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| Problems found in using other mfg's E-Loads or LED's for testing drivers |
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As a constant current source, the LED driver has an output voltage range with a constant output current. LED drivers are usually tested in one of the following ways:
With LEDs;
Using resistors for loading;
Using Electronic Loads in Constant Resistance (CR) mode or Constant Voltage (CV) mode.
However each of these testing methods have their own disadvantages.
As shown on the V-I curve in figure 1, the LED has a forward voltage VF and a operating
resistance (Rd). When using a resistor as loading, the V-I curve of the resistor is not able to
simulate the V-I curve of the LED as shown in blue on figure 1. This may cause the LED driver
to not start up due to the difference in V-I characteristic between the resistors and the LEDs.
When using Electronic Loads, the CR and CV mode settings are set for when the LED is
under stable operation and therefore, is unable to simulate turn on or PWM brightness control
characteristics. This may cause the LED driver to function improperly or trigger it’s protection
circuits. These testing requirements can be achieved when using a LEDs as a load; however,
issues regarding the LED aging as well as different LED drivers may require different types of
LEDs or a number of LEDs. This makes it inconvenient for mass production testing.
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| Chroma's Solution |
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Chroma has created the industries first LED simulator for LED driver testing with our 63110A electronic load. The LED’s forward voltage and operating resistance can be set to further adjust the loading and ripple current to better simulate LED characteristics. The 63110A load also has increased bandwidth to allow for PWM dimming testing.
Figure 2 shows the current waveform from a LED load. Figure 3 shows the current waveform from 63110A's LED mode load function. From figures 2 and 3, the start up voltage and current of the LED driver is very similar. Figure 4 shows the dimming current waveform of the LED. Figure 5 shows the dimming current waveform when using 63110A as a load. |
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| The internal resistance (Rr) can be adjusted to simulate the LED driver output ripple current. The traditional E-load can not simulate the ripple current of LED shown as Figure 6. Figure 7 shows the ripple current waveform from a LED load. Figure 8 shows the ripple current waveform from the 63110A LED mode load function.
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| Figure 9 shows the current waveform from a resistive load. Figure 10 shows the current waveform from a CR mode of an Electronic Load loading. Figure 9 and 10 current waveform differs significantly from that of LED loading, especially the voltage and current overshoot, which may cause the LED driver to go into protection. Using a resistive load or CR mode to test LED drivers may cause the LED drivers to fail to turn on as shown in Figure 11. |
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| Conclusion |
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Most E-Load manufacturers have similar designs but are unable to simulate the I-V curve of the LED as well as internal capacitances causing abnormal OCP, OVP. Therefore, other E-Loads are not suitable for testing LED drivers.
The 63110A was specifically designed to simulate LED characteristics to test the functions of LED drivers. Not only can it test in stable conditions, it can also test turn on, PWM dimming characteristics of the LED driver and the Rd value can be adjusted according to the LED V-I curve making it an irreplaceable load choice for LED driver testing. |
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| 6312A |
Mainframe for 1 or 2 Modules |
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| 6314A |
Mainframe for up to 4 Modules |
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| 63110A |
LED Simulating DC Load Module, 2A/300V/100Wx2 channels |
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New Standard for Low Power Programmable AC Power Sources |
The 61500 series defines a new standard of lower power AC power sources. Features included are power line disturbance simulation, programmable output impedance, comprehensive measurement functions and wave shape synthesis.
Provides 0-300VAC or 0-424VDC output from a single source. Ultra-pure/low distortion output for designed for commercial applications.
Smaller, lighter and expanding setting and read-back functions.
Provides 6:1 peak current capability and includes power amplifier mode. |
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The 66201 Digital Power Meter is packaged in a 2U high, half rack enclosure suitable for bench top or system integration and includes simple measurement functions designed for low power applications (maximum current 2A).
Model 66202 Digital Power Meter includes a 2-shunt design to provide highly accurate readings for both low and high current measurements. In addition to the parameters measured by Model 66201, the 66202 includes Inrush current, Total Harmonic Distortion of V/I, and Energy measurements. With these practical functions, The Model 66202 is suitable for the most demanding of R&D and quality control departments.
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