Why does DVD power supply "pulse"?

[microbe]

Hey folks,

I am trying to learn about electronics mucking around, pulling things apart playing with arduino - a bit of everything.

When a DVD player died I thought "Aha, a cheap DC power supply", but what I have found is that it seems to put out brief (.1 sec?) bursts of power every .5 second or so rather than a continuous supply.

Why would they do something like that in a DVD player?

Thanks in advance.

 

[Resqueline]

I'd figure that the DVD-player died for a reason, namely that the PSU went bust..
What you're seeing there is a short-circuit protection circuit in action.
Most likely there's a shorted diode in the secondary side.

 

[jackorocko]

Your not talking about PWM are you? Are you testing out the new PSU, I take it this is a linear supply?

 

[davelectronic]

DVD psu

Hi there.
Some units need a load on the supply rails, ive tried rescuing a DVD psu and had no luck, more than once, i think the main DVD board sends signals back to the psu for its demands, a theory. Dave. PS oh a dream cast game console i had and pulled apart working did exactly the same, again an optical drive load.

 

[JoeyAVR]

Dave's right. Some 'intelligent' PSUs send out pulses to decide if there's a load to drive or not. If it detects open circuit, it saves power by doing nothing. If it detects a short, it obviously avoids damaging itself by not switching on. If the load is as expected during the pulse, it switches to supplying continuous power. Try putting a 10-20ohm power resistor across the output and see if it gives a steady voltage.

Many phone chargers are a good source of well-regulated 5V for small projects.