4-Quadrant

In the context of power supplies, "4-quadrant" refers to the four possible operating modes defined by the polarity (positive or negative) of the output voltage and current. These modes are typically visualized on a voltage-current (V-I) graph, where the vertical axis represents voltage and the horizontal axis represents current. This creates four distinct operating regions:

Quadrant 1 (Source): Positive Voltage, Positive Current (+V, +I)
Quadrant 2 (Sink): Positive Voltage, Negative Current (+V, -I)
Quadrant 3 (Source): Negative Voltage, Negative Current (-V, -I)
Quadrant 4 (Sink): Negative Voltage, Positive Current (-V, +I)

Power supplies are classified by the number of quadrants in which they can operate.

Single-quadrant (or one-quadrant) power supplies typically operate only in Quadrant 1, sourcing power with a positive voltage and current.
Two-quadrant power supplies can both source and sink power. For example, a device operating in Quadrants 1 and 2 can source (+I) and sink (-I) current, both at a positive voltage.
Four-quadrant power supplies can operate in all four quadrants.

Most high-voltage power supplies are unipolar, meaning their output polarity is fixed. Users typically select either a positive polarity model (Quadrant 1 operation) or a negative polarity model (Quadrant 3 operation) based on their application requirements. Conversely, general-purpose low-voltage DC power supplies often feature floating outputs. These can be configured for either Quadrant 1 or Quadrant 3 operation depending on which output terminal is grounded.

A two-quadrant device is often called a bidirectional power supply. When such a power supply has the ability to return the absorbed (sunk) energy back to the AC power line, it is specifically referred to as a regenerative power supply.

A power supply that covers all four quadrants is known as a bipolar power supply. It can seamlessly transition between sourcing (acting as a power supply) and sinking (acting as an electronic load) for both positive and negative polarities of voltage and current.

A key advantage of bipolar power supplies is their high-speed response and ability to output a seamless waveform that transitions through zero without discontinuity. This makes them ideal for use as fast-slewing power amplifiers. Their four-quadrant capability allows them to effectively drive reactive loads (capacitive or inductive). Common applications include high-frequency ripple simulation tests for capacitors and impedance measurements.

SOURCE：The direction of voltage and current is same(supply). SINK：The direction of voltage and current is opposite(absorption).