2. www.fairchildsemi.com2
FL7701 Features
• Digital PFC Function
• Self Biasing
• Cycle-by-Cycle OCP
• Programmable Frequency
• Programmable LED Output
Current
• Internal Soft Start
• Flicker-Free Analog Dimming
• Open & Short LED Protection
• High Voltage, AC or DC Input
• 8-Pin Narrow Body SOIC
FL7701 Smart LED Driver with PFC
GND
RT OUT
HVVCC
Reference
ADIM
JFET
AOCP
IAD
UVLO
QR
S
TSD
Leading Edge
Blanking
ZCD
DAC
Soft start
Digital Block
CS
Oscillator
-
+
LEB
-
+
time
VCC
ZCD
2.5V
1
2
83
5
4
6
FL7701
1
2
3
4 5
6
7
8
NC
HV
GND
ADIMRT
VCC
OUT
CS
3. www.fairchildsemi.com3
FL7701 Typical Applications
• Non-isolated, low-power (<10W) LED lamps operating from US or EU, AC line
voltage
• Residential, non-dimming, LED luminaries (A, E, MR, PAR, GU, etc)
• Decorative LED lighting
• Low-power LED driver with 1V-10V analog or PWM dimming
• T-style LED ballast
• LED desk lamps with step dimming
FL7701 Benefits
• High power factor
• High efficiency
• Maintains high PF during analog dimming
• Non-isolated buck topology uses commonly available, low-cost, off-the-shelf inductors
• Non-isolated buck topology requires no output bulk capacitor
• Low component count, small form factor
FL7701 Applications & Benefits
5. www.fairchildsemi.com5
• Removed all Potting Material
• Removed Utilitech LED Driver Power Supply
• Machined Bulb Base and Aluminum Heatsink to Allow Cutaway View of Exposed Bulb
Base
• Redesigned FL7701, FEBL031-2 EVB to Meet Electrical and Mechanical Requirements
of Utilitech Pro PAR20 Bulb Housing
• Utilitech Pro PAR20 LED Bulb used as Load to Demonstrate FL7701 Technology
Features
Utilitech Pro PAR20 LED Bulb
Cutaway Bulb Base
8. www.fairchildsemi.com8
LED Driver Electrical Performance Comparison
• Utilitech Pro PAR20 Power Supply Topology is Isolated Flyback that is
Triac Dimmable
• FL7701 Topology is Non-Isolated Buck that is self-biased from the AC
line voltage and is therefore not Triac Dimmable
• FL7701 Flicker-Free, Analog Dimming is Demonstrated BUT is not
Feasible for Residential LED Replacement Bulbs Requiring Dimming
• FL7701 Solution has Fewer Components, Higher Power Factor and
Comparably Similar Efficiency
VIN(V) PIN(W) VOUT(V) IOUT(mA) POUT(W) PF η
Utilitech PAR20
Power Supply
120 7.2 12.15 430 5.22 0.82 72.6%
FEBL031-2
(Unmodified)
220 8.71 32.8 260 7.56 0.95 86.8%
FEBL031-2A
(Modified)
120 7.2 12.17 431 5.25 0.942 72.8%
9. www.fairchildsemi.com9
FEBL031-2A Typical Test Set Up
Required Test Equipment:
1. Plugs into any standard 120VAC US line wall outlet
2. (3) battery powered DVMs (VIN, VLED, ILED)
3. (1) Oscilloscope
4. (2) Current Probes
5. (2) High Voltage Differential Probes (DO NOT USE GROUNDED VOLTAGE PROBES)
Recommended Test Equipment:
1. (1) Power meter can be used to show PF and THD verses dimming. Depending upon the
capabilities of the oscilloscope, PF may be shown using oscilloscope calculation measurement
(as done in test set up shown above).
WARNING
• Do not use standard
oscilloscope voltage probes to
probe any signals from back of
demo box. The demo is
operating directly from AC, off-
line and is non-isolated so
attaching any scope ground will
damage the circuit.
10. www.fairchildsemi.com10
FEBL031-2A, PAR20 Demo Operation
• (A) Non-operational Static FEBLO31-2A EVB (shows reverse side of EVB from what is shown inside LED bulb)
• (B) LIVE operational demo protected by acrylic cover. Everything on the demo is safe to touch.
• (C) Open LED momentary push button (when pushed and held, bulb output disables and recovers when push button is
released)
• (D) Short LED momentary push button (when pushed and held, bulb output disables and recovers when push button is
released)
• (E) Dimming function potentiometer varies the FL7701 ADIM voltage. LED bulb can turn on in any DIM position.
• (F) ON/OFF rocker switch provides AC power to bulb
A
B
C D E
F
11. www.fairchildsemi.com11
FEBL031-2A, PAR20 Demo Back Panel
• (A) High Voltage Diff Probe (measure AC line voltage, oscilloscope channel 1)
• (B) Battery powered DVM (measure AC line RMS voltage)
• (C) 5A replaceable AC line Fuse
• (D) AC line cord is split apart in this location to allow current probe connection (measure AC line current, oscilloscope
channel 2)
• (E) ON/OFF switch for blue light on front panel “power symbol”. The blue LED is independent from AC line voltage and
is powered by 2 AA batteries.
• (F) High Voltage Diff Probe (measure LED voltage, oscilloscope channel 3), OR connect a battery powered DVM here to
display the RMS LED voltage
• (G) Battery powered DVM (measure LED RMS voltage). IMPORTANT NOTE: Must connect either the DVM (set to
measure current), OR shunt jumper (shown) to allow current to flow to the PAR20 LED array. Current probe
(measure LED current, oscilloscope channel 4) can now be connected to either the DVM lead or the shunt jumper.
A
B
C
D
E
F
G
14. www.fairchildsemi.com14
• Open LED Fault
• LED Current is Zero
• LED Voltage is Peak AC Line
Voltage
FEBL031-2A LED Fault Testing
CH1=VIN, CH2=IIN, CH3=VLED, CH4=ILED
• Short LED (String) Fault
• LED Current is Max Limited
by FL7701 OCP Function
• LED Voltage is Zero
15. www.fairchildsemi.com15
• 120VAC Soft Start
• AC Phase is detected on VCC
• EA voltage reference set to AC
• CS voltage threshold set to
0.365V
FEBL031-2A AC vs. DC Soft Start
CH1=VIN, CH2=IIN, CH3=VLED, CH4=ILED
• 170VDC Soft Start
• No AC phase detected on VCC
• EA voltage reference set to DC
• CS voltage reference set to
0.5V
17. www.fairchildsemi.com17
FEBL031-2A LED Capacitor Comparison
Cap VIN(VAC) PIN(W) VOUT(V) IOUT(mA) POUT(W) η PF THD
0 120 7.3 11.86 441 5.23 71.6% .944 29.78%
10µF 120 7.3 11.93 441 5.26 72.06% .944 29.16%
470µF 120 7.3 12.00 442 5.3 72.6% .934 29.18%
1000µF 120 7.3 12.04 442 5.32 72.8% .934 29.74%
• Reduced output LED, high frequency, ripple current is sometimes desirable for
improving LED reliability
• Aluminum electrolytic capacitor can be added in parallel with LED load
• 16V rated capacitor voltage used for 12V LED output
• During open LED condition, LED output voltage equals peak AC line voltage
so appropriately rated high voltage capacitor is necessary
• For residential LED bulb applications, high voltage output capacitors may not
be feasible due to their large size
• For LED loads that include open LED shunt protection, capacitor voltage
rating can be rated for clamped LED voltage (16V)
• 16V rated capacitor easily fits within residential Edison based LED bulb bases
18. www.fairchildsemi.com18
FL7701 OVP Output LED Voltage Clamp
• Recommended FL7701 configuration for LED loads that DO NOT include parallel open LED
shunt protection
• When LED voltage is greater than zener voltage, the BJT is turned on and discharges the VDD
capacitor
• LED voltage is now limited to the zener voltage allowing the use of low voltage output bulk
capacitor on LED output
AC input
85Vac~265Vac
LED
FUSE
FRD
Lm
C
VDD
HV
GND
FL7701
Varistor
N.C
Adim
R
RT
CS
GATE
EMI FILTER
R
C
R
R
D
ZD
C
OVP Protection
20. www.fairchildsemi.com20
FEBL031-2A LED Driver, THD
(Chroma 61502 Programmable AC Source)
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
Harmonic
Current(A)
Harmonic Number
FEBL031-2A Measured THD
EN61000-3-2, 115VAC
Measured Harmonic Current
Class C (Lighting) Limit
• FEBL031-2A, EMI filter not optimized resulting in AC line
current distortion
• Measured THD is close to Class C limits and could be
improved by optimizing EMI filter
