Lamp Driver

Traditional incandescent and fluorescent lamps are mains-driven devices that operate directly from a 240 V 50 Hz AC supply (UK figures). Today, though, these are increasingly being replaced by higher-efficiency, longer lifetime LED lamps that run on a DC voltage – typically 12 Volts. Accordingly, LED lamps must have a power supply to convert 240 VAC into the DC level they require.

However, a simple AC/DC power supply that simply rectifies and converts the incoming electricity feed into DC power is insufficient for safe and reliable LED lighting operation. This is primarily because the forward voltage (Vf) of a light emitting diode (LED) – the voltage needed for the LED to start conducting and light up – decreases as the LED’s temperature increases. This means that more current will be drawn from the power supply. While a moderate increase in current will result in a higher LED light output, the effect can become cumulative and lead to thermal runaway. The LED device will become steadily hotter and eventually burn itself out.

The solution is to use a specialist power supply called an LED driver; this is available as either a constant-current or constant-voltage device. Constant-current drivers supply a constant current irrespective of the voltage drop that appears across their output terminals; this current-limiting capability prevents excess current, thermal runaway and any associated damage.

Constant-voltage drivers are lower-cost, more suitable solutions that will suffice with pre-manufactured assemblies like LED bars, strips or ropes, as these have built-in current-limiting resistors.