Transformerless LED Bulb Circuits using Capacitors

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.

Safety Note: These circuits operate directly from mains AC voltage without galvanic isolation, meaning live components carry high voltage when energized. Standard electrical safety practices must be strictly followed during assembly and testing to prevent accidental contact. The author assumes no liability for compliance with safety procedures or handling errors.

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

Capacitive 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.

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)

90 LED Bulb Transformerless, using Capacitor Power Supply

Warning: This circuit is not isolated from mains, so be extremely careful while testing it in switched ON position, to avoid a fatal electric shock. The whole assembly must be housed inside a sturdy plastic container for proper safety. BUILD IT ONLY IF YOU FULLY AWARE OF THE DANGERS OF ELECTRIC SHOCK AND KNOW HOW TO TAKE THE NECESSARY PRECAUTIONS AGAINST IT.

An LED bulb circuit can be a very intriguing project to build for any beginner or a school student, since this homemade project can be so useful and could be used for illuminating homes during night.

Although, the commercial LED bulbs are more sophisticated and employ an SMPS circuit, nevertheless the below shown LED bulb circuit could be built using capacitive power supply which is also equally efficient.

Note that the circuit can be customized as desired and any number of LEDs can be connected depending on the input AC supply level. For 220V, the number of LEDs can be up to 90 LEDs, and for 120V AC input the LEDs can be up to 45 nos.

The zener diode value will be equal to the value of the total forward voltage drop of the LEDs. For example if 90 LEDs are used then.

Total FWD drop = 90 x 3.3 = 297V.

So the zener diode value can be rated at 300 V.

Remember that the filter electrolytic filter capacitor value must be at least 25V higher than the zener value, if higher values than this is used, that will be fine.

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.

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 constant 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