LYT0002 Datasheet, PDF (5/18 Pages) Power Integrations, Inc. – Lowest Component Count, Off-Line Switcher IC for Non-Isolated LED Lighting Applications

LYT0002/0004-0006
600
500
400
V_DRAIN
300
200
100
0
68 kHz
64 kHz
0
20
Time (µs)
Figure 5. Frequency Jitter.
high. If the FEEDBACK pin is not pulled high for 50 ms, the
power MOSFET switching is disabled for 800 ms. The auto-
restart alternately enables and disables the switching of the
power MOSFET until the fault condition is removed.
Applications Example
A 6 W (Output) Universal Input Buck LED Driver Converter
The circuit shown in Figure 6 is a typical implementation of a
non-isolated, power factor corrected buck power supply for
LED driver applications. The simplicity and low component
count make this ideal for space constrained, cost sensitive
designs such as GU10 or A19 size lamps. This design was
optimized to drive an LED string at a voltage of 54 V with a
constant current of 110 mA, giving 6 W of output power. The
design operates over a universal input range from 90 VAC to
265 VAC and achieves an output current tolerance of < ±5%
at nominal line voltage. The input capacitance (C1 + C2) was
reduced to achieve the highest possible power factor input
while still meeting conducted EMI limits. Power factor is >0.5
at 230 VAC and >0.7 PF at 120 VAC meeting requirements for
LED lamps in Europe and USA.
The input stage comprises fusible resistor RF1, bridge rectifier
BR1, capacitors C1 and C2, and inductor L1. Resistor RF1 is a
flame proof, fusible, wire wound resistor. It accomplishes
several functions: a) Inrush current limitation to below specification
of BR1; b) Differential mode conducted EMI noise attenuation; c)
Fuse should any other component fail short-circuit; d) Higher
power factor. Capacitor C1, C2 and inductor L1 forms a π filter
to reduce differential mode EMI. Capacitor C2 provides local
decoupling for the switching current through U1. There is an
optional parallel resistor on the board across L1 which damps
the resonance of the pi filter.
The power processing stage is formed by the integrated
MOSFET switch within LYT0006 (U1), a free-wheeling diode
(D1), sense resistor (R2), power inductor (L2) and output
capacitor (C5). To reduce reverse recovery losses in D1 the
value of L2 was designed such that the converter operates in
mostly discontinuous conduction mode. Diode D1 is an
ultrafast diode with a reverse recovery time (t_RR) ≈35 ns. This
recovery is recommended due to the high ambient operating
time temperature which will increase diode reverse recovery
charge. A bobbin based EE10 core size indictor was selected
for L2 in order to prevent changes in inductance value when
placed inside a metal enclosure. Lower cost drum core or dog
bone inductor types may also be used, however these have an
open magnetic path which can be shorted by a metal enclosure.
This reduces the effective inductance and requires the value to
be adjusted to take this into account when placed inside the
final enclosure.
Capacitor C5 is the output filter capacitor; its primary function is
to limit the output current ripple and ensures high frequency
currents flow within as small as a loop area as possible to
reduce EMI.
RF1
L ^{4.7 Ω}
BR1
MB6S
600 V
90 - 265
VAC
N
RV1*
275 VAC
R1
4.7 kΩ
L1
4.7 mH
C1
47 nF
630 V
FB
BP
D
S
LYTSwitch-0
U1
LYT0006P
C2
330 nF
450 V
C4
C3 _{22 µF}
100 nF _{16 V}
25 V
R2
18.7 Ω
1%
5
4
L2
C5
47 µF
63 V
D1
MURS160T3G
54 V, 110 mA
+
*Optional <1 kV Surge Requirements
Figure 6. Universal Input, 54 V, 110 mA Constant Current Power Supply using LYTSwitch-0.
www.powerint.com
PI-6998f-061313
RTN
5
Rev. A 06/13