A simple BP2857D power supply for LED lights. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A simple BP2857D power supply for LED lights. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Continuing the topic of power supplies for LED lamps, the author offers a simple device on a specialized microcircuit. In a simplified version, without an input filter and a passive power factor corrector, the source contains only a little over two dozen elements.

In the July issue of the magazine for 2016, the design of a power supply for an office LED lamp [1] was published, which can conditionally be attributed to the older segment (premium class) of such devices due to its high technical parameters and complexity. In the September issue of the journal for 2016, an improved and simplified version of it was published [2], which, in terms of its characteristics and relative simplicity, can easily be attributed to the middle, more budgetary segment. In order to get a kind of line of such devices, it would be logical to assume that one more, very simple and inexpensive budget option is missing. Such a power supply for LED lamps is proposed in this article.

Today it is completely superfluous to talk about the popularity of LED lighting. I would just like to note that the rapid growth in production volumes and the variety of LEDs and lamps based on them, as well as power supplies for them, caused a corresponding reaction from manufacturers of specialized microcircuits. Like mushrooms after rain, families of inexpensive specialized microcircuits began to appear to build simple and cheap power supplies on their basis. An example is the BP2857D chip from the Chinese manufacturer BPS. It is designed to build a cheap small-sized step-down pulse converter without galvanic isolation with output current stabilization.

The BP2857D chip requires minimal "strapping", contains a built-in field effect transistor (MOSFET), plus it has protection functions from idle and load shorting. At the same time, its price at the time of this writing when buying through the ebay.com Internet service is only 30 ... 40 rubles.

Rice. 1. Power supply circuit based on BP2857D (click to enlarge)

The power supply circuit based on BP2857D is shown in fig. 1. If you wish, you can get a very simple and inexpensive source by removing the C1-C4L1L2RU1 noise suppression filter, the passive power factor corrector (the microcircuit does not have a built-in power factor correction function) VD5-VD7C6C7R1 and increasing the capacitance of the capacitor C5 to 33 uF.

The source collected according to the scheme of fig. 1, has the following specifications:

Input AC voltage, V.......165...265
Output current, mA.......350
Output current instability (dependence on input voltage), %, no more.......3
Output voltage interval, V .......60...110
Efficiency, %, not less.......93
Coefficient of pulsation of the light flux, % ....... 1
Power Factor (PF)......0,91

At the moment the mains voltage is applied, the field-effect transistor built into the DA1 chip is open. The current flows through the circuit: plus of the diode bridge (power factor corrector), drain of the field-effect transistor (pins 5 and 6 of the DA1 microcircuit), source (pin 8), current-measuring resistor R2-R4, inductor L3, load, minus diode bridge. At this time, the inductor accumulates energy, while the capacitor C10 is charged. When the field-effect transistor closes, the load will begin to feed on the energy stored in the capacitor C10, and the inductor L3 will maintain the current through the diode VD9, feeding the capacitor C10. Chip DA1 controls the voltage across the capacitor C10 through the divider R8R9C8. Pin 8 of the microcircuit is both the source of the field-effect transistor and the input of the current-measuring circuit. The voltage drop across the current sensor R2-R4 is used to control the microcircuit flowing through the field effect transistor and the current load.

The moments of opening and closing of the switching field-effect transistor depend on the voltage levels at pins 8 and 2 of the microcircuit. The microcircuit is started and powered through the divider R5-R7. The R10VD8 circuit connected to pin 4 of the microcircuit is additional power in operating mode. Three resistors R2-R4 connected in parallel allow you to set the output current with great accuracy. If desired, you can get by with one resistor with a power of 0,5 W. The operation of the microcircuit and its parameters are described in more detail in [3].

Simple power supply on BP2857D for LED lamps
Rice. 2. Appearance of the board of the assembled device

Simple power supply on BP2857D for LED lamps
Rice. 3. Appearance of the board of the assembled device

The power supply circuit board has been designed to fit into a low profile downlight. The height of the printed circuit board with all elements installed on it, determined by the height of the inductor L3, is 16 mm. The appearance of the board of the assembled device is shown in fig. 2 and fig. 3. The drawing of the board is shown in fig. 4, and the arrangement of elements - in fig. 5. Inductor L3 with an inductance of 0,9 mH is made on a standard small-sized magnetic core E16/8/5 (material N87 or similar) with a non-magnetic gap of 0,9 mm. Its winding contains 186 turns of wire with a diameter of 0,3 mm. The noise filter inductor L2 has an inductance of 30 mH. It is wound on a standard small-sized magnetic core E10 / 5,5 / 5, each winding contains 110 turns of wire with a diameter of 0,2 mm. You can use a suitable standard inductor from the switching power supply filter.

Simple power supply on BP2857D for LED lamps
Rice. 4. Board drawing

Simple power supply on BP2857D for LED lamps
Rice. 5. Location of elements on the board

Dumbbell choke L1 - standard, suitable size, with an inductance of 3 mH and a permissible current of at least 150 mA. Instead of SMA4007 (VD1-VD4) diodes, you can use any small-sized surface-mount rectifiers with a permissible reverse voltage of at least 400 V. Power corrector diodes VD5-VD7, as well as VD8 - small-sized fast-acting FR107FH in surface-mounted version or similar. Diode VD9 - ultra-fast HS1K or similar. For an output current of 350 mA, the resistors of the current sense shunt R2-R4 should have a resistance of 1,6 ohms each.

A properly assembled device starts working immediately, however, for safety reasons, the first start is best done through an incandescent lamp connected in series.

Literature

Lazarev V. UCC28810 power supply for 18...48 W LED lamp. - Radio, 2016, No. 7, p. 18-23.
Lazarev V. Improved power supply on UCC28810 for LED lamps. - Radio, 2016, No. 9, p. 32-34.
BP2857D Non-isolated Buck Offline LED Driver. - URL: bpsemi.com/en/Data/BP2857D_EN_DS_Rev. 1.0.pdf

Author: V. Lazarev

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