International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
Design Methodology of Power Supply
for Led Lamps
G. Sai Sireesha#1, M. Anil Kumar*2,
#
ECE Department, K L University,
Vaddeswaram, Andhra Pradesh, India.
Abstract - Designing an off-line power supply
involves many aspects of electrical engineering
analog and digital circuits, bipolar and MOS
power device characteristics, magnetics, thermal
considerations, safety requirements, control loop
stability,
etc.
This
represents
an
enormous
challenge involving complex trade-offs with a large
number of design variables. As a result, new
off-line power supply development has always been
tedious and time consuming even for the experts in
the field. This application note introduces a simple,
yet highly efficient methodology for the design of
TOP Switch family based off-line power supplies.
For TOP Switch designs.
Keywords— MOS,TOP Switch,ILIMIT
Bridge Rectifier,Feedback Circuitry.
I.Introduction
The design of a switching power supply,
by nature, is an iterative process with
many variables requiring adjustment to
optimize the design. The design method
described in this document consists of
two major sections: A design flow chart
and a step-by-step design procedure.
The flow chart shows the design
sequence at a conceptual level for TOP
Switch power supply design. The
step-by-step procedure gives details
within each step of the design flow chart,
including empirical design guidelines
and look-up tables.
II.Basic Circuit Configuration
Because of the high level integration of
TOP Switch, many power supply design
issues are resolved in the chip. Far fewer
issues are left to be addressed externally,
ISSN: 2231-5381
resulting in one common circuit
configuration for all applications.
Different output power levels may
require different values for some circuit
components, but circuit configuration
stays unchanged. TOP Switch is a
feature-rich product family. Advanced
features like under-voltage, overvoltage,
external ILIMIT, line feed forward, and
remote ON/OFF are easily implemented
with a minimal number of external
components,but do involve additional
design considerations. Other application
specific issues such as constant current,
constant power outputs,etc. are beyond
the scope of this application note.
However, such requirements may be
satisfied by adding additional circuitry
to the basic converter configuration. The
only part of the circuit configuration that
may change from application to
application is the feedback circuitry. The
basic circuit configuration used in TOP
Switch power supplies, which also
serves as the reference circuit for
component identifications used in the
description throughout this application
note.
III.The problem with LEDs
Variation in the forward voltage will
affect the forward current and hence the
luminous flux.
Powering an LED chip from an AC
source requires a regulator to step-down
the 110 to 115 or 230 to 240 V, 50 or 60
Hz mains supply used by most countries
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
to the modest voltage and current
requirements of LEDs. Note that
luminaires typically use six to eight
LED chips per fixture, so the power
requirement for each unit is higher than
that for a single LED.
One basic form of LED driver comprises a full
wave rectifier connected to an LED string with a
resistor in series to limit the current. This
approach modulates the LEDs at twice the AC
frequency (i.e., 100 to 120 Hz). Because the
luminous intensity is proportional to the current,
the LED flickers at this rate
IV.Design Flow
With the basic circuit configuration
as its foundation, the logic behind this
design approach can be summarized as
follows:
1. Determine system requirements and
decide on feedback circuit accordingly.
2. Choose the smallest TOP Switch
capable of the required output power.
3. Design the smallest transformer for
the TOP Switch chosen.
4. Select all other components to
complete the design.
The overriding objective of this
procedure is “design for cost
effectiveness.”
Step 1: Determine system Requirements
V AC max, VAC min,Line
frequency,Output voltage,voltage
power,power supply efficiency
Universal value,
V AC min=85V
V AC max=280V
Step 2: Choose feedback circuit and bias
voltage.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
voltage ,output voltage and output power.
RCD (resistor/capacitor/diode) clamp may
be used with Top switch to protect it
especially under startup or out put over
load conditions.
Step 8: Calculate primary inductance.
Step 3: Determine VDC max and VDC
min ,a storage capacitance based on input
voltage and output power.
Lp 
10 6  Po
Z  1  n   n

2
n
Ip  Kp  1  0.5Kp   Fs (min)
Z= loss allocation factor
n=Efficiency
V max  2 VAC min
Step 4: Set current wave form parameter Kp. Step 9: Choose core and bobbin width based
on switching frequency and output power.
*Core effective cross-sectional area
Ae:cm2
*Core effective path length Le: cm
*Core ungapped effective inductance Al in
nH/ turn2
*Bobbin width BW in mm
Step 5: Calculate primary peak current.
Ip 
Step 10: Set value for
Iavg
1  0.5 Kp  D max
Where, D max 
Vor
V min  Vds   vor
Po
n  V min
Drain to source voltage VDS=10V
Vor=Rectified output voltage=135V
Iavg 
Step 6:Calculate primary RMS current
IRMS.
Step 7: Choose Top Switch based on input
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number of primary layers(L).
number of secondary turns(Ns).
Calculate number of primary turns(Np)
Calculate number of bias turns (Nb)
Starting with L=2
Starting with Ns=0.6 turns/volt
Vor
Vo  Vd
Vb  Vdb
Nb  Ns 
Vo  Vd
VD = 0.4 V for schottky diode
VDB= 0.7 V
Np  Ns 
Step 11: Determine primary winding
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
diameter and secondary winding diameter.
Step 12: Check Magnetic flux density BM ,
3000>Bm>2000 (gauss),0.3>Bm>0.2(tesla).
Step 13: Calculate secondary peak current
and secondary RMS current.
Step 14: Determine out put capacitor ripple
current I ripple
.
Iripple  ( I srms 2  Io 2 )
Step 15: Select clamp zener and blocking
diode.
PS output
Vor
Blocking
diode
Clamp
zener
Multiple
outputs
100V
BYV26C
MUR160
UF4005
P6KE150
Single
output
120V
BYV26C
MUR160
UF4005
P6KE180
VI. References

“A Review of the Literature on
Light Flicker: Ergonomics, Biological
Attributes, Potential Health Effects, and
Methods in Which Some LED Lighting
May Introduce Flicker,” IEEE Standard
P1789, February 2010.

“The Evaluation of Flicker in
LED Luminaires,” Michael Grather,
President, Luminaire Testing Laboratory,
Inc.
Profile:G. Sai Sireesha,
IV/IV B-Tech,
ECE Department,
K L University,
Step 16: Select output rectifier and output
capacitor.
Vr >1.25X PIVs
Secondary winding maximum peak inverse
voltage,
PIVs  Vo  (V max
Ns
)
Np
V.Conclusion
Thus by designing a top switch supply
the constant voltage will be given to the
LED lamp based on the feedback sent to
TOP SWITCH. This acts as AC to DC
Converter. This will increase the
efficacy of the lamp as it gives constant
voltage which will not affect the
working of LEDs.
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