Modular DC Electronic Load – 6310/A

Versatile System Configuration

The Chroma 6310A Programmable DC Electronic Load integrates microprocessor capabilities into each load module and a mainframe to provide simple and accurate parallel operations to optimize the speed and control among multiple load modules. All load modules may be configured to work synchronously or to test multiple outputs simultaneously, thus simulating real life applications.

Compatibility With 6310 Series

The 6310A series load modules are compatible with the 6310 series mainframes (6312/6314). In addition, the remote control commands are compatible between the 6310 and the 6310A series without needing to re-writing any remote control programs.

Module Load Design

The Chroma 6314A 1200W and 6312A 600W DC electronic load mainframes accept the user-installable 6310A series load modules for easy system configuration, and will mount in a 19″ instrument rack. The 6314A holds up to four 63102A load modules, which will result in an 8-channel 100W/channel load with standard front-panel inputs. This makes it ideal for testing multiple output switching power supplies and multiple DC-DC converters. There are also higher wattage modules that may be mixed and matched for an even more versatile system. Additionally, the GO/NG output port is useful for UUT’s pass/fail testing on an automated production line. All modules on the 6314A/6312A mainframe share a common GPIB address to synchronize and speed up the control of the load modules and the readback of data.

Application of Specific Load Simulation

The 6310A load modules operate in constant current, constant voltage, constant power or constant resistance to satisfy a wide range of test requirements. For example, the test of a battery charger can be simulated easily by setting the load to operate in constant voltage mode.

Each load module is designed with state-of-the-art technology and connects all the power MOSFET devices in parallel to insure high accuracy load control with a minimum drift of less than 0.1%+0.1%F.S. of the current setting. Chroma’s use of FET technology provides minimum input resistance and enables the load to sink high current even at very low voltages. For example, the model 63103A is capable of sinking 60A at 1V, and well-suited for testing the new 3.3V low voltage power supplies. Low voltage operation, down to zero volts, is possible at reduced current levels. The 6310A load module uses a photo coupler for isolation between the output and control sections, thus each load is isolated and floating. The user can use multiple load modules independently to test multi-output power supplies, or parallel them for high power testing applications.

Dynamic Loading and Control

Modern electronic devices operate at very high speeds and require fast dynamic operation of their power providing components. To satisfy these testing applications, the 6310A loads offer high speed, programmable dynamic load simulation and control capability. The figure below shows the programmable parameters of the 6310A modules:

The programmable slew rate makes the simulation of transient load changes demanded by real life applications possible. The 6310A internal waveform generator is capable of producing a maximum slew rate of 10A/μs, and dynamic cycling up to 20kHz. It’s dedicated remote load sense and control circuit guarantee
minimum waveform distortion during continuous load changes.

Parallel Control

The 6310A provides parallel control, which enables high power testing when a single module cannot meet the requirements of high power applications. Two or more load modules can be paralleled together to achieve the desired load. The 6310A comes with RS-232 standard for remote control and automated testing applications. USB and GPIB interfaces are available as options.

In addition, the 6310A, through its synchronized controls, provides an efficient solution for testing single output AC to DC or DC to DC converters by controlling multiple loads. The 6310A provides the capability to test up to 8 UUTs at a time.

Powerful Measurements

Each 6310A DC electronic load module has an integrated 16-bit precision A/D converter for voltage measurement with an accuracy of 0.025%+0.025% of full scale. The built-in resistive load current sensing circuit is capable of measuring current with an accuracy of 0.05%+0.05% of full scale. Also, short circuit can be simulated.
All measurements are done using remote sensing to eliminate any error due to voltage drops along the measurement path. The user can also select from a complete set of voltage and current measurements.

OCP Test

Modern switching power supplies are designed with over current protection (OCP) circuitry; therefore, it is important to test the OCP circuitry to make sure it is functioning within its designed specifications. The 6310A series provides an easy and fast solution for this testing.

By simply choosing the channel and setting the OCP parameters (start current, end current, step current and dwell time) from the front panel, the 6310A series provides a fast and easy OCP testing solution. The 6310A series will automatically detect the OCP point, making it an ideal solution for design verification as well as production line testing.

Timing Function

The 6310A DC electronic load includes a unique timing & measurement function, which allows precise time measurements in the range of 1ms to 86,400s. This feature allows the user to set the final voltage & timeout values for battery discharge testing and other similar applications.

For example, the figure on the right shows the 6310A internal timer starting at load ON, and ending when the battery voltage reaches the final voltage. The Timing function can be used in testing battery and super capacitor discharge, or other similar applications.

Digital I/O

The digital I/O interface makes the 6310A DC Load an ideal choice for automated testing requirements. Through the digital I/O, the 6310A can accept digital signals to trigger its functions (Load On/Off, OCP test, etc.) as well as current output status signals.

Problems found in using other mfg’s E-Loads or LED’s for testing drivers

As a constant current source, an 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 LEDs as a load; however, issues regarding the LED aging as well as different LED drivers may require different types of LEDs or a large number of LEDs. This makes it inconvenient for mass production testing.

Chroma’s Solution

Chroma has created the industries first LED simulator for LED driver testing with our 63110A/13A DC electronic load modules. 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/13A 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/13A’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/13A as a load.

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/13A LED mode load function.

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.

Conclusion

Most DC electronic 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 and OVP. For this reason, other E-Loads are not suitable for testing LED drivers.

The 63110A/13A 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.