Powerful LED lamp. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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When developing the proposed device, the task was to create an LED lamp that consumes less than 220 W from a 10 V network, with a higher luminous brightness compared to a 100 W incandescent lamp. The HVLED805 microcircuit [1] was chosen as the basis for the voltage converter of the LED power supply. It allows you to stabilize the LED load current without the use of optocouplers, voltage and current sensors in the load circuit, as a result of which the power supply is greatly simplified. The design was facilitated by the program for automated calculation of the transducer, which is described in detail in the article [2].

Rice. 1 (click to enlarge)

The stable current through the applied SPHCWTHDD803WHROJC LED at 9 W of power consumption should be equal to 0,51 A (see Table 2 in [3]), which is approximately 10% more than the maximum current calculated by the program of 0,45 A. After increasing the standard size proposed by the program magnetic circuit from EE13 to EE16, it is necessary to check that the converter can provide the required LED mode. To verify this will allow the control of the parameters of the manufactured device. To correct the converter mode, it will be necessary to recalculate the resistance of the resistors in the divider of the impulse voltage supplied to the DMG output of the microcircuit, as well as the current sensor. For this, it is necessary to use the calculation formulas from the reference sheet [1] or the technical description of the microcircuit [4]. You can also use the spreadsheet Iamp805.xls attached to the article, developed by the author. Such a corrected result of designing a converter for powering the SPHCWTHDD803WHROJC LED with a stabilized current of 0,51 A is illustrated by the circuit diagram shown in fig. 1.

Thermistor RK1 reduces the current pulse at the time of connection to the network. The diode bridge VD1 rectifies the mains voltage. Capacitors C1 and C2 smooth out the ripple of the rectified voltage. These capacitors and inductor L1 form a filter that suppresses impulse noise from the supply network, and also prevents high-frequency ripples created by the converter from penetrating into it. The pulse transformer T1 has one primary winding (I) and two secondary windings (II and III). The primary (I) is shunted by a circuit of anti-series connected protective diode VD2 and a conventional VD3, which limits the voltage on this winding and thereby protects the output powerful field-effect transistor of the HVLED805 (DA1) chip from breakdown. The source of this transistor (pins 1 and 2) is connected to the common wire of the microcircuit (pin 4) through resistor R4, which acts as a current sensor.

Winding II of the transformer T1 is used to power the DA1 chip. The voltage rectified by the VD4 diode and smoothed by the capacitor C6 is applied to the VCC power pin. Resistor R5 limits the amplitude of the current pulses through the diode VD4. Also, the signal from winding II through a resistor divider R1R2 is fed to pin 6 of the DA1 chip. By processing this signal, the microcircuit can control the voltage on the EL1 LED and the current flowing through it, as described in the article [1].

Winding III is used to power the EL1 LED. The voltage from this winding rectifies the VD5 diode, high-frequency ripples are suppressed by capacitor C8, and low-frequency ones by C9. Resistor R6 - the minimum load of the power supply. The frequency compensation circuit R3C3C4 prevents parasitic generation of the converter at frequencies above the main one. Capacitor C5, connected to pin 5 of the DA1 chip, is used to stabilize the current through the EL1 LED, which is also described in the article [1].

Fig. 2

The converter is mounted on a printed circuit board (Fig. 2) made of one-sided foil-coated fiberglass 1,2 mm thick. The board is designed for surface-mounted elements of size 0805 and through-hole elements. It is fixed in the lamp with three screws on insulating posts. When designing the board, it was taken into account that the printed conductor connected to the drain terminal of a powerful switching transistor in the microcircuit (DRAIN) serves as a heat sink for it.

The pulse transformer T1 is wound on the EE16/8/5 magnetic core. Winding I contains 120 turns of PETTL-2 wire with a diameter of 0,21 mm (winding inductance - 2 mH), winding II - 17 turns of PETV-2 with a diameter of 0,1 mm, winding III - 20 turns of litz wire 10x0,12 mm. When winding on a frame using interwinding and interlayer insulation, the first winding section I of 60 turns is placed in series, then winding III and the second winding section I of 60 turns, the last - winding II. Winding sections I are connected at the free output of the transformer, this output is not soldered to the board. To obtain the required inductance of the primary winding, it was necessary to shorten the central core with a diamond file to form a non-magnetic gap of 0,17 mm.

The inductor L1 with an inductance of 0,47 ... 1 mH was taken from a faulty energy-saving lamp. Diodes VD2 and VD3 are connected at a common point by surface mounting. Resistor R4 (current sensor) is made up of two parallel-connected resistors R4.1 and R4.2 of 2,2 ohms, 0,125 watts.

Fig. 3

Structurally, the LED lamp is made on the basis of a faulty 26 W compact fluorescent lamp, from which the electronic ballast and spiral bulb have been removed. In the remaining plastic case, a 25 mm wide window was cut out on the side of the heat sink mounting, where the converter board is placed so that the printed conductors and surface-mounted elements face the heat sink, as shown in Fig. 3. The edges of the printed circuit board, 24 mm wide, are glued with nitro glue at the point of contact with the lamp body. A heat sink with a diameter of 60 mm and a height of 43 mm is screwed to the case, to which the EL8 LED is pressed with four M2 screws using heat-conducting paste KPT-1. The effective cooling surface of the heat sink is about 300 cm2.

During the tests, the mode of the EL1 LED was checked: the direct voltage on it is 18 V at a current of 0,52 A. This mode remained stable when the supply voltage was changed using a laboratory autotransformer within 176 ... 254 V. If necessary, the LED current can be adjusted by selecting resistors R4.1 and R4.2, forming the current sensor R4.

When first turned on, the peak value and current shape of the switching transistor were controlled by the voltage drop across the current sensor - resistor R4. The shape of the current pulses is sawtooth. The measured peak value of 0,28 A is less than the maximum value of 0,303 A simulated by the program. As a result, the absence of saturation of the magnetic circuit was confirmed.

The operation of the converter in the short circuit and load break modes was checked. The results of these tests coincided with the calculations according to the program. With a load current of 0,2 A, the converter operates in the mode of skipping one valley at a frequency of 132 kHz. When the load current increases to 0,4 A, switching occurs at the first cavity, the frequency increases to 140 kHz. With a further increase in the load current to 0,53 A, the frequency decreases to 105 kHz.

In the load closing mode, the converter generates short pulses with a frequency of 13,5 kHz with a duration slightly less than 2 μs. Without a load (LED), the converter maintains a voltage of about 20 V at the output, generating bursts of pulses with a frequency of 2,17 kHz.

The measured efficiency of the converter is 82% at a mains voltage of 220 V. The measurements showed that the temperature of the microcircuit in a steady thermal regime does not exceed 54 °C. In the LED lamp (Fig. 3), the temperature of the LED housing in the steady state does not exceed 62 °C. Taking into account the thermal resistance of the crystal-case transition 2,24 °C/W, it is possible to estimate the temperature of the crystal 62+9-2,24=82 °C, which is much less than the maximum allowable value of 150 °C [3] and is quite acceptable from the point of view of ensuring durability of the device.

Fig. 4

To compare an LED lamp with a 100 W incandescent lamp, the light of both lamps from the same distance is directed to a plate of milky plexiglass. As seen in fig. 4, the light spot from the LED lamp, located on the right, is noticeably brighter than from the incandescent lamp.

Literature

1. Kosenko S. HVLED805 chip for switching network power supplies - Radio, 2012, No. 11, p. 40-42.
2. Kosenko S. Calculation of SMPS on microcircuits of the VlPer-plus series. - Radio. 2012, no. 12, p. 19, 20.
3. SPECIFICATION MODEL: SPHCWTHDD803 WHROJC. - simpex.ch/fileadmin/bereiche/systemkomponen ten/News/24082011/SPHCWTHDD803WHR0JC.pdf.
4. Off-line LED driver with piimary-sensing HVLED805. - st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00287280.pdf.

Author: S. Kosenko

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