IRPLLED1
IRPLLED1 (Rev D Version)
350mA to 1.5A High Voltage LED Driver using
IRS2540,1 or IRS25401,11
Table of Contents
Page
1. Introduction………………………………………………………………...….1
2. Constant Current Control.......................................................................3
3. Frequency Selection..............................................................................6
4. Output L1 and COUT Selection .............................................................6
5. MOSFET vs Diode for the low side switch.…………...………………….12
6. VCC Supply ...……………………………………………………………….15
7. VBS Supply ………………………………………………………………….16
8. Enable Pin ……….………………………….……………………………….17
9. Over voltage protection………………….……………………………....….22
10. Other Design Considerations .…………….……………………………...24
11. Design Procedure Summary ……….…………………………………….25
12. Bill of Materials ………………………..……………………………….26-27
13. PCB Layout ………………………………………………………………...27
EVALUATION BOARD - IRPLLED1
1. Introduction
Development of LED technology over the last few years has produced high power devices with luminous efficacies
surpassing Fluorescent and HID light sources. These solid state light sources also posses the added advantages of
longer operating life span, up to 50000 hours as well greater robustness that other less efficient light sources.
For these reasons high power LEDs have now become a viable alternative for many general lighting applications.
High power LEDs are driven with constant regulated DC current, requiring a "ballast" or "converter" to provide the
required current from an AC or DC power source. The IRS2540/1/01/11 series Buck LED driver provides an
accurately controlled current and protects the LEDs against damage from overload, while providing the ability to
dim the light level. The IRS2540/1/01/11 will be replaced by the fully compatible revised IRS25401/11.
The IRPLLED1evaluation board is a high voltage LED driver designed to operate from a DC input voltage of 50V
to 170V and produce an output voltage of 16V-24V to supply a programmable load current of 350mA, 700mA, 1A,
or 1.5A. It uses the IRS2540/1/01/11 or revised version IRS25401/11, a high voltage, high frequency Buck control
IC for constant LED current regulation. The IRS2540/1/01/11 controls the average load current by a continuous
mode time-delayed hysteretic method using an accurate on chip band gap voltage reference. The 8-pin, 200V/600V
rated IRS2540/1/01/11 inherently provides short-circuit protection with open-circuit protection incorporated by a
simple external circuit and has dimming capability.
The evaluation board documentation will briefly describe the functionality of IRS2540/1/01/11, discuss the selection
of the output stage, switching components and surrounding circuitry. This board was tested with a single HBLED
panel for the 350mA and 700mA settings, using two similar flood boards in parallel to provide test loads for the 1A
and 1.5A settings.
Important Safety Information
The IRPLLED1 does not provide galvanic isolation of the LED drive output from the line input. Therefore if the
system is supplied directly from a non-isolated input, an electrical shock hazard exists at the LED outputs and these
should not be touched during operation. Although the output voltage is low this electrical shock hazard still exists.
It is recommended that for laboratory evaluation that the IRPLLED1 board be used with an isolated DC input
supply. The IRS2540/1/01/11 series Buck topology is suitable only for final applications where isolation is either not
necessary or provided elsewhere in the system.
www.irf.com
RD-0608
2
2. Constant current control
The IRS2540/1/01/11 is a time-delayed hysteretic Buck controller. During normal operating conditions the output
current is regulated via the IFB pin voltage to a nominal value of 500mV. This feedback signal is compared to an
internal high precision band gap voltage reference. An on-board dV/dt filter has also been used to prevent erroneous
transitioning. This is necessary since the IFB pin is sensitive to noise.
The Buck topology may use a fast recovery diode for the lower switch or a synchronous MOSFET shown as M2 in
Fig 1. On power up as the VCC supply to the IR2540/1/01/11 reaches VCCUV+ the LO output is held high and the
HO output low for a predetermined period of time. This initiates charging of the bootstrap capacitor establishing the
VBS floating supply for the high side output. The chip then begins toggling HO and LO outputs as needed to
regulate the load current monitored and fed back through the current sense resistor RCS. The dead times of
approximately 140ns between the LO and HO gate drive signals prevents shoot through and reduce switching losses,
particularly at higher frequencies.
Fig. 1 IRS2540/1/01/11 Constant Current LED Driver Typical Schematic
(see Fig. 16 for evaluation board full schematic)
Note: Cout and Rout are optional and may be required in some applications
Under normal operating conditions, if VIFB is below VIFBTH, HO will be high and the load receives current from
VBUS through the Buck inductor L1. This simultaneously stores energy in the output stage comprised of L1 and
COUT as VIFB begins to increase. When VIFB crosses VIFBTH, HO transitions low after the delay t_HO_off.
Once HO is low, LO will transition high after the deadtime. The inductor and output capacitor release the stored
energy into the load and VIFB starts decreasing. When VIFB crosses VIFBTH again, LO switches low after the
delay t_LO_off and HO switches high after the delay t_HO_on. The cycle then repeats continuously at a frequency
depending on the load current and the values of the output inductor and capacitor.
www.irf.com
RD-0608
3
(A)
Fig. 2 (A) Storing Energy in Inductor
(B) Releasing Stored Inductor Energy
(B)
HO
50%
50%
50%
t_HO_off
DT1
t_HO_on
DT2
LO
t_LO_on
50%
50%
t_LO_off
IFB
IFBTH
Fig. 3 IRS2540/1/01/11 Control Signals, Iavg=1.2A
Fig. 4 IRS2540/1/01/11 Time Delayed Hysteresis
The switching continues to regulate the current at an average value determined as follows: when the output
combination of L1 and COUT is large enough to maintain a low ripple on IFB (less than 100mV), Iout(avg) can be
calculated:
Iout
(
avg
)
=
VIFBTH
RCS
Having load current programmable from 350mA to 1.5A, series and parallel combinations of resistors must be used
to correctly set the current as well as distribute power accordingly. Equivalent resistances for each current setting
are calculated as follows:
0.5
V
=
1.43
Ω
350
mA
0.5
V
=
0.71
Ω
R
700
mA
=
700
mA
0.5
V
=
0.5
Ω
R
1
A
=
1
A
0.5
V
=
0.33
Ω
R
1.5
A
=
1.5
A
R
350
mA
=
www.irf.com
RD-0608
4
Since some of these equivalent values of resistance are not available, series and parallel combinations are used and
are specified as follows (all combinations use standard value resistors: 1.43Ω, 0.56Ω, and 0.47Ω):
R
350mA
=
1.43
Ω
R
700mA
=
0.71
Ω ≈
(1.43
Ω
|| 1.43
Ω
)
=
0.715
Ω
R
1A
=
0.5
Ω ≈
(0.47
Ω +
0.56
Ω
) || (0.47
Ω +
0.56
Ω
)
=
0.515
Ω
R
1.5
A
=
0.33
Ω ≈
(0.47
Ω +
0.56
Ω
) || (0.47
Ω +
0.56
Ω
) || (0.47
Ω +
0.56
Ω
)
=
0.343
Ω
Although some of the series and parallel combinations do not yield the exact resistance needed for tolerance
purposes, they are accurate enough. For this evaluation board an extremely tight current regulation is achieved with
a worst case result of ±1.2% for the 350mA setting over the bus voltage range from 50V to 170V. Likewise a precise
regulation of ±0.25% can be maintained for a range of load voltage from 16V to 24V at the 350mA current setting.
The jumper positions on the evaluation boards (JSET) for setting the different load currents are shown below:
Fig. 4a: JSET LED Current Programming Settings
1600
1400
1200
Iout (mA)
1000
800
600
400
200
0
30
50
70
90
110
Vin (V)
±0.3%
±0.5%
±0.6%
±1.2%
350mA
700mA
130
150
1A
170
1.5A
Fig. 5 Vout = 16V, L1 = 470uH, COUT = 33uF
www.irf.com
RD-0608
5
微控制器 MCU
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
