Real Simulation LED loading

Real Simulation LED loading

1. Entering LED mode

Press the key Shift + R-set to enter LED mode menu.

LED Mode

LED Mode Set *Enter LED Mode  Return

Choose the item Enter LED Mode and enter LED mode.

2.      Setting the parameters

Press the key Shift + R-set to enter LED mode menu. Then select the item LED mode set to set the parameters. The rotary knob at the upper right front panel can be used to adjust the V_o.

LED Mode Set

*LED Vo  :  12.000 V  LED Io  :  0.3500 A  Rd Coeff:  0.173  Return

LED V_o :              LED power supply working voltage

LED I_o :                LED power supply working current

Rd Coefficient:  Working point resistance coefficient（range 0.001 ~ 1）

3.      Rd Coefficient significance

I_O is working current, which should be set as the rated current of measured LED power supply.

Vo is working voltage, which can be set as any value of output voltage range of the measured LED power supply

Rd is LED power supply inherent parameter, which can be found in LED power supply specification. Please refer to the part 4 for the detail.  

Rd Coefficient = R_d / (V_o / I_o)

Note：Vo、Io、Rd Coefficient are all the parameters describing the LED characteristic. Since the actual output current of LED power supply slightly deviates from the rated current, so there is also a slight deviation to the actual output voltage. This is normal.   

4.      Counting Rd Coefficient

Suppose there is a LED string, 10 LEDs in series. The V-I characteristic curve of a single LED is as follows:

The output current I_o of LED power supply is350mA. Then according to the above diagram, the working voltage V_o of a single LED is 3.44V.

The tangent line slope (ΔV/ΔI) of the working point is the operating point resistance R_d, so a single LED Rd = (3.52 – 3.35) / (0.4 – 0.3) = 1.7Ω

Coeff. = Rd / ( V_o / I_o ) = 1.7 / ( 3.44 / 0.35 ) = 0.173

5.      The advantage of setting Rd Coefficient

In LED power supply specification, there is voltage output range, for example: 9-36V. Different output voltage means different number of LED in series, and then Rd is different.

If setting R_d, each time when the test voltage is changed, Rd needs to be set again. It is very inconvenient. Since R_d is in proportion to the test voltage, users only need set an R_d Coeff and the electronic load will automatically count its corresponding R_d.

6.      Simulating LED loading

After exit the menu, press the key On/Off and start loading. After LED power supply is connected to the electronic load terminals, then turn on the LED power supply because some LED power supply cannot be turned on with no load.

7.      Observing average voltage/current and ripple voltage/current

LED ON

Vpp   =      0.29 V  Vp+   =     25.23 V   Vp-   =     24.94 V

Vo  = 25.000V

 

LED ON

V     =    25.088 V   I     =   0.35790 A   P     =     8.978 W

Vo  = 25.000V

 

LED ON

25.088V   0.35790A    8.978W   70.2556Ω     0.29Vp   0.0238Ap

Vo  = 25.000V

LED ON

Ipp   =     0.0238 A  Ip+   =     0.3690 A   Ip-   =     0.3452 A

Vo  = 25.000V