There are a large number of different circuit solutions, but in our case we will analyze several PWM options LED brightness control() on the PIC microcontroller.

PIC10F320/322 is an ideal option for designing various dimmers. At the same time, we obtain a fairly sophisticated device with the lowest cost and minimal time spent on construction. Let's look at several dimmer options.

First option. A basic LED brightness control in which the brightness of the LEDs is changed by rotating the variable knob, while the brightness changes from 0 to 100%

The brightness of the LEDs is set by removing the potential from the variable resistor R1. This variable voltage goes to the RA0 input, which functions as an analog input and is connected to the AN2 input of the microcontroller ADC. The PWM pin RA1 controls the power switch on transistor V1.

It is possible to choose an arbitrary power transistor with a logical control level, that is, these are those transistors that, when receiving 1...2 volts to the gate, completely open their channel.

For example, with the IRF7805 transistor it is possible to control a current of up to 13 amperes while meeting the necessary requirements, and under any other conditions up to 5 amperes are guaranteed. Connector CON1 is needed only for in-circuit programming of the microcontroller; for the same purpose, resistances R2 and R5 are also needed, that is, if the microcontroller is programmed, then all these radio elements may not be installed.

Resistance R4 and BAV70 serve to protect against overvoltage and improper connection of the power supply. Capacitors C1 and C2 are ceramic and serve to reduce impulse noise and for reliable operation of the LM75L05 stabilizer.

Second option. Here, the brightness of the LEDs is also controlled by a variable resistor, and switching on and off is done using buttons.

Third option. As you can see, there is no variable resistor in the circuit. In this version, the brightness of the LEDs is controlled exclusively by two buttons. The adjustment is stepwise, the brightness changes with each subsequent press.

Fourth option. Essentially the same as the third option, but when you hold down the button, the LED glow changes smoothly.

The simplest LED brightness control circuit presented in this article can be successfully used in car tuning, or simply to increase comfort in the car at night, for example, to illuminate the instrument panel, glove compartments, and so on. To assemble this product, you do not need technical knowledge, you just need to be careful and careful.
Voltage 12 volts is considered completely safe for people. If you use an LED strip in your work, then you can assume that you will not suffer from a fire, since the strip practically does not heat up and cannot catch fire from overheating. But accuracy in work is needed to avoid a short circuit in the mounted device and, as a result, a fire, and therefore to preserve your property.
Transistor T1, depending on the brand, can regulate the brightness of LEDs with a total power of up to 100 watts, provided that it is installed on a cooling radiator of the appropriate area.
The operation of transistor T1 can be compared with the operation of an ordinary water faucet, and potentiometer R1 with its handle. The more you unscrew, the more water flows. So it is here. The more you unscrew the potentiometer, the more current flows. When you tighten it, the LEDs leak less and the LEDs shine less.

Regulator circuit

For this scheme we will not need many parts.
Transistor T1. You can use KT819 with any letter. KT729. 2N5490. 2N6129. 2N6288. 2SD1761. BD293. BD663. BD705. BD709. BD953. These transistors need to be selected depending on how much LED power you plan to regulate. Depending on the power of the transistor, its price also depends.
Potentiometer R1 can be of any type with a resistance from three to twenty kilos. A three-kilo-ohm potentiometer will only slightly reduce the brightness of the LEDs. Ten kilo-ohms will reduce it to almost zero. Twenty – will adjust from the middle of the scale. Choose what suits you best.
If you use an LED strip, then you won’t have to bother with calculating the damping resistance (in the diagram R2 and R3) using formulas, because these resistances are already built into the strip during manufacture and all you need to do is connect it to a voltage of 12 volts. You just need to buy a tape specifically for 12 volts. If you connect a tape, then exclude resistances R2 and R3.
They also produce LED assemblies designed for 12 volt power supply, and LED bulbs for cars. In all these devices, quenching resistors or power drivers are built in during manufacture and are directly connected to the on-board network of the machine. If you are just taking your first steps in electronics, then it is better to use just such devices.
So, we have decided on the components of the circuit, it’s time to start assembling.

We screw the transistor onto a bolt to the cooling radiator through a heat-conducting insulating gasket (so that there is no electrical contact between the radiator and the vehicle's on-board network, in order to avoid a short circuit).

Cut the wire into pieces of the required length.

We strip the insulation and tin it with tin.

Clean the contacts of the LED strip.

Solder the wires to the tape.

We protect the exposed contacts with a glue gun.

We solder the wires to the transistor and insulate them with heat shrink casing.

We solder the wires to the potentiometer and insulate them with heat-shrinkable casing.

The standard RT4115 LED driver circuit is shown in the figure below:

The supply voltage should be at least 1.5-2 volts higher than the total voltage across the LEDs. Accordingly, in the supply voltage range from 6 to 30 volts, from 1 to 7-8 LEDs can be connected to the driver.

Maximum supply voltage of the microcircuit 45 V, but operation in this mode is not guaranteed (better pay attention to a similar microcircuit).

The current through the LEDs has a triangular shape with a maximum deviation from the average value of ±15%. The average current through the LEDs is set by a resistor and calculated by the formula:

I LED = 0.1 / R

The minimum permissible value is R = 0.082 Ohm, which corresponds to a maximum current of 1.2 A.

The deviation of the current through the LED from the calculated one does not exceed 5%, provided that resistor R is installed with a maximum deviation from the nominal value of 1%.

So, to turn on the LED at constant brightness, we leave the DIM pin hanging in the air (it is pulled up to the 5V level inside the PT4115). In this case, the output current is determined solely by resistance R.

If we connect a capacitor between the DIM pin and ground, we get the effect of smooth lighting of the LEDs. The time it takes to reach maximum brightness will depend on the capacitor capacity; the larger it is, the longer the lamp will light up.

For reference: Each nanofarad of capacitance increases the turn-on time by 0.8 ms.

If you want to make a dimmable driver for LEDs with brightness adjustment from 0 to 100%, then you can resort to one of two methods:

1. First way assumes input to DIM DC voltage in the range from 0 to 6V. In this case, brightness adjustment from 0 to 100% is carried out at a voltage at the DIM pin from 0.5 to 2.5 volts. Increasing the voltage above 2.5 V (and up to 6 V) does not affect the current through the LEDs (the brightness does not change). On the contrary, reducing the voltage to a level of 0.3V or lower leads to the circuit turning off and putting it into standby mode (the current consumption drops to 95 μA). Thus, you can effectively control the operation of the driver without removing the supply voltage.
2. Second way involves supplying a signal from a pulse-width converter with an output frequency of 100-20000 Hz, the brightness will be determined by the duty cycle (pulse duty cycle). For example, if the high level lasts 1/4 of the period, and the low level, respectively, 3/4, then this will correspond to a brightness level of 25% of the maximum. You must understand that the driver operating frequency is determined by the inductance of the inductor and in no way depends on the dimming frequency.

The PT4115 LED driver circuit with constant voltage dimmer is shown in the figure below:

This circuit for adjusting the brightness of LEDs works great due to the fact that inside the chip the DIM pin is “pulled up” to the 5V bus through a 200 kOhm resistor. Therefore, when the potentiometer slider is in its lowest position, a voltage divider of 200 + 200 kOhm is formed and a potential of 5/2 = 2.5V is formed at the DIM pin, which corresponds to 100% brightness.

How the scheme works

At the first moment of time, when the input voltage is applied, the current through R and L is zero and the output switch built into the microcircuit is open. The current through the LEDs begins to gradually increase. The rate of current rise depends on the magnitude of the inductance and supply voltage. The in-circuit comparator compares the potentials before and after resistor R and, as soon as the difference is 115 mV, a low level appears at its output, which closes the output switch.

Thanks to the energy stored in the inductance, the current through the LEDs does not disappear instantly, but begins to gradually decrease. The voltage drop across the resistor R gradually decreases. As soon as it reaches a value of 85 mV, the comparator will again issue a signal to open the output switch. And the whole cycle repeats all over again.

If it is necessary to reduce the range of current ripples through the LEDs, it is possible to connect a capacitor in parallel with the LEDs. The larger its capacity, the more the triangular shape of the current through the LEDs will be smoothed out and the more similar it will become to a sinusoidal one. The capacitor does not affect the operating frequency or efficiency of the driver, but increases the time it takes for the specified current through the LED to settle.

Important assembly details

An important element of the circuit is capacitor C1. It not only smoothes out ripples, but also compensates for the energy accumulated in the inductor at the moment the output switch is closed. Without C1, the energy stored in the inductor will flow through the Schottky diode to the power bus and can cause a breakdown of the microcircuit. Therefore, if you turn on the driver without a capacitor shunting the power supply, the microcircuit is almost guaranteed to shut down. And the greater the inductance of the inductor, the greater the chance of burning the microcontroller.

The minimum capacitance of capacitor C1 is 4.7 µF (and when the circuit is powered with a pulsating voltage after the diode bridge - at least 100 µF).

The capacitor should be located as close to the chip as possible and have the lowest possible ESR value (i.e. tantalum capacitors are welcome).

It is also very important to take a responsible approach to choosing a diode. It must have a low forward voltage drop, short recovery time during switching, and stable parameters when increasing temperatures p-n transition to prevent an increase in leakage current.

In principle, you can take a regular diode, but Schottky diodes are best suited to these requirements. For example, STPS2H100A in SMD version (forward voltage 0.65V, reverse - 100V, pulse current up to 75A, operating temperature up to 156°C) or FR103 in DO-41 housing (reverse voltage up to 200V, current up to 30A, temperature up to 150 °C). The common SS34s performed very well, which you can pull out of old boards or buy a whole pack for 90 rubles.

The inductance of the inductor depends on the output current (see table below). An incorrectly selected inductance value can lead to an increase in the power dissipated on the microcircuit and exceeding the operating temperature limits.

If it overheats above 160°C, the microcircuit will automatically turn off and remain in the off state until it cools down to 140°C, after which it will start automatically.

Despite the available tabular data, it is permissible to install a coil with an inductance deviation greater than the nominal value. In this case, the efficiency of the entire circuit changes, but it remains operational.

You can take a factory choke, or you can make it yourself from a ferrite ring from a burnt motherboard and PEL-0.35 wire.

If maximum autonomy of the device is important (portable lamps, lanterns), then, in order to increase the efficiency of the circuit, it makes sense to spend time carefully selecting the inductor. At low currents, the inductance must be larger to minimize current control errors resulting from the delay in switching the transistor.

The inductor should be located as close as possible to the SW pin, ideally connected directly to it.

And finally, the most precision element of the LED driver circuit is resistor R. As already mentioned, its minimum value is 0.082 Ohms, which corresponds to a current of 1.2 A.

Unfortunately, it is not always possible to find a resistor of a suitable value, so it’s time to remember the formulas for calculating the equivalent resistance when resistors are connected in series and in parallel:

• R last = R 1 +R 2 +…+R n;
• R pairs = (R 1 xR 2) / (R 1 +R 2).

By combining different connection methods, you can obtain the required resistance from several resistors at hand.

It is important to route the board so that the Schottky diode current does not flow along the path between R and VIN, as this can lead to errors in measuring the load current.

The low cost, high reliability and stability of driver characteristics on the RT4115 contribute to its widespread use in LED lamps. Almost every second 12-volt LED lamp with an MR16 base is assembled on PT4115 (or CL6808).

The resistance of the current-setting resistor (in Ohms) is calculated using exactly the same formula:

R = 0.1 / I LED[A]

A typical connection diagram looks like this:

As you can see, everything is very similar to the diagram LED lamp with driver for RT4515. The description of the operation, signal levels, features of the elements used and the layout of the printed circuit board are exactly the same as those, so there is no point in repeating.

CL6807 sells for 12 rubles/pcs, you just need to be careful that they don’t slip soldered ones (I recommend taking them).

SN3350

SN3350 is another inexpensive chip for LED drivers (13 rubles/piece). It is almost a complete analogue of PT4115 with the only difference being that the supply voltage can range from 6 to 40 volts, and the maximum output current is limited to 750 milliamps (continuous current should not exceed 700 mA).

Like all the microcircuits described above, the SN3350 is a pulsed step-down converter with an output current stabilization function. As usual, the current in the load (and in our case, one or more LEDs act as the load) is set by the resistance of the resistor R:

R = 0.1 / I LED

To avoid exceeding the maximum output current, resistance R should not be lower than 0.15 Ohm.

The chip is available in two packages: SOT23-5 (maximum 350 mA) and SOT89-5 (700 mA).

As usual, by applying a constant voltage to the ADJ pin, we turn the circuit into a simple adjustable driver for LEDs.

A feature of this microcircuit is a slightly different adjustment range: from 25% (0.3V) to 100% (1.2V). When the potential at the ADJ pin drops to 0.2V, the microcircuit goes into sleep mode with a consumption of around 60 µA.

Typical connection diagram:

For other details, see the specifications for the microcircuit (pdf file).

ZXLD1350

Despite the fact that this chip is another clone, there are some differences in technical specifications do not allow their direct replacement with each other.

Here are the main differences:

• the microcircuit starts at 4.8V, but reaches normal operation only with a supply voltage of 7 to 30 Volts (up to 40V can be supplied for half a second);
• maximum load current - 350 mA;
• resistance of the output switch in the open state is 1.5 - 2 Ohms;
• By changing the potential at the ADJ pin from 0.3 to 2.5V, you can change the output current (LED brightness) in the range from 25 to 200%. At a voltage of 0.2V for at least 100 µs, the driver goes into sleep mode with low power consumption (about 15-20 µA);
• if the adjustment is carried out by a PWM signal, then at a pulse repetition rate below 500 Hz, the range of brightness changes is 1-100%. If the frequency is above 10 kHz, then from 25% to 100%;

The maximum voltage that can be applied to the ADJ input is 6V. In this case, in the range from 2.5 to 6V, the driver produces the maximum current, which is set by the current-limiting resistor. The resistor resistance is calculated in the same way as in all of the above microcircuits:

R = 0.1 / I LED

The minimum resistor resistance is 0.27 Ohm.

A typical connection diagram is no different from its counterparts:

Without capacitor C1 it is IMPOSSIBLE to supply power to the circuit!!! At best, the microcircuit will overheat and produce unstable characteristics. In the worst case, it will fail instantly.

More detailed characteristics ZXLD1350 can be found in the datasheet for this chip.

The cost of the microcircuit is unreasonably high (), despite the fact that the output current is quite small. In general, it’s very much for everyone. I wouldn't get involved.

QX5241

QX5241 is a Chinese analogue of MAX16819 (MAX16820), but in a more convenient package. Also available under the names KF5241, 5241B. It is marked "5241a" (see photo).

In one well-known store they are sold almost by weight (10 pieces for 90 rubles).

The driver operates on exactly the same principle as all those described above (continuous step-down converter), but does not contain an output switch, so operation requires the connection of an external field-effect transistor.

You can take any N-channel MOSFET with suitable drain current and drain-source voltage. For example, the following are suitable: SQ2310ES (up to 20V!!!), 40N06, IRF7413, IPD090N03L, IRF7201. In general, the lower the opening voltage, the better.

Here are some key features of the LED driver on the QX5241:

• maximum output current - 2.5 A;
• Efficiency up to 96%;
• maximum dimming frequency - 5 kHz;
• maximum operating frequency of the converter is 1 MHz;
• accuracy of current stabilization through LEDs - 1%;
• supply voltage - 5.5 - 36 Volts (works normally at 38!);
• output current is calculated by the formula: R = 0.2 / I LED

Read the specification (in English) for more details.

The LED driver on the QX5241 contains few parts and is always assembled according to this scheme:

The 5241 chip comes only in the SOT23-6 package, so it’s best not to approach it with a soldering iron for soldering pans. After installation, the board should be thoroughly washed to remove flux; any unknown contamination can negatively affect the operation of the microcircuit.

The difference between the supply voltage and the total voltage drop across the diodes should be 4 volts (or more). If it is less, then some glitches in operation are observed (current instability and inductor whistling). So take it with reserve. Moreover, the greater the output current, the greater the voltage reserve. Although, perhaps I just came across a bad copy of the microcircuit.

If the input voltage is less than the total drop across the LEDs, then generation fails. In this case, the output field switch opens completely and the LEDs light up (of course, not at full power, since the voltage is not enough).

AL9910

Diodes Incorporated has created one very interesting LED driver IC: the AL9910. It is curious in that its operating voltage range allows it to be connected directly to a 220V network (via a simple diode rectifier).

Here are its main characteristics:

• input voltage - up to 500V (up to 277V for alternating);
• built-in voltage stabilizer for powering the microcircuit, which does not require a quenching resistor;
• the ability to adjust brightness by changing the potential on the control leg from 0.045 to 0.25V;
• built-in overheating protection (triggered at 150°C);
• operating frequency (25-300 kHz) is set by an external resistor;
• an external field-effect transistor is required for operation;
• Available in eight-legged SO-8 and SO-8EP packages.

The driver assembled on the AL9910 chip does not have galvanic isolation from the network, so it should be used only where direct contact with the circuit elements is impossible.

When altering instrument panels, there is a need to adjust the brightness of the installed boards. This is especially necessary if you drive for a long time in the dark. All the same, LEDs shine richer and brighter than conventional lamps, and even without a regulator the work looks unfinished.

The issue can be resolved by purchasing a ready-made dimmer for adjustment LED strips or a simple variable resistor installed in the network break. This is not our method. The regulator must be PWM (pulse width modulator).

PWM adjustment is in periodically turning on and off the current through the LED for short periods of time. To avoid the flickering effect perceived by human vision, the frequency of this cycle must be at least 200Hz.

One option for dimming LEDs is a simple device based on the popular 555 timer, which performs this operation using a PWM signal. The main component of the circuit is a 555 timer, which generates a PWM signal; the built-in generator changes the duty cycle of pulses with a frequency of 200 Hz.

A variable resistor with the help of two pulse diodes adjusts the brightness. An important element of the circuit is a key field-effect transistor operating according to a common-source circuit. The dimmer circuit is capable of adjusting brightness in the range from 5% to 95%.

Theory passed. Let's move on to practice.

Two conditions were set:
1. The circuit must be assembled using SMD components
2. Minimum dimensions.

Difficulties immediately arise in selecting components. In my case, the main thing was to buy radio amateurs in Mecca - the Chip and Dip store and wait two weeks for delivery by fucking Russian Post. Find the rest in local stores.

This is the most difficult thing, because... There are only a couple of them. I’ll say right away that it didn’t work out the first time, I had to rack my brains with the field-effect transistor and redo/redraw/resolder several times.

The classic scheme is taken as a basis:

Changes have been made to the diagram:
1. Capacitances were replaced with 0.01 µF and 0.1 µF
2. Replaced the transistor with IRF7413. Holds 30V 13A. Gorgeous!

First and second options.

Version 1 and version 2.

As you can see in the second version, the overall dimensions were further reduced and the field filter and capacity were replaced.

Comparison. For clarity of sizes.

Taking into account all the errors, I redid the diagram and reduced the overall measurements a little more.

Victory!

We connect a piece of the scale:

Maximum brightness

Rich Rosen, National Semiconductor

Introduction

The exponential growth in the number of LED light sources is accompanied by an equally rapid expansion of the range of integrated circuits designed to control LED power. Switching LED drivers have long replaced power-hungry linear regulators, which were unacceptable for a world concerned with energy savings, becoming the de facto standard for the industry. Applications ranging from hand-held flashlights to stadium signage require precise control of stabilized current. In this case, it is often necessary to change the intensity of LED radiation in real time. Controlling the brightness of light sources, and LEDs in particular, is called dimming. This article outlines the basics of LED theory and describes the most popular dimming methods using switching drivers.

LED brightness and color temperature

LED brightness

The concept of brightness of the visible set emitted by an LED is quite easy to understand. The numerical value of the perceived brightness of an LED can be easily measured in units of surface luminous flux density called candela (cd). The total power of light emitted by an LED is expressed in lumens (lm). It is also important to understand that the brightness of the LED depends on the average value of the forward current.

Figure 1 shows a graph of the luminous flux of a certain LED versus forward current. In the range of used values ​​of forward currents (I F), the graph is extremely linear. Nonlinearity begins to appear as I F increases. When the current leaves the linear section, the efficiency of the LED decreases.

Picture 1.

When operating outside the linear region, a significant portion of the power supplied to the LED is dissipated as heat. This wasted heat overloads the LED driver and complicates the design's thermal design.

LED color temperature

Color temperature is a parameter characterizing the color of the LED and is indicated in the reference data. The color temperature of a particular LED is described by a range of values ​​and shifts with changes in forward current, junction temperature, and also as the device ages. The lower the color temperature of the LED, the closer its glow is to the red-yellow color, called “warm”. Blue-green colors, called “cool” colors, correspond to higher color temperatures. Often for color LEDs, instead of a color temperature, a dominant wavelength is specified, which can shift just like the color temperature.

Ways to control the brightness of LEDs

There are two common ways to control the brightness (dimming) of LEDs in circuits with switching drivers: pulse width modulation (PWM) and analog regulation. Both methods ultimately come down to maintaining a certain level of average current through an LED, or a chain of LEDs. Below we will discuss the differences between these methods and evaluate their advantages and disadvantages.

Figure 2 shows a switching LED driver circuit in a buck converter configuration. The voltage V IN in such a circuit must always exceed the sum of the voltages on the LED and resistor R SNS. The inductor current flows entirely through the LED and resistor R SNS, and is regulated by the voltage supplied from the resistor to the CS pin. If the voltage at the CS pin begins to fall below the set level, the duty cycle of the current flowing through L1, the LED, and R SNS increases, causing the average LED current to increase.

Analogue dimming

Analog dimming is cycle-by-cycle control of the direct current of an LED. In simple terms, this is maintaining the LED current at a constant level. Analog dimming is accomplished either by adjusting the current sense resistor R SNS or by changing the DC voltage level applied to the DIM pin (or similar pin) of the LED driver. Both examples of analog control are shown in Figure 2.

Analog dimming with R SNS control

From Figure 2 it can be seen that for a fixed reference voltage at the CS pin, changing the value of R SNS causes a corresponding change in the LED current. If it were possible to find a potentiometer with a resistance of less than one ohm that could withstand high LED currents, such a dimming method would have a right to exist.

Analogue dimming via supply voltage control via CS pin

A more complex method involves direct cycle-by-cycle control of the LED current using the CS pin. To do this, in a typical case, a voltage source taken from the LED current sensor and buffered by an amplifier is included in the feedback loop (Figure 2). To adjust the LED current, you can control the gain of the amplifier. It is easy to add additional functionality to this feedback circuit, such as current and temperature protection.

The disadvantage of analog dimming is that the color temperature of the light emitted can be affected by the forward current of the LED. In cases where changing the color of the glow is unacceptable, LED dimming by direct current regulation cannot be used.

Dimming using PWM

Dimming using PWM consists of controlling the moments of turning on and off the current through an LED, repeated with sufficient high frequency, which, taking into account the physiology of the human eye, should not be less than 200 Hz. Otherwise, a flickering effect may occur.

The average current through the LED now becomes proportional to the duty cycle and is expressed by:

I DIM-LED = D DIM × I LED

I DIM-LED - average current through the LED,
D DIM - duty cycle of PWM pulses,
I LED - rated current of the LED, set by choosing the resistance value R SNS (see Figure 3).

Figure 3.

LED Driver Modulation

Many modern LED drivers have a special DIM input to which PWM signals can be supplied over a wide range of frequencies and amplitudes. The input provides a simple interface with external logic circuits, allowing you to turn the converter output on and off without delays in restarting the driver, without affecting the operation of other components of the chip. A number of additional functions can be implemented using the output enable pins and auxiliary logic.

Two-wire PWM dimming

Two-wire PWM dimming has gained popularity in automotive interior lighting circuits. If the voltage at the VINS pin becomes 70% less than the voltage at VIN (Figure 3), the internal power MOSFET is disabled and current through the LED is turned off. The disadvantage of this method is the need to have a PWM signal conditioner circuit in the converter power supply.

Fast PWM dimming with shunt device

The delay in the moments of turning the converter output on and off limits the PWM frequency and the range of change in the duty cycle. To solve this problem, you can connect a shunt device, such as, say, the MOSFET transistor shown in Figure 4a, in parallel with the LED, or string of LEDs, to quickly bypass the output current of the converter bypassing the LED(s).

A)
b)
Figure 4.	Fast PWM dimming (a), current and voltage shapes (b).

The inductor current remains continuous while the LED is turned off, due to which the rise and fall of the current is no longer delayed. Now the rise and fall times are limited only by the characteristics of the MOSFET transistor. Figure 4a shows the circuit diagram connecting a shunt transistor to an LED driven by an LM3406 driver, and Figure 4b shows waveforms illustrating the difference in results obtained when dimming using the DIM pin (top) and when connecting a shunt transistor (bottom). In both cases, the output capacitance was 10 nF. Shunt MOSFET transistor type .

When shunting the current of LEDs controlled by converters with current stabilization, one must take into account the possibility of current surges when the MOSFET transistor is turned on. The LM340x family of LED drivers feature converter turn-on timing to help address emissions issues. To maintain maximum on/off speed, the capacitance between the LED terminals must be kept to a minimum.

A significant disadvantage of fast PWM dimming, compared to the converter output modulation method, is the reduction in efficiency. When the shunt device is open, it dissipates power, which is released in the form of heat. To reduce such losses, you should choose MOSFET transistors with minimal open channel resistance R DS-ON.

Multi-mode dimmer LM3409

• The eye "tool" is good, but without "numerical" values. Only a spectrometer can show something specific. Link please. And do you seriously believe that something is being done outside of “China” (Asian countries)?
• Link please.
• =Vlad-Perm;111436][B]Vladimir_007 [B]"To extend the service life, several more LEDs are placed next to it (butt-to-shoulder)"? - I have a lot of LEDs nearby to increase the total brightness........... I apologize, I ended up on this thread again by accident. Numbers 6 - 8 ago there was an article in the radio pilot where I also inserted my remark. It’s not modest to mention the quality of LED products; a couple of magazines ago, a motorist had an article on headlights about LED overheating. So 6 - 8 issues ago in the article there was a driver circuit, which is a garland switch for 4 channels. “thanks to the driver, we increase the service life of the LED by 4 times due to the fact that it works 4 times less often, also 2_th +, the duration of operation of the diode crystal with a graph exponentially increases the service life by reducing the temperature of the crystal” - approximately verbatim from memory . As for photographing headlights, an LED is a strobe for the human eye, but with a very high switching speed and so far no one has boasted of an increase (afterglow) of the LED after a power failure.
• Dear [b]Vladimir_666, hello. Why did you decide this? When the LED is powered with direct current, a continuous stream of light radiation is formed. When powered with pulsed current, light pulses are formed. The LED [B] is inertialess. This remarkable property is widely used when transmitting digital information over optical fiber at speeds of tens of gigabytes per second or more. It also requires an appropriate phosphor that does not create an afterglow. I think you understand this perfectly well. When talking about a strobe, you obviously mean individual quanta of light. But they have not yet learned how to use them separately. It’s not clear who gave the “minus” and for what?
• [b] SATIR, you are partly grass in that [I] The LED is inertia-free. This is true for bare-chip LEDs. White LEDs developed for lighting have a layer of phosphor. And it has some afterglow time (several milliseconds), which is quite sufficient when powered by pulses with a frequency of kilohertz. In addition, a filter capacitor is installed in the drivers.
• Dear [b]lllll, hello. Absolutely with you, absolutely. Agree, the phosphor is only an accessory of the LED itself to give it the necessary properties.
• Good afternoon. By the word strobe with high frequency, I meant exactly a strobe. If you take the glow of an ordinary light bulb with a maximum voltage of 220V and a minimum of 0 and this with a frequency of 50 Hz - the temperature of the filament at 220V is 2200 degrees, but when the voltage drops to 0 and rises again to 220V, the temperature of the filament does not fall to 0, but drops to 1500 - 1800 degrees, which is what we see “with the naked eye”. As for the LED, their operating principle is a strobe, with a high switching speed, which is not visible to the human eye, but this does not mean that it does not affect vision. As for data transfer gigabytes per second - usually data transfer is transmitted (in Morse code, a flashing light), I understand that a person would put (-), you can be stupid, if, according to people's reviews, you consider yourself to be just as smart - decide for yourself where You have a constantly burning light bulb and which of us needs to turn it on -.
• Well, like 50 Hz. These are two half-sine waves and actually blink at 100 Hz. and the amplitude voltage is about 300 V. Who told you this? Or where did you read this? Read about the principle of operation in Wik, but the topic seems to be about powering LEDs. A normal driver powers the LED constantly. PWM controllers are used only if you need to CHEAPLY reduce the brightness of the glow. A good driver, again, can reduce the current to the LED without using PWM. PWM is used in multi-mode flashlights - and if the driver is at least somewhat adequate, the PWM frequency is from several kHz. Completely unnoticeable during any use. Yeah, for me too, when the hard drive transmits data, the “light” (LED) blinks, blinks so quickly! She is the one transmitting the data!
• Don't touch Vladimir666. He doesn't understand how the LED works. And obviously he won't understand. He came up with an incorrect explanation for himself and pushes it to everyone left and right.
• All of the above is exactly the opposite
• ctc655 I think I explained to you in a clear form that a constantly burning light bulb cannot transmit information if you are trying to protect LED manufacturers with your backing track through your [B]unprofessional actions
• Thanks Vladimir666. My opinion of you has not improved. Alas. Even in childhood, about 38 years ago, they made a light telephone using a LIGHT BULB. It was powered by direct current. It worked. He conveyed information. Another thing is at what speed, so to speak. But your idea of ​​how an LED works is nonsense. Either you have it as a spark gap or as a strobe light. Young people revere and then start talking nonsense. If it's hard to understand, don't bother. For this we received -1. This is an assessment of the informativeness of the message. Your messages not only are not informative, but also give an erroneous idea of ​​the topic. Where there is no such big nonsense, I don’t put anything.
• Look at the topic on the same site to make it clear why again! http://www..php?p=199007#post199007 Discussion: Lighting devices based on AC LEDs are finding their niche and, perhaps, will go beyond it. I’m also not 10 or 30 years old, but it will be useful for you to read. Increase knowledge in addition to a high-tech device with a p-n junction. I wonder how you transmitted information 30 years ago with a light bulb burning on direct current? All lighting devices, no matter - optocoupler, optothyristor, etc. all work by interrupting the light flow. Perhaps a patent was created specifically for this?
• Justify or confirm. I am an “electronics engineer” - you don’t have to be limited in terminology. The fact that the driver (powered by 220 V.) operates according to the circuit AC (220 V.) - DC (300 V.) - AC PWM - DC (stable required current CC) - CC to the LED does not make it PWM regulator. (this can also be simply called a voltage rectifier!) Feedback PWM is simply one way to maintain a stable brightness (current) of an LED. But you can adjust the brightness in two ways: in the specified chain in “AS PWM”, additionally introduce a “fill” adjustment (the LED will be powered by an adjustable stable current) or regulate the PWM directly [B] the average current per light. In the first case, it is powered by a stable current (no ripple!) In the second case, the LED is powered by “pulses” and they are, in principle, visible. (not necessarily with the eyes - in flashlights I have encountered frequencies of both 200 Hz and 9 kHz.) Using Morse code - is this not the transfer of information?
• To be honest, I don’t know why I need to confirm a known truth. Maybe, of course, there are some nuances in the development of adjustable drivers (and they should be). I haven't done this yet. Therefore, the methods of regulation you propose have the right to life. But each one is used in its own way. Regarding Morse code. Yes, this is the transfer of information, but with a break in the light flux. And that light telephone worked by changing the brightness of the light bulb without going out. In the absence of speech, the light was constantly on. I didn't find the diagram. We did it in a circle and didn’t yet have the habit of sketching diagrams. Also, some closed optocouplers, resistor for example, can operate without interrupting the light flow.
• Dear [b]ctc655, hello. [B]You are absolutely right. A similar method of sound transmission is still used in cinema. Along the edge of the film there is a light path that modulates the light flux, which is converted into an electrical signal. The method has existed since the invention of sound cinema! It was he who destroyed the tapers.
• I somehow forgot about this. Although it may be different now. Honestly, I haven’t been interested in cinema for a long time.
• I don’t argue that without the lights going out, the circuits can be different, from ordinary logic to 554CA..(3) comparators, you can just light the light bulb and pull the “flag” in front of the light bulb, but signal transmission has always worked by changing “1” and "0".
• On digital devices - yes. Do light level sensors also work when a light bulb or the sun goes out? Moreover, the illumination level is adjustable......
• The previous topic or dispute, if you read it, was about the transfer of data “supposedly with a constantly burning light bulb” from a direct current source, that is, a battery or a stabilized power source. (I don’t want to raise the topic - where does it end? AC voltage and the constant begins, since there is now a lot of controversy on this topic on the internet, starting with the battery itself.....) As for the level of illumination, are you talking about motion sensors or about night lighting, say, around store windows? It seems that in 1_x the light in the usual concept is a little inconsistent with the theme, but the principle is almost the same!