Parallel circuit? Series circuit? LED driver circuit selection

LED era, we can see it in all aspects of life figure, whether it is automotive, intelligent or industrial areas, because of its high efficiency, energy saving, long life, environmental protection and other characteristics, has become the current lighting Technology options, and gradually be applied to lighting. One of the key factors driving people to focus on LED lighting technology is that it significantly reduces energy consumption and enables reliable, long-term work. Today we are from a practical LED circuit for everyone to extend the introduction of LED lighting driver circuit.

 

This paper starts with a constant current source circuit, the main components of the transistor circuit, requiring its voltage to 400V or more, but also more than 10W power of high-power tube, such as MJE13003, MJE13005, and to add heat sink, Filter capacitor C capacity of 4.7uF, pressure to have more than 400V, LED current size determined by the R2 adjustment, to facilitate the adjustment can be used to adjust the variable resistor and then put on the same resistance of the fixed resistance, the circuit can be with LED The number can be more than a dozen, up to more than 90, although an increase of some cost, but the use of the effect than only the resistance current limiting circuit is much better, even if the voltage fluctuation, the circuit can still maintain constant current , Which is the life of the LED is very beneficial in this range of current can be maintained basically constant. The number of the circuit using the LED can not be too little, the less its efficiency is also lower. The total power consumption of this circuit is about 6W.

 

 

 

Constant current source circuit

 

Here to give you the way to talk about LED and parallel connection method is good or series connection method?

 

LED using and or series connection, the main power circuit should be based on the form and requirements of the circuit.

 

The series connection of the circuit, when one of the LED when the entire string of LED off, but when one LED short circuit when the other LED can also light. When one of the LEDs is short-circuited, the power of the whole circuit will be short-circuited, so that not only the other LEDs can not work normally, but also the other LEDs can not work normally. There may be damage to the power supply. Therefore, compared with the series connection of the circuit is more advantageous.

 

And the connection method only need to apply a lower voltage at each end of each LED, but the need to use a ballast resistor or current source to ensure that each LED brightness consistent. If the bias current flowing through each LED is different, their brightness will be different, resulting in the uneven brightness of the whole light source. However, the use of ballast resistors or current sources to ensure consistency of LED brightness will shorten the battery life. The use of series connection in essence can be very good to ensure consistency of flow through each LED current, but requires higher power supply voltage. LED and parallel connection method, the total current of the circuit is the sum of the various LED current, so the power supply to be able to supply a large enough current.

 

In fact, strictly parallel or series connection method has their advantages and disadvantages. You need to be considered in a practical many factors. In practice, often used in series and parallel form of LED arrays, so as to overcome or reduce the single LED circuit or short circuit caused by the whole string LED does not light or the entire circuit and power supply. The so-called series-parallel connection is first with a small amount of LED series and then string the ballast resistor to form a slip road, and then a number of slip road parallel component "slip group." In addition, the use of string and string form, is in the composition of the "slip group" basis, and then a number of "slip group" in series to form the entire lamp circuit, this connection not only reduces a LED fault And the ballast resistance of the whole will be zero, a few high-power resistance into a few small power resistance, from centralized installation into a decentralized installation, this will help both resistance to heat, but also the lighting design more compact.

 

First of all, any circuit we must consider its power driver, usually drive LED using a dedicated constant current source or driver chip, vulnerable to volume and cost and other factors, the most economical and practical method is to use the capacitor step-down power supply. It is not afraid of load short circuit, the circuit is simple and so on, and a circuit can drive 1 ~ 70 low-power LED (However, this power circuit starts when the current impact, especially the frequent start, will give LED Of course, take appropriate protection can avoid this impact, in this regard, you can use ON Semiconductor's NUD4700 LED shunt protection solution in the LED work properly, the leakage current is only 100 μA; Transient or surge conditions, the LED will open, then NUD4700 shunt protector where the shunt channel is activated, the voltage drop is only 1.0V, will bring the impact of the circuit as much as possible to reduce this device A space-saving, small package designed for 1 W LED (350 mA @ 3 V nominal) and supports operation greater than 1 A if the thermal processing is appropriate.

 

 

 

Capacitive buck power supply of the typical circuit

 

Check the drive circuit, you should carefully check the circuit according to the circuit is connected to the wrong, pay special attention to check the rectifier bridge (long feet is the positive output, the diagonal is the negative output, the other two feet are AC input) or rectifier diodes and Zener Diode Polarity (printed with black or white line is one end of the negative), and check the crystal transistor or regulator integrated circuit of the three electrodes are wrong and so on.

 

C1 for the step-down capacitor (using metallized polypropylene capacitor), R1 for the C1 to provide discharge circuit. Capacitor C1 provides a constant operating current for the entire circuit. Capacitor C2 is the electrolytic capacitor, its voltage value depends on the number of LEDs connected in series (about 1.5 times of its total voltage), its main role is to suppress the voltage transient caused by the sudden change, thus reducing the impact of voltage on the LED Life. R4 is the discharge resistance of capacitor C2, the resistance should be increased with the number of LED appropriate increase.

 

As the capacitor step-down power supply is a non-isolated power supply, the power will have a large instantaneous current, that is, the so-called inrush current. In addition, due to the impact of the external environment (such as lightning) grid system will invade a variety of surge signals, some surge will lead to LED damage. Therefore, to provide thermistor protection, the main negative temperature coefficient thermistor protection (NTC thermistor, NTC is Negative Temperature Coefficient abbreviation) and positive temperature coefficient thermistor protection (PTC (Positive Temperature Coefficient)) and then there are Transient Voltage Suppressor Protection ((Transient Voltage Suppressor), referred to as TVS)

 

Negative temperature coefficient means a negative temperature coefficient, generally refers to a large temperature coefficient of the semiconductor material or components, the most simple and effective way to limit the inrush current in the line input is in series with an NTC thermistor

 

Positive temperature coefficient of current through the PTC thermistor caused by the temperature rise, the fever of the temperature rise, when more than Curie temperature, the resistance increases, thus limiting the current increase, so the current drop led to the component temperature, resistance Reduce and make the circuit current increases, the component temperature rises again and again.

 

Transient voltage suppressors are mainly used for fast overvoltage protection of circuit components. When the TVS tube poles are subjected to reverse transient high energy shock, it can change the high impedance between two poles to a very low impedance at a speed of the order of 10-12s, absorb high energy surges, connect the voltage clamp between the poles Located in a predetermined value, the protection of electronic components in the circuit from a variety of surge pulse damage.

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