Network LED lamp with a power supply on a VIPer22A chip. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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Recently, incandescent lamps, which have a very limited resource of about 1000 hours, and gas-discharge lighting lamps with a resource of approximately 20 hours, are being vigorously replaced by LED counterparts that can operate without replacement for much longer - 000 hours. They have the highest efficiency among artificial light sources for converting electrical energy into light, which forces the governments of many countries, including Russia, to more vigorously introduce energy-saving technologies in lighting technology. This is also facilitated by the steady decline in the cost of super-bright LEDs due to competition from their global manufacturers.

Unfortunately, most household LED lamps use the simplest mains power supplies with a ballast capacitor. And this is despite the fact that the well-known shortcomings of the latter (current surge when turned on, a narrow range of mains voltage corresponding to the permissible current limits through the LEDs, as well as the possibility of damage during breaks in the load) lead to premature failure of the fixtures. This means that such a circuitry solution, in principle, cannot ensure the effective long-term operation of LED light sources with an estimated resource of 100 hours.

Fig. 1

The proposed design of a simple small-sized network SMPS for an LED lamp (Fig. 1) is free from such shortcomings and, despite the high reliability of operation, is very cheap (about 50 rubles without LEDs). The use of computer-aided design tools for this device allows the radio amateur to independently flexibly vary the range and number of connected LEDs.

The operation of such a pulsed step-down voltage stabilizer and the physical principles of its operation are described in [1] (Fig. 1, c and Fig. 2,6, 17). Therefore, let us consider in more detail the sequence of designing a network converter for powering 1 ultra-bright LEDs used in the described device (Fig. 1). Among them, EL8- EL5 are standard 503mm LC1TWN15-9G LEDs and EL11-EL5060 are ARL-3WYC chip LEDs, 6pcs each. in a rectangular PLCC5 package with dimensions of 5x40 mm with a permissible forward current of up to 3,2 mA and a forward voltage drop of approximately 15 V per diode. This choice of LEDs in the author's copy is due to the need to illuminate the computer keyboard. The first LEDs have a small radiation angle - 120° at half power, the second - a large one - XNUMX°. As a result, there will be no sharp boundaries in the total light spot, and the illumination in the center is greater than at the periphery. The color shade of such a light source is between cold and warm white, which is due to the parameters of the LEDs used.

For design reasons, LEDs of the same type are connected in series, and the LEDs shown in Fig. 1 two circuits (of 8 and 9 LEDs, respectively), which are connected in parallel through current-limiting resistors R2 and R3. The output voltage of the converter for both circuits is 32 V at a load current of 40 mA.

To design the converter, the program Non-Isolated VIPer Design Software v.2.3 (NIVDS) was used, which is described in the article [2]. The mains voltage interval is left selected by the program by default 88 ... 264 V. A SHI controller is used - a VIPer22A chip with a conversion frequency of 60 kHz, discontinuous conversion mode (DCM - Discontinuous Current Mode), output voltage - 32 V at a current of 40 mA. The inductance of the storage inductor L1, calculated by the program, was 2,2 mH. Other parameters of the converter: efficiency - 74%, maximum current amplitude of the switching transistor of the DA1 microcircuit - 169 mA, its maximum temperature - 47 ° C, effective value of the consumed current - 17 mA at a maximum mains voltage of 264 V.
Inductor L1 - modified high-frequency DM-0,1 500 μH. To increase its inductance to 2,2 mH, 2 layers of 100 turns of PEV-2 wire with a diameter of 0,12 mm are added to the existing winding, without changing the winding direction. The insulation between the added layers, as well as the overall coating of the inductor, is performed with adhesive tape (adhesive tape). The bending of the inductor leads for mounting on a printed circuit board is carried out no closer than 5 mm from the ferrite case, otherwise the factory winding leads will be damaged. Instead of the modified choke DM-0,1, inductors KIG-0,2-2200 or SDR1006-2200 can be used.

Fig. 2

A drawing of the printed circuit board of the converter, made of one-sided foil fiberglass with a thickness of 1 ... 1,2 mm, is shown in fig. 2, and its appearance is shown in Fig. 3. Capacitor C1 is soldered with a gap of 7 ... 8 mm to the board, since it must be tilted to the center of the board so that it fits in the used base from a burned-out energy-saving lamp.

Fig. 3

Imported oxide capacitors with a maximum operating temperature of 105 °C can be used in the converter. Capacitors C2 and C5 - film or ceramic with a rated voltage of at least 50 V. Fusible jumper FU1 - wire from a fuse with a rated current of 1 A. The slot protects the board when FU1 burns out. But the slot is not needed if the jumper is replaced with a fuse-link in a ceramic case (from the VP1-1, VP1-2 series) or a safety resistor P1-25 (or a similar imported resistance 8 ... 10 Ohm). In the case of using a safety resistor, the resistance of the resistor R1 is reduced to 10 ... 12 ohms.

Fig. 4

The R2R3EL1 - EL11 LED load is mounted on another printed circuit board made of double-sided foil fiberglass with a thickness of 0,5 ... 1 mm (Fig. 4). The polygonal foil section in the center of the board is designed to remove heat from the EL9-EL11 surface mount LEDs. Current-limiting resistors R2 and R3 - RN1-12, size 1206. Two boards are connected by soldering in the corresponding contact pads of three pieces of copper wire with a diameter of 0,7 mm and a length of approximately 7 mm, on which, as restrictive axle boxes, pieces of hollow plastic rods from ball bearings are put on. pens. Two wires supply power to the board with LEDs, and the third provides the necessary structural rigidity. When connected, the sides that are free from elements on both boards are adjacent. Short pieces of wire are inserted into the holes of the contact pads marked with asterisks and soldered on both sides.

First, using LATR, it is desirable to make sure that the output voltage of 32 V is stable throughout the entire range of mains voltage changes (88 ... 264 V), while resistors with a total resistance of 800 Ohms are connected instead of LEDs. R2 temporarily solder trimmers with a resistance of 3 ohms. When measuring, you should beware of electric shock, since all elements of the device are galvanically connected to the mains supply. All changes are made only in the disabled state. Trimmer resistors are adjusted with a dielectric screwdriver. The current through each LED circuit is controlled with a milliammeter. Although the LEDs used are capable of a direct current of up to 150 mA with a corresponding increase in brightness, in order to achieve the declared durability of the LEDs, the current is set to 40 mA by adjusting the resistors. Approximately 20 minutes after switching on, the thermal regime of the LEDs stabilizes, therefore, additional current adjustment is necessary. With one milliammeter, the current in each LED circuit is regulated in turn. Finally, the tuning resistors are replaced by the constants of the found resistance.

Fig. 5

Using the Waveforms tool, the NIVDS program allows you to simulate the PWM controller modes. On fig. Figure 5 shows a diagram of the pulsed current in the controller at a mains voltage of 220 V, which practically coincided with the results of control measurements. The interval O ... 1,5 μs corresponds to the open state of the switching transistor of the DA1 microcircuit (forward operation of the converter). The blue color shows the graph of the current in the storage choke during the reverse run of the converter. The interval 1,5 ... 13 µs corresponds to the stage of transferring the energy accumulated by the throttle during the forward stroke to the load. An interval of 13...16,6 µs is the so-called dead time in the operation of the converter, when free damped voltage and current oscillations occur in the output circuit. More clearly, these fluctuations are illustrated by the taken diagram of the voltage at the source of the transistor relative to the common power wire (Fig. 6), where it is clearly seen that damped voltage fluctuations occur relative to the level of 32 V, corresponding to the output voltage of the converter. The C4C5 output filter reduces the output voltage ripple to 300 mV.

Fig. 6

As can be seen from fig. 5 and 6, the peak current of the switching transistor of the microcircuit (169 mA) is several times less than the maximum allowable value of 700 mA, the drain voltage of this transistor (300 V) is also less than the maximum allowable 730 V. This ensures the operation of the converter with a large electrical safety margin, which, along with with thermal protection built into the microcircuit, as well as protection against short circuits and breaks in the load, guarantees many years of reliable operation of the described device.

The appearance of the LED lamp is shown in fig. 7. It uses a reflector from a faulty flashlight.

Literature

1. Kosenko S. Features of the operation of inductive elements in single-cycle converters. - Radio. 2005. No. 7. p. 30-32.
2. Kosenko S. Computer-aided design of small-sized SMPS on VIPer chips - Radio, 2008, No. 5, p. 32. 33.

Author: S. Kosenko, Voronezh; Publication: radioradar.net

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