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In an ideal world, all loads would be resistive without any reactive component (inductance or capacitance), but this is not the case in the real world. Many types of loads, for example, batteries and electromagnets, have a high capacitance and inductance respectively, and as such, require a tailored solution to the application at hand. These parameters are defined as follows:

Capacitive reactance is defined as -JXC = 1 / (2 * π * F * C)

Inductive reactance is defined as +JXL = 2 * PI * π * L

Where: j is the imaginary component of reactance
XC is the capacitive impedance in Ohms
XL is the inductive impedance in Ohms
F is the frequency at which the power supply is being driven in Hertz (Hz)
C is the value of the capacitance of the load in Fahrads (F)
L is the value of the inductance of the load in Henries (H)


Inductive loads are characterized by having an impedance that is not purely resistive, but rather a combination of DC resistance and inductance: R + JL.

The (+)J indicates a leading phase angle for inductive reactance. The JL component can be ignored while operating the power supply in DC or at very low frequencies; however, at higher frequencies, the JL component, or inductance, increases as a function of frequency.

If the JL component is too high due to a high frequency programming signal driving the power supply, the power supply will tend to oscillate. This oscillation can be compensated for by adding a capacitor at the output to cancel out the JL component.

KEPCO has power supplies specially designed to work well with inductive loads as they have already been compensated to work with high inductances. These power supplies are excellent drivers of motors, magnets, and any other device that has a high inductance. The only thing to be aware of is that the dynamic response of the power supply will become slower as more compensation is added, however this is a necessity when driving high inductance loads. Inductive loads are usually driven in current mode, so the current control loop of the power supply is slowed down to provide high accuracy and precision without oscillation when high inductive loads are used.


Capacitive loads are characterized by having an impedance that is not purely resistive, but rather a combination of DC resistance and capacitance: R - JC. The (-)J indicates a lagging phase angle for capacitive reactance.

The JC component adds to the output capacitance which already exists internally in the power supply as filters. Addition of more capacitance may cause the output to oscillate, as is the case with inductive loads (see Inductive loads, above). KEPCO has power supplies specialized in driving high capacitance loads. The dynamic response of these power supplies has been slowed down so that a high capacitive load will not cause it to oscillate. If your application has a high output capacitance, please contact us so that we can discuss your specific application and requirements.


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