Constant current (CC) and constant voltage (CV) are two fundamental modes used in power supplies and DC-DC converters. Understanding the difference is essential when working with battery charging, LED driving and adjustable power modules.
This article explains how CC and CV modes work, when to use them and why many modern modules combine both.
What is Constant Voltage (CV)?
In constant voltage mode, the power supply maintains a fixed output voltage regardless of the load (within its limits).
- Voltage stays constant
- Current changes depending on load
Example:
- 5V power supply
- Load draws 100mA → supply provides 100mA
- Load draws 1A → supply provides 1A (if capable)
This is the most common mode for powering electronics.
What is Constant Current (CC)?
In constant current mode, the power supply limits the current to a fixed value.
- Current stays constant
- Voltage adjusts as needed
Example:
- Set current limit: 500mA
- Voltage increases or decreases to maintain 500mA
This mode is essential when the load must not exceed a certain current.
Key Difference
| Mode | What is Fixed? | What Changes? | Typical Use |
|---|---|---|---|
| CV | Voltage | Current | Powering circuits |
| CC | Current | Voltage | Charging, LEDs |
Why Constant Voltage is Used for Electronics
- Microcontrollers require stable voltage
- Digital circuits depend on defined voltage levels
- Most modules are designed for fixed voltage operation
Example: Arduino and ESP32 systems require stable 5V or 3.3V.
Why Constant Current is Important
- Protects devices from excessive current
- Used for battery charging
- Required for LED driving
Without current limiting, some loads can draw too much current and be damaged.
CC/CV Combined Mode
Many power modules support both modes simultaneously:
- Operate in CV mode under normal conditions
- Switch to CC mode when current limit is reached
This makes them very versatile.
Example: Battery Charging
- Start with constant current (CC)
- Voltage rises as battery charges
- Switch to constant voltage (CV) at target voltage
- Current gradually decreases
This is the standard CC/CV charging method for lithium batteries.
Example: LED Driving
- LEDs require controlled current
- Voltage varies depending on LED characteristics
A constant current driver ensures consistent brightness and prevents damage.
Adjustable CC/CV Modules
Many DC-DC converter modules allow setting both voltage and current:
- Set maximum output voltage
- Set maximum current limit
These modules are widely used for:
- Battery charging (non-lithium or controlled setups)
- LED applications
- General-purpose adjustable power supplies
Visual Behavior
- CV mode: flat voltage, current varies
- CC mode: flat current, voltage varies
The system transitions smoothly between both modes depending on load conditions.
Common Mistakes
- Using CV mode for current-sensitive devices
- Ignoring current limits
- Charging batteries without proper CC control
- Driving LEDs without current limiting
Conclusion
Constant voltage and constant current modes serve different purposes in electronics. CV is used for powering circuits, while CC is essential for protecting components and controlling loads.
Understanding both modes allows you to use DC-DC converters, charging modules and power supplies more effectively and safely.