above the output tolerance level the protection circuit should open the output circuit and protect the downstream equipment. I have seen some power supplies that use a crowbar circuit on the output in addition so that if the output voltage rises it will turn on and short out the power supply pulling the output down to 0 and of course destroying the power supply in the process. A power supply is cheep compared to what it is supplying.
There may be a better explanation on this found on the net

Simple fact, whether something "Appears to Work" or not...

If you apply a device out of spec, don't rely on it.

If something fails because you apply a device out of spec, it is your fault.

If someone gets hurt because you apply a device out of spec, enjoy the Lawyer and Safety and Heath time.