How a Variable DC Bench Power Supply Regulates Current

CV and CC form two regulation limits

The voltage setpoint and current limit define the requested operating window. In CV mode, voltage is regulated and the load draws current below the ceiling. When load demand would exceed that ceiling, the current loop becomes active and the supply lowers voltage to regulate current. The required operating point must still fit the supply’s power limit.

A simple resistive example

With a 10V setpoint and a 2A current ceiling, a 10Ω resistor draws 1A in CV operation. An ideal 2Ω resistor would demand 5A at 10V, so the supply instead reaches CC operation near 4V and 2A. This arithmetic example does not predict the startup behaviour of a nonlinear DUT.

How the feedback loop works

The instrument measures output current, compares it with a reference and adjusts the power stage to reduce the error. The implementation varies: a linear pass stage and a switching converter do not use an identical control mechanism. Filtering, sensing and control-loop dynamics affect the response to a load change.

Current limiting is not OCP shutdown

A current limit can maintain CC operation. OCP may disable output, latch a fault or require a reset depending on the instrument. Constant-power modes or autoranging features also vary by model; they are not a universal third mode on every bench supply.

Verify the result at the load

Measure the relevant voltage and current under the intended load, including startup if it matters. A lower voltage can be expected CC behaviour, but unexpected operation also warrants checks of load demand, connections, supply range and protection status.

Updated October 9, 2026