LED Lighting has proven to be more efficient and have a longer life than the Incandescent and fluorescent lights. The Led is now available in almost all applications for lighting from Residential, Commercial and Industrial Lighting. Uses include the full range from Mood Lighting, Task Lighting, Security Lighting, Signage, and Computer/TV displays just to name a few.

Because LED’s are a current driven DC device they require a converter so they can be powered from an AC voltage. These Power supplies for LED lighting are most commonly referred to as LED Drivers. LED Drivers have different operating characteristics from the typical AC to DC, and DC to DC Power Supplies used for most electronic equipment. They are often a constant Current output rather than a Constant Voltage Output.

Chroma has created the industries first Electronic Load with an LED operating mode for simulating LED loading: the Chroma 63110A load module, for our 6310A series.

Key Features Include:

• Unique LED mode for LED driver test
• Programmable LED operating resistance (Rd)
• Programmable internal resistance (Rr) for simulating LED ripple current
• Fast response for PWM dimming test
• Up to eight channels in one mainframe
• 16-bit precision voltage and current measurement with dual-range
• Full Protection: OV, OC, OP and OT protection
• Two voltage ranges 0-100Vdc and 0-500Vdc
• Two 100Watt loads in 1 Load Module: Up to 500Vdc and up to 2Amps
• Loads can be paralleled for high current and power applications.

Chroma’s 63110A LED Load allows you to set the LED driver's output voltage, and current, the Electronic Load can then simulate the LED’s loading characteristics. The LED’s forward voltage and operating resistance can also be set to further adjust the loading current and ripple current to better simulate an LED. The 63110A LED Load design also has increased bandwidth to allow for PWM dimming testing.

What Makes LED Load Characteristics Unique

As shown on the V-I curve in Figure 1, the LED has a forward voltage VF and a operating resistance (Rd).

LED drivers are usually tested in one of the following ways;

• Using LEDs
• Using resistors for loading
• Using Electronic Loads in Constant Resistance (CR) mode, or Constant Voltage (CV) mode

However, all the above loading methods each have distinct disadvantages. First, those manufacturers who use LED’s as a load run into problems with the aging of the LEDs. Different LED drivers may require different types of LED’s or a number of LED’s. This makes it inconvenient for mass production testing. Second, resistive or linear loads can not simulate the Vf and Rd coefficient of an LED.

When using a Typical Electronic Load to test LED drivers, the CR (Constant Resistance) and CV (Constant Voltage) mode settings are used. These settings only can test stable operation and therefore, are unable to simulate turn on or PWM Dimming/intensity control.

Compare the actual LED characteristics to the Chroma 63110A Load

Figure 2 shows the current waveform from an actual LED.
Figure 3 shows the current waveform from 63110A's LED mode load function.
Figures 2 & 3, show the start up voltage and current of the LED driver with an LED versus the Chroma 63110A Electronic Load in LED Mode and they are very similar.
Figure 4 shows the dimming current waveform of an LED.
Figure 5 shows the dimming current waveform when using 63110A as a LED load.

Chroma’s 63110A LED Load will calculate and simulate the LED characteristics from the Vo, Io, Rd coefficient settings, as shown in the diagram below, Vo and Io are not the real loading values.

Io is determined by the LED driver, if the Io varies from the setting value then Vo will also vary. For Example, if Io setting is 100mA, but the LED driver output 110mA, then Vo will also increase. This is different from the standard CC and CV mode.