Compact electronic DC load
The LD300 is an inexpensive electronic load which is suitable for testing and characterising a wide variety of dc power sources.
It can be used to investigate the behaviour of many different types of power source such as batteries, solar cells, fuel cells or wind generators, as well as electronic power supply units.
Its wide voltage/current range, multiple operating modes and built-in transient generator give it the versatility to offer test solutions from the design laboratory through to the component test area.
Low minimum operating voltage
The LD300 can operate at voltages below 500mV for currents up to 10 amps. At higher currents the fixed internal resistance of 25mW gradually raises the minimum operating voltage, but it remains below 1 volt up to 40 amps and below 2 volts up to 80 amps.
This low operating voltage allows it to be used for many low voltage applications for which other electronic loads are unsuitable.
Transient generator and variable slew
The LD300 incorporates a full variable frequency, variable duty cycle transient generator.
Switching between the two preset levels can be done at any frequency between 0.1Hz and 10kHz.
The transient generator can be used in all operating modes.
The rate of change between levels (slew rate) is controllable over a wide range.
Slew rate control applies to all changes of level including remote control and manual changes between level A and level B.
A slow-start function can be selected for situations where latching would otherwise occur at switch-on.
High resolution setting & measurement
The levels for each operating mode are set using high quality ten turn potentiometers for both level A and level B.
Levels are displayed using four digit meters which provide resolution down to 1mA, 1mV and 1mW.
Settings for slew rate, transient frequency, duty cycle and drop-out voltage can also be displayed.
In measurement mode the meters have an accuracy of 0.1% for voltage and 0.2% for current.
Current waveform monitor
It is often important to be able to observe the load current waveform on an oscilloscope. The LD300 provides a calibrated monitor output for this purpose as well as a sync output from the transient generator.
The monitor output has several volts of compliance with respect to the load input, thus allowing it to be connected to a grounded oscilloscope without current divertion.
Five modes of operation
Constant current mode is used for load testing of normal voltage-source power supplies and for constant current discharge testing of batteries.
This mode provides rapid measurement of power source regulation (V/I characteristics).
Constant voltage mode is used for load testing of constant current power supplies. The unit operates as a high power shunt regulator.
Constant power mode simulates a load whose power consumption is independant of the applied voltage. This is true of many types of equipment that incoporate switchmode regulators.
This mode may be particularly suitable for testing power sources of portable devices such as Lithium-ion batteries.
Constant resistance mode simulates a standard resistive load by providing a current drain proportional to voltage. Settings are displayed in Ohms or milli-Ohms.
Unlike fixed resistors or rheostats, the load provides a precisely controllable resistance with high power dissipation over a wide value range.
Constant conductance (CG) mode is also incorporated. As well as showing settings in amps per volt, this mode provides better resolution when setting very low equivalent resistance values.
Adjustable voltage drop-out
Some power sources, such as rechargeable batteries, can be damaged if their output voltage falls below a certain level.
The LD300 provides automatic protection by incoprorating fully variable voltage dropout (CI, CR, CG and CP modes). If the voltage applied to the load falls below a preset level, the load current is rapidly reduced to zero.
The LD300 incorporates analogue remote control for all modes of operation. When "external voltage" is selected the level becomes linearly proportional to the voltage applied to the remote control inputs on the rear panel.
Any waveform can be used as the control voltage allowing complex load conditions to be simulated using, for example, an arbitrary waveform generator.
Alternatively, a logic signal can be used to switch between levels. When "external TTL" is selected, the level is switched between the two preset levels in response to an external logic signal.
The remote control inputs have a wide common mode range allowing the control voltage to be referenced independently of the load terminal voltages.