Texas Instruments LM3448 -120VAC, 6W Isolated Flyback LED Driver Eval Board LM3448-120VFLBK/NOPB LM3448-120VFLBK/NOPB 데이터 시트
제품 코드
LM3448-120VFLBK/NOPB
V
AUX
C15
Q5
D12
FLTR2
R19
D13
DIM
V
CC
FLTR2
R11
C10
R10
Q3
Design Guide
13.5 TRIAC Holding Circuit
An optional TRIAC holding current circuit is also provided on the evaluation board as shown in
The DIM pin signal is applied through an RC filter as a varying DC voltage to Q3 such that the voltage on
the FLTR2 pin is adjusted and additional holding current can be sinked.
the FLTR2 pin is adjusted and additional holding current can be sinked.
Figure 36. TRIAC Holding Circuit
13.6 Overvoltage Protection
The circuit described in
provides over-voltage protection (OVP) in case of LED open circuit
failure. The use of this circuit is recommended for stand-alone LED driver designs where it is essential to
recover from a momentary open circuit without damaging any part of the circuit. In the case of an
integrated LED lamp (where the LED load is permanently connected to the driver output) a simple zener
diode or TVS based overvoltage protection is suggested as a cost effective solution. The zener diode/TVS
offers protection against a single open circuit event and prevents the output voltage from exceeding the
regulatory limits. Depending on the LED driver design specifications, either one or both techniques can be
used to meet the target regulatory agency approval
recover from a momentary open circuit without damaging any part of the circuit. In the case of an
integrated LED lamp (where the LED load is permanently connected to the driver output) a simple zener
diode or TVS based overvoltage protection is suggested as a cost effective solution. The zener diode/TVS
offers protection against a single open circuit event and prevents the output voltage from exceeding the
regulatory limits. Depending on the LED driver design specifications, either one or both techniques can be
used to meet the target regulatory agency approval
Figure 37. OVP Circuit
The OVP threshold is programmable and is set by selecting appropriate value of zener diode D13. The
resistor capacitor (R19, C15) combination across the base of transistor Q5 is used to filter the voltage
ripple present on the auxiliary voltage and prevent false OVP tripping due to voltage spikes caused by
leakage inductance.
resistor capacitor (R19, C15) combination across the base of transistor Q5 is used to filter the voltage
ripple present on the auxiliary voltage and prevent false OVP tripping due to voltage spikes caused by
leakage inductance.
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AN-2090 LM3448 -120VAC, 6W Isolated Flyback LED Driver
SNOA554C – October 2011 – Revised May 2013
Copyright © 2011–2013, Texas Instruments Incorporated