Datasheet

SW
TSD
V
TRIG
/V
ARM
ZC
OVP
ON
OCP
iLimit
T
ON
Peak
Hold
CONTROL
V
ONpk
V
ONpk
D UVLO
DRV
OFT
ZC
DELAY ON
I
DLY
V/I
COMP
COMP
T
ON
Control
T
ON
VCC
ZCD
DLY
ISNS
BIAS & VRef
VC1
I
REF
UVLO
VC1
V
REF
MODE
Decode
MODE1
MODE2
GND
GND
LEB
LEB
SW
SW
SW
TPS92311
SNVS811B –MAY 2012–REVISED MAY 2013 www.ti.com
Simplified Internal Block Diagram
Figure 14. Simplified Block Diagram
APPLICATION INFORMATION
The TPS92311 is an off-line convertor specifically designed to drive LEDs. This device operates in Critical
Conduction Mode (CRM) with adaptive Constant ON-Time control, so that high power factor can be achieved
naturally. The TPS92311can be configured as an isolated or non-isolated off-line converter. Please refer to
TPS92311 typical application Figure 1, on the front page, in the following discussion. The TPS9231 flyback
converter consists of a transformer which includes three windings L
P
, L
S
and L
AUX
, an internal MOSFET Q
1
and
inductor current sensing resistor R
ISNS
. Secondary side components are secondary side transformer winding L
S
,
output diode D
3
, and output capacitor C
OUT
. An auxiliary winding is required, and serves two functions. Auxiliary
power is developed from the winding to power the TPS92311 after start-up, and detect the zero crossing point
due to the end of a complete switching cycle. During the on-period, Q
1
is turned on, and current flows through L
P
,
Q
1
and R
ISNS
to ground, input energy is stored in the primary inductor L
P
. Simultaneously, the I
SNS
pin of the
device monitors the voltage of the current sensing resistor R
ISNS
to perform the cycle-by-cycle inductor current
limit function. During the time MOSFET Q
1
is off, current flow in L
P
ceases and the energy stored during the on
cycle is released to output and auxiliary circuits. During Q
1
off-time current in the secondary winding L
S
charges
the output capacitor C
OUT
through D
3
and supplies the LED load. During Q
1
on-time, C
OUT
is responsible to
supply load current to LED load during subsequent on-period. Also during Q
1
off-time current is delivered to the
auxiliary winding through D
2
and powers the TPS92311. The voltage across L
AUX
, V
LAUX
is fed back to the ZCD
pin through a resistor divider network formed by R
2
and R
3
to perform zero crossing detection of V
LAUX
, which
determines the end of the off-period of a switching cycle. The next on period of a new cycle will be initiated after
an inserted delay of 2 x t
DLY
. The t
DLY
is programmable by a single resistor connecting the DLY pin and ground.
8 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated
Product Folder Links: TPS92311