The LED lighting is expanding in a surprising way in both the consumer market in the industry. Recently it was rare to find a house lit entirely with LEDs , but today is something that attracts attention. The same happens in a car, street lighting and many other applications. To vary the light intensity of these elements is used PWM control and high efficiency is achieved with a considerable energy savings. The assembly will now show uses an integrated circuit Maxim, the MAX16805 / MAX16806 , which will surprise you with its ease of use and performance. The lighting of the future, today arg.
series of integrated circuits for Maxim MAX16800 has an input voltage range as high as interesting. Prepared to work up to 40Volts input voltage, these Dimmers or active attenuators are ideal for automotive applications and systems which use voltages between 12Vots and 24Volts. Ie they are designed specifically so they can be plugged in directly to the battery a car (electrical installation) without surge protection. Recall that the area of \u200b\u200ba vehicle can be hostile to electronic systems and in most cases the necessary protective measures must be important. However, in the case of these devices, that care is self care. The integrated circuit generates a constant current to the LED that can be set and pre-determined by specific resistance, Rsense , connected in series with the LED diodes s. To improve accuracy and increase immunity to external noise, the line circuit MAX16800 uses an input configured in differential mode ( CS + , CS-) to determine the meaning of the current and actual voltage across Rsense .
The best performance of an attenuation of brightness for LEDs s is obtained by modulation pulse width (PWM ). One of the options series operation MAX16800 is by applying a PWM signal the enable input. Thus, the current through the LED is connected or not and turns off the pace set by the PWM signal external control. Immunity to electromagnetic interference (EMI ) is important in automotive applications. It has equal importance is the fact not generate EMI that may damage the operation of other electronic systems within the same vehicle. Switching current (To turn the / the LED s) is, however, a typical source of EMI radiation . Therefore, to reduce EMI emissions during operation of the PWM and external labor regulation, the MAX16800 use elaborate circuits so that they are able to soften the edges of the signal switching and thus significantly reduce the emission of electrical noise from outside the enclosure that houses the circuit.
Many lighting applications do not require a microcontroller to generate the PWM signal regulation. Integrated circuits "LED Drivers " MAX16805 and MAX16806 are available for such situations. Both can generate a PWM signal internally with a "modulation " established by an external voltage is applied to the input DIM. The MAX16806 also has the ability to connect a switch input (SW) to replace an analog potentiometer settings. That is, both devices can be handled by a signal from external PWM from a microcontroller, besides being able to operate autonomously and lonely thanks to a simple adjustment knob or a button "On-Off ( MAX16806 ). Detection mode of operation is automatic and integrated circuit adopts the mode of work prompted by this pin ( DIM). In the case of choosing a control PWM, the device synchronizes its internal generator PWM with the external signal (which can vary over a frequency range from 80Hz to 2kHz) and she uses PWM modulation . ( 0 to 100% duty-cycle ). In turn, an analog voltage (provided by a potentiometer) which can vary between 0.2 and 3Volts provide a total lighting control from minimum to maximum.
In some lighting applications very careful track conditions working temperature of LED s. This practice deepens in a special way in places with limited space where heat dissipation is poor. The excess temperature of an LED reduces its life and therefore is contrary to one of the main advantages of this light source: its long duration compared to known systems (CFL, incandescent, etc.). Fortunately, this situation can be avoided by reducing the brightness of the LED or what would be the same, by mitigating the duty cycle of LED . The MAX16806 has inputs for external temperature sensor (working of LED s) and also has a temperature control system of work that prevents over-heating of the chip itself ( Over Temperature Protection). When excess temperature is detected, the device increases the attenuation of the duty cycle until the temperature returns to an acceptable value. The threshold temperature and the desired level can be programmed with the serial interface (I2C bus ) and can be stored in the EEPROM memory installed the device brings. This temperature sensing feature eliminates the need for a heat sink, ensuring thus saving costs and building size.
As mentioned earlier, scheduling is performed records MAX16805 and they can adjust various settings such as the workflow of the final system, temperature thresholds of LED and his own IC, the desired values \u200b\u200bfor the excursion of the ramp, potentiometer means, determine the level of light delivered by the LEDs, and other variables such as the voltage differential input the sensor LED current s. However, data sheets MAX16805 / MAX16806 are very clear about the values \u200b\u200bthey buy records when you connect the integrated circuit supply voltage. We must remember that the records always return a value "Start " and do not retain the data for each outage. For these cases, using the I2C bus , the control system must be ordered to read the internal EEPROM device and load it into the respective records at the time of an operation from scratch. In the case of the ramp that can handle the pot, they understand values \u200b\u200bfrom 0 to 3Volts. As for Rsense , consider that it will fall on a voltage of 198mV.
With the above values \u200b\u200bwe can build a very simple way for our LED Dimmer . Using 5Volts regulator incorporating the integrated circuit, we use a 25K variable resistor and a series consisting of a 12K resistor and a 4K7. Thus, we 3Volts potentiometer and regulation throughout the operating range. Meanwhile, in the case of Rsense , we must know in advance how many LED diodes use. In our case, we decided to use an array of 36 LEDs, we consider 12 sets series (all in parallel) 3 LEDs operating at 20mA current for each branch about 3 LEDs. This results in a total current of 240mA. Therefore, the result of dividing 0.198 volts (198mV) by 0.24 A (240mA) provides a value Rsense equal to 0.825 Ohms.
As this value is not what we had at hand, we calculate the current to a resistance of 1 Ohm and the result was 198mA for all the LED s. Distributing this power through 12 branches, we obtain a current of 16.5 mA for each series of 3 LEDs, a current very sure that we provide a long life LEDs used . Finally, we can tell that these IC are available on request and free samples (samples ) to Maxim from your website. Without external power transistors, microcontrollers and without special circuits. Only the MAX16805 / MAX16806, a pair of resistors and capacitors, and there you have a complete s LED Dimmer for high efficiency that meets every need. Enjoy it and show your results in Electronics Forum arg!
Source:
http://www.neoteo.com/max16805-max16806-dimmer-para-leds.neo
0 comments:
Post a Comment