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 provide the entire range of functional requirements for modern power supplies.
Rice. 1.
Series controllers NCP101X were discussed in detail in an article by Konstantin Staroverov in issue 3 of the magazine for 2010, therefore, in the article we will limit ourselves to considering only the key features of the NCP1014 microcircuit, and will focus on considering the features of the calculation and operating mechanism of the IP presented in the reference design.
The NCP1014 controller is available in three types of packages - SOT-223, PDIP-7 and PDIP-7 GULLWING (see Fig. 2) with the pinout arrangement shown in Fig. 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 the NCP1014 controller in flyback ( Flyback) converter is shown in Figure 4.
Rice. 4.
Let's consider the method of step-by-step calculation of a flyback converter based on NCP1014 using the example of a reference design of a power supply with an output power of up to 5 W to power a system of three series-connected LEDs. One-watt white LEDs with a normalization current of 350 mA and a voltage drop of 3.9 V are considered as LEDs.
The first step is to determine the input, output and power characteristics of the developed IP:
Pin=4.1W/0.78=5.25W
Vdc(min) = Vdc(min) x 1.41 = 85 x 1.41 = 120 V (dc)
Vdc(max) = Vdc(max) x 1.41 = 265 x 1.41 = 375 V (dc)
The first input link is the fuse and 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 selected. We will not delve into the procedure for calculating the input filter, but only note that the degree of suppression of common-mode and differential noise largely depends on the topology of the printed circuit board , as well as the proximity of the filter to the power connector.
The third step is the calculation of parameters and selection of a diode bridge. The key parameters here are:
IFSM ≥ 5 x IF = 5 x 0.066 = 330 mA.
The fourth step is to calculate 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. A larger input capacitor provides lower ripple values, but increases the inrush current of the power supply. 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 considered);
DV is the permissible ripple level (20% of Vdc(min) in our case).
Cin = 5.25/ = 17 µF.
In our case, we choose an aluminum electrolytic capacitor with a capacity of 33 μF.
The fifth and main step is the calculation of a winding product - a pulse transformer. The calculation of the transformer is the most complex, important and “subtle” part of the entire calculation of the power source. The main functions of the transformer in a flyback converter are the accumulation of energy when the control switch is closed and current flows through its primary winding, and then its transmission 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 power supply calculated in the first step, as well as the requirements for ensuring the operation of the power supply in the transformer continuous current mode, the maximum value of the fill factor ( duty cycle) is equal to 48%. We will carry out all calculations of the transformer based on this fill factor value. Let us summarize the calculated and specified values of the key parameters:
Now we can calculate the inductance of the primary winding of the transformer:
Lpri = Vin(min) x dmax/(Ipeak x fop) = 2.09 mH
The ratio of the number of turns of windings is determined by the equation:
Npri/Nsec = Vdc(min) x dmax/(Vout + V F x (1 - dmax)) ≈ 7
All we have to do is check the ability of the transformer to “pump” the required output power through itself. This can be done using 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.
From the results it follows that our transformer can pump the required power.
It can be noted that here we have not given a complete calculation of the parameters of the transformer, but have only determined its inductive characteristics and shown the sufficient power of the chosen solution. Many works have been written on the calculation of transformers, and the reader can find calculation methods of interest, for example, in or. Coverage of these techniques is beyond the scope of this article.
The electrical circuit of the power supply, corresponding to the calculations performed, is presented 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 are of great importance for the functioning of our IP and understanding the features of the implementation of the protective mechanisms implemented by the NCP1014 controller.
The secondary part of the circuit consists of two main blocks - a unit for transmitting current to the load and a power supply unit for the feedback circuit.
When the control switch is closed (direct mode), the power supply circuit of the feedback circuit 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 the optocoupler and shunt regulator IC3 .
During reverse stroke, the energy stored in the transformer is transferred to the load through diode D10. At the same time, storage capacitor C6 is charged, which smoothes out 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.
The 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 regulator of the OS circuit. A short circuit occurs under the condition of a short breakdown of all load LEDs (if one or two LEDs fail, their functions are taken over by parallel zener diodes D11...D13). The value of resistor R6 is selected so that at an operating load current (350 mA in our case), the voltage drop across it is less than 1.25 V. When a short circuit occurs, the current through R6 increases sharply, which leads to the opening of the shunt IC3 and the activation of the optocoupler IC2 and forces controller NCP1014 reduce the output voltage.
The protection mechanism against load disconnection is based on connecting the zener diode D9 in parallel with the load. When the load circuit opens and, as a consequence, the output voltage of the power supply increases to 47 V, the zener diode D9 opens. This turns on the optocoupler and forces the controller to reduce the output voltage.
For those who, before starting to develop their own IP based on NCP1014, want to make sure that this is a truly simple, reliable and effective solution, ONSemiconductor produces several types of evaluation boards (see Table 1, Fig. 6; available for order through COMPEL) .
Table 1. Review 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 the use of an additional PFC chip. The 8 W output power makes this solution ideal for powering structures like the Cree XLAMP MC-E, which contain four LEDs in series in one package. |
| NCP1014STBUCGEVB | Non-inverting buck converter | The board is proof of the statement that the NCP1014 controller is sufficient to build low-price power supplies for harsh operating conditions. |
Rice. 6.
In addition, there are several more examples of ready-made designs of various IPs, in addition to those discussed in the article. This is a 5 W 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 the ONSemiconductor company - http://www.onsemi.com/.
The COMPEL company is the official distributor of ONSemiconductor and therefore on our website you can always find information about the availability and cost of chips produced by ONS, and also order prototypes, including NCP1014.
Using the NCP1014 controller, manufactured by ONS, allows you to develop highly efficient AC/DC converters to supply loads with stabilized current. Proper use of the key capabilities of the controller allows you to ensure the safe operation of the final power supply in conditions of open or short-circuit of the load with a minimum number of additional electronic components.
1. Konstantin Staroverov “Use of NCP101X/102X controllers in the development of medium-power network power supplies,” Electronics News magazine, No. 3, 2010, pp. 7-10.
4. Mack Raymond. Switching power supplies. Theoretical foundations of design and guidance for practical application / Transl. from English Pryanichnikova S.V., M.: Publishing house "Dodeka-XXI", 2008, - 272 pp.: ill.
5. Vdovin S.S. Design of pulse transformers, L.: Energoatomizdat, 1991, - 208 pp.: 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.
Obtaining technical information, ordering samples, delivery - e-mail:
NCP4589 - new 300 mA CMOS LDO regulator from ON Semiconductor. The NCP4589 switches to low consumption mode at low current loads and automatically switches back to "fast" mode once the output load exceeds 3 mA.
The NCP4589 can be put into permanent fast mode by forcing mode selection (control via a special input).
Main characteristics of NCP4589:
Low Consumption Mode - 1.0 µA at V OUT< 1,85 В
Fast mode - 55 µA
Power saving mode - 0.1 µA
NCP4620 - This is a CMOS LDO regulator for a current of 150 mA from ON Semiconductor with an input voltage range from 2.6 to 10 V. The device has 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 in standard and Auto Discharge versions.
Main characteristics of NCP4620:
This article describes how to assemble a simple but effective LED brightness control based on PWM brightness control () of LEDs.
LEDs (light emitting diodes) are very sensitive components. If the supply current or voltage exceeds the permissible value, it can lead to their failure or significantly reduce their service life.
Typically, the current is limited using a resistor connected in series to the LED, or by a circuit current regulator (). Increasing the current to the LED increases its glow intensity, and decreasing the current reduces it. One way to regulate the brightness of the glow is to use a variable resistor () to dynamically change the brightness.
But this only applies to a single LED, since even in one batch there may be diodes with different luminescence intensity and this will affect the uneven glow of a group of LEDs.
Pulse width modulation. A much more effective method is to regulate the brightness of the glow by using (PWM). With PWM, groups of LEDs are supplied with the recommended current, and at the same time it becomes possible to dim the brightness by supplying power at a high frequency. Changing the period causes a change in brightness.
The duty cycle can be represented as the ratio of the time of turning on and off the power supplied to the LED. Let’s say, if we consider a cycle of one second and the LED will last 0.1 seconds when it’s off, and 0.9 seconds when it’s on, then it turns out that the glow will be about 90% of the nominal value.
The simplest way to achieve this high-frequency switching is with an IC, one of the most common and most versatile ICs ever created. The PWM controller circuit shown below is designed for use as a dimmer to power LEDs (12 volts) or a speed controller for a 12 volt DC motor.
In this circuit, the resistance of the resistors to the LEDs must be selected to provide a forward current of 25 mA. As a result, the total current of the three lines of LEDs will be 75mA. The transistor must be designed for a current of at least 75 mA, but it is better to take it with a reserve.
This dimmer circuit adjusts from 5% to 95%, but by using germanium diodes instead, the range can be extended from 1% to 99% of the nominal value.
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.
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 solved by purchasing a ready-made dimmer for adjusting LED strips or using 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
If you skip the details and explanations, the circuit for adjusting the brightness of the LEDs will appear in its simplest form. This control is different from the PWM method, which we will look at a little later.
So, an elementary regulator will include only four elements:
Both the resistor and the stabilizer can be purchased at any radio store. They are connected exactly as shown in the diagram. Differences may lie in the individual parameters of each element and in the method of connecting the stabilizer and resistor (with wires or soldering directly).
Having assembled such a circuit with your own hands in a few minutes, you can make sure that by changing the resistance, that is, by rotating the resistor knob, you will adjust the brightness of the lamp.
In an illustrative example, the battery is taken at 12 Volts, the resistor is 1 kOhm, and the stabilizer is used on the most common Lm317 microcircuit. The good thing about the circuit is that it helps us take our first steps in radio electronics. This is an analog way to control brightness. However, it is not suitable for devices that require finer adjustments.
Now let’s look at the question in a little more detail, find out why brightness adjustment is needed, and how you can control the brightness of LEDs differently.
In some devices, it is not possible to simply reduce the current value by increasing the resistance, since this may lead to a change in the white color to greenish. In addition, an increase in resistance leads to an undesirable increase in heat generation.
The way out of a seemingly difficult situation was PWM control (pulse width modulation). Current is supplied to the LED in pulses. Moreover, its value is either zero or nominal - the most optimal for glow. It turns out that the LED periodically lights up and then goes out. The longer the glow time, the brighter it seems to us that the lamp shines. The shorter the glow time, the dimmer the light bulb shines. This is the principle of PWM.
You can control bright LEDs and LED strips directly using powerful MOS transistors or, as they are also called, MOSFETs. If you need to control one or two low-power LED light bulbs, then ordinary bipolar transistors are used as keys or the LEDs are connected directly to the outputs of the microcircuit.
By rotating the rheostat knob R2, we will adjust the brightness of the LEDs. Here are LED strips (3 pcs.), which are connected to one power source.
Knowing the theory, you can assemble a PWM device circuit yourself, without resorting to ready-made stabilizers and dimmers. For example, such as is offered on the Internet.
NE555 is a pulse generator in which all timing characteristics are stable. IRFZ44N is the same powerful transistor capable of driving high power loads. The capacitors set the pulse frequency, and the load is connected to the “output” terminals.
Since the LED has low inertia, that is, it lights up and goes out very quickly, the PWM control method is optimal for it.
A regulator that is sold ready-made for LED lamps is called a dimmer. The frequency of the pulses created by them is high enough so that we do not feel flickering. Thanks to the PWM controller, smooth adjustment is possible, allowing you to achieve maximum brightness or dimming of the lamp.
By installing such a dimmer into the wall, you can use it like a regular switch. For exceptional convenience, the LED brightness control can be controlled by a radio remote control.
The ability of lamps based on LEDs to change their brightness opens up great opportunities for holding light shows and creating beautiful street lighting. And it becomes much more convenient to use a regular pocket flashlight if you can adjust the intensity of its glow.
