Hi, I am using a DC supply to bias a LED. In the middle of my experiment, I found that the DC supply shuts down from 2.2 V to 0 V making a noise and showing a stack of bars on its display. Why does this happen?

 

Not enough current capacity?
What is the nature of the supply?
Max.

 

The ratings on PS1505 D power supply : 0 to 15 V and 0 to 1 A.
Can you further explain what you meant by not enough current capacity?

 

The supply cannot deliver the amount of current your circuit requires is one possible reason.
Show your schematic/circuit.
Max.

 

Post a schematic of what you have connected to the power supply and describe what you're doing when it "shuts down".

 

Hello,

Do you have a datasheet of the led and powersupply?
How did you connect the led to the powersupply?

Bertus

 

Did you connect resistor in series with your led?
Else, most likely, led becomes damaged and power supply is shorted.

 

Hi, I am using a DC supply to bias a LED. In the middle of my experiment, I found that the DC supply shuts down from 2.2 V to 0 V making a noise and showing a stack of bars on its display. Why does this happen?

Not nearly enough information.

What kind of noise? A click? A buzz? A continuous hum? A pop?

What kind of experiment?

What is the exact circuit you have connected to it and what are you doing with it shuts down?

You are probably exceeding the current capability of the supply and either it is detecting the overcurrent or it is heating up and reaching a point where it's thermal protection circuitry shuts down the output.

 

The LED is biased using a tee bias. The experiment is a visible light communication set up where data from waveform generator is modulated over LED.
I found that by turning the amplifier ON (increasing its supply voltage) leads to drop in the voltage level shown on the DC supply panel.

The sound is like a continuous hum, the one we get when the ends of the supply are shorted.

 

A box with an arrow pointing toward it that says, "Tee bias" doesn't give us much to go on.

What is the circuitry inside that box.

I'm assuming that the stuff to the right of the box represents a coax (or other two-lead) cable that has a 20 Ω resistor in series with the LED.

What current is the LED rated at?

What voltage is the DC supply being set to?

 

Here is the circuit for tee bias

 

How big is your RF signal?

If the Vf of the diode is 2.2 V (which is just a typical value, not a guaranteed value, by the way) and you are applying 2.2 V, then you will get virtually not current through the diode and are relying on half of the RF signal to raise it above and start conducting.

I would expect that you would want it to be on even without the presence of an RF signal so that your RF signal can modulate it both up and down around the bias point.

 

Hi, I am using a DC supply to bias a LED. In the middle of my experiment, I found that the DC supply shuts down from 2.2 V to 0 V making a noise and showing a stack of bars on its display. Why does this happen?

If RF voltage is 3V RMS, then bias current not exceed 70mA, therefore unusual behavior of DC supply may arise from RF incursion to DC supply. It may happens by 2 reasons - too small inductance of choke or series LC resonance (choke, capacitor) inside Tee bias.
About bias selection. For LED it should be current, not voltage.
Diagrams below shows how LED works on different bias currents (V_rf =3V RMS).