Current source (constant current, bench CC mode) · Exterior view
Voltage display (V)Current display (A)Voltage adjustment (CV)Current limit adjustment (CC)On / off switchOutput terminals (+ red, − black) · green: chassis ground
CC indicator, current setting and red-black output terminals
Benchtop power supply; current and voltage setting on the front panel
Power supply

Current source (constant current, bench CC mode)

In simple terms
What is this?

A source that always tries to push the same amount of current. Like a pump that moves water at the same speed uphill or on the flat.

What is it for?

The current stays constant even if the load changes; you see how the voltage moves accordingly.

Where do you see it?

While a phone charges, when the battery is empty the charger mostly keeps the current constant.

How do you spot it?

A bench box with current and voltage knobs on the front; there are two output sockets.

Caution:

The voltage is not unlimited; with the output open or a very large load the current goal cannot be reached.

Technical definition

A source that adjusts its output voltage to keep the current through the load constant. A lab supply’s CC mode shows this behavior at the current limit. The voltage does not rise without limit; when it reaches the compliance voltage limit, the target current cannot be supplied and the source switches to CV mode.

Example current10 mA adjustable
ModeCC, constant current
Compliance voltageAt most 30 V on the example source
Schematic symbol Same in IEC and ANSI

IEC 60617: the drawing style used in Türkiye and Europe.

Pins 2
1Current output (p)Red terminal; delivers conventional current to the loadp
2Current return (n)Black terminal; current flows back to the sourcen
Features typical
Example current
10 mA adjustable
Mode
CC, constant current
Compliance voltage
At most 30 V on the example source
Load effect
In the CC range the voltage varies with the load
Circuits: Light
Reaches the voltage limit; the current drops to zero
Short circuit
Limits the current; power and connection limits apply
Ideal model
Mathematical approximation with no compliance limit
Example part
0–30 V lab supply, example of 10 mA in CC mode
Common mistakes
Thinking the voltage is unlimitedIf the current goal and the voltage the load demands exceed the source limit, CC cannot be maintained.
Leaving the output openIn an open circuit the output rises to the voltage limit. Turn the output off before connecting the load and set the voltage ceiling.
Thinking it protects every loadSet the current to suit the load’s limit. When connecting an LED, the stored output charge can also cause a surge; follow the manufacturer’s procedure.

Test with a multimeter

Test whether this part is good with the multimeter on the measurement screen.

Take a measurement
Where it is used
Studying the difference between CC and CVLow-current load testMeasuring voltage as the load changes
Related lessons
Voltage, current, resistance
Module 1 · From zero to your first circuitOhm’s law
Module 1 · From zero to your first circuitMeasuring current and the fuse
Module 2 · Measuring with a multimetersoon
Try it in the Lab