Re: Is "Direct drive LED" more efficient than using a switch mode LED driver?
Is "Direct drive LED" more efficient than using a switch mode LED driver?
Strictly electrically speaking, No. SMPS are to this day the most efficient because the main principle of operation is timed controlled On Off as a mean of determining how much power goes to the load. In between the voltage source and the load there is a switch and some coils and capacitors. Switch do not absorb energy, where as coils and capacitors will absorb energy only to eject it at a further moment. In theory, no power is lost during the transformation cycle. In practice today's SMPS reach 95% efficiency.
In a Direct Drive Mode, to power some LEDs, first those leds are not the typical 3V type (or if they are, there are a multitude in series such that each LED receive no more then it's maximum rated voltage) Direct Drive mode will exploit the LED range from minimum Light emission voltage to the Maximum rated voltage. LEDs can receive a little more voltage then the typical max without burning immediately. This feature is exploited in Direct Drive mode. Simply put, Direct Drive Mode is an arrangement for which the LEDs receive a range of voltage from 0 to beyond max and will emit light in a not so efficient way compared to a pure DC power. This method will result in some power absorption that will not necessarily transform into light as efficiently as DC.
It's pretty much the same as if you were driving a 3V LED with a 5V supply with a resistor in series to avoid overheating the LED. Direct Mode is not 100% direct. It is a kind of Direct Switched mode that will happen many times during the 1/100 second cycle. The Direct Mode circuit that monitor the LED power is powering each LED gang in such a way that each gang do not receive more then the absolute tolerable maximum voltage. Such slack method has it's disadvantages, the first being that you are not using the LEDs in the most efficient way possible. That inefficiency is reflected in lost heat instead of the desired light. The LEDs are going to emit light and Infrared as a form of heat energy as well as heat by convection to the ambient air or heat dissipating material to which it is fixed. In such case the LED will act as a light emitting diode as well as the resistor in series stated in the above hypothetical circuit. In Direct Mode Drive it is the engineer responsibility to make sure all the LEDs are not receiving more then the critical maximum current for life expectancy.
So, electrically speaking, Direct Mode, which should rather be called Direct Switched Mode, will not exhibit 95% efficiency like an SMPS but will end-up costing much less then a bulky Coil,Electrolytic Capacitor, Switcher SMPS unit and will be much smaller and much lighter.