ELM916DA
450V LED controller
■Application notes
ELM916DA, buck, boost or buck-boost converter controller with low cost, is specifically designed for driving
multiple LED strings or arrays. It can be operated from either universal 90 to 240Vac or DC voltage between 8
and 450Vdc. ELM916DA is able to drive multiple strings of High-Brightness (HB) LEDs and regulate constant
current to ensure brightness and spectrum of the LEDs. With constant current driving method, LED lifetime
can be lengthened. ELM916DA provides soft start function to reduce inrush current. It is possible to charge
LD capacitor by letting current of 1 to 5uA to flow to the resistor between VDD and LD. The voltage increases
slopingly until it rises the current limit level of CS. By setting suitable resistor in CS, ELM916DA, with feed-
forward control, is capable of providing constant current to LED series while input voltage varies.
It is possible that while ELM916DA is providing power supply to the internal circuit which consists of high
voltage regulator for generating fixed VDD, ELM916DA is able to serve as a bias supply for low voltage
external circuit.
1. LED driver operation
ELM916DA can operate as basic types of converter controller under dis/continuous non-isolated current mode.
When external power N-Mosfet is turned on by GATE, the input energy would be stored in the inductor through
LED driver. When N-Mosfet is switched off, the energy stored in the inductor would be discharged toward
LED.
The internal power supply activates when voltage of VDD exceeds UVLO threshold. The output current is
controlled current of CS. The current limit level of ELM196DA is set by LD.
To avoid unstable regulation while ELM916DA is adopted in Buck topology, it is required to keep duty ratio
under 50%; the input voltage is required to be designed as 2 times higher than the forward voltage of LEDs.
2. Supply current
The current consumption under operation of ELM916DA is 0.2mA which can be generated from the internal
HV circuit. For ELM916DA, it is not required to use bulky startup resistors which are typically necessary for
offline applications. Moreover, since the internal regulator supplies 7.5V, it is possible that ELM916DA is able
to supply the power continuously. Because the current consumption of ELM916DA is extremely low, the power
consumption can be kept low even if the input voltage of ELM916DA is high.
3. Current detection
The current detection input of ELM916DA is connected to non-inverting inputs of two comparators; inverting
terminal of one comparator is connected to internal 245mV reference while it is connected to LD of the other
one. Outputs of both comparators are connected to OR gate while output of OR gate is connected to reset pin of
the flip-flop. Hence, the comparator whose voltage at inverting terminal is lower controlls when GATE output is
turned off.
The outputs of the comparators also include a 500ns blanking time due to the turn on spike current. Some
solution will add RC filter to prevent this situation.
4. Dimming
There are two types of dimming function of ELM916DA; linear and PWM types:
1) Linear dimming
The linear dimming function of ELM916DA can be adjusted voltage level of LD by changing current limit.
6- 4
Rev.1.3
ELM-TECH [ ELM Technology Corporation ]
