In this post we are going to learn about a few easy to build, compact 1 watt LED bulb circuits. The first circuit is SMPS based, the second design uses a capacitive power supply, while the remaining concepts show how to used a DC source to illuminate a 1 watt LED.
Warning: Many of the circuits explained below are not isolated from mains AC, and therefore are extremely dangerous to touch in the powered and open condition. You should be extremely careful while building and testing these circuits, and make sure to take the necessary safety precautions. The author cannot be held responsible for any mishap due to any negligence by the user
1) Small 1 watt SMPS LED Driver
In the first design which is the most recommended one, we study an SMPS LED driver circuit which can be used for driving high watt LEDs rated anywhere between 1 watt LED upto 12 watts. It can be directly driven from any domestic 220V AC or 120V AC mains outlets.
Introduction
The first design explains a small non isolated SMPS buck converter design (non-isolated Point of Loads), which is very accurate, safe and easy to build circuit. Let's learn the details.
You may also want to learn How to Design LED Driver Circuits
Main Features
The proposed smps LED driver circuit is extremely versatile and specifically suited for driving high watt LEDs.
However being a non-isolated topology does not provide safety from electric shocks at the LED side of the circuit.
Apart from the above drawback, the circuit is flawless and is virtually protected from all possible mains surge related dangers.
Although a non-isolated configuration may look a bit undesirable, it relieves the constructor from winding complex primary/secondary sections on E-cores, since the transformer here is replaced with a couple of simple ferrite drum type of chokes.
The main component here responsible for the execution of all the features is the IC VIPer22A from ST microelectronics, which has been specifically designed for such small transformerless compact 1 watt LED driver applications.
Circuit Diagram
Image Courtesy: © STMicroelectronics - All rights reserved
Circuit Operation
The circuit functioning of this 1 watt to 12 watt LED driver can be understood as given under:
The input mains 220V or 120V AC is half wave rectified by D1 and C1.
C1 along with the inductor L0 and C2 constitute a pie filter network for cancelling EMI disturbances.
D1 should be preferably replaced with two diodes in series for sustaining the 2kv spikes bursts generated by C1 and C2.
R10 ensures some level of surge protection and acts like a fuse during catastrophic situations.
As can be seen in the above circuit diagram, the voltage across C2 is applied to the internal mosfet drain of the IC at pin5 to pin8.
An inbuilt constant current source of the VIPer IC delivers a 1mA current to pin4 of the IC which is also the Vdd pin of the IC.
At about 14.5V at Vdd, the current sources gets switched OFF and forces the IC circuitry into an oscillatory mode or initiates pulsing of the IC.
The components Dz, C4 and D8 become the circuit regulation network, where D8 charges C4 to the peak voltage in the freewheeling period and when D5 is forward biased.
During the above actions, the source or the reference of the IC is set to about 1V below ground.
For a comprehensive info about the circuit details of the 1 watt to 12 watt LED driver, please go through the following pdf datasheet by ST microelectronics.
2) Using Transformerless Capacitive Power Supply
The next 1 watt LED driver explained below shows how to build a few simple 220 V or 110 V operated 1 watt LED driver circuit,that would cost you not more 1/2 a dollar, excluding the LED of course.
I have already discussed capacitive type of power supply in a couple posts, like in LED tube light circuit and in a transformerless power supply circuit, the present circuit also utilizes the same concept for driving the proposed 1 watt LED.
Circuit Operation
In the circuit diagram we see a very simple capacitive power supply circuit for driving a 1 watt LED, which may be understood with the following points.
The 1uF/400V capacitor at the input forms the heart of the circuit and functions as the main current limiter component of the circuit. The current limiting function makes sure that the voltage applied to the LED never exceeds the required safe level.
However high voltage capacitors have one serious issue, these do not restrict or are not able to inhibit the initial switch ON mains power in rush, which can be fatal for any electronic circuit LEDs are no exceptions.
Adding a 56 Ohm resistor at the input helps to introduce some damage control measures, but still it alone cannot do the complete safeguarding of the involved electronics.
An MOV would certainly do, also what about a thermistor? Yep, a thermistor would also be a welcome proposition.
But these are relatively at the costlier side and we are discussing a cheap version for the proposed design, so we would want to exclude anything that would cross a dollar mark as far as the total cost goes.
So I thought of an innovative way of replacing an MOV with an ordinary, cheap alternative.
What is the function of an MOV
It's to sink the initial burst of high voltage/current to ground such that it is ground before reaching the LED in this case.
Wouldn't a high voltage capacitor do the same function if connected across the LED itself. Yes it would surely operate the same way as an MOV.
The figure shows the insertion of another high voltage capacitor directly across the LED, which sucks the instantaneous influx of voltage surge during power switch ON, it does this while charging up and thus sinks almost the entire initial voltage in rush making all the doubts associated with a capacitive type of power supply distinctly clear.
The end result as shown in the figure is a clean, safe, simple and a low cost 1 watt LED driver circuit, which can be built right at home by any eletronic hobbyist and used for personal pleasures and utility.
CAUTION: THE CIRCUIT SHOWN BELOW IS NOT ISOLATED FROM THE AC MAINS, THEREFORE IS EXTREMELY DANGEROUS TO TOUCH IN POWERED POSITION.
Circuit Diagram
NOTE: The LED in the above diagram is a 12V 1 watt as shown below:
In the above shown simple 1 watt led driver circuit, the two 4.7uF/250 capacitors along with the 10 ohm resistors form a kind of "speed breaker" in the circuit, this approach helps to arrest the initial switch ON surge inrush which in turn helps to safeguard the LED from getting damaged.
This feature can be replaced with an NTC which are popular for their surge suppressing features.
This enhanced way of tackling the initial surge inrush problem could be by connecting an NTC thermistor in series with the circuit or the load.
Please check out the following link for knowing how to incorporate an NTC thermister in the proposed 1 watt LED driver circuit
The above circuit can be modified in the following manner, however the light may be a little compromised.
A good way of tackling the initial surge inrush problem is by connecting an NTC thermistor in series with the circuit or the load.
Please check out the following link for knowing how to incorporate an NTC thermister in the proposed 1 watt LED driver circuit
https://www.homemade-circuits.com/2013/02/using-ntc-resistor-as-surge-suppressor.html
3) A Stabilized 1 watt LED Driver using Capacitive Power Supply
As can be seen, 6nos of 1N4007 diodes are used across the output, in their forward biased mode. Since each diode would produce a drop of 0.6V across itself, 6 diodes would create a total drop of 3.6V, which is just the right amount of voltage for the LED.
This also means that the diodes would shunt the rest of the power from the source tp ground, and thus keep the supply for the LED perfectly stabilized and safe.
Another Stabilized 1 watt Capacitive Driver Circuit
The following MOSFET controlled design is probably the best universal LED driver circuit that guarantees a 100% protection for the LED from all types of hazardous situations, such as sudden over voltage and over current or surge current.
A 1 watt LED connected with the above circuit would be able to produce around 60 Lumens of light intensity, equivalent to a 5 watt incandescent lamp.
Prototype Images
The above circuit can be modified in the following manner, however the light may be a little compromised.
4) 1 Watt LED Driver Circuit Using a 6V Battery
As can be seen in the fourth diagram, the concept hardly utilizes any circuit or rather does not incorporate any hi-end active component for the required implementation of driving a 1 watt LED.
The only active devices that's been employed in the proposed simplest 1 watt LED driver circuit are a few diodes and a mechanical switch.
The initial 6 volts from a charged battery is dropped to the required 3.5 volts limit by keeping all the diodes in series or in the path of the LED supply voltage.
Since each diode drops 0.6 volts across it, all four together allow only 3.5 volts to reach the LED, lighting it safely, yet brightly.
As the illumination of the LED drops, each diode is bypassed subsequently using the switch, to restore the brightness of the LED.
The use of the diodes for dropping the voltage level across the LEDs makes sure that the procedure does not dissipate any heat and therefore becomes very efficient in comparison to a resistor, which would have otherwise dissipated a lot of heat in the process.
5) Illuminate 1 Watt LED with a 1.5V AAA Cell
In the 5th design let's learn how to illuminate a 1 watt LED using a 1.5 AAA cell for a reasonable amount of time.The circuit is obviously based on boost driver technology, other wise driving such a huge load w such minimal source is beyond imagination.
A 1 watt LED is relatively huge when compared to a 1.5 V AAA cell source.
A 1 watt LED needs minimum 3 volts supply which is double the above cell rating.
Secondly a 1 watt LED would require anywhere between 20 to 350 mA of current for operating, 100 mA being a respectable current for driving these light machines.
Therefore using a AAA penlight cell for the above operation looks very remote and out of question.
However the discussed circuit here proves all of us wrong and successfully drives a 1 watt LED without much complications.
THANKS TO ZETEX, for providing us with this wonderful little IC ZXSC310, which requires just a few ordinary passive components for making this feat possible.
Circuit Operation
The diagram shows a rather simple configuration, which is basically a boost converter set up.
The input DC of 1.5 volts is processed by the IC to generate a high frequency output.
The frequency is switched by the transistor and the schottky diode via the inductor.
The rapid switching of the inductor provides the required boost in the voltage which becomes just appropriate for driving the connected 1 watt LED.
Here, during the completion of each frequency, the equivalent stored energy inside the inductor is pumped back into the LED generating the required voltage boost, which keeps the LED illuminated for long hours even with a source that's as small as a 1.5 volt cell.
Prototype image
1 Watt Solar LED Driver
This is school exhibition project which can be used by children to show how solar energy can be used for illuminating a 1 watt LED.
The idea was requested by Mr. Ganesh, as given below:
Hi Swagatam, I have come across your site and find your work very inspiring. I am currently working on a Science, Technology, Engineering and Math (STEM) program for year 4-5 students in Australia. The project focuses on increasing children’s curiosity about science and how it connects to real-world applications.
The program also introduces empathy in the engineering design process where young learners are introduced to a real project (context) and engages with their fellow school peers to solve a worldly problem. For the next three years, our focus is on introducing children to the science behind electricity and the real-world application of electrical engineering. An introduction to how engineers solve real-world problems for the greater good of society.
I am currently working on online content for the program, which will focus on young learners(Grade 4-6) learning the basics of electricity, in particular, renewable energy, i.e. solar in this instance. Through a self-directed learning program, children learn and explore about electricity and energy, as they are introduced to a real-world project, i.e. providing lighting to children sheltered in the refugee camps around the world. On completion of a five-week program, children are grouped in teams to construct solar lights, which are then sent to the disadvantaged children around the world.As a not 4 profit educational foundation we are seeking your assistance to layout a simple circuit diagram, which could be used for the construction of a 1 watt solar light as practical activity in class. We have also procured 800 solar light kits from a manufacturer, which the children will assemble, however, we need someone to simplify the circuit diagram of these light kits, which will be used for simple lessons on electricity, circuits, and calculation of power, volts, current and conversion of solar energy to electrical energy.
I look forward to hearing from you and keep on with your inspiring work.
The Circuit Design
Whenever a simple yet safe solar controller is required we inevitably go for the ubiquitous IC LM317. Here too, we use the same inexpensive device for implementing the proposed 1 watt LED lamp using a solar panel.
The complete circuit design can be seen below:
A quick inspection reveals that if a current control is present, voltage regulation can be ignored. Here's a simplified version for the above concept, using only a current limiter circuit.
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