Today we will try to make a controller that will adjust the brightness of the LED. The materials for this test were taken from the website led22.ru from the article "Do-it-yourself LEDs for cars". The 2 main parts used in this experiment are the LM317 current regulator and the variable resistor. They can be seen in the photo below. The difference between our experiment and that given in the original article is that we left the variable resistor to control the light of the LED. In a radio parts store (not the cheapest, but very well known to everyone), we purchased these parts for 120 rubles (stabilizer - 30r, resistor - 90r). It should be noted here that the resistor Russian production"timbre", which has a maximum resistance of 1 kOhm.

Wiring diagram: the right leg of the LM317 current stabilizer is supplied with a "plus" from the 12V power supply. A resistor is connected to the left and middle legs alternating current. Also, the positive leg of the LED is connected to the left leg. The negative wire from the power supply is connected to the negative leg of the LED.

It turns out that the current passing through Lm317 decreases to the value specified by the resistance variable resistor.

In practice, it was decided to solder the stabilizer directly to the resistor. This was done primarily to remove heat from the stabilizer. Now it will heat up along with the resistor. The resistor has 3 pins. We use the central and extreme. Which last one to use is not important for us. Depending on the choice, in one case, turning the knob clockwise will increase the brightness, in the opposite case, it will decrease. If you connect the extreme contacts, the resistance will be constant 1 kOhm.

Solder the wires as in the diagram. The "plus" from the power supply will go to the brown wire, the blue - "plus" to the LED. When soldering, we leave more tin on purpose so that heat transfer is better.

And finally, we put on heat shrink to eliminate the possibility of a short circuit. Now you can try.

For the first test, we use LEDs:

1) Epistar 1W, operating voltage - 4V (at the bottom of the next photo).

2) Flat diode with three chips, operating voltage - 9V (at the top of the next photo).

The results (can be seen in the next video) cannot but rejoice: not a single diode burned out, the brightness is smoothly adjusted from minimum to maximum. To power a semiconductor, the supply current is of primary importance, not the voltage (the current grows exponentially relative to the voltage, with an increase in voltage, the probability of "burning out" the LED sharply increases.

After that, a test is carried out with LED modules at 12V. And our controller works on them without problems. This is exactly what we were striving for.

Thank you for your attention!

The standard PT4115 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.

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

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 is calculated by the formula:

I LED = 0.1 / R

The minimum allowable value 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 the resistor R is installed with a maximum deviation from the nominal value of 1%.

So, to turn on the LED for constant brightness, we leave the DIM output 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 the resistance R.

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

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

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

  1. First way involves supplying a constant voltage in the range from 0 to 6V to the DIM input. In this case, the 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, a decrease in voltage to a level of 0.3V or lower leads to the shutdown of the circuit and its transfer to standby mode (the current consumption drops to 95 μA). Thus, it is possible to effectively control the operation of the driver without removing the supply voltage.
  2. Second way implies 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 is held for 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. It must be understood that the frequency of the driver is determined by the inductance of the inductor and in no way depends on the dimming frequency.

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

This LED dimming scheme works great because the DIM pin inside the chip is "pulled up" to the 5V bus through a 200 kΩ resistor. Therefore, when the potentiometer slider is in its lowest position, a voltage divider of 200 + 200 kΩ 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 key built into the microcircuit is open. The current through the LEDs begins to gradually increase. The rate of current rise depends on the value of the inductance and the supply voltage. The in-circuit comparator compares the potentials before and after the resistor R and, as soon as the difference is 115 mV, a low level appears at its output, which closes the output switch.

Due 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 also gradually decreases. As soon as it reaches a value of 85 mV, the comparator will again give a signal to open the output key. And the whole cycle repeats from the beginning.

If it is necessary to reduce the current ripple through the LEDs, it is allowed to connect a capacitor in parallel with the LEDs. The larger its capacitance, the more the triangular shape of the current through the LEDs will be smoothed out and the more it will become similar to a sinusoidal one. The capacitor does not affect the operating frequency or efficiency of the driver, but it does increase the settling time for the desired current through the LED.

Important assembly details

An important element of the circuit is the capacitor C1. It not only smooths 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 rail 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 be covered. And the greater the inductance of the inductor, the more likely it is to burn the mikruha.

The minimum capacitance of the capacitor C1 is 4.7 uF (and when the circuit is powered by a pulsating voltage after the diode bridge, it is at least 100 uF).

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

It is also very important to responsibly approach the choice of the diode. It should have a low forward voltage drop, a short recovery time during switching, and a stable performance as the temperature rises. p-n junction to prevent an increase in leakage current.

In principle, you can take an ordinary diode, but Schottky diodes are best suited for 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 package (reverse voltage up to 200V, current up to 30A, temperature up to 150 °C). The common SS34s showed themselves very well, which you can pull from 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 beyond the operating temperature range.

When overheated 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 allowed to mount a coil with an inductance deviation upwards from the nominal value. This changes the efficiency of the entire circuit, but it remains operational.

The inductor can be taken from the factory, or you can do it yourself from a ferrite ring from a burnt motherboard and PEL-0.35 wires.

If the 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 on careful selection of the throttle. At low currents, the inductance must be larger to minimize current control errors due to the delay in switching the transistor.

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

And finally, the most precise element of the LED driver circuit is the resistor R. As already mentioned, its minimum value is equal to 0.082 ohm, 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 calculation formulas equivalent resistance with series and parallel connection of resistors:

  • R last \u003d R 1 + R 2 + ... + R n;
  • R pairs = (R 1 xR 2) / (R 1 + R 2).

Combining various ways switching on, you can get the required resistance from several resistors at hand.

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

The low cost, high reliability and stability characteristics of the PT4115 driver contribute to its widespread use in LED lamps. Almost every second 12-volt LED lamp with an MR16 base is assembled on a 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 wiring diagram looks like this:

As you can see, everything is very similar to the scheme led lamp with driver for PT4515. Description of operation, signal levels, features of the elements used and layout printed circuit board exactly the same as y, so it makes no sense to repeat.

CL6807 is sold at 12 rubles / pc, you just need to watch so that they do not slip soldered ones (I recommend taking it).

SN3350

SN3350 - another inexpensive microcircuit for LED drivers(13 rubles / piece). It is almost a complete analog of PT4115 with the only difference 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 above microcircuits, SN3350 is a pulse step-down converter with output current stabilization function. As usual, the current in the load (and in our case, one or more LEDs act as a load) is set by the resistance of the resistor R:

R = 0.1 / I LED

In order not to exceed the value of the maximum output current, the resistance R should not be lower than 0.15 ohm.

The microcircuit 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 in the region of 60 μA.

Typical switching circuit:

For other details, see the chip specification (pdf file).

ZXLD1350

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

Here are the main differences:

  • the microcircuit starts already at 4.8V, but it enters normal operation only when the supply voltage is from 7 to 30 Volts (it is allowed to supply up to 40V for half a second);
  • maximum load current - 350 mA;
  • resistance of the output key in the open state - 1.5 - 2 Ohm;
  • 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 change is 1-100%. If the frequency is above 10 kHz, then from 25% to 100%;

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

R = 0.1 / I LED

The minimum resistance of the resistor is 0.27 ohms.

A typical switching circuit is no different from its counterparts:

It is IMPOSSIBLE to supply power to the circuit without capacitor C1 !!! At best, the chip will overheat and give out unstable characteristics. In the worst case, it will instantly fail.

More detailed specifications 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, strongly on the fan. I wouldn't contact.

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 works on exactly the same principle as all of the above (continuous step-down converter), however, it does not contain an output switch, therefore, an external field-effect transistor is required for operation.

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

Here are some key features of the QX5241 LED driver:

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

Read more in the specification (in English).

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

The 5241 microcircuit is only available in the SOT23-6 package, so it is better not to approach it with a soldering iron for soldering pans. After installation, the board should be thoroughly washed from the flux, any obscure contamination can adversely 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 less, then there are some glitches in operation (current instability and throttle whistle). So take it with a margin. Moreover, the greater the output current, the greater the voltage margin. Although, perhaps, I just got an unsuccessful copy of the microcircuit.

If the input voltage is less than the total drop across the LEDs, then the generation fails. At the same time, the output field switch opens completely and the LEDs glow (naturally, 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 you to connect it directly to a 220V network (through a simple diode rectifier).

Here are its main characteristics:

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

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

Chip NCP1014 is a PWM controller with a fixed conversion frequency and a built-in high-voltage switch. Additional internal blocks implemented as part of the microcircuit (see Fig. 1) allow it to meet the entire range of functional requirements for modern power supplies.

Rice. one.

Series controllers NCP101X were discussed in detail in an article by Konstantin Staroverov in issue 3 of the journal for 2010, therefore, in the article we will limit ourselves to considering only key features microcircuits NCP1014, and we will focus on the consideration of the calculation features and the mechanism of operation of the IP, presented in the reference design.

Features of the NCP1014 controller

  • Integrated output 700V low on-resistance MOSFET (11Ω);
  • providing driver output current up to 450mA;
  • the ability to work at several fixed conversion frequencies - 65 and 100 kHz;
  • the conversion frequency varies within ± 3 ... 6% relative to its preset value, which allows you to "blur" the power of radiated interference within a certain frequency range and thereby reduce the EMI level;
  • the built-in high-voltage power supply system is able to ensure the operability of the microcircuit without the use of a transformer with a third auxiliary winding, which greatly simplifies the winding of the transformer. This feature is designated by the manufacturer as DSS ( Dynamic Self-Supply- autonomous dynamic power), however, its use limits the output power of the IP;
  • the ability to work with maximum efficiency at low load currents due to the PWM pulse skipping mode, which makes it possible to achieve low no-load power - no more than 100 mW when the microcircuit is powered from the third auxiliary winding of the transformer;
  • the transition to the pulse skipping mode occurs when the load current is reduced to a value of 0.25 from the nominal value, which eliminates the problem of generating acoustic noise even when using inexpensive pulse transformers;
  • implemented soft start function (1ms);
  • conclusion feedback voltage is directly connected to the output of the optocoupler;
  • a short circuit protection system with subsequent return to normal operation after its elimination has been implemented. The function allows you to track both directly a short circuit in the load, and the situation with an open feedback circuit in case of damage to the decoupling optocoupler;
  • built-in overheating protection mechanism.

The NCP1014 controller is available in three package types - SOT-223, PDIP-7 and PDIP-7 GULLWING (see Figure 2) with the pinout shown in Figure 2. 3. The latest package is a special version of the PDIP-7 package with special pin molding, making it suitable for surface mounting.

Rice. 2.

Rice. 3.

Typical application diagram of NCP1014 controller in flyback ( flyback) converter is shown in Figure 4.

Rice. four.

IP calculation method based on NCP1014 controller

Consider the method of step-by-step calculation of a flyback converter based on NCP1014 using the example of a reference development of a power supply with an output power of up to 5 W to power a system of three LEDs connected in series. One-watt white LEDs with a normalization current of 350 mA and a voltage drop of 3.9 V were considered as LEDs.

first step is to determine the input, output and power characteristics of the developed IP:

  • input voltage range - Vac(min) = 85V, Vac(max) = 265V;
  • output parameters - Vout = 3x3.9V ≈ 11.75V, Iout = 350mA;
  • output power - Pout \u003d VoutxIout \u003d 11.75 Vx0.35 A ≈ 4.1 W
  • input power - Pin = Pout / h, where h is the estimated efficiency = 78%

Pin=4.1W/0.78=5.25W

  • DC input voltage range

Vdc(min) = Vdc(min) x 1.41 = 85 x 1.41 = 120V (dc)

Vdc(max) = Vdc(max) x 1.41 = 265 x 1.41 = 375V (dc)

  • average input current - Iin(avg) = Pin / Vdc(min) ≈ 5.25/120 ≈ 44mA
  • peak input current - Ipeak = 5xIin (avg) ≈ 220mA.

The first input link is a fuse and an EMI filter, and their selection is second step when designing IP. The fuse must be selected based on the breaking current value, and in the presented design, a fuse with a breaking current of 2 A is chosen. We will not delve into the input filter calculation procedure, but only note that the degree of suppression of common mode and differential noise is highly dependent on the layout of the printed circuit board , as well as the proximity of the filter to the power connector.

third step is the calculation of parameters and selection of the diode bridge. The key parameters here are:

  • permissible reverse (blocking) diode voltage - VR ≥ Vdc (max) = 375V;
  • forward current of the diode - IF ≥ 1.5xIin (avg) = 1.5x0.044 = 66mA;
  • allowable overload current ( surge current), which can reach five times the average current:

IFSM ≥ 5 x IF = 5 x 0.066 = 330 mA.

fourth step is the calculation of the parameters of the input capacitor installed at the output of the diode bridge. The size of the input capacitor is determined by the peak value of the rectified input voltage and the specified level of input ripple. Larger input capacitor provides more low values ripples, but increases the starting current of the IP. In general, the capacitance of a capacitor is determined by the following formula:

Cin = Pin/, where

fac is the frequency of the AC mains (60 Hz for the design in question);

DV- allowable level ripples (20% of Vdc(min) in our case).

Cin \u003d 5.25 / \u003d 17 uF.

In our case, we choose a 33uF aluminum electrolytic capacitor.

Fifth and main step is the calculation of the winding product - a pulse transformer. The calculation of the transformer is the most complex, important and "thin" part of the entire calculation of the power supply. The main functions of a transformer in a flyback converter are the accumulation of energy when the control key is closed and the current flows through its primary winding, and then its transfer to the secondary winding when the power to the primary part of the circuit is turned off.

Taking into account the input and output characteristics of the MT, calculated at the first step, as well as the requirements for ensuring the operation of the MT in the continuous current mode of the transformer, the maximum value of the duty cycle ( duty cycle) is equal to 48%. We will carry out all calculations of the transformer based on this value of the fill factor. Let us summarize the calculated and specified values ​​of the key parameters:

  • controller operating frequency fop = 100 kHz
  • fill factor dmax= 48%
  • minimum input voltage Vin(min) = Vdc(min) - 20% = 96V
  • output power Pout= 4.1W
  • estimated value of efficiency h = 78%
  • peak input current Ipeak= 220mA

Now we can calculate the inductance primary winding transformer:

Lpri = Vin(min) x dmax/(Ipeak x fop) = 2.09 mH

The ratio of the number of turns of the windings is determined by the equation:

Npri / Nsec \u003d Vdc (min) x dmax / (Vout + V F x (1 - dmax)) ≈ 7

It remains for us to check the ability of the transformer to “pump” the required output power through itself. You can do this with the following equation:

Pin(core) = Lpri x I 2 peak x fop/2 ≥ Pout

Pin(core) = 2.09 mH x 0.22 2 x 100 kHz/2 = 5.05 W ≥ 4.1 W.

It follows from the results that our transformer can pump the required power.

It can be seen that here we have given a far from complete calculation of the parameters of the transformer, but only determined its inductive characteristics and showed the sufficient power of the chosen solution. Many works have been written on the calculation of transformers, and the reader can find the calculation methods of interest to him, for example, in or. The coverage of these techniques is beyond the scope of this article.

The electrical circuit of the IP, corresponding to the calculations performed, is shown in Figure 5.

Rice. 5.

Now it's time to get acquainted with the features of the above solution, the calculation of which was not given above, but which have great importance for the functioning of our IP and understanding the implementation features of the protective mechanisms implemented by the NCP1014 controller.

Features of the operation of the scheme that implements IP

The secondary part of the circuit consists of two main blocks - a block for transferring current to the load and a power supply for the feedback circuit.

When the control key is closed (direct mode), the feedback circuit power supply operates, implemented on diode D6, current-setting resistor R3, capacitor C5 and zener diode D7, which, together with diode D8, sets the required supply voltage (5.1 V) of optocoupler and shunt regulator IC3 .

During the reverse run, the energy stored in the transformer is transferred to the load through diode D10. At the same time, the storage capacitor C6 is charged, which smoothes the output ripples and provides a constant supply voltage to the load. The load current is set by resistor R6 and controlled by shunt regulator IC3.

IP has protection against load disconnection and load short circuit. Short circuit protection is provided by the TLV431 shunt regulator, the main role of which is the OS circuit regulator. A short circuit occurs under the condition of a short breakdown of all load LEDs (in the event of failure of one or two LEDs, their functions are taken over by parallel zener diodes D11 ... D13). The value of the resistor R6 is selected so that at the operating load current (350 mA in our case) the voltage drop across it is less than 1.25 V. controller NCP1014 reduce the output voltage.

The load shutdown protection mechanism is based on the inclusion of a Zener diode D9 in parallel with the load. Under conditions of opening of the load circuit and, as a result, an increase in the output voltage of the IP to 47 V, the zener diode D9 opens. This turns on the optocoupler and forces the controller to reduce the output voltage.

Interested in getting to know NCP1014 in person? - No problem!

For those who, before starting to develop their own IP based on NCP1014, want to make sure that this is a really simple, reliable and effective solution, ONSemiconductor produces several types of evaluation boards (see Table 1, Fig. 6; available for order through COMPEL) .

Table 1. Overview of evaluation boards

Order code Name Short description
NCP1014LEDGTGEVB 8W LED driver with 0.8 power factor The board is designed to demonstrate the possibility of building an LED driver with a power factor > 0.7 (Energy Star standard) without using an additional PFC chip. The output power (8 W) makes this solution ideal for powering structures like the Cree XLAMP MC-E containing four LEDs in series in one package.
NCP1014STBUCKGEVB Non-inverting buck converter The board is proof of the claim that the NCP1014 controller is enough to build a low price range power supply for harsh environments.

Rice. 6.

In addition, there are several more examples of the finished design of various IPs, in addition to those discussed in the article. This and a 5W AC/DC adapter for cell phones, and another IP option for LED, as well as a large number of articles on the use of the NCP1014 controller, which you can find on the official website of ONSemiconductor - http://www.onsemi.com/.

COMPEL is the official distributor of ONSemiconductor and therefore on our website you can always find information on the availability and cost of chips manufactured by ONS, as well as order prototypes, including the NCP1014.

Conclusion

The use of the NCP1014 controller manufactured by ONS makes it possible to develop high-performance AC/DC converters for supplying loads with a stabilized current. Proper use of the key features of the controller makes it possible to ensure the safety of the final power supply in the conditions of an open or short circuit of the load with a minimum number of additional electronic components.

Literature

1. Konstantin Staroverov "The use of NCP101X / 102X controllers in the development of medium-power network power supplies", Electronics News magazine, No. 3, 2010, ss. 7-10.

4. Mac Raymond. Pulse sources nutrition. Theoretical foundations of design and guidance on practical application / Per. from English. Pryanichnikova S.V., M.: Dodeka-XXI Publishing House, 2008, - 272 p.: ill.

5. Vdovin S.S. Design of pulse transformers, L .: Energoatomizdat, 1991, - 208 p.: ill.

6. TND329-D. "5W Cellular Phone CCCV AC-DC Adepter"/ http://www.onsemi.com/pub_link/Collateral/TND329-D.PDF.

7. TND371-D. "Offline LED Driver Intended for ENERGY STAR"/ http://www.onsemi.com/pub_link/Collateral/TND371-D.PDF.

Receipt technical information, sample order, delivery - e-mail:

NCP4589 - LDO Regulator
with automatic energy saving

NCP4589 - new 300mA CMOS LDO regulator from ON Semiconductor. The NCP4589 switches to low current mode at low current load and automatically switches back to "fast" mode as soon as the output load exceeds 3 mA.

NCP4589 can be put into permanent mode fast work by forced mode selection (control by special input).

Key Features of NCP4589:

  • Operating range of input voltages: 1.4 ... 5.25V
  • Output voltage range: 0.8…4.0V (in 0.1V increments)
  • Input current in three modes:

      • Low Power Mode - 1.0µA at V OUT< 1,85 В

      Fast Mode - 55µA

      Power saving mode - 0.1 uA

  • Minimum voltage drop: 230mV at I OUT = 300mA, V OUT = 2.8V
  • High voltage ripple rejection: 70dB at 1kHz (in fast mode).

NCP4620 Wide Range LDO Regulator

NCP4620 - This is a CMOS LDO regulator for 150mA from ON Semiconductor with an input voltage range of 2.6 to 10 V. The device has a high output accuracy - about 1% - with a low temperature coefficient of ±80 ppm/°C.

The NCP4620 has overheat protection and an Enable input, and is available with a standard output and an Auto Discharge output.

Key Features of NCP4620:

  • Operating input voltage range from 2.6 to 10V (max. 12V)
  • Output fixed voltage range from 1.2 to 6.0V (100mV steps)
  • Direct minimum voltage drop - 165mV (at 100mA)
  • Power supply ripple suppression - 70dB
  • Chip power off when overheated up to 165°C

This article describes how to assemble a simple but effective LED brightness control based on PWM dimming () LED lighting.

LEDs (light emitting diodes) are very sensitive components. When the supply current or voltage exceeds allowable value may lead to their failure or significantly reduce the service life.

Usually, the current is limited using a resistor connected in series with the LED, or by a circuit current regulator (). Increasing the current on the LED increases its intensity, and reducing the current reduces it. One way to control the brightness of the glow is to use a variable resistor () to dynamically change the brightness.

But this is only applicable to a single LED, since even in one batch there may be diodes with different luminous intensity and this will affect the uneven glow of a group of LEDs.

Pulse width modulation. A much more efficient method of regulating the brightness of the glow by applying (PWM). With PWM, groups of LEDs are supplied with the recommended current, while at the same time dimming is possible by supplying power at a high frequency. Changing the period causes a change in brightness.

The duty cycle can be thought of as the ratio of the power on and off times supplied to the LED. For example, if we consider a cycle of one second and at the same time the LED will be 0.1 seconds off, and 0.9 seconds on, it turns out that the glow will be about 90% of the nominal value.

Description of PWM dimmer

The easiest way to achieve this high frequency switching is to use a IC, one of the most common and most versatile ICs ever made. The PWM controller circuit shown below is for use as a dimmer to power LEDs (12 volts) or a speed controller for a motor. direct current at 12 V.

In this circuit, the resistors to the LEDs need to be adjusted to provide a forward current of 25mA. As a result, the total current of the three lines of LEDs will be 75mA. The transistor must be rated for a current of at least 75 mA, but it is better to take it with a margin.

This dimmer circuit is dimmable from 5% to 95%, but by using germanium diodes instead of , the range can be extended from 1% to 99% of the nominal value.

LEDs are used in almost every technology around us. True, sometimes it becomes necessary to adjust their brightness (for example, in flashlights, or monitors). by the most easy way out in this situation, it seems to change the amount of current passed through the LED. But it's not. The LED is a rather sensitive component. Permanent change the amount of current can significantly reduce its life, or even break it. It should also be borne in mind that a limiting resistor cannot be used, since excess energy will accumulate in it. This is not allowed when using batteries. Another problem with this approach is that the color of the light will change.

There are two options:

  • PWM regulation
  • analog

These methods control the current flowing through the LED, but there are certain differences between them.
Analog regulation changes the level of current that passes through the LEDs. And PWM regulates the frequency of the current supply.

PWM regulation

The way out of this situation can be the use of pulse-width modulation (PWM). With this system, the LEDs receive the required current, and the brightness is regulated by applying power at a high frequency. That is, the frequency of the feed period changes the brightness of the LEDs.
The undoubted plus of the PWM system is the preservation of the productivity of the LED. The efficiency will be about 90%.

Types of PWM regulation

  • Two-wire. Often used in the lighting system of cars. The converter power supply must have a circuit that generates a PWM signal at the DC output.
  • shunt device. To make the on/off period of the converter use a shunt component that provides a path for the output current besides the LED.

Pulse parameters for PWM

The pulse repetition rate does not change, so there are no requirements for determining the brightness of light. In this case, only the width, or time, of the positive pulse changes.

Pulse frequency

Even taking into account the fact that there are no special claims to the frequency, there are boundary indicators. They are determined by the sensitivity of the human eye to flickering. For example, if in a movie the flickering of frames must be 24 frames per second, so that our eye perceives it as one moving image.
In order for the flickering of light to be perceived as uniform light, the frequency must be at least 200 Hz. There are no restrictions on the upper indicators, but there is no way below.

How a PWM controller works

To directly control the LEDs, a transistor key stage is used. Usually they use transistors that can store large amounts of power.
This is required when using LED strips or powerful LEDs.
For a small amount or low power, the use of bipolar transistors is quite sufficient. You can also connect LEDs directly to the chips.

PWM generators

In a PWM system, a microcontroller or a circuit consisting of circuits of a small degree of integration can be used as a master oscillator.
It is also possible to create a regulator from microcircuits that are designed for switching power supplies, or K561 logic microcircuits, or an NE565 integrated timer.
Craftsmen even use an operational amplifier for this purpose. For this, a generator is assembled on it, which can be adjusted.
One of the most used circuits is based on the 555 timer. In fact, this is a regular generator rectangular pulses. The frequency is controlled by capacitor C1. at the output of the capacitor should be high voltage(this is the same with the connection to the positive power supply). And it charges when there is a low voltage at the output. This moment gives rise to pulses of different widths.
Another popular circuit is PWM based on the UC3843 chip. in this case, the switching circuit has been changed towards simplification. In order to control the pulse width, a control voltage of positive polarity is used. In this case, the desired PWM pulse signal is obtained at the output.
The control voltage acts on the output in the following way: with a decrease, the latitude increases.

Why PWM?

  • The main advantage of this system is ease. The usage patterns are very simple and easy to implement.
  • The PWM control system gives a very wide range of brightness control. If we talk about monitors, then it is possible to use CCFL backlighting, but in this case the brightness can only be reduced by half, since CCFL backlighting is very demanding on the amount of current and voltage.
  • Using PWM, you can keep the current at a constant level, which means the LEDs will not suffer and the color temperature will not change.

Disadvantages of using PWM

  • Over time, image flicker can be quite noticeable, especially at low brightness or eye movement.
  • If the light is constantly bright (such as sunlight), the image may become blurry.