Circuit Types

Constant Current vs Constant Voltage

There is often confusion surrounding LED drivers and the requirements for different circuits. There are two main driver/PSU types used - Constant Current (CC) & Constant Voltage (CV) - and each relate to a different circuit wiring configuration; Series or Parallel.

Constant Current (CC)

LEDs typically require a fixed (constant) forward current (IF) across the P-N junction for normal operation. Many LEDs can be driven at different currents; for example a single high power LED may be able to run at 350mA, 500mA or 700ma, resulting in an increase in Forward Voltage (VF) across the diode, greater energy consumption (W), more heat and typically higher lumen output (Lm).

An LED driver may be designed with a single fixed or variable output current and a defined output voltage range. Typically there may be a minimum load requirement, but as more LEDs are connected to the array, and depending on the selected current, the voltage requirements on the driver will increase up to the maximum voltage.

Multiple LEDs within a circuit or array must be wired in series, whereby all components are connected along a single path allowing the same current to flow through each LED. A break in the circuit results in a loss of continuity meaning none of the LEDs will work.

Constant Voltage (CV)

Constant voltage circuits typically have a fixed voltage of 12VDC or 24VDC supplied to the circuit. In general this type of circuit is used in linear LED lighting applications such as MONOFLEX LED tape. So rather than the driver delivering a fixed current and the voltage demand being regulated by the load, the opposite is true, whereby a fixed (constant) voltage is delivered to the circuits. Multiple LED strips can then be connected to the driver in parallel and each strip will receive the same voltage being delivered by the driver. So why do linear LED circuits differ?

Well, in the case of most flexible linear LED you typically have a 5m reel of LED that can be cut at 100mm intervals (MONOFLEX-S60). Each of the 100mm sections is in fact a series circuit typically consisting of 6 LED, each LED requires a fixed (constant) current. Cheap, poor quality LED tape will use in-line resistors to regulate the current to the 6 LED circuit. However, with high quality products such as MONOFLEX, an on-board constant current Integrated Controller (IC) is used. The IC is in fact a miniature driver accurately controlling the current to the LEDs within each of the 100m sections.

Each section of the tape is then joined together in parallel ensuring that each section of the tape is receiving the same fixed voltage (12VDC or 24VDC). This allows the tape to be cut in between each section, a power cable connected and a new independent circuit created. It also means that if a section of the tape gets damaged or fails the rest of the tape will continue to work, you also then have the possibility to remove the damaged section and solder in a new piece as required.