NSIC2050JB, NSIC2030JB: 120 Vac, Dimmable, Low-Cost, Parallel-to-Series with Switch-In CCR LED Lighting Circuit

DN05052/D
120 VAC, Low‐Cost,
Dimmable, Linear,
Parallel‐to‐Series with
Switch‐In CCR
LED Lighting Circuit
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DESIGN NOTE
Table 1. DEVICE DETAILS
Device
Application
Topology
Efficiency
Input Power
Power Factor
THD
NSIC2030JB,
NSIC2050JB
AC LED
Lighting
Linear
79%
7.9 W
0.99
12%
Overview
The circuit uses ON Semiconductor CCRs to provide
constant LED current and protect LEDs from over-voltage
conditions. The circuit also employs a second CCR to
increase LED current at high voltages for improved PF and
THD performance.
This circuit is an innovative take on the parallel-to-series
topology and provides an effective 120 VAC LED lighting
solution. Its primary features are its PF and THD
performance, dimmability, low cost, and high efficiency and
light output.
This circuit uses a parallel-to-series topology that
dynamically adjusts LED forward voltage as the bridge
output varies. The circuit also switches two CCRs
independently to match the input current waveform to the
bridge output voltage for excellent PF and THD
performance.
The circuit is designed for input voltages between
110 VAC and 130 VAC.
F1
D1
D3
MOV1
D2
D4
Key Circuit Features
•
•
•
•
•
•
Functional with Standard Phase-Cut Dimmers
Low-Cost
PF > 0.99
THD = 12%
Adjustable for Different LED Voltages
Adjustable for Different Power Levels/Currents
CCR1
Vin
LED1
R4
Q2
R6
LED2
LED3
R3
R1
Q5
CCR2
R5
R7
C1
D5
R8
LED4
Q3
LED5
Q1
R2
LED6
R9
C2
Q4
Figure 1. 2-stage Parallel-to-Series LED Lighting Circuit, with Switch-In CCR
© Semiconductor Components Industries, LLC, 2014
June, 2014 − Rev. 3
1
Publication Order Number:
DN05052/D
DN05052/D
this device at 25°C is 0.68 V. Using the values R4 = 590 W
and R5 = 100 kW in the formula:
Circuit Description
The circuit consists of a full-wave bridge rectifier
(D1−D4), parallel-to-series switching circuitry (C1−C2,
R1−R3, R6−R9, Q1, Q3−Q5, D5), CCR switching circuitry
(C3, R4−R5, Q2), CCRs (CCR1−CCR2), and LEDs
(LED1−LED6).
ǒ
Ǔ
V SWITCH(Q2) + V BE(sat) @ R4 ) R5
R4
Using these values, VSWITCH(Q2) is about 116 V.
Circuit Operation
Design Considerations
The full-wave bridge rectifier outputs a positive half-sine
wave peaking at 170 V (120 VAC). The rectified supply
voltage is referenced between the cathodes of D3 and D4 and
the anodes of D1 and D2.
The circuit has two different switching mechanisms
acting at all times. The first is the parallel-to-series
switching component, which controls the effective LED
forward voltage (Vf) seen by the circuit. The
parallel-to-series switching components are driven by the
Q1 transistor, whose VBE is driven by the R1/R2 voltage
divider. With the chosen R1/R2 values in this circuit, this
switching voltage is 122 V†.
The second switching component in the circuit is the
switch-in CCR, wherein a second CCR (CCR2) switches on
at high voltages to provide additional input current, boosting
PF and lowering THD. The transistor Q2 acts as a switch for
CCR2. Q2’s VBE is driven by the R4/R5 voltage divider. By
the chosen values in this circuit, this switching voltage is
116 V††. With about 8 V across the CCR2 to ensure full
regulation, this additional current activates at about 124 V
bridge output.
At low voltages (bridge output < 122 V), the LEDs are in
a parallel configuration for earlier turn-on, and CCR2 is off.
Q1 is off, leaving Q3 on and supplying base current for Q4
and Q5, each providing a separate current path for the two
strings of LEDs.
When the bridge output surpasses 122 V, the LEDs switch
into series mode, effectively doubling the forward voltage of
the LEDs and protecting the CCRs from over voltage in the
circuit. CCR2 is still off at this point.
When the bridge output increases past 124 V, CCR2
begins to switch on, providing more current to the LEDs. It
is important to ensure that CCR2 turns on after the LEDs
enter into the series configuration to provide the most
sinusoidal input current waveform possible. The late turn-on
also improves efficiency.
In the modification of this circuit, it is important to
consider several specifics in its design.
The driver is tunable to drive between 60 to 160 V of
LEDs in two strings (30–80 V per string). To protect CCRs
from over-voltage conditions the total Vf of all LEDs in the
series stage should be greater than 60 V. To obtain the benefit
of the parallel configuration stage, the total LED Vf of one
string should be less than 80 V. (Example 1: Two strings of
16 LEDs with Vf = 3.2 V, one string Vf = 51.2 V, total series
Vf = 102.4 V. Example 2: Two strings of 3 LEDs with
Vf = 20 V, one string Vf = 60.0 V, total series Vf = 120.0 V)
The use of higher Vf LED strings will boost circuit
efficiency, but with a later LED turn-on voltage, will reduce
dimmability and PF/THD.
If greater currents are desired through CCR2 and Q2,
a darlington-connected PNP pair (may use two
MMBT5401L devices) or a PFET may be considered to
reduce base current and obtain higher gain. Multiple CCRs
may be added in parallel to CCR1 at no consequence to the
circuit.
Circuit Performance Data
Table 2. PERFORMANCE DATA ACROSS VOLTAGE
RANGE OF THE CIRCUIT SHOWN IN FIGURE 1
110 VAC
130 VAC
IRMS(IN) (mA)
64.00
66.07
69.33
PF
0.9911
0.9923
0.9931
THD (IRMS, %)
13.01
12.02
11.52
PIN (W)
6.99
7.88
8.90
Efficiency (%)
82.9
78.6
75.0
Dimming Compatibility
Table 3. THE CIRCUIT DIMMED SMOOTHLY AND
HELD OPERATION WITH NO FLICKER, FLASHES,
ETC. WITH THESE AVAILABLE DIMMERS
†A
typical value for the VBE(sat) of Q1,
an ON Semiconductor MMBT3904L, at 25°C is 0.68 V.
With the values R1 = 1 MW and R2 = 5.6 kW, the turn-on
voltage for Q1 may be found using the following formula:
ǒ
120 VAC
Manufacturer
Ǔ
V SWITCH(Q1) + V BE(sat) @ R1 ) R2
R2
Using these values, VSWITCH(Q1) is about 122 V.
†† Similarly, we may calculate the turn-on voltage of Q2,
an ON Semiconductor MMBT5401L. A typical VBE(sat) for
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Serial Number
Lutron
500−15591A
Lutron
TGCL−153PH
Lutron
Skylark CTCL−153PDH
Pass & Seymour
450 W − CFL/LED
Leviton
IPL06−10Z
Leviton
6674−POW
Lutron
SCL−153P
Lutron
AYCL−153P
DN05052/D
Representational Circuit Diagrams
CCR1
LED1
Q2
CCR1
Q5
LED2
LED3
CCR2
D5
LED4
Q4
LED5
LED1
LED4
LED2
LED5
LED3
LED6
LED6
Figure 2. Stage 1, showing parallel configuration of LEDs and single CCR. Transistors Q4 and Q5 are on,
and the D5 routing diode is reverse-biased. The LEDs are in parallel below the CCR and split the regulated
current. The driver is in this configuration at bridge outputs below 122 V.
CCR1
LED1
Q2
CCR1
Q5
LED2
LED1
LED3
LED2
CCR2
Q4
D5
LED3
LED4
LED4
LED5
LED5
LED6
LED6
Figure 3. Stage 2, showing series LED configuration and single CCR operation. Transistors Q5 and Q6 are
switched off and current flows through the D5 routing diode, enabling series configuration.
The driver is in this configuration at bridge outputs between 122 V and 124 V.
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DN05052/D
CCR1
LED1
Q2
CCR2
CCR1
Q5
LED2
LED3
LED1
CCR2
LED2
D5
LED3
LED4
Q4
LED4
LED5
LED5
LED6
LED6
Figure 4. Stage 2, showing two parallel CCRs driving an LED series configuration. This occurs at bridge outputs
above 124 V after the transistor Q2 has saturated.
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DN05052/D
Waveforms
Figure 5. Transient capture of the total input voltage and current waveforms. Note the sinusoidal shape
of the input current closely follows the voltage, resulting in good PF and THD performance.
Figure 6. LED currents through both strings. LED String 1 contains LED1 through LED3, and String 2 contains
LED4 through LED6. Note the identical current waveforms and the two distinct levels in current, corresponding
to the parallel/series LED configurations.
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DN05052/D
Figure 7. LED string voltages are equal at all times. The distinct levels in forward voltage are a result
of the different LED current levels in the two stages of operation. Given an LED string Vf of 60 V,
the LEDs are on about 81% of the time.
Figure 8. Total LED voltage. Measured from the anode of LED1 to the cathode of LED6 (bridge ground),
the parallel and series configurations of the LEDs can be seen. The LEDs spend most of their time
in the series configuration.
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DN05052/D
Figure 9. Anode-Cathode voltages for both CCRs. The sharp valleys in the CCR1 waveform are where the LED
voltage increases, which reduces the Vak across the device. CCR2 is left off until the bridge voltage is high
and the LEDs are in series configuration.
Figure 10. Q2 and CCR2 are in series, together paralleled with CCR1. Q2 blocks CCR2 from conducting during
the parallel mode of operation, and after entering saturation, allows CCR2 to conduct.
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DN05052/D
Figure 11. The circuit receives no current when the TRIAC is off, and the general shape of the input current
waveform is preserved when the TRIAC is on.
Figure 12. LED current turns off when the TRIAC is off, and the currents are identical every half-cycle,
resulting in smooth, flicker-free dimming.
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DN05052/D
Figure 13. The LED total voltage continues to switch between parallel and series configurations normally,
even with a TRIAC. The LEDs are off while the TRIAC is off.
Design Modifications
the switching resistor (R2) as a function of LED string
voltage to expedite design. This curve is based on the
VSWITCH(Q1) equation on page 2. Finding the optimal
switching resistors is important for maximizing efficiency
and minimizing THD.
When altering the LED load, the driver’s switching
behavior must be adjusted to match the voltage levels of the
LED load. The plot below is a ball park (additional
optimization may yield better performance) for the value of
Switching Resistor (R2) Value vs. LED String Vf
For Parallel-to-Series Applications
given R1 = 1 MW, and MMBT3904L (0.68 V VBEon)
12.0
Rswitch Resistor Value (kW)
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
30
35
40
45
50
55
60
65
70
75
80
LED String Voltage (V)
Figure 14. Plot showing suggested switching resistor value as a function of LED string voltage.
The driver is tunable for strings between 30 and 80 Vf.
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DN05052/D
increases, additional optimization may be useful to help
reduce THD, such as reducing the R2 switching threshold
resistor value.
For higher power levels, additional CCRs may be added
in parallel with CCR1 at little cost to performance. Below is
data taken of performance parameters while sweeping
CCR1 and increasing LED power. As the circuit power
Table 4. PERFORMANCE EVALUATING AT VARIOUS CCR CONFIGURATIONS
CCR Config
(CCR1 + CCR2)
Power Factor
Input Power
Output Power
(Pin * 79%)
THD
(%, Arms)
Input Current
50 + 30 mA (Original)
0.992
7.9 W
6.2 W
12.0%
70 mArms
80 + 30 mA
0.987
11 W
8.7 W
15.4%
93 mArms
100 + 30 mA
0.985
12.8 W
10.1 W
16.8%
105 mArms
130 + 30 mA
0.982
15.7 W
12.4 W
18.8%
134 mArms
Changing CCR2 requires redesigning the R4/R5/Q2
turn-on circuitry, and for higher power levels (or switching
on higher CCR2 currents), a structure like the R4−R7,
Q2−Q3 structure in DN05063/D is more scalable.
Circuit Data
Table 5. USING METAL-CLAD EVALUATION BOARD
Evaluation Board
The evaluation kit CCR120PS3GEVK implements this
circuit on metal-clad board and includes a driver and LED
boards. If the user desires to use their own LEDs, the driver
board may be obtained singularly via the
CCR120PS3AGEVB evaluation board (driver circuitry,
pictured left). Note that the R2 resistor must be changed as
according to Figure 14, and the formulas on page 2.
110 VAC
120 VAC
130 VAC
IRMS(IN) (mA)
65.72
67.72
68.69
PF
0.9915
0.9927
0.9931
THD (IRMS, %)
12.89
11.88
11.53
PIN (W)
7.18
8.10
8.95
Efficiency (%)
81.4
77.2
72.6
Figure 15. Driver and LED Boards
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DN05052/D
Bill of Materials
Table 6. BILL OF MATERIALS, AS DESIGNATED BY FIGURE 1 SCHEMATIC
Designator
Qty
Description
Value
Tolerance
Manufacturer
Part Number
CCR1
1
Constant Current
Regulator
120 V, 50 mA
±15%
ON Semiconductor
NSIC2050JB
CCR2
1
Constant Current
Regulator
120 V, 30 mA
±15%
ON Semiconductor
NSIC2030JB
F1
1
Fuse
250 V, 1 A
−
Any
−
MOV1
1
Varistor
150 V
−
Any
−
D1−D4
4
Diode
400 V, 1 A
−
ON Semiconductor
MRA4004
D5
1
Diode
75 V, 200 mA
−
ON Semiconductor
BAS16H
C1
1
Capacitor
2.2 nF, 200 V
−
Any
−
C2
1
Capacitor
1 nF, 10 V
−
Any
−
R1
1
Resistor
1 MW, 1/8 W
±1%
Any
−
R2
1
Resistor
5.6 kW, 1/8 W
±1%
Any
−
R3
1
Resistor
301 kW, 1/8 W
±1%
Any
−
R4
1
Resistor
590 W, 1/8 W
±1%
Any
−
R5
1
Resistor
100 kW, 1/8 W
±1%
Any
−
R6, R9
2
Resistor
2.2 kW, 1/8 W
±1%
Any
−
R7, R8
2
Resistor
27 kW, 1/8 W
±1%
Any
−
Q1
1
NPN Transistor
40 V, 200 mA
−
ON Semiconductor
MMBT3904L
Q2, Q5
2
PNP Transistor
150 V, 500 mA
−
ON Semiconductor
MMBT5401L
Q3
1
NPN Transistor
350 V, 100 mA
−
ON Semiconductor
MMBT6517L
Q4
1
NPN Transistor
140 V, 600 mA
−
ON Semiconductor
MMBT5550L
LED1−LED6
6
LEDs
20 V, 175 mA
−
Any
−
Further References
• Design Note – DN05063/D: 2-Stage Parallel-to-Series,
For similar 120 VAC LED lighting solutions with CCRs,
please refer to these other design notes:
• Design Note – DN05046/D: 120 VAC, Low-Cost,
Dimmable, Linear, Parallel-to-Series LED Driving
Circuit
ENERGY STAR® Low-Cost Linear LED Driver
Design
ENERGY STAR and the ENERGY STAR mark are registered U.S. marks.
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