Requirements for LED drivers
LED lamps and luminaires are on the rise. More and more manufacturers are starting to implement their own ideas here. Along with this, it is inevitable to deal with new technology as well. For the complete specification of an LED luminaire, the properties of the LEDs used contribute only in part. Especially with regard to service life, dimmability and also system luminous efficacy, the LED control gear used plays a key role. These properties of a constant current source are explained in more detail below for our customers and readers.
Overview
What is a LED driver?
In contrast to a constant voltage source, an LED driver functions as a constant current source. This "drives" a constant, controlled or limited current through an LED or LED module. Unlike incandescent lamps, for example, controlled operation of LEDs via a constant voltage is not possible. Thus so-called current driver circuits are integrated here. Accordingly, LED drivers are special operating devices for LEDs and LED modules. See also constant current sources. When attempting to operate an LED with a constant voltage, small specimen variations, temperature fluctuations and age-related changes are sufficient to allow the current to grow into uncontrolled quantities. These then usually lead to a premature failure.
What is the lifetime of an LED Driver?
On the one hand, people like to advertise the high durability of LEDs, as long as a sufficient coloing of the LEDs is ensured. On the other hand, the operating conditions for the LED driver integrated in the luminaire housing must also be correct. For example, data of ta = -25 - +50°C (ta = temperature ambient) and a lifetime of 50,000 hours can only be expected, if the temperature is maintained at the tc point (tc = temperature case), e. g. <70°C.
Usually the LEDs are cooled via the housing, which is often already a steamy environment for the LED control gear. This is often the reason why manufacturers sometimes operate the LED control gear in an external housing.
By the way, a high tc value does not automatically indicate that the LED driver can also be operated at higher ambient temperatures..
As a general rule: the lower the temperatures in and around the LED driver, the longer the electrolytic capacitors will last.
Further articles on this topic can be found here.
The topic of switching frequency as a characteristic that determines the lifetime is more applicable to the switch itself, since the inrush currents of some LED operating devices can be unexpectedly high and can cause some fuses to trip. These inrush currents can assume values of 5-20A for a short time (e. g. 50µs). If several devices are operated in parallel, the fuse will react.
What about dimmability?
Whereas luminaires with energy-saving lamps or incandescent bulbs could previously be dimmed simply using triac dimmers (trailing edge control), it is important to take a close look when replacing LED luminaires. If this contains a suitable LED control gear such as the proven DC-Jolly-MD from the company TCI, it can be replaced. Knowing that it is no longer possible to dim down completely to zero via this operating mode. This LED driver is one of many examples from the universal product family of TCI from Italy.
With the "Jolly family" TCI offers a wide range of operating devices which, depending on the selection, enable the following operating modes for dimming LEDs:
Push Button mode:
The LED driver is permanently connected to the supply voltage 230V AC. A line is wired between phase and key input via a push-button instead of previously the switch). The lamp can be switched on or off by briefly pressing the buttons. If the button is pressed longer, either up or down is dimmed.
1-10V mode:
The LED control gear, often also called LED converter, is controlled by means of a potentiometer (with activated 1-10V interface) at the two relevant connections. Alternatively, an equivalent DC voltage can also be applied.
Some of the LED drivers also have a DALI input (DALI = Digital Addressable Lighting Interface). This bus system allows each luminaire to be controlled individually via addressing.
Not yet supported by the Jolly family, but mentioned for completeness:
DMX mode:
A symmetrical transmission method with low voltage levels between ±1. 5 V and ±5 V. These must be routed separately from the mains cable. This technology is often used in stage and event technology. So far only a few LED drivers are compatible with this controller.
What is the influence of the LED driver on the system luminous efficacy?
System luminous efficacy is defined as the consideration of the entire chain of electrical energy in, light out. The product of all efficiencies often results in a sobering value. Usually a system consists of
- LED driver (0,7 / 0,9)
- LED according to data sheet (e. g. 115 lm/W)
- LED Correction (derating e. g. 0. 9) based on operating temperature deviating from data sheet
- Optic (ca. 0,9)
Example 1:
Use of a good LED driver with 90% efficiency and other values from the table above:
0,9 * 115 lm/W * 0,9 *0,9 = ca. 84 lm/W
Example2:
Use of poor LED driver with 70% efficiency:
0,7 * 115 lm/W * 0,9 *0,9 = ca. 65 lm/W
Conclusion:
It is not only worth investing in the best LEDs, all components have to play along
Other relevant characteristic values of LED control gear:
In addition to efficiency, operating temperature, tc, dimmability and operating current, there are other criteria to consider when selecting a LED driver.
- PWM frequency (Flicker)
- max. operating voltage,
- Secondary interruption possible (test voltage),
- Shutdown in case of overtemperature,
- Surge resistance,
- Protection class (SELV, I, II) ,
- Protection type,
- PFC
- Cascading
- Standards, norms
As far as not available in data sheet, contact us.
