Transistor led driver

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Switch Power Circuit. From the circuit point of view, compared with the charge pump circuit, it contains magnetic components, that is inductor or high-frequency transformer. The switching power supply circuit can achieve a wide range of voltage output, and the output voltage is adjustable continuously, the output power is large, so the application range is wider, especially in the medium and large power situations.

Linear Circuit. The linear control circuit regards the semiconductor power device working in the linear region as a dynamic resistor and realizes constant current drive through its control level control. The disadvantage of the linear control circuit is low efficiency, but it has a fast response to the input voltage and load change.

The circuit is relatively simple. It is easy to control the current of LED directly, and it is easy to control the high precision of the current. The actual feedback control of the switching power supply is the output voltage, and the output current control is not easy to be accurate, and the LED lamp is easily damaged when the control of the switching power supply is biased; the efficiency of the linear circuit is not high.

Based on the above reasons, a novel LED drive circuit is designed. The circuit uses a single-end flyback switching power supply as the front stage control, and the linear pressure control constant current source is used as the post level control. After converting the single-ended flyback power supply, the DC voltage output can be obtained, which is used as the input of the post-stage voltage-controlled constant current source. Because the input voltage of the constant current source is controlled by a high-efficiency single flyback switching power supply, the pressure control constant current source can accurately control the LED and can change the input voltage of the constant current source in a large range, so the efficiency and precision are guaranteed, and the power supply can be supplied by the city.

At the same time, the two-level control is not easy to damage the LED lamp. Figure 2. Novel Driver Circuit Design. The system circuit is shown in Figure 2. The transformer T1, the switch tube Q1, the diode D1 and the capacitor C1 constitute the single end flyback switching power supply, and the operational amplifiers U1, U2 and power transistor Q2 constitute the pressure controlled constant current source, and the MCU STC89C51 is the core control device.

When the gray value changes, the microcontroller generates a corresponding brightness control voltage based on the gray value obtained. The brightness control voltage is added to the same phase input of U1.

The output voltage of the U1 is the control voltage of the MOS tube Q2, which is known by the concept of the operational amplifier's deficiency. The reverse input voltage of the U1 is equal to the voltage on its forward input, that is, the current on the R12 is controlled by the brightness control voltage, and does not change with the change of the load.

Single-chip produces a corresponding luminance control voltage according to the gray value it gets, and also produces a PWM signal. Then the MCU changes the duty ratio of the PWM signal according to the LED current signal obtained and changes the output voltage of the switching power supply , that is to change the constant. The input voltage of the flow source reduces the voltage on the power tube Q2, so that it works in the adjustable resistance zone or near the adjustable resistance zone in the case of the constant output current, in order to improve the efficiency.

TL is the three-terminal adjustable shunt reference, where the existence of TL and its corresponding electric phase is to limit the maximum output voltage of the switching power supply and further improve the security of the system. When the light is relatively good, the MCU controls the output of the luminance control voltage according to the gray value obtained, so that the output current of the constant current source is relatively small, and the energy-saving effect can be achieved.

The design of an LED driver is not difficult, but we must have a good idea. As long as we do debug before calculation, debugging and aging after debugging, we believe that anyone can do well in LED. As for the impact, there is no specific indicator yet. This is mainly for the high-voltage driver chip with a built-in power modulator, which not only reduces the power consumption of the chip but also does not introduce additional power consumption for heat dissipation.

The power consumption of the power tube is divided into two parts, switching loss and conduction loss. LED is an electric drive application, and the switch damage is much larger than the conduction loss. The switching loss is related to the CGD and CGS of the power pipe and the driving ability and working frequency of the chip.

So solving the heat problem of the power pipe can be solved from the following aspects:. MOS power tube can not be selected based on the size of the conduction resistance. The rest is frequency and chip drive capability. Here we only talk about the influence of frequency. The frequency is directly proportional to the conduction loss. So when the power tube is heating, we should first consider whether the frequency selection is a bit high.

When the frequency is reduced, in order to get the same load capacity, the peak current must be larger or the inductance becomes larger, which may lead to the inductor into the saturation area. If the inductance saturation current is large enough, the CCM continuous current mode can be changed into DCM discontinuous current mode , which requires an increase of load capacitance. Frequency reduction is mainly caused by two aspects.

The ratio of input voltage to load voltage is small and system interference is large. For the former, be careful not to set the load voltage too high, though the load voltage is high, the efficiency will be high. For the latter, we can try the following aspects: A, the smallest current set the smallest point; B, wiring clean point, especially the key path of sense; C, the selection of the inductor or the inductance of the closed magnetic circuit; D, RC low pass filter, this effect is a little bad.

C is not good consistency, the deviation is a bit big, but it should be enough for lighting. As the high power light-emitting diode operating voltage is only 3V, the full-bridge rectifier turns the V AC into DC, the voltage drop on the full bridge is about 1. According to the principle of three basic color synthesis white light, 31W high-power light-emitting diodes with red, green and blue are connected in series, and the brightness of the LED equivalent to the white light of 3W can be obtained.

At the same time, 6 kinds of color light can be combined to satisfy people's preference for color conversion. The LED drive circuit uses a switching power supply as the first level of control, and a pressure control constant current source as the second level of control.

Combining the advantages of the two can ensure efficiency and control accuracy. Moreover, it is directly provided by the city with electricity, two-layer drive, high safety, and it is not easy to damage the expensive LED lights. What is an LED driver used for? LED drivers are devices which regulate and supply the power used to 'drive' runs of LED strip lighting. Similar to traditional transformers, they transform mains voltage alternating current v AC to a lower voltage.

Do I need a driver for LED lights? Every LED light source requires a driver. Some LEDs already include an integrated driver within the bulb. What is the difference between a transformer and an LED driver? A transformer is by convention a double wound device, just ac in, ac out. Drivers are more sophisticated than that and usually give a dc output using a switched-mode system, also they have current regulating and monitoring circuits in them.

Can a LED driver be used as a power supply? Constant current and Constant voltage drivers are both viable options for a power supply for LED light sources, what differs is the way in which they deliver the power. How many LEDs can a driver power? How many lights can one driver power?

Drivers are not limited by the number of LED lights they power. They are restricted by the total wattage of the LED lights they power. How long does an LED driver last? Namely, the life of the driving circuit expires prior to when the LED stops emitting light or has its brightness dropped. The typical nominal lifetime of these elements is often times less than 25, hours, while the lifetime of LED itself could be as long as 50,, hours.

Do LED drivers get hot? Heat is the enemy of electronics and this goes for LED drivers too. This doesn't mean that LED drivers cannot operate in hot environments, they can. The output capacity of a switch-mode power supply, including LED drivers reduces as the temperature increases. How do I choose an LED driver? The driver must have a higher output power than your LEDs require for extra safety.

If the output is equivalent to the LED power requirements, it is running at full power. Running at full power may cause the driver to have a shorter life span. How do I know if my LED drivers are bad? LED drivers rectify higher voltage alternating current to low voltage. Usually the circuits burn out and fail. How does an LED driver circuit work? The voltage drop across an LED is approximately constant over a wide range of operating current; therefore, a small increase in applied voltage greatly increases the current.

It is quite clear that economic growth is closely linked to energy availability. Energy availability can be approached by two ways; the first way is to build more power plants to cover the increased demand. Assuming the transistor conducts fully in saturation, there will be negligible resistance across its emitter-collector junctions, and therefore the voltage across the series resistor RL will be 3. This is very simple to deduce because the forward bias voltage of the LED is 1.

Since we now have the voltage across resistor RL, which is 3. Note that this is a standard textbook formula where the 0. It is a shortcut formula, which enables you to calculate the base resistance without requiring much mathematics or any understanding of saturation curves. Its derivation is outside the scope of this article. From the P2NA documentation, we select a suitable minimum current gain value hFE of the transistor as We know that the load resistance RL is , therefore the following calculation should provide the value of the base resistor.

The Raspberry Pi and Arduino are usually 3. Hence, the value of the current limiting series resistance, and base resistance, will be different. However, the steps to calculate them are the same as before.