This power-saving LED dimming table lamp source uses 1W high power and φ5mm low-power LED hybrid components. The dimming circuit also has a unique trigger dimming circuit. The structure is simple and an op amp is used. The actual illumination is no less than 25W incandescent lamp. It is energy-saving, reliable and has a long service life.
The circuit principle power supply is taken from the transformer T plus the bridge rectifier D1 ~ D4 to change the commercial power 220V into a DC 14V working power supply. The operational amplifier A1 and the regulator IC1 form a reference voltage for the operational amplifier A2 and the peripheral resistor R3-R6 to form a non-inverting input reference voltage of the flip-flop circuit, and the inverting input is sampled by the resistor R9, and compared with the non-inverting input to make the output The end pulse width is adjusted by the reference potentiometer RP, and is amplified by the driving transistor BG1 and the power transistor BG2 to illuminate the LED1~LEDl5 LED components, and the potentiometer RP can control the current level to complete the actual dimming function. Here, the freewheeling diode D5 and the energy storage inductor smooth the output current.
The component requirements T is the power transformer, and the commercially available specification is 8W9V. LED components LED1 ~ LED6 and LED10 ~ LED15 is φ5mm straw hat-shaped natural light color, 12 on each side, less than 6 paintings, a total of 24; LED7 ~ LED8 is 1W high power is also natural light color, has a heat sink, the market price Has been greatly reduced to 7 yuan, can be drawn. However, when assembled, three pieces are combined, and a suitable strip of aluminum is added to increase the heat dissipation effect. The op amps A1 and A2 are dual op amps LM358. If the LM324 is fully versatile, only two op amps are added. The IC1 regulator is TL31, the regulation voltage is 2.5V, and the remaining resistors and capacitors are conventional.
The inductor L1 is selected to have an outer diameter of φ15 mm and a high-frequency magnetic ring can be wound around 40T with a φ0.25 mm enameled wire. The current limiting resistor R9 has a power of 1W and a resistance value of 2.2Ω to 3.0Ω.
After the power is turned on, the DC voltage of 14V can be measured across the capacitor C1, and it is 10.5V at full load. The total current of the LED assembly is determined by R9. The appropriate value is selected to ensure that the working current flowing through LED7~LED9 is not less than 350mA. The working current of each side of φ5mm straw hat is not more than 20mA. It can be connected in series with LEDl-LED6 and LEDl0-LEDl5. A small 20Ω resistor to keep the operating current normal. The mains input should be equipped with a power switch, the specifications are optional.
Several dimming plates are simply assembled into the dimming lamp shown in Figure 1, and the potentiometer is adjusted, and the white LED changes brightly and darkly. According to personal preference, LEDs can be connected in parallel in multiple groups.
In Figure 1, there is a group that can be used as a night light, and multiple groups can be read in parallel. The resistance of R1 or R2 can be appropriately reduced to increase the brightness, but the dimming effect is not obvious at this time. The CZ socket can be inserted into the soldering iron to adjust the temperature. At this time, the temperature of the soldering iron can be roughly indicated according to the brightness change of the LED. CZ can also be inserted into the LED lamp shown in Figure 2. At this time, adjusting the potentiometer will make the circuit of Figure 2 become a dimming lamp.
Figure 2 is a small series of LED lights assembled with mail-ordered high-gloss white LED panels. The LED board is 146mm long and 16mm wide. Each board has 8 LEDs, 4 strings, and a 15V voltage regulator. Xiaobian uses a total of 72 plates of _ED to form an LED square array, 18 strings, and is powered by 12V. It can be used as a night light or a book to learn. It is a low-cost energy-saving dimming lamp.
12V LED lamp dimming circuit
Dimming lamp circuit made with CD4017
This design drive circuit uses a triode drive. A triode is a control element that is mainly used to control the magnitude of the current. Taking the common emitter connection as an example (signal from the base input, from the collector output, the emitter is grounded), when the base voltage UB has a slight change When the base current IB also has a small change, the collector current IC will have a large change under the control of the base current IB. The larger the base current IB, the larger the collector current IC. Conversely, the smaller the base current, the smaller the collector current, that is, the base current controls the change in collector current. However, the change in collector current is much larger than the change in the base current, which is the amplification of the triode. The ratio of the amount of change in IC to the amount of change in IB is called the amplification factor β of the triode (β = ΔIC / ΔIB, Δ represents the amount of change.), the amplification factor β of the triode is generally tens to hundreds of times.
When the triode amplifies the signal, it must first enter the conduction state, that is, to establish a suitable static working point, also called the establishment of the offset, otherwise the distortion will be amplified. Selecting a suitable magnification triode, driving the LED by amplifying the current, the three-stage tube amplification has the advantages of low cost, easy implementation, and easy control.
The LED driver circuit in the design is shown in Figure 8. In this design, 12 LED lights are used in series and parallel to simulate LED table lamps to achieve lighting effects. The driving transistor used is the SS8550, which is a PNP type triode.
Dimming implementation
The brightness of the LED is controlled by the current, and the brightness of the LED lamp is adjusted by controlling the current. Using formula 
(I is the amplitude of the current, and LI is the average current value of the output). It can be seen that by adjusting the different duty cycles of the PWM. 
It is possible to control the magnitude of the current.
In this design, the PWM wave is output through the pin P1.3 of the STC89C51 microcontroller. When the PWM wave is high, the transistor Q1 outputs a small current. When the PWM wave is low, Q1 outputs a large current. That is, when the PWM changes the duty ratio, the average current of the output changes, and the average luminance changes, thereby realizing the dimming of the LED lamp.
Simple led desk lamp dimming circuit diagram (6)
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