What is an electronic load ?
Keywords: Operating Modes, Dynamic Load, AC Simulation / LIN CC, Battery Testing.
A load can be resistive, inductive, or capacitive. True load types are more complex; they can be dynamic, constant current, constant resistance, constant voltage, peak factor, power factor, or short-circuit loads, etc.
GW Instek and its sub-brand "PRODIGIT" offer DC electronic loads that can simulate constant current, constant resistance, constant voltage, dynamic, and short-circuit loads; GW Instek's AC/DC electronic loads can simulate constant current, linear constant current, constant resistance, constant voltage, constant power, peak factor, power factor, and short-circuit loads.
Electronic loads draw power from a power source using active components. All AC & DC electronic loads are equipped with voltage and current meters, and communication interfaces such as GPIB (IEEE-488), USB, LAN, and RS-232C.
These loads can be controlled by computer software, and voltage/current readings can be obtained/exported via the communication interface. These important features make automated test systems (ATE) more integrated, allowing users to operate the instruments smoothly and easily.
The following are the definitions and applications of electronic load operating modes:
| Mode / Feature | Applicable Electronic Loads |
|---|---|
| Constant Current (CC) | AC and DC electronic loads |
| Linear Constant Current (LIN CC) | AC electronic loads |
| Constant Resistance (CR) | AC and DC electronic loads |
| Constant Voltage (CV) | AC and DC electronic loads |
| Constant Power (CP) | AC and DC electronic loads |
| Dynamic Load | AC and DC electronic loads |
| Crest Factor | AC electronic loads |
| Power Factor | AC electronic loads |
| Short Circuit | AC and DC electronic loads |
1. Constant Current (CC) Mode
In constant current mode, regardless of the input voltage, the electronic load will draw current according to the set value.
Application:
Constant current mode can be used to test the load regulation of voltage sources and AC & DC power supplies.
Load regulation is the ability of a power supply to provide a stable output voltage under varying load conditions. It is the percentage of the power supply's output voltage deviation and is calculated using the following formula:
2. Linear Constant Current (LINear CC) Mode
In linear constant current mode, regardless of the input voltage, GW Instek's AC/DC electronic loads' exclusive LIN CC mode draws current according to the set value, and the current waveform changes linearly according to the input voltage waveform.
Application:
LIN CC mode features an AGC circuit, where the control signal reacts to changes in the input voltage. This is called LIN CC mode.
As long as the amplitude of the input signal exceeds the adjustable reference voltage applied to the peak detector, the AGC circuit generates a fixed-amplitude output signal. The range of the input voltage can be changed by altering the reference voltage, thus achieving a fixed-amplitude output.
The AGC circuit can respond almost instantaneously to and control sudden increases in the input voltage. The AGC circuit is particularly suitable for stepped waveforms, square waves, and situations where the input voltage waveform is distorted.
3. Constant Resistance (CR) Mode
In constant resistance mode, the electronic load draws sufficient current to control the voltage source to a set value.
Application:
Constant resistance mode can be used to test voltage or current sources, and is typically used to test the startup and current-limiting characteristics of power supplies.
4. Constant Voltage Mode
In constant voltage mode, the electronic load draws sufficient current to control the voltage source to a set value.
Application:
Constant voltage mode can be used to test current sources. It is typically used to test the current-limiting characteristics of power supplies. Furthermore, constant voltage mode loads can simulate the terminal voltage of batteries, so they can also be used to test battery chargers.
5. Constant Power Mode
In constant power mode, the electronic load draws sufficient current based on the voltage to control the power to the set value.
Application:
Primarily used for battery capacity and lifespan testing.
Currently, most portable electronic devices on the market require primary or secondary batteries. During use, the battery's output voltage gradually decreases with usage time and power (as shown in (a)), while its output current increases over time (as shown below) to maintain a certain level of output power (as shown in (c)). The duration for which the output power can be maintained at a certain level is one of the important indicators of the battery's energy storage capacity.
GW Instek's full series of AC/DC and DC electronic loads allow users to set the power level and generate a load current at that power level based on the battery voltage. The load current is automatically adjusted according to changes in the battery voltage to ensure that the battery discharge power is always maintained at the set value (as shown in (d)). By combining this with time recording, the battery's stored energy or capacity life can be verified.
In constant power mode, the load variation of the battery during actual use can also be simulated. By selecting the dynamic constant power load in dynamic mode, the battery capacity and life test under the actual power variation environment can be carried out (as shown in (e)).
Application of constant power operation mode
6. Dynamic Load
A dynamic load operates by periodically switching between two load levels. The regulation and transient response of a power supply are monitored using an oscilloscope to observe the output voltage waveform under a mixture of high and low current levels, duration, and rate of increase/decrease. Therefore, all GW Instek DC electronic loads have a constant current mode that also provides a dynamic mode.
Application:
Dynamic load mode can be used to test the overall circuit response of a power supply. In practice, most loads used are dynamic loads; for example, the operating current of a computer disk drive changes when it is active or inactive. Dynamic load mode simulates this situation.
7. Peak Factor Load
The peak factor is the ratio of the peak value of a waveform to its RMS value. This specification is typically used to describe the ability of an AC power supply to output peak load current without distortion.
Application:
Most power input circuits include a rectifier diode and capacitor filter circuit, thus generating a pulsed alternating current.
The primary purpose of AC/DC electronic loads is to simulate current waveforms. The peak factor of computer input current ranges from approximately 2.0 to 3.0. GW Instek’s AEL-5000 series AC/DC electronic loads can simulate peak factors from 1.414 to 5.0.
8. Power Factor Load
Power factor is the average power value divided by Vrms × Arms.
When the voltage and current waveforms are sinusoidal, the following formula is valid:
When there is only a resistive load, the voltage and current waveforms are in phase, that is
When the load changes from purely inductive to resistive and then to purely capacitive, the phase difference between the current and voltage changes from -90° to 0° and then to +90°. Simultaneously, the power factor changes from 0 to 1 and then back to 0.
Application:
GW Instek’s AEL-5000 series AC/DC electronic loads can simulate inductive or capacitive loads with a programmable power factor from 0 to ±1. All settings are readable and can be configured via the front panel or GPIB interface, with load V/A/W via the GPIB interface.
9. Load Short Circuit
A DC or AC power supply has a very low output impedance at its output terminal. When a short circuit occurs, the power supply's protection circuitry should activate to limit the output current. This important feature is to protect the power supply from danger.
Application:
GW Instek's full series of AC/DC electronic loads and DC electronic loads can simulate short-circuit conditions with a single short-circuit function key, eliminating the need for external short-circuit relays to test AC & DC power supplies.
The digital ammeter and voltmeter on the front panel of the electronic load will display the current and voltage during a short circuit.
When using electronic loads from GW Instek and PRODIGIT, no external short-circuit relay is required to test the DC or AC power supply.
From "Energy Consumption" to "Energy Provision": In-depth Analysis of the Core Technologies and Application Matrix of Modern Electronic Loads.
In the development of power electronic systems, if the power supply is the inexhaustible "heart," then the electronic load is the "strict teacher" defining the system boundaries. It is not merely for consuming electrical energy; a more precise definition would be: "a programmable energy extraction system designed to simulate the behavior of real loads under various extreme conditions."
1. The Essence of Electronic Loads: Active Simulation beyond Resistance
Traditional slide wire rheostats can only provide a fixed linear load, while modern electronic loads (such as those from GW Instek and its sub-brand Prodigit) utilize active power devices (MOSFETs/IGBTs) operating in the linear region. Through a high-speed feedback circuit, they adjust the current drawn in real time, achieving the following four basic DC modes:
Constant Current, CC
I remains constant regardless of voltage variations.
• Key applications:
Testing current sources or simulating battery voltage characteristics. In battery charger testing, CV mode can simulate the process of a battery going from low voltage to saturation voltage.
Constant Voltage, CV
The electronic load adjusts the current drawn to maintain the terminal voltage at a set value.
• Key applications:
Testing current sources or simulating battery voltage characteristics. In battery charger testing, CV mode can simulate the process of a battery going from low voltage to saturation voltage.
Constant Resistance, CR
Simulates a linear resistor, obeying Ohm's law V = I x R.
• Key applications:
Startup behavior testing of power supplies to prevent damage to the device under test caused by overcurrent during startup.
Constant Power, CP
Maintaining P = V x I as a constant, the current increases linearly as the voltage decreases.
• Key applications:
Battery discharge capacity (Wh) measurement. For mobile devices (such as laptops and AI phones), CP mode can realistically simulate the constant power consumption requirements of the device during operation.
2. AC Load: Defining an Advanced Dimension of Power Quality
For inverters or uninterruptible power supplies (UPS), AC electronic loads offer more sophisticated simulation capabilities, marking a watershed moment in high-end testing technologies:
• LIN CC (Linear CC)
This is a technological highlight of GW Instek. When the input voltage waveform is distorted, LIN CC ensures that the current waveform changes linearly and synchronously with the voltage waveform, which is crucial for testing power supply systems with harmonic interference.
• Crest Factor, CF：C.F. = Ipeak/ Irms
Simulates the pulse current generated by a rectifier circuit. The CF value of a typical computer load is about 2.0 to 3.0, while a high-efficiency AC load can be simulated up to 5.0.
• Power Factor, PF：P.F. = P/S
By controlling the phase difference between current and voltage, an inductive or capacitive load can be simulated, which is essential for evaluating the virtual power handling capability of power distribution equipment.
3. Practical Scenarios: Why Do You Need "Dynamic Load" and "Short-Circuit Simulation"?
In today's high-performance computing (HPC) and AI server power supply development, the load is not constant.
- Dynamic Load
When an AI chip switches operations, the current experiences sudden changes with an extremely high slew rate. An electronic load can be used to set the T_1/T_2 time intervals and rise/fall rates to test the transient response of the power feedback loop. If the system is unstable, noticeable oscillations will be observed on the oscilloscope. - Short Circuit
Manual short-circuiting is physically dangerous and cannot be repeated. By utilizing the built-in short-circuit function (low R_on state) of the electronic load, it is safe to verify whether the PSU's protection action enters "hiccup mode" or "latch-off".
4. Digital Transformation: Integration of ATE Automated Test Systems
Modern electronic loads come standard with LAN, USB, and GPIB communication interfaces. Through software control, testing is no longer just about reading numerical values, but also includes:
• Automated report generation: reducing human error in transcription.
• Long-term monitoring: automatically recording voltage decay curves for hundreds of hours in battery life testing.
• Remote diagnostics: real-time monitoring of test status in AI-powered automated production lines.
Editor's Note
The value of an electronic load lies not in how many watts it can "consume", but in how closely it resembles a real load. From basic CC/CV/CR/CP to sophisticated LIN CC and dynamic transformations, selecting the appropriate mode and slew rate setting is key to determining the reference value of the test data.
Contact Us:
Diana
Digital Service Specialist
E-mail: diana@goodwill.com.tw