How a Bidirectional Power Supply Works
Unlike conventional power supplies that deliver energy in only one direction, a bidirectional power supply is engineered to manage electrical energy flowing in two directions simultaneously. Internally, it integrates both AC/DC and DC/DC conversion circuits, giving it the dual capability to either supply power to a load or absorb and return energy back to the source.
This energy-return capability—commonly referred to as regeneration—is perhaps the most defining characteristic of these devices. Because excess energy is fed back into the grid rather than converted into waste heat, bidirectional power supplies are frequently described as "regenerative power supplies," and the two terms are largely treated as synonymous in engineering practice.
The block diagram of a typical bidirectional power supply reveals a three-stage internal architecture:
AC/DC Bidirectional Converter — Handles conversion between the AC utility grid and the internal DC bus in both directions, enabling two-way energy exchange with the power line. DC/DC Bidirectional Converter with Isolation — Provides galvanic isolation between the grid-side and output-side circuits, while regulating the DC power flow across both directions. Step-Up/Step-Down DC/DC Converter — Fine-tunes the output voltage to the precise level required for a given test scenario, offering flexible voltage delivery to the Device Under Test (DUT). Through this architecture, the power supply can seamlessly interact with both the commercial grid and the connected test load, enabling dynamic, bidirectional energy exchange.
Why Choose a Bidirectional Power Supply?
Superior Battery Simulation
One of the most valuable applications of bidirectional power supplies lies in their ability to emulate real-world battery behavior. The rapid growth of portable consumer electronics and electric vehicles (EVs) has made battery simulation an increasingly critical capability in product development. In practice, batteries do not maintain a fixed output: terminal voltage decreases as load current rises, and the electrical profile of a battery shifts considerably depending on its charge level, age, and condition.
Replicating these complex characteristics with a conventional DC power supply is inherently limited—such units can only source power and cannot absorb it. A programmable bidirectional power supply, by contrast, can faithfully reproduce a wide range of battery states, making it an indispensable tool for both R&D and quality assurance.
Seamless Source/Sink Transitions for High-Power Testing In demanding applications such as EV drivetrain testing, smooth transitions between power delivery (sourcing) and energy absorption (sinking) are essential. Bidirectional power supplies accomplish this without introducing voltage notches at the crossover point or causing current overshoot and undershoot—artifacts that can damage actual battery packs or compromise measurement integrity. This ensures stable, repeatable test conditions throughout the entire test cycle.
Practical Use Cases
Use Case 1: Constant Voltage / Constant Current (CV/CC) Operation One straightforward application is using the bidirectional power supply in conventional CV/CC mode—providing a stable, programmable voltage or current to a DUT. This is particularly effective for reliability testing, where engineers must verify how a device responds to varying supply voltages under real-world conditions.
While a standard power supply can adequately replicate primary (non-rechargeable) batteries in this role, testing rechargeable battery-powered devices demands a bidirectional unit. The power supply can accurately recreate the charge and discharge voltage profiles of various battery chemistries—from lithium-ion and lead-acid formulations to multi-cell configurations ranging from 12 V automotive batteries all the way up to the high-voltage packs used in modern EVs.
Use Case 2: Simulating Internal Resistance and Battery Aging Real batteries are not ideal voltage sources—they contain internal resistance that changes dynamically with the state of charge (SOC), temperature, and age. This resistance affects how much voltage actually reaches the load under different current draws.
By programming the internal resistance parameter (represented as r) within the bidirectional power supply, engineers can replicate these non-ideal characteristics. When r is set to zero, the unit operates as a pure CV source. Increasing r allows the simulated output voltage to droop under load, just as a real battery would.
Beyond SOC-dependent resistance, batteries also degrade over time. This degradation takes two forms: permanent capacity loss due to aging, and temporary performance reduction caused by factors such as low temperatures. A battery's State of Health (SOH) encapsulates both of these long-term changes.
By leveraging the variable resistance capability of a bidirectional power supply, test engineers can simulate the State of Degradation (SOD) of an aged or compromised battery. This allows products to be evaluated under "worst-case" power conditions—verifying, for example, that a device either continues to operate correctly or correctly triggers a low-battery warning when the source is degraded. Such testing is essential for ensuring product reliability across its full operational lifespan.
Use Case 3: Automotive and Electrified Vehicle System Testing Beyond consumer electronics, bidirectional power supplies play a central role in the development and validation of automotive systems—especially hybrid and electric vehicles.
A relevant example is the 48 V Mild Hybrid architecture, which incorporates regenerative braking and torque-assist functions. These systems involve complex energy flows between a 48 V belt-integrated starter-generator and the conventional 12 V vehicle electrical network, bridged by a bidirectional DC/DC converter.
A bidirectional power supply is well-suited to act as a simulator for both the generator and the converter in this topology. Engineers can validate the energy management logic under a variety of simulated driving conditions—accelerating, braking, and idling—without requiring a physical powertrain. This accelerates development timelines and enables more controlled, reproducible test environments than on-vehicle testing alone.
Bidirectional power supplies represent a significant advancement over traditional test power equipment, offering capabilities that are increasingly essential as electrification expands across industries.