Hello guys,

I have in my posession some 3W LED's that are designed to work on mains voltage (230V) in series with a resistor (1 resistor per 1 LED).
I've done a few test boards with them and they light up very well, but they have some noticeable flicker.
Another problem is, that one LED paired with a 1,6 kOhm resistor will be 2.8W at 220V but will be just 2.1W at 210V (just an example, there are different resistor values for different voltages and desired power outputs). And where I am using these LEDs, the voltage is very unstable, sometimes goes as low as 190V, and then the LEDs work at only ¬1.2W
I think that by adding a bridge rectifier, that would greatly reduce the flicker, and will increase the voltage way over 230V.
And I need a way to limit the voltage after the rectifier to steady 220V (or 210V doesn't matter as long as it is stable, I can use the correct resistor ratings to get the desired output).

What would be the best way to limit the Voltage after the bridge rectifier? Hi, spec, and thanks for your response.

So the LEDs I am using are these ones:
https://octa-electronics.com/web/files/product_groups/53/files/Data Sheet BA2 v1.2__.pdf

They are not the standard LEDs as you see.
Here is another document for the recommended resistor values to use with them:
https://octa-electronics.com/web/files/product_groups/53/files/BA2_Recommended Resistors Values-V1.1.pdf

My experiments with those show slightly different results, but generally 1,5/1,6/1,8 kOhm are fine.

The wiring is pretty simple. A resistor is connected to the anode, and you plug the whole thing to mains power. An array is made by connecting more of these blocks in parallel.

I've made a couple of small lights (using just 3 LED's) to light up my CNC router and work table. I also made one larger board with 24 of those LEDs.
I don't have a picture of them now. But I've found a picture of the first board a created for 3 of those LEDs.

As you see it is pretty simple. The two leads from mains power go to the bottom left and right. The lumpy piece of copper left in the middle has been left out to serve as heat spreader. The bottoms of the LEDs are soldered to it. Hi,

Yes i agree, you cant use a rectifier with this LED. It's made for AC not DC so you must feed it with AC if you want to get the full brightness.
If you did use DC you'd have to use a capacitor with that, and then you'd have to be careful not to over power it with too high of an average DC voltage. Max power then would be about 2.5 watts but only half of the LEDs inside would be lighting up. So best bet is to just follow the recommended hook up which is with just one resistor, looks like ohms at 230vac. ohms would allow it to run a little bit cooler. Might get away with a 1/2 watt resistor but check that first. Thanks guys.
I myself didn't see this small schematic on page 8 I thought that I shouldn't connect those LEDs in series, but I'll give it a try. Strange why the resistors are not shown on this schematic. Does it mean that I should power them without a resistor?
And yes, TRIAC dimmers do work with this
As for resistors, It was hard, but I finally found some 3W SMD resistors, they are pretty expensive though. I should probably give it a try with 1W resistors, if it works it will be a lot cheaper.

And as for the low voltage issue.... Can I place something to limit the voltage to 190V? This way I would get equal light output, when Hooked up to a propper 230V mains, or a unstable one that fluctuates from day to day. Yes, It will be dim. I already saw this effect on the crappy mains in my storage yard.
But I can get it to work at higher brightness with a lower Ohm resistor.

The idea is to make these lamps work equally well on 190V and 230V. So if I am able to limit the voltage to 190V and the LEDs have resistors for this voltage, the lamps should light up equally well on 190V/200V/210V mains and on 230V mains.

And what can I use to limit the flicker? Even at 230V/50Hz it is well noticeable. And when hooked to 190V with slightly lower frequency (~42Hz) the flicker is awful!

P.S. Here is my design for the PCB with the 24 LEDs. the traecs and the solder mask. The large circles in three rows (top, middle and bottom) are for bolting holes.

Hi, spec, and thanks for your response.

So the LEDs I am using are these ones:
https://octa-electronics.com/web/files/product_groups/53/files/Data Sheet BA2 v1.2__.pdf

They are not the standard LEDs as you see.
Here is another document for the recommended resistor values to use with them:
https://octa-electronics.com/web/files/product_groups/53/files/BA2_Recommended Resistors Values-V1.1.pdf

My experiments with those show slightly different results, but generally 1,5/1,6/1,8 kOhm are fine.

The wiring is pretty simple. A resistor is connected to the anode, and you plug the whole thing to mains power. An array is made by connecting more of these blocks in parallel.

I've made a couple of small lights (using just 3 LED's) to light up my CNC router and work table. I also made one larger board with 24 of those LEDs.
I don't have a picture of them now. But I've found a picture of the first board a created for 3 of those LEDs.
View attachment
As you see it is pretty simple. The two leads from mains power go to the bottom left and right. The lumpy piece of copper left in the middle has been left out to serve as heat spreader. The bottoms of the LEDs are soldered to it.

Hi Zeox,

Thanks for the above information- very useful.

I have looked at various ways to do what you want and it seems to boil down to two main approaches:
(1) Replace the resistor in series with the LED string with a constant current generator
(2) Drive the LED strings (with resistors in series as normal) from an inverter which would provide a constant 240V AC power line.

As far as I can tell at this stage, option (1) would require 2 x MOSFETS, 2 x BJT (normal transistors), 2 x rectifier diodes, 2 x Zener diodes, and 6 resistors.

Option (2) can have a few implementations but the simplest/easiest would be to have a mains to DC power supply to produce a stable 12V. This 12V would then power an inverter which would produce a constant 250V AC to power your LED strings.

Both the power supply and inverter are freely available standard items at a reasonable price.

A square wave inverter should eliminate the LED flicker that you mentioned.

If you are interested in either of these options please let us know.

spec WARNING: The circuit in this post involves dangerous voltages. You must observed safety precautions. Never touch the circuit when the power is applied. If you are not experienced in high voltage electronics do not attempt to build this circuit.

POST ISSUE 3 of _02_07

Hi Zeox,

Below is the schematic for a constant current LED driver:

NOTES
(1) The circuit above will drive a constant 24 mA into one single LED unit.
(2) The two LED strings shown on the schematic represent the innards of one of your LED units.
(3) Constant current is a technical term and does not mean that the current will always be present but the circuit will ensure that each LED string in the LED unit will get a constant current and longer during each half cycle of the mains supply.
(4) The circuit will provide a constant current irrespective of the mains voltage variations, within limits of course.
(5) The constant current is defined by the formula, Ik = 0.6V/R2, where Ik is in Amps and R3 is in Ohms.
(6) The NMOSFET will get warm so should be in free cool air. A heatsink is advisable.
(7) The NMOSFET is a high-voltage, low-threshold voltage type- no other type of MOSFET should be used without checking with the designer.
(8) There are safety aspects to the circuit and the fuse must not be omitted.
(9) Q2 can be pretty much any small-signal transistor but the higher the voltage, VCEo, the better. In addition to the ideal transistor (BC546) shown on the schematic, other transistors can be used: BC547/8/9, 2N, PN, BC337, BC182/3/4, BC107/8/9
(10) If you would like to drive more than one LED unit in parrallel with this circuit we can discuss how that can be done, but ideally one constant current driver for each LED unit would give the best performance.

DATASHEETS

Attachments

• Vish_1N_thru_1N.pdf
• Fair_BC546-BC550_NBJT.pdf
• Fair_FCP190N60_NM_600V_20.2A_200mR_600mDCW_20VGS_3.5VGT_TO220_$$.pdf

Understanding the Diode Bridge Rectifier: From AC to DC Power

In our modern world, electronic devices are powered by direct current (DC), yet most of our electricity comes as alternating current (AC). Enter the unsung hero: the diode bridge rectifier. This clever arrangement of diodes, like the silent traffic controllers of electricity, transforms AC into the stable DC that powers everything from your smartphone to your refrigerator. This article will dissect the diode bridge rectifier, providing a thorough explanation of its operation, various applications, and a practical understanding of its importance in our technology driven lives.

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What is a Diode Bridge Rectifier?

A diode bridge rectifier is an essential electronic circuit utilizing four diodes in a bridge configuration to efficiently convert alternating current (AC) into direct current (DC). This fundamental component is ubiquitous in power supplies and various electronic devices, providing a stable DC output from an AC source.

How the Diode Bridge Rectifier Works: A Step-by-Step Explanation

The diode bridge rectifier efficiently converts alternating current (AC) to pulsating direct current (DC) through a carefully orchestrated sequence of diode conduction during alternating AC cycles. This conversion relies on the unidirectional conduction property of diodes.

Here's a breakdown of the operational steps:

1. Positive Half-Cycle of AC Input
   When the AC input voltage is positive, current flows from the positive terminal of the AC source, through diode D1, then through the load, and returns through diode D3 to the negative terminal of the AC source. Diodes D2 and D4 are reverse-biased and do not conduct during this half-cycle. The load receives a current pulse with the voltage polarity consistent with direct current.
2. Negative Half-Cycle of AC Input
   When the AC input voltage switches to negative, current now flows from the negative terminal of the AC source, through diode D2, then through the same load (in the same direction as before), and returns through diode D4 to the positive terminal of the AC source. Diodes D1 and D3 are reverse-biased and do not conduct during this half-cycle. Again, the load receives a current pulse with the same DC voltage polarity as before.
3. Pulsating DC Output
   The output across the load consists of successive half-cycles of the input AC voltage, all with the same polarity, resulting in pulsating DC. This pulsating DC can then be smoothed out by filtering circuits, typically using capacitors, to obtain a relatively constant DC voltage.

The key is that regardless of the polarity of the AC input, current flows through the load in the same direction due to the bridge configuration, ensuring full-wave rectification. This process effectively utilizes both the positive and negative half-cycles of the AC input to produce DC output.

Full-Wave Rectification vs. Half-Wave Rectification

The diode bridge rectifier enables full-wave rectification, a significant improvement over half-wave rectification. Full-wave rectification utilizes both halves of the AC input cycle to produce a DC output, resulting in higher efficiency and a smoother DC output with less ripple.

The key advantage of full-wave rectification, achieved through a diode bridge, lies in its ability to convert more of the AC power into usable DC power. This is reflected in its efficiency. In contrast, half-wave rectification discards half of the AC input, leading to lower efficiency and a more irregular DC output requiring heavier filtering.

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Key Components: The Role of Each Diode in the Bridge

Within a diode bridge rectifier, each of the four diodes plays a crucial and distinct role in converting alternating current (AC) to direct current (DC). These roles can be analyzed by understanding how current flows through the circuit during both the positive and negative half-cycles of the AC input. Each diode is strategically placed to facilitate current flow in only one direction, thereby ensuring that the output current is always unidirectional.

The diodes are typically labeled D1, D2, D3, and D4, and they are arranged in a closed-loop configuration resembling a bridge. The AC input is applied to two opposite corners of this bridge, while the DC output is taken from the other two corners. During the positive half-cycle of the AC input, current flows through two diodes; during the negative half-cycle, it flows through the other two, all while ensuring the current flow at the output is in the same direction. This alternating conduction by the diodes ensures that both halves of the AC waveform contribute to the DC output.

In summary, D1 and D4 conduct together during one half-cycle, while D2 and D3 conduct during the other. This push-pull action of the diodes ensures that the load receives current during both halves of the AC input, converting it to a pulsating DC output. By doing so, they rectify the alternating current into a form of DC that while still rippling, is suitable for further regulation in most electronic power supplies.

Advantages of Using a Diode Bridge Rectifier

Diode bridge rectifiers offer significant advantages over other rectification methods, primarily due to their ability to perform full-wave rectification, which results in a more efficient and smoother DC output. These benefits contribute to their widespread use in various electronic applications.

• High Efficiency
  By utilizing all portions of the AC waveform, bridge rectifiers achieve higher efficiency than half-wave rectifiers, converting a larger amount of AC power into usable DC power. This improved efficiency directly translates to reduced energy waste and less heat generation, improving overall system performance.
• Improved DC Output
  The full-wave rectification process yields a DC output with a lower ripple factor, meaning the voltage is more consistent, less pulsed, and smoother than that produced by half-wave rectifiers. This reduces the need for additional filtering circuitry, saving costs and component space.
• Full-Wave Rectification
  The primary function of a diode bridge is full-wave rectification, converting both positive and negative halves of the AC cycle into a single polarity DC output. This characteristic ensures no energy is wasted, providing the most effective AC-to-DC power conversion.
• Compact Size
  Despite comprising four diodes, bridge rectifiers can be implemented in relatively small form factors. Integrated bridge rectifier packages are readily available, making it convenient to implement on circuit boards. This is advantageous where space is a constraint.
• Reliability
  Bridge rectifiers have a robust and simple design, making them highly reliable. The well-understood operation of diodes and the clear current paths in bridge rectifiers contribute to their longevity and consistent performance, minimizing failure rates.

Diode Bridge Rectifier Applications in Real-World Electronics

Diode bridge rectifiers are ubiquitous in modern electronics due to their efficiency and reliability in converting AC power to DC power. These circuits are fundamental components in a vast array of devices, ranging from everyday consumer products to sophisticated industrial and renewable energy systems.

• Consumer Electronics Power Supplies
  Virtually all electronic devices that operate on DC power but are plugged into an AC wall outlet utilize a diode bridge rectifier. This includes chargers for smartphones, laptops, and tablets, as well as power adapters for various electronic gadgets. The rectifier is crucial for converting the AC from the mains to a stable DC supply required by the device's internal circuits.
• Industrial Equipment
  In industrial settings, diode bridge rectifiers are essential in power supplies for motor drives, automated machinery, and control systems. They provide the necessary DC power to operate these systems reliably and efficiently. Heavy-duty rectifiers are often used in these applications to handle higher voltage and current demands.
• Automotive Systems
  Automotive electrical systems utilize diode bridge rectifiers as part of the alternator circuit. The alternator generates AC power that needs to be converted to DC to charge the car's battery and operate the various electrical systems within the vehicle. The robustness of diode bridge rectifiers makes them ideal for the harsh environment within an automobile.
• Renewable Energy Systems
  In solar photovoltaic (PV) systems, diode bridge rectifiers play a vital role in converting the AC output of inverters to DC for battery charging and storage. Similarly, they can also be found in wind power systems, converting AC from wind turbines into DC for grid connection and energy storage. These applications highlight the importance of diode bridge rectifiers in facilitating the transition to renewable energy.
• Welding Machines
  Many welding machines, especially those that use DC output, rely on diode bridge rectifiers to convert the incoming AC power into the DC current needed for the welding process. The rectifiers in welding equipment need to be robust to handle the high currents and voltage demands.
• LED Lighting
  LED (light emitting diode) lighting systems, particularly those powered directly from the AC mains, use bridge rectifiers to create the DC voltage needed to drive the LEDs. This is a crucial step to ensure LEDs operate correctly and safely as they require DC current.

Choosing the Right Diode Bridge Rectifier: Key Parameters

Selecting the correct diode bridge rectifier is crucial for the reliable and efficient operation of any electronic circuit. The selection process involves careful consideration of several key parameters that must match or exceed the demands of the application. These parameters primarily include voltage ratings, current ratings, temperature specifications, and physical packaging. Ignoring these parameters can lead to component failure, inefficient operation, or even safety hazards. Therefore, a detailed understanding of these considerations is essential for design engineers and hobbyists alike.

The diode bridge rectifier is a pivotal element in converting AC to DC, powering countless devices around us. Its clever arrangement of diodes ensures a consistent DC output, vital for the reliable operation of electronic circuits. By understanding its working principle, advantages, and real-world applications, we not only grasp a fundamental concept of electrical engineering but also gain a greater appreciation for the technology that shapes our daily lives. From the smallest USB adapter to the most advanced industrial machinery, the reliable diode bridge rectifier is there, silently ensuring that AC power is converted to the steady DC power we need. As we move towards more efficient and compact electronic devices, the crucial role of the diode bridge rectifier will only continue to grow.

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anypcba.com January 18,