AN2067 Datasheet, PDF (1/25 Pages) STMicroelectronics – LED manufacturers propose white LEDs inside a monolithic chip

AN2067
Application note
VIPower™: dimmable white LED power supply with the VIPer53-E
Introduction
LED manufacturers propose white LEDs inside a monolithic chip, or single-chip white LED.
A current source is the most appropriate way to drive LEDs. A large voltage range must be
supported on the output due to the threshold of these white LEDs.
Furthermore, these dimmed LEDs must be driven by a PWM (current generator).
As a consequence, the key feature for this offline power supply is a current generator, which
can work as a pulse width-modulated mode, with a wide output voltage range, and with any
input voltage standard, and a galvanic isolation.
The VIPer53-E, the first multichip device of the VIPer® family, has a very low R_DS(on) of 1 Ω
allowing a typical power of 35 W in wide range in a standard DIP8 package without a
heatsink. Thanks to a lower power dissipation, the VIPer53-E meets higher efficiency and
reduced space.
Some general features:
– The block diagram is given in Figure 1. An adjustable oscillator drives a current
controlled PWM at a fixed switching frequency.
– The peak drain current is set for each cycle by the voltage present on the COMP
pin.
– The useful range of the COMP pin extends from 0.5 V to 4.5 V, with a
corresponding drain current range from 0 A to 2 A. This COMP pin can be either
used as an input in case of secondary feedback configuration, or as an output
when the internal error amplifier connected on the VDD pin operates in primary
feedback to regulate the VDD voltage to 15 V.
The VDD undervoltage comparator drives a high voltage start-up current source, which
switches off during the normal operation of the device. This feature together with the burst
mode capability allows a very low level of input power in standby mode, when the converter
is lightly loaded.
Parameter
Table 1. White LED power supply specifications
Name
Conditions
Min. Typ. Max. Unit
Output current
Output voltage
Output power
Input voltage
I_OUT
V_OUT
P_OUT
V_IN
V_OUT = 20 V
I_OUT = 1 A
200
1000
mA
5
40
V
40
W
82
265
V_AC
November 2014
DocID10973 Rev 2
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