LYT1402-1604
Applications Design Example
Wide Input 8 W Bulb Driver Accurate Regulation, High
Power Factor, Low ATHD Design Example (RDK-464)
Rꢆ
1ꢇ.ꢆ ꢈΩ
1ꢉ
R7
ꢆ0ꢇ ꢈΩ
1ꢉ
R6
ꢇ.ꢆꢃ Ω
1ꢉ
1/ꢄ ꢊ
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ꢙꢙ10
1 ꢗꢘ
1/ꢄ ꢊ
ꢐ1
ꢓ.ꢓ ꢗꢘ
ꢂ
ꢀꢁ
60 ꢉꢊ 1ꢋꢌ ꢍꢎ
ꢏꢉ
ꢔ
ꢃ
ꢄ
1
Rꢋ
0.6ꢄ Ω
1ꢉ
ꢌꢋ
ꢆ.7 µꢍ
ꢕꢀ
BR1
10 ꢎ
B10ꢅꢂꢚ
1000 ꢎ
Rꢍ1
10 Ω
ꢇ ꢊ
LYTꢃꢄꢅꢆꢇꢈ-1
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ꢐꢑꢒ160ꢓꢔ
L
ꢌ1
ꢆ7 µꢍ
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ꢌꢆ
1ꢋ0 ꢖꢍ
ꢆꢋ0 ꢎ
Rꢄ
ꢌ6
ꢔ1
ꢏꢅ1ꢕ
100 ꢈΩ
1ꢋ0 µꢍ
Rꢎ1
ꢓ00 ꢎꢛꢌ
ꢒ0 - ꢋ00
ꢉꢎꢓ
1/ꢄ ꢊ
6ꢓ ꢎ
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ꢀꢁꢂ7ꢃꢄ7ꢂ0610ꢅ16
Figure 5. Schematic from RDK-464 8 W, 60 V, 135 mA, Non-isolated A19 LED Driver for Wide Input Range: 90 – 300 V VAC using LYT1603D in High-Side Buck
Configuration.
The circuit shown in Figure 5 is configured as high-side buck power
supply utilizing the LYT1603D from the LYTSwitch-1 family of ICs.
This is a low-cost LED driver designed to drive a 60 V LED voltage
string at 135 mA output current with an input voltage range of
90 VAC to 300 VAC.
The rectified AC supply through BR1 is filtered by the input capacitors
C1 and C4. Too much capacitance degrades power factor and THD,
so the values of the input capacitors were adjusted to the minimum
values necessary to meet EMI with a suitable margin. Inductor L1,
C1 and C4 form a π (pi) filter, which attenuates conducted differential
and common mode EMI currents. A resistor of at least 10 kΩ (not
shown) across L1 can be used damp the Q-factor of the filter inductor
to improve filtering high frequency EMI without reducing low
frequency attenuation.
Circuit Description
LYTSwitch-1 is a SO-8 package LED driver controller IC designed for
non-isolated buck topology applications. The LYTSwitch-1 provides
high efficiency, high power factor and accurate LED current regula-
tion. It incorporates a high-voltage 725 V power MOSFET and a
control engine to switch the FET in critical conduction mode with
variable frequency and variable on-time for low EMI, accurate current
regulation, high power factor, low THD and high efficiency. The
controller also integrates protection features such as input and output
overvoltage protection, thermal fold-back, over-temperature
shutdown, output short-circuit and over-current protection.
LYTSwitch-1 Controller Stage
The LED driver circuit is a high-side buck configuration operating in
critical condition mode. During the time the internal MOSFET is on,
current ramps up through inductor T3, storing energy in the magnetic
field and at the same time supplying current to the load. Then when
the internal MOSFET turns off, the current will continue to flow in the
same direction ramping down, to the output load via flywheel diode D1.
Capacitor C5 provides local decoupling for the BYPASS (BP) pin of
LYTSwitch-1 IC, which provides power to the controller during the
switch on time. The IC internal regulator draws power from the
high-voltage DRAIN (D) pin and charges the bypass capacitor C5
during the power switch off-time. The typical BYPASS pin voltage is
5.22 V. To keep the IC operating normally especially during the dead
zone, where VIN < VOUT, the value of the capacitor should be large
enough to keep the bypass voltage above the VBP(RESET) reset value of
4.5 V. Recommended minimum value for the bypass capacitor is
4.7 mF, X7R if using a ceramic type capacitor.
Input Stage
The input fusible resistor RF1 provides safety protection and also
serves as a current limiting component against high-voltage differen-
tial surge. Varistor RV1 acts as a voltage clamp that limits the voltage
spike on the primary during line transient voltage surge events. A
300 VAC rated part was selected with a maximum clamping voltage
specification of 710 VDC lower than the device drain voltage (725 V).
The AC input voltage is full wave rectified by BR1 to achieve good
power factor and low THD. For higher surge capability such as
>1 kV, C1 and L1 can be placed before the bridge rectifier BR1 in the
same order and RV1 after BR1 but, a safety X-capacitor is required to
be used for C1.
3
Rev. B 07/16
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