The basic of Electronic Load
Loads can be resistive,inductive,or capacitive. Real load behavior is typically more complex. They can be dynamic, constant current, constant voltage, crest factor, power factor or short circuit loads,etc.Prodigit DC Electronic Load can emulate constant current (CC), constant resistance (CR), constant voltage (CV), Dynamic and short circuit load; Prodigit AC Electronic Load can emulate constant current (CC),constant resistance(CR),crest factor (CF),power factor(PF)and short circuit load.Prodigit's Electronic Loads use Active components (such as Operation Amplifier and Power MOSFET) to sink power from power source. All Prodigit AC & DC Electronic Loads are equipped with Voltage/Current meter,GPIB (IEEE-488), RS-232C interface. The load can be controlled by software program,and Voltage/Current can be read back via GPIB/RS232 interface.These important feature makes Automatic Test System (ATE) integration more user friendly and flexible.
1. Constant Current (CC) mode : (AC/DC)
In the constant current mode Prodigit's Electronic Loads will sink a current in accordance with the programmed value regardless of input voltage.
The CC mode can be used to test voltage sources, and load regulation of DC & AC power supply. Load regulation is a power supply's ability to provide a stable output voltage under load variations.It is specified as a percentage deviation from normal output at a fixed input voltage and is calculated using the following formula:
2. Constant Resistance (CR) mode : (AC/DC)
In the constant resistance mode Prodigit's Electronic Loads will sink a current linearly proportional to the input voltage in accordance with the programmed resistance.
The CR mode can be used to test either voltage or current sources, and is normally used in testing power source start up and current limit.
3. Constant Voltage (CV) mode : (DC)
In the constant Voltage mode Prodigit's Electronic Loads will sink enough current(if available)to control the source voltage to the programmed value.
The CV mode can be used to test current source. It is frequently used to test current limit characteristic of power supplies. It can also be used for testing battery chargers where CV mode load can emulate a bettery's terminal voltage.
Dynamic load operation causes Prodigit's Electronic Loads to periodically switch between two load levels.A power supply's regulation and transient response can be evaluated by monitoring its output voltage under varying combination of Load High/Low current levels, High/Low current level duration, and Rise/Fall slew rate. The 3310 series Electronic Load offer CC mode only when using Dynamic mode.
Dynamic mode can be used to test the transient response of a power supply. Most commonly used loads are dynamic;for example, in a computer the disk drive draws varying amounts of current. The dynamic mode can simulate this condition.
Crest factor is the ratio of the zero to peak value to the rms value of a load current wave form. This term is often used to specify the maximum peak amplitude the an AC power supply (or UPS) can source (relative to its maximum rms rating) without distortion.
Most power input circuitry (without power factor correction) consists of a rectifier diode and capacitor filter circuit, which generates a pulse AC line current. The major purpose of Prodigit AC Electronic Loads is to simulate this current wave form. Typical crest factor of the input current of a computer system ranges from 2.0 to 3.0. Prodigit AC Electronic Loads can simulate crest factor from 1.414 to 3.5 in eight steps, i.e. same RMS current with different peak current (for example, with 10A RMS load current, the peak current can be 14.14A to 35A),The Crest Factor feature can test output high peak currents.
Power Factor is the ratio of average power value to the Vrms×Arms
The following equation is true when the voltage and current wave form are Sinusoidal.
With a pure resistive load, voltage and current wave form are in phase, that is
When loads very from pure inductive through resistive to capacitive, the phase angle varies from -90¢Xto 0¢Xto + 90¢X, and power factor veries from zero to unity.
Prodigit 3260 series AC Electronic loads can simulate Inductive or capacitive loads by programming the power factor from 0 to unity. These are the first active AC loads to simulate inductive and capacitive load. All the settings are programmable via front panel or GPIB interface. The load V/A/W can be read back to computer via GPIB interface.
7. Short Circuit Load : (AC & DC Load)
An DC/AC power supply's output terminals having very low resistance. A power supply's protection circuit should be activated to limit output current power when these conditions exist (short circuit). This is an important power supply feature as it protects equipment from damage.
Prodigit's 3310 and 3320 series DC Electronic Loads and 3260 series AC Electronic Loads can simulate short circuit conditions with a dedicated short function key.It is not necessary to have an external shorting relay to test AC & DC power supplies when using Prodigit's Electronic Loads.
Short circuit current and voltage is displayed on the front panel's digital current and voltage meters. There is no more necessary to have an external short relay to test AC & DC Power Supply when using Prodigit AC & DC Electronic Load.