Isolated offline-flyback controller LT3799 enables to create a powerful LED driver with a minimum of external components, which is moreover compatible with common triac dimmers.
At the design of a new LED driver, we usually have to consider more factors like for example an output current stability, shortcut or open LED protection, efficiency, safety (isolated secondary circuit form the primary one), power factor correction, EMI, number of external components and other.
LT3799 meets all these requirements and offers another benefits, like for example a possibility to use a smaller transformer thanks to the use of critical conductivity mode, powerful external MOSFET driver, internal LDO regulator and also a very good output current regulation – typically +-5%, moreover with no opto-isolator. A big bonus is the active power factor correction, thanks to which it reaches typical values of 0,96 (at 230V AC), thus meeting the most stringent requirements in this field, as well as IEC 61000-3-2 class C about harmonic currents emission. When we look closer at the recommended application circuit, we´ll find out that behind a diode bridge we won´t find any (otherwise common) input electrolytic capacitor with value of tens or hundreds of uF. That´s why the input voltage of the controller and a of the power transformer “copies” input sinusoid. Excellent power factor is reached just thanks to it, that LT3799 knows immediate input voltage value and based on this value, it sets the input current limit (in a given cycle of the SMPS), proportionally to the immediate value of the input AC voltage. Further LT3799 gains information about the immediate current from the primary side, that´s why it doesn´t require an opto-coupler. Thanks to this, LT3799 works like a current source in every period of input voltage, that´s why it is even possible to use classic triac regulators, which are often already a part of the buildings installation. In other words – LT3799 doesn´t try to compensate “dropouts” in power supply caused by a phase control of a triac, what causes decreasing of an output LED current and their fluent dimming. Neither this control method doesn´t cause LED blinking, because there is an electrolytic capacitor on the transformer output.
LT3799 – create a LED driver with an active PFC - [Link]
Ivan Sergeev writes:
This project was used as a wireless light dimmer, but in principle can be used to dim resistive loads and wirelessly turn on/off loads. The current code includes a routine to dim a light bulb in a “heartbeat” pattern, with the heartbeat frequency remotely adjustable.
The top left of the schematic shows the wall outlet (US 120VAC) being stepped down with a small transformer, then full rectified and regulated. This powers the entire board from the wall. The top right shows a microcontroller, ATmega48, its programming header, and a UART connection to the microcontroller (for debugging). The bottom right shows the XBee and its basic voltage regulation (it’s 3.3V), as well as an LED that indicates when the XBee is connected.
Wireless TRIAC dimmer - [Link]
Test Thyristor and Triac using this circuit. Pay attention on mains voltage!
Thyristor – Triac Tester - [Link]
With this tool you can test various electronic components like diodes, LEDs, all kinds of transistors (PNP, NPN, several types of MOSFETs), capacitors, resistors as well as triacs and thyristors. It will show you several physical characteristics after the test was completed, like forward voltages, (gate) capacity and amplification factor. More over, it will show the polarity of the component and identifies the several pins of a package. A very nice and sophisticated project I host for Markus Frejek. I’ve done an additional layout for the device you can see on the left side. This project has found a lot of fans, including myself. The device is powered by an AVR ATmega 8 MCU.
Component tester - [Link]
It doesn’t matter how you connect the test clips to the component, the Atlas DCA can analyse a vast number of different component types including bipolar transistors, enhancement mode MOSFETs, depletion mode MOSFETs, Junction FETs (only gate pin identified), low power thyristors and triacs (less than 5mA trigger and hold), diodes, multiple diode networks, LEDs, bi-colour and tri-colour LEDs. It will even identify special component features such as diode protection and shunt resistors in transistors.
Semiconductor analyser determines part type and value - [Link]
After our recent post about the commercial semi-conductor tester we started a discussion about building a similar open source project. What came up is this AVR based transistor tester (machine translation) by Markus.
It’s built around an ATmega8 IC that interfaces with a standard HD44780 16×2 character LCD. The circuit that does the testing is simplicity itself. Three pairs of resistors are connected to 6 pins of the microcontroller, and each pair is connected on the other end to one of the transistor pins.
The theory of operation is also relatively simple. The microcontroller cycles through different patterns on its output pins until a recognizable pattern is read on its input pins. It supports a very large range of devices:
- NPN and PNP bipolar junction transistors.
- P and N channel, enhanced and D type mosfet transistors.
- P and N channel JFET transistors.
- Common anode and common cathode dual diodes.
- Two diodes in connected in anti-parallel or series configuration.
- Single diode.
AVR-based transitor tester - [Link]
TRIAC Dimmable LED Driver
LT3799 isolated LED controller with active power factor correction (PFC) is specifically designed for driving LEDs over a wide input range of 24V to 480V+. It is ideal for LED applications requiring 4W to over 100W of LED power and is compatible with standard TRIAC in-wall dimmers. The LT3799’s unique current sensing scheme delivers a well regulated current to the secondary side with no opto-coupler, enabling it to provide ±5% LED current accuracy. It also offers low harmonic distortion while delivering efficiencies as high as 90%. Open and short LED protection ensures long term reliability and a simple, compact solution footprint addresses a wide range of applications.
TRIAC Dimmable LED Driver - [Link]
This project shows how to build a solid state relay based on opto-triac and triac. The opto-triac isolates the output from the input. With this solid state relay you are able to switch high current loads like with a normal relay. Another advantage of this relay is that it can switch loads fast. Check schematics on the link below.
Solid state relay - [Link]
The pulse generator at a particular frequency generates the clock pulses. The clock pulses are counted by a counter and gives output after every 10 pulses. The counter drives the transistors, which form the triac firing circuit. The transistors fire the triacs and they provide sufficient current to the load. Decorative bulbs are connected as load for each triac. The bulbs are sequentially turned ON and OFF in forward and reverse way.
6 Channel Auto Reverse Sequential Disco Running Lights - [Link]