G7102 Single-Stage Flyback And PFC Controller With Primary-Side Control For LED Lighting

G7102
Single-Stage Flyback And PFC Controller With
Primary-Side Control For LED Lighting
1. General Description
The G7102 is a single-stage Flyback and PFC
controller targeting at LED lighting applications. It
is a primary-side controller without applying any
secondary feedback circuit for low cost, and
drives the Flyback converter in the quasiresonant mode to achieve higher efficiency. It
keeps the Flyback converter in constant on time
operation to achieve high power factor.
G7102 provides primary side control to eliminate
the opto-couplers or the secondary feedback
circuits, which would cut down the cost of the
system.
High power factor is achieved by constant on
operation mode, with which the control scheme
and the circuit structure are both simple.
The device directly drives a MOSFET and
operates in quasi-resonant mode to provide high
efficiency along with a number of key built-in
protection features while minimizing the external
component count, simplifying EMI design and
lowering the total bill of material cost.
Features
◆ Primary side control eliminates the
opto-coupler.
◆ Valley turn-on of the primary MOSFET to
achieve low switching losses.
◆ 0.3V primary current sense reference
voltage.
◆ Internal high current MOSFET driver.
◆ Low start up current.
◆ Reliable short LED and Open LED
protection.
◆ Power factor >0.90 with single-stage
conversion.
◆ Compact package: SOT23-6
Applications
●
●
●
●
●
LED lighting
Down light
Tube lamp
PAR lamp
Bulb
Typical Applications
Fig1. G7102 Typical Application Circuit
Global Semiconductor Co., LTD.
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
2. Products Information
2.1 Pin configuration
Fig2. G7102 Pin Configuration (SOT23-6)
Pin Name
CS
I/O
I
Description
Current sense pin. Connect this pin to the source of the
primary switch. Connect the sense resistor across the
source of the primary switch and the GND pin.
(current sense resister RS: RS
Rev 1.1
= k×
VREF × N PS
, k=0.334)
I OUT
GND
P
Ground.
COMP
I
Loop compensation pin. Connect a RC network across
this pin and ground to stabilize the control loop.
ZCD
I
Inductor current zero-crossing detection pin.This pin
receives the auxiliary winding voltage by a resister
divider and detects the inductor current zero crossing
point.This pin also provides over voltage protection and
line regulation modification function simultaneously. If
the voltage on this pin is above VZCD,OVP, the IC would
enter over voltage protection mode. Good line
regulation can be achieved by adjusting the upper
resistor of the divider.
VIN
P
Power supply pin.This pin also provides output over
voltage protection along with ZCD pin
DRV
O
Gate driver pin. Connect this pin to the gate of primary
MOSFET.
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
2.2 Block diagram
Fig3. G7102 Functional Block Diagram
3. Absolute Maximum Ratings (Note 1)
Parameter (Note 1)
Symbol
Value
Units
DC supply voltage range (Pin 5)
VIN
-0.3 to 40.0
V
Continuous DC supply current at VIN pin
IVIN
30
mA
DRV Output (Pin 6)
VDRV
-0.3 to 40.0
V
ZCD Iutput (Pin 4)
VZCD
-0.3 to 7.0
V
VCOMP
-0.3 to 7.0
V
CS Input (Pin 1)
VCS
-0.3 to 7.0
V
Power Dissipation (@TA=25℃, SOT23-6)
PMAX
0.6
W
θJA
θJC
170
130
℃/W
℃/W
-40 to 150
℃
260
℃
-65 to 150
℃
Symbol
Value
Units
DC supply voltage range (Pin 5)
VIN
8.5 to 15.0
V
Junction Temperature Range
TJ
-40 to 125
℃
Ambient Temperature Range
TA
-40 to 105
℃
COMP Input (Pin 3)
Package Thermal Resistance (Note2)
SOT23-6, θJA
SOT23-6, θJC
Temperature Range
Lead temperature (Soldering, 10 seconds)
TJ_MAX
Storage Temperature Range
4. Recommended Operating Conditions (Note 3)
Parameter (Note 3)
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
5. Electrical Characteristics
(VIN=12V (Note 3), TA = 25℃, unless otherwise noted)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
15.0
V
Power Supply Section
Input voltage range
VIN
8.5
VIN turn-on threshold
VIN,ON
16.5
V
VIN turn-off threshold
VIN,OFF
6.9
V
VIN OVP threshold
VIN,OVP
22.7
V
Startup current
IST
VIN<VIN,OFF
2.3
uA
Operating Current
IVIN
CL=100pf, f=15kHz
0.6
mA
VREF
0.3
V
VCS,MAX
0.5
V
VZCD,OVP
1.42
V
VDRV
VIN
V
ISOURCE
0.25
A
ISINK
0.5
A
22
us
500
ns
31
us
Error Amplifier Section
Internal reference voltage
Current Sense Section
Current limit
ZCD Pin Section
OVP voltage threshold
Gate Driver Section
Gate driver voltage
Maximum source current
Minimum sink current
Max ON Time
TON,MAX
Min ON Time
TON,MIN
Max OFF Time
TOFF,MAX
Min OFF Time
TOFF,MIN
2
us
fMAX
120
kHz
TSD
150
℃
Max switching frequency
VCOMP=3.8V
VCOMP=3.8V
Thermal Section
Shutdown Temperature
Note 1: Stresses beyond the “Absolute Maximum Ratings” may cause permanent damage to the device.
These are stress ratings only. Functional operation of the device at these or any other conditions beyond
those indicated in the operational sections of the specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
Note 2: θJA is measured in the natural convection at TA= 25℃ on a low effective single layer thermal
conductivity test board of JEDEC 51-3 thermal measurement standard. Test condition: Device mounted
on 2”x 2” FR-4 substrate PCB, 2oz copper, with minimum recommended pad on top layer and thermal
vias to bottom layer ground plane.
Note 3: Increase VIN pin voltage gradually higher than VIN,ON voltage then turn down to 12V.
Rev 1. 1
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
6. Theory of Operation
G7102 is a constant current Flyback controller with primary-side control and PFC
function that targets at LED lighting applications.
The Device provides primary side control to eliminate the opto-couplers or the secondary
feedback circuits, which would cut down the cost of the system.
High power factor is achieved by constant on operation mode, with which the control
scheme and the circuit structure are both simple.
In order to reduce the switching losses and improve EMI performance, Quasi- Resonant
switching mode is applied, which means to turn on the power MOSFET at voltage valley;
the startup current of G7102 is rather small (5uA typically) to reduce the standby power
loss further; the maximum switching frequency is clamped to 120 kHz to reduce
switching losses and improve EMI performance when the converter is operated at light
load condition.
G7102 provides reliable protections such as Short Circuit Protection (SCP), Open LED
Protection (OLP), Over Temperature Protection (OTP), etc.
G7102 is available with SOT23-6.
7.1 Start-up
After AC supply or DC BUS is powered on, the capacitor CVIN across VIN and GND pin is
charged up by BUS voltage through a startup resistor RST. Once VIN rises up to VIN,ON,
the internal blocks start to work. VIN will be pulled down by internal consumption of IC
until the auxiliary winding of Flyback transformer could supply enough energy to maintain
VIN above VIN,OFF. The whole start up procedure is divided into two sections shown in
Fig.4. tSTC is the CVIN charged up section, and tSTO is the output voltage built-up section.
The startup time tST composes of tSTC and tSTO, and usually tSTO is much smaller than
tSTC.
The startup resistor RST and CVIN are designed by rules below:
(a) Preset start-up resistor RST, make sure that the current through RST is larger than IST
and smaller than IVIN,OVP:
VBUS
IVIN ,OVP
< RST <
VBUS
I ST
(1)
(b) Select CVIN to obtain an ideal startup time tST, and ensure the output voltage is built
up at one time.
VBUS
− I ST ) × t ST
RST
=
VIN ,ON
(
CVIN
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(2)
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
(c) If the CVIN is not big enough to build up the output voltage at one time. Increase CVIN
and decrease RST, go back to step (a) and redo such design flow until the ideal
startup procedure is obtained.
Fig4. Startup Sequencing Diagram
7.2 Internal pre-charge design for quick startup
After VIN exceeds VIN,ON, VCOMP is pre-charged by an internal current source. The PWM
block won’t start to output PWM signals until VCOMP is over the initial voltage VCOMP,IC,
which can be programmed by RCOMP. Such design is meant to reduce the startup time
shown in Fig.5.
VIN
VIN,ON
G7102
COMP
CCOMP2
RCOMP
VIN,OFF
VCOMP
t
600mV
VCOMP,IC
(opt.)
CCOMP1
PWM
t
t
Fig5. Pre-charge Scheme in Startup
The voltage pre-charged VCOMP,IC in startup procedure can be programmed by RCOMP:
VCOMP , IC = 600mV − 300uA × RCOMP
Rev 1. 1
(3)
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
Where VCOMP-IC is the pre-charged voltage of COMP pin.
Generally, a big capacitance of CCOMP is necessary to achieve high power factor and
stabilize the system loop (1µF~2µF recommended); the voltage pre-charged in startup
procedure can be programmed by RCOMP; On the other hand, larger RCOMP can provide
larger phase margin for the control loop; A small ceramic capacitor is added to suppress
high frequency interruption (10pF~100pF is recommended if necessary).
7.3 Shut Down
After AC supply or DC BUS is powered off, the energy stored in the BUS capacitor will be
discharged. When the auxiliary winding of Flyback transformer cannot supply enough
energy to VIN pin, VIN will drop down. Once VIN is below VIN,OFF, the IC will stop working
and VCOMP will be discharged to zero.
7.4 Primary-side Constant Current Control
Primary side control is applied to eliminate secondary feedback circuit or opto-coupler,
which reduces the circuit cost. The switching waveforms are shown in Fig.6. The output
current IO can be represented by,
IO =
I PKS TR
×
2 TS
(4)
Where IPKS is the peak current of the secondary side; tR is the discharge time of Flyback
transformer; tS is the switching period.
The secondary peak current is related with primary peak current, if the effect of the
leakage inductor is neglected.
I PKS = N PS × I PKP
(5)
Where NPS is the turns ratio of primary to secondary of the Flyback transformer. Thus, IO
can be represented by,
IO =
N PS × I PKP TR
×
2
TS
(6)
The primary peak current IPKP and inductor current discharge time tR can be detected by
the IC, and the effect of the leakage inductor can be compensated by internal control
scheme. IO can be induced finally by,
IO =
k1 × k2 × VREF × N PS
RS
(7)
Where k1 is the output current weight coefficient; k2 is the output modification coefficient;
VREF is the internal reference voltage; RS is the current sense resistor. k1, k2 and VREF are
all internal constant parameters, IO can be programmed by NPS and RS.
RS =
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k1 × k2 × VREF × N PS
IO
(8)
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
Fig.6 Switching Waveforms
7.5 Quasi-Resonant Operation
QR mode operation provides low turn-on switching losses for Flyback converter.
Fig.7 QR Mode Operation
The voltage across drain and source of the primary MOSFET is reflected by the auxiliary
winding of the Flyback transformer. ZCD pin detects the voltage across the auxiliary
winding by a resistor divider. When the voltage across drain and source of the primary
MOSFET is at voltage valley, the MOSFET would be turned on.
Rev 1. 1
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
7.6 Over Voltage Protection (OVP) & Open LED Protection (OLP)
The output voltage is reflected by the auxiliary winding voltage of the Flyback transformer,
and both ZCD pin and VIN pin provide over voltage protection function. When the load is
null or large transient happens, the output voltage will exceed the rated value. When VIN
exceeds VIN,OVP or VZCD exceeds VZCD,OVP, the over voltage protection is triggered and
the IC will discharge VIN by an internal current source IVIN,OVP. Once VIN is below VIN,OFF,
the IC will shut down and be charged again by BUS voltage through startup resistor. If
the over voltage condition still exists, the system will operate in hiccup mode.
Thus, the turns of the auxiliary winding NAUX and the resistor divider is related with the
OVP function.
VZCD ,OVP
VOVP
=
N AUX
RZCD 2
×
NS
RZCD1 + RZCD 2
VIN ,OVP
VOVP
≥
(9)
N AUX
NS
(10)
Where VOVP is the output over voltage specification; RZCD1 and RZCD2 compose the
resistor divider. The turn ratio of NS to NAUX and the ratio of RZCD1 to RZCD2 could be
induced from equation (9) and (10).
D2
RAUX
VIN
CVIN
RZCD1
G7102
ZCD
RZCD2
Fig.8 OVP&OLP
7.7 Short Circuit Protection (SCP)
When the output is shorted to ground, the output voltage is clamped to zero. The voltage
of the auxiliary winding is proportional to the output winding, so VIN will drop down
without auxiliary winding supply. Once VIN is below VIN,OFF, the IC will shut down and be
charged again by the BUS voltage through the startup resistor. If the short circuit
condition still exists, the system will operate in hiccup mode.
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
In order to guarantee SCP function not effected by voltage spike of auxiliary winding, a
filter resistor RAUX is needed (10Ω typically) shown in Fig.8.
7.8 Line Regulation Modification
The IC provides line regulation modification function to improve line regulation
performance. Due to the sample delay of CS pin and other internal delay, the output
current increases with increasing input BUS line voltage. A small compensation voltage
∆VCS is added to CS pin during ON time to improve such performance. This ∆VCS is
adjusted by the upper resistor of the divider connected to ZCD pin.
ΔVCS = VBUS ×
N AUX
1
×
× k3
NP
RZCD1
(11)
Where RZCD1 is the upper resistor of the divider; k3 is an internal constant as the
modification coefficient; NAUX and NP are the turns of auxiliary winding and primary
winding of the transformer.
The compensation is mainly related with RZCD1, larger compensation is achieved with
smaller RZCD1. Normally, RZCD ranges from 100kΩ~1MΩ. Then RZCD2 can be selected by,
VZCD ,OVP
N
× S
VO
N AUX
× RZCD1 > RZCD 2
VZCD ,OVP
NS
×
1−
VO
N AUX
(12)
VZCD ,OVP
N
× S
VOVP
N AUX
>
× RZCD1
VZCD ,OVP
NS
×
1−
VOVP
N AUX
(13)
And,
RZCD 2
Where VOVP is the output over voltage protection specification; VO is the rated output
voltage; RZCD1 is the upper resistor of the divider; NS and NAUX are the turns of secondary
winding and auxiliary winding separately.
Rev 1. 1
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G7102
Single-Stage PFC Controller With Primary-Side Control For LED Lighting
8. Package Information
SOT23-6
Symbol
Dimension in Millimeters
Dimensions in Inches
Min
Max
Min
Max
A
2.692
3.099
0.106
0.122
B
1.397
1.803
0.055
0.071
C
--
1.450
--
0.057
D
0.300
0.500
0.012
0.020
F
0.95
H
0.080
0.254
0.003
0.010
I
0.050
0.150
0.002
0.006
J
2.600
3.000
0.102
0.118
M
0.300
0.600
0.012
0.024
θ
0°
10°
0°
10°
0.037
Data and specifications are subject to change without notice.
This product has been designed and qualified for Industrial Level and Lead-Free.
Qualification Standards can be found on GS's Web site.
Global Semiconductor HEADQUARTERS:
Scotia Centre,4th Floor,P.O.Box 2804,George Town,Grand Cayman KY1-1112,Cayman
Visit us at www.globalsemi-group.com for sales contact information.
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