Maxim Integrated Products introduces the MAX16840, a new model of dimmable LED driver, suitable for 12V AC and 24V AC lamps (e.g. MR16) and immune to flickering phenomena.
MAX16840 is a device that includes all the functionalities needed to design LED drivers for 12V AC and 24V AC light bulbs, while also allowing the retrofit of traditional halogen light bulbs, such as the MR16 (Multifaceted Reflector, with bulb diameter of 2 inches), shown in the image below:
MAX16840: LED lighting
The advantages of LED lighting are substantial, and one of the main advantage is to allow a saving of electricity, lower usage costs, increased efficiency and reduced emissions of carbon dioxide.
For a long time, MR16 halogen lamps were considered a viable and more efficient alternative to the (back then) traditional incandescent lamps, both for domestic and public lighting applications. The absorption of a halogen MR16 light bulb usually ranges between 10W and 50W, while the light emission is between 150 lumens and 800 lumens (lm). It follows that the luminous efficacy of a lamp of this type is approximately 15 lumens per watt (lm/W). In other words, we could say that the light efficiency of a MR16 light bulb is approximately equal to 15%. This is a much better value when compared with the inefficient incandescent bulbs, but it is a value that leaves much to be desired.
Current LED technology offers new types of lamps, MR16-compatible, built in solid state technology, that can drastically reduce power consumption and costs. For example, are now available on the market lamps made with high power LED (5W or 10W) able to reach an efficacy of 45 lm/W at a current of 1A and at a junction temperature (TJ) of 120 °C. These LED lamps consume up to 50% less than the halogen bulbs (with the same light output), and have a theoretical life of up to 100,000 hours (compared to 2,000 hours for halogen). This remarkable increase in life time means that lamp replacement operation becomes no longer necessary in the case of LED lamps, because their duration can not exceed that of the application where it is uesd.
MAX16840 adopts a proprietary technique to control the input current which makes the LED lamps used with this device compatible with electronic transformers, and adjustable in intensity by both trailing-edge (in case of electronic transformers) and leading-edge (in case of electromagnetic transformers) dimmer.
Trailing-edge dimmers use the technique of cutting the falling part of the waveform, that is a control phase technique in which phase control is on the end of the half-wave (trailing edge). This type of dimmer generally involves the use of transistors. The following image shows the principle adopted by this type of dimmer:
Leading-edge dimmers instead use the technique of cutting the raising part of the waveform, that is a control phase technique in which the cut is made on the ascending phase of the half-wave (leading edge) and is therefore anticipated. This type of dimmer generally involves the use of thyristors, SCR and Triac in particular. SCR device is a mono directional switch, while the triac is essentially equivalent to two SCR devices that allow bi-directional control. The following image shows the principle adopted by this type of dimmer:
- α=on angle
- λ=currente flowing in the circuit
The MAX16840 device is based on Maxim's proprietary architecture that guarantees operation with brightness adjustment and no flickering even with electronic transformer and trailing/leading-edge dimmers. This technique of Maxim, patent pending, allows the use of LED lamps as retrofit to replace the old halogen MR16, without making any modifications to the existing power. The IC uses an input current mode control according to which the current itself present at the FB pin input is measured and adjusted so that its average remains constant. The input pin REFI is used to set the desired level of input current.
Below is shown a typical application of the MAX16840, where you can clearly see the single input7output pins:
The IC has also a built-in internal protection against voltage surges, applied to the input pin IN, in order to protect the MOSFET against possible damage when the LED is in open circuit voltage or the voltage on the LED itself is too high. The device can be used in various topologies such as buck, boost, and buck-boost, and has an integrated 0.2? (max)-48V switching MOSFET, capable of delivering up to 10W of output power. The device is guaranteed over the temperature range from 0°C to +125°C, and is available in a 10-pin 3mmx3mm TDFN package, with heat treatment.
The technical characteristics of the MAX16840 are as follows:
- control of the average input corrent to achieve operation with electronic transformers and dimmability
- Buck, Boost, SEPIC, and Buck-Boost topologies
- integrated 0.2Ω (max), 48V switching MOSFET
- analog dimming and thermal foldback
- external npn to guarantee minimum load to electronic transformers at startup
- output overvoltage protection
- internal overtemperature protection
- 0°C to +125°C operating temperature range
- 3mm x 3mm, 10-Pin TDFN package