Transformerless Current-Controlled LED Bulb Circuits you can Build at Home

In this post I have elaborately explained how to build simple transformerless LED bulb circuits using many LEDs in series and powering them through current controlled capacitive power supply circuit.

Warning: Circuits I have 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 the negligence of the user.

Want to Build your own LED Drivers? Read this post on How to Design LED Drivers.

UPDATE:

After doing a lot of research in the field of cheap LED bulbs, I could finally come up with a universal cheap yet reliable circuit that ensures a fail-proof safety to the LED series without involving costly SMPS topology. Here's the finalized design for you all:

These designs incorporate constant current and current limiting feature which makes them highly reliable, efficient and long lasting LED bulbs, and moreover they are extremely cheap compared to the commercial bulbs.

You just have to adjust the pot to set the output according to the total forward drop of the LED series string.

Meaning, if the total voltage of the LED series is say 3.3V x 50nos = 165V, then adjust the pot to get this output level and then connect it with the LED string.

This will instantly illuminate the LEDs at full brightness and with complete over voltage and over current or surge inrush current protections.

R2 can be calculated using the formula: 0.6 / Max LED current Limit

Improving the above Design

Although the above simple current controlled MOSFET LED driver looks easy and safe for illuminating high watt LEDs, it has one serious drawback.

The MOSFET can generate a lot of heat if the output is adjusted for low voltage LED strings.

The heat dissipation is basically due to the bridge rectifier and the C1 which converts the full AC cycle to DC, causing a lot of stress on the MOSFETs.

This aspect can be improved drastically by replacing the bridge rectifier with a single diode and moving the C1 capacitor parallel to the output LED, as shown in the following diagram:

In the above diagram due to the presence a single diode D1 only half AC cycles are delivered across the MOSFET, causing 50% less stress and heat dissipation on the MOSFET.

However, the capacitor C1 parallel to the LED string ensures that the LED keeps getting the required power even during the absence of the other AC half cycles.

You can add more number of LEDs in series, a maximum upto 300 / 3.3 = 90 LEDs.

Make sure to adjust the P1 pot accordingly to adjust the output voltage to match the LED string's max forward voltage.

Likewise adjust the base/emitter resistor of T2 (BC547) to match the LED max current spec.

Using BJTs

If you do not want to incorporate a MOSFET, then you can simply build the above design using BJTs as shown below:

How it Works

The main feature and operation of the design is controlling current and providing a safe consent current supply to the LEDs.

So we know, if the current is restricted then the LEDs can never burn regardless of the input supply voltage.

In this design, the capacitor CY does the main current limiting operation for the LEDs. Meaning, the reactance of the capacitor produces a resistance which limits the input 220V AC current to the maximum desired limit of the LEDs.

So, if the required maximum LED current is 300 mA, then you can select and adjust the value of the CY to ensure that it never allows the input current to exceed the 300 mA.

But if the CY capacitor itself can control the current for the LEDs, then why do we need the BJT current control stage, won't it be redundant?

The BJT current controller is necessary because the input AC 220V or 120V is never constant. If the input supply rises then CY will also start passing proportionally higher amounts of current to the LEDs, eventually causing damage to the LEDs.

The BJT current controller stage makes sure that even if the input AC supply happens to increase, it limits the excess current and ensures a constant current for the LEDs consistently and safely.

Moreover this BJT current controller stage also controls the switch ON in rush current making sure the LEDs are never subjected to any form of dangerous current inputs from the AC mains.

Calculating the Part Values:

Provided Data:

Input Voltage: 220V AC

LED Configuration: Let' us assume, 50 LEDs are in series

• Forward voltage per LED_(VF​) = 3.3V
• Total forward voltage V_LEDs = 50 * 3.3=165V

LED Current Requirement: 300 mA (0.3A)

Capacitor CX: Acts as a filter for rectified DC voltage

CY: Limits the AC current to 300 mA

Transistors (MJE13003 and MJE340): Used as current regulators

Resistor RX: Used to calculate current regulation

Step 1: Capacitor CY for Current Limiting

The current through CY depends on its capacitive reactance X_CX and the input AC voltage.
The formula is:

I_CY = V_AC / X_C

Where:
X_C = 1 / (2 * π * f * C)

For 50Hz mains frequency:

C_CY = I_CY / (2 * π * f * V_AC)

Substitute:

C_CY = 0.3 / (2 * π * 50 * 220)

C_CY = 4.33 µF

Select C_Y = 4.7 µF (400V AC-rated).

Step 2: Resistor RX for Current Regulation

The resistor RX determines the current through the BJTs. The formula is:

R_X = V_BE / I_LED

Where:

• V_BE is the base-emitter voltage drop of the BJTs, typically 0.7V.

Substitute:

R_X = 0.7 / 0.3

R_X = 2.33 Ω

Select RX = 2.2Ω (5W-rated for safety).

Step 3: Filter Capacitor CX

The filter capacitor CX smooths the rectified DC voltage. Its value depends on the LED current and ripple voltage. Use the formula:

C_X = I_LED / (2 * π * f * V_ripple)

Assume V_ripple = 5V:
C_X = 0.3 / (2 * π * 50 * 5)
C_X = 191 µF

The voltage rating of C_X must be higher than the total forward voltage of the LEDs, which is 165V.

Select C_X = 191 µF (200V-rated). 1000uF is not required as shown in the diagram.

Step 4: Calculating the MJE13003 Base Resistor (100 Ω is wrongly shown in the diagram)

Collector Current (I_C): 300 mA (LED current).

Current Gain (h_FE) of MJE13003:

Typical h_FE for the MJE13003 is around 8 to 10 at I_C = 0.3A. Let’s use h_FE = 10 as a conservative value.

Base Current (I_B) Requirement:

The base current is given by:

I_B = I_C / h_FE

Substituting:

I_B = 0.3 / 10 = 0.03 A (30 mA)

Base-Emitter Voltage (V_BE):

The base-emitter drop for MJE13003 is typically 0.7V.

Available Base Drive Voltage:

We will assume that the circuit supplies 165V rectified DC (across the LEDs and CX), because of the current limiting the 310V DC peak voltage from the 220V AC RMS will be forced to drop to the level of the LED total forward drop value. So, let us assume a standard voltage available at the base resistor is 165V.

Base Resistor Value (R_B)

The base resistor limits the base current. Using Ohm's law:

R_B = (V_base - V_BE) / I_B

Where:

• V_base = 165 V
• V_BE = 0.7 V
• I_B = 30 mA

Substituting:

R_B = (165 - 0.7) / 0.03

R_B = 164.3 / 0.03 = 5476.67 Ω

Power Rating of Resistor

The power dissipated by the resistor is:

P_R = I_B² * R_B

Substituting:

P_R = (0.03)² * 5476.67

P_R = 0.09 * 5476.67 = 492.9 mW

Select a resistor with a slightly higher power rating for safety.

Resistor Value: Closest standard value = 5.6 kΩ.

Power Rating: 1W or higher (to handle power dissipation safely).

Step 5: Voltage Ratings of Components

Diodes (1N4007):

• Voltage rating: 1000V
• Current rating: 1A (sufficient for 300 mA)

Transistors:

• MJE13003: Suitable for high voltage switching
• MJE340: Handles low-side switching

LED Voltage Drop:

• Total forward voltage: 165V
• Ensure capacitor CX and diodes can handle this voltage

Finalized Component Values:

• CY = 4.7 µF (400V AC-rated)
• CX = 191 µF (200V-rated)
• RX = 2.2Ω (5W-rated)
• MJE13003 Base Resistor = 5.6 k (100 Ω is wrongly shown in the diagram)
• 1N4007 diodes: 4 pieces for rectification
• MJE13003: High-voltage transistor
• MJE340: Low-side current regulator

LED Bulb with Many Series LEDs

The next circuit of a LED bulb explained below is easy to build and the circuit is fairly reliable and long lasting.

The reasonably smart surge protection feature included in the circuit ensures an ideal shielding of the unit from all electrical power ON surges.

How the Circuit Functions

1. The diagram shows a single long series of LEDs connected one behind the other to form a long LED chain.
2. To be precise we see that basically 40 LEDs have been used which are connected in series. Actually for a 220V input, you could probably invorporate around 90 LEDs in series, and for 120V input around 45 would suffice.
3. These figures are obtained by dividing the rectified 310V DC (from 220V AC) by the forward voltage of the LED.
4. Therefore, 310/3.3 = 93 numbers, and for 120V inputs it's calculated as 150/3.3 = 45 numbers. Remember as we go on reducing the number of LEDs below these figures, the risk of switch ON surge increases proportionately, and vice versa.
5. The power supply circuit used for powering this array is derived from a high voltage capacitor, whose reactance value is optimized for stepping down the high current input to a lower current suitable for the circuit.
6. The two resistors and a capacitor at the at the positive supply are positioned for suppressing the initial power ON surge and other fluctuations during voltage fluctuations. In fact the real surge correction is done by C2 introduced after the bridge (in between R2 and R3).
7. All instantaneous voltage surges are effectively sunk by this capacitor, providing a clean and safe voltage to the integrated LEDs at the next stage of the circuit.

CAUTION: THE CIRCUIT SHOWN BELOW IS NOT ISOLATED FROM THE AC MAINS, THEREFORE IS EXTREMELY DANGEROUS TO TOUCH IN POWERED POSITION.

Circuit Diagram#1

Parts List

• R1 = 1M 1/4 watt
• R2, R3 = 100 Ohms 1watt,
• C1 = 474/400V or 0.5uF/400V PPC
• C2, C3 = 4.7uF/250V
• D1---D4 = 1N4007
• All LEDs = white 5mm straw-hat type input = 220/120V mains...

The above design lacks a genuine surge protection feature and therefore could be severely prone to damage in the long run....in order to safeguard and guarantee the design against all sorts of surge and transients

The LEDs in the above discussed LED lamp circuit can be also protected and their life increased by adding a zener diode across the supply lines as shown in the following image.

The zener value shown is 310V/2 watt, and is suitable if the LED light includes around 93 to 96V LEDs. For other lower number of LED strings, simply reduce the zener value as per the total forward voltage calculation of the LED string.

For example if a 50 LED string is used, multiply 50 with the forward drop of each LED that is 3.3 V which gives 50 x 3.3 = 165V, therefore a 170V zener will keep the LED well protected from any sort of voltage surge or fluctuations....and so on

Video clip showing an LED circuit circuit using 108 numbers of LED (two 54 LED series strings connected in parallel)

High Watt LED Bulb using 1 watt LEDs and Capacitor

A simple high power LED bulb can be built using 3 or 4nos 1 watt LEDs in series, although the LEDs would be operated only at their 30% capacity, still the illumination will be amazingly high compared to the ordinary 20mA/5mm LEDs as shown below.

Moreover you won't require a heatsink for the LEDs since these are being operated at only 30% of their actual capacity.

Likewise, by joining 90nos of 1 watt LEDs in the above design you could achieve a 25 watt high bright, highly efficient bulb.

You may think that getting 25 watt from 90 LEDs is "inefficient", but actually it is not.

Because these 90nos of 1 watt LEDs would be running at 70% less current, and therefore at zero stress level, which would allow them to last almost forever.

Next, these would be comfortably working without a heatsink, so the entire design could be configured into a much compact unit.

No heatsink also means minimum effort and  time consumed for the construction. So all these benefits ultimately makes this 25 watt LED more efficient and cost effective than the traditional approach.

Circuit Diagram#2

Surge Controlled Voltage Regulation

If you require an improved or a confirmed surge control and voltage regulation for the LED bulb, then the following shunt regulator could be applied with the above 3 watt LED design:

Video Clip:

In the videos above I have purposely flickered the LEDs by twitching the supply wire just to test ensure that the circuit is 100% surge proof.

Solid State LED Bulb Circuit with Dimmer Control using IC IRS2530D

A simple yet efficient mains transformerless solid state LED controller circuit is explained here using a single full bridge driver IC IRS2530D.

Highly Recommended for you: Simple Highly Reliable Non-Isolated LED Driver - Don't Miss this, Fully Tested

Introduction

Normally LED control circuits are based on buck boost or flyback principles, where the circuit is configured to produce a constant DC for illuminating an LED series.

The above LED control systems have their respective drawbacks and the positives in which the range of operating voltage and the number of LEDs at the output decide the efficiency of the circuit.

Other factors like whether the LEDs are included in parallel or series or whether they need to bedimmed or not, also affects the above typologies.

These considerations make these LED control circuits rather dicey and complicated.The circuit explained here employs a different approach and relies on a resonant mode of application.

Though the circuit does not provide direct isolation from the input AC, it has the features of driving many LEDs with current levels as high as 750 mA. The soft switching process involved in the circuit ensures greater efficiency to the unit.

How the LED Controller Functions

Basically the mains transformerless LED control circuit is designed around the fluorescent lamp dimmer control IC IRS2530D. The circuit diagram shows how the IC has been wired up and how its output has been modified for controlling LEDs in place of the usual fluorescent lamp.

The usual preheating stage required for a tube light utilized a resonant tank which is now effectively replaced by a LC circuit suitable for driving LEDs.Because the current at the output is an AC, the need of a bridge rectifier at the output became imperative; this makes sure that current is continuously passing through the LEDs during every switching cycle of the frequency.

The AC current sensing is done by the resistor RCS, placed across the common and the bottom of the rectifier.This provides an instant AC measurement of the amplitude of the rectified LED current.The DIM pin of the IC receives the above AC measurement via the resistor RFB and capacitor CFB.

This allows the dimmer control loop of the IC to keep track of the LED current amplitude and regulates it by instantaneously varying the frequency of the half bridge switching circuit, such that the voltage across the LED maintains a correct RMS value.

The dimmer loop also helps to keep the LED current constant irrespective of the line voltage, load current and temperature changes.Whether a single LED is connected or a group in series, the LED parameters is always maintained correctly by the IC.

Alternatively the configuration may also be used as a high current transformerless power supply circuit.

Circuit Diagram#3

Original article can be found here

Why use LEDs

• LEDs are being Incorporated in vast magnitudes today for everything that may involve lights and illuminations.
• White LEDs have especially become very popular due to their mini size, dramatic illuminating capabilities and high efficiency with power consumptions. In one of my earlier post I discussed how to make a super simple LED tube light circuit, here the concept is quite similar but the product is a bit different with its specs.
• Here we are discussing the making of a simple LED bulb CIRCUIT DIAGRAM, By the word "bulb" we mean the shape of the unit and the fitting secs will be similar to that of an ordinary incandescent bulb, but actually the whole body of the "bulb" would involve discrete LEDs fitted in rows over a cylindrical housing.
• The cylindrical housing ensures proper and equal distribution of the generated illumination across the entire 360 degrees so that the entire premise is equally illuminated. The image below explains how the LEDs needs to be installed over the proposed housing.