power supply issues

[aliyesami]

I am using LEDgroup power supply 500w , 7.2 Amp to drive a 300mA LDD driver which in turns drives a 50v-3.3v circuit.
there are 8 other 700mA LDD drivers connected to the power supply .
when the circuit is not loaded i get perfect 3.3v but when i load the other LDD drives the 3.3v drops to 2.95v.
also I hear a whistleing noise coming out of the board where the LDD drivers and 3.3v power supply componetns
are mounted.
now i am not sure the whistleing noise is coming from the LDD drivers or the inductors or capacitors mounted .
how can i tell and what is this issue iam facing ?

the 3.3v circuit is as shown in the URL
http://obrazki.elektroda.pl/8784363900_1404712310.jpg

I am also wondering if its possible to build such a powersupply myself ?

 

[cl10greg]

It depends on the kind of power supply that it is. If it is calibrated to be constant current than the voltage can change to meet the current demand. The loading could be from the driver or the topography of the driving chip. What are the LDD chips? Could use some more application information? The power supply converts 50V to 3.3V? What kind of buck system is it?

 

[aliyesami]

the main power supply is 500W 7.2A sold by www.ledgroupbuy.com and the led drivers are also from same company sold as LDD700H and LDD300H .
The LDD300H i am using to drive two power supplies one 3.3v and other 12v. Then there are eight LDD700H drivers driving the chains of LEDs .
the powersupply components you can see from the url i posted above.
my question is what component could make this hissing or whistleing noise ? the LDD drivers? or the caps? or even the 300uh inductor coil iam using in the 3.3v power supply ?

how can i find out if the LDD drivers are constant current or constant voltage ?

 

[cl10greg]

Well most likely it would be from the drivers. Since it is a buck configuration, there is some kind of switching that is taking place to absorb the energy in the circuit to reduce the voltage. Depending on the switching frequency, this could be in the high audible range and produce such a hiss. It does say that the PWM frequency is from 100-1kHz, so it could be just part of the switching topography. Caps usually don't hum, inductors might depending on the energizing frequency. What is your input voltage and power? Anymore drawings or details about the application maybe helpful.

That same company makes constant current power supplies (usually it just says if they are).