Intro: 5 Watt LED Bulb
Dear Friends , this Led Bulb has light output equal to 12 watt CFL. Saving of electricity is approx. 80 Units which saves INR 500 / $ 8 per year on basis of 24 hours usage.
Step 1: Components & Their Purpose
1) Metallized Polyster Capacitor
1 uf/250 Volt(105K) ,
Together they are capable of providing approx. 85mA current to circuit.
These are used in parallel for acquiring 5 Watt output.
2) Noise Suppression Capacitor
103 M or 103 K X1 ,Y2 (.01uf)
Voltage rating should be more than 250 Volt.Here 2 KV rating is used.
The purpose of using this component is to lowering down the High frequency signals generated by the circuit itself and eliminates the buzzing sound in metallized polyster capacitor.
3) Negative Temperature Coefficient (NTC) Surge protection Thermistor.
10D-9 Ohm Ntc is used as ICL(inrush current limiting).
It is energy efficient in comparison of bleeder resistance.
It's resistance decrease with increase in temperature.So in operation it initially provides some resistance and after that negligible resistance is offered by NTC.
4) Electrolytic Capacitor
Alternatively use 100uf/100 V capacitor.
Due to local availability, two 470 uf/63 V capacitor are conneced in series ,so that their voltage rating becomes doubles and filteration capacity just halfed according to series rule of capacitor.
This series combination is equivalent to 235 uf/126 V.
5) Discharging resistor
a.)47 kilo ohm / 1 Watt or 1/2 Watt resistance is responsible for quickly absorption of charge present in the electrolytic capacitor when the switch is turned off.
Discharging Cap Value is choosen from R-C time constant formula.
b.) 1 Mega Ohm / 1/4 watt is used for metallized polyster cap.
6) Series Resistance
1 Ohm/2 Watt
For avoiding the Short Circuiting of LED's when the surge is bypassed to load , this 2 watt resistance drops surge across it before going to the load.So it ensures safety of load in such type of conditions.
7) 27 x 1 watt Led
Use adhesive on the back side of led and place directly on aluminum sheet of around 24 gauge in thickness .
8) General purpose diode
1N4007 is the most common diode(1000Volt/1 Amp) which forms full wave bridge rectifier and provides 80% efficiency in compare of half bridge rectifier.
Step 2: Circuit and Heatsink Building
We Require 2mm MDF or higher for making heatsink.
For placing 27 led's we require a suitable heatsink.
With 2.5 inch Hole cutter ,cut four circles and two aluminium sheet
or alternatively use scissors for cutting MDF board and aluminum sheet.
Join them as shown in picture i.e layer by layer.
After that take LED's and bend their anode and cathode terminal to atmost 90° for avoid shorting with heatsink and place them such a way that they form a circle and also their positive and negative terminal comes around the hole of heatsink. Apply solder paste and solder all the led in series fashion if they are far from each other then place the cutting pins of components for making connection. Avoid any solder contact with heatsink.
2.) Circuit Building
Follow the circuit and picture carefully for reference .
In this circuit a jumper wire is placed between Capacitor neagtive terminal and bridge rectifier for simplicity.
Don't touch circuit in ON Condition ,this gives you a lethal shock.
Step 3: Testing and Measurements
Individual Led measurement
1. Current- 57mA
2. Voltage- 2.9 VDc
= Voltage x Current
= 2.9 x .057
= total no. of led x wattage of individual led
= 27 x 0.16587 watt
= 4.48 Watt
Power monitor readings at 248 Volt A.C
=5.11 watt / 0.250 Power factor
So power lossed is
= 5.11 Watt - 4.48 Watt
This loss is due to
1.) Poor Power factor of unregulated capacitive power supply.
2.) High ESR of Electrolytic capacitor.
3.) Stray Capacitance of Solder Tracks.
Scope of Improvement
1.) If S.M.P.S is used it will deliver good power factor i.e low wattage loss.(Buck,Buck-Boost,Flyback topologies)
2.) Attain a large potential drop from these supplies which is equal to rectified volatge i.e 300 Volt or higher for power factor greater than 0.50 which is dangerous and not possible for bulb enclosure.
Challenges with Switch mode power supply
1.) High Component Count
2.) High Complexity
3.) Smps transformer is not readily available.