Led desk lamp circuit introduction makes home warm and more emotional

Any kind of lamps have circuits. The led lamp circuit should be familiar to everyone in life. Because everyone learned the circuit course in junior high school, many people still know more about the circuit diagram. So, how much do you know about the led lamp circuit? When we buy led desk lamps, we must have a detailed understanding of its circuit, do a detailed job, the following small series for everyone to introduce the led desk lamp circuit .

First, the working principle of led desk lamp

A high-efficiency solid-state light source based on a semiconductor PN junction that emits light with weak electrical energy. Under a certain forward bias voltage and injection current, the holes injected into the P region and the electrons injected into the N region diffuse into the active region. Photons are emitted by radiation recombination to convert electrical energy directly into light energy.

Led desk lamp working principle

The design idea of ​​the LED desk lamp scheme is to first convert the high-voltage AC power into a low-voltage DC constant current source to illuminate the LED light source. The most cost-effective way to step down and perform AC-DC conversion is the primary consideration in design. Today's portable electronic products use AC power AC-DC buck converters - Adapters are both affordable, ready-made, and Easy to use. The output voltage of the adapter is required to be stable at DC12V. The output current should be selected according to the power of the LED light source. Generally, a margin of 30% should be given. Take a 3×1W white LED light source as an example. The standard operating current of a 1W white LED should be It is 350mA, so the current required for the circuit connection of 3 LED light sources is also 350mA. Considering the extension of LED life and reducing the light decay, it can be designed to be 300mA~330mA, which will not obviously affect the brightness of LED illumination, so the output current of the adapter should be Choose 750mA ~ 1A.

Second, led desk lamp circuit

1, led desk lamp circuit - lighting process

When the normal light is off: C1 is charged to +B by +1 (+B is the lead battery voltage) through R1, R2, R3, and the light is not on standby. When using SW and then releasing, the positive pole of C1 is shorted to the b pole of Q1, and the negative pole of C1 is connected to the e pole of Q1. Since the voltage across C1 is +B and cannot be abrupt, Q1 is very high due to Ube1 voltage. It will quickly enter saturation state. After Q1 is saturated, its C pole potential is almost 0V. +B is added to the b pole of Q4 through the partial pressure of R1 and R2. Ube4 is positively biased, so Q4 is also rapidly saturated and turned on, making Q4 The C pole potential is almost +B.

Led desk lamp circuit

It produces two functions: one is to make the Zener diode ZD1 (regulation value is about 2.5V) reverse breakdown, D3 forward conduction, then the residual voltage is added to the b pole of Q1, so that Q1 maintains saturation, self-protection . Second, the +B voltage is applied to the b-pole of Q3 via the partial voltage of R6 and R5, so that Q3 is also saturated and turned on, so that the high-brightness LED has a current flowing and illuminates, and the electric lamp starts to illuminate. Q1 maintains saturation conduction due to self-protection. Its C-pole potential is almost 0V, and C1 is discharged through R3 and Uce1 to make the voltage across it 0V.

2, led desk lamp circuit - the closing process

If SW is pressed and released again in the illumination state, since the voltage across C1 is 0V, the be junction voltage of Q1 is turned off by 0V, and the c pole of Q1 is turned off to +B potential due to Q1. The b-pole of Q4 is also due to the partial voltage of R1 and R2 being +B potential, and the be-junction of Q4 is off due to 0V. The c-pole of Q4 loses +B voltage to turn off Q3, and the three LEDs are extinguished without current (lights are Close), at this time C1 is charged by +B through R1, R2, R3 to prepare for the next action.

3, led desk lamp circuit - when charging state

The DC power supply Vcc of the charger is connected to +B through D1 to charge the lead battery. At the same time, Vcc is added to the b pole of Q4 through D2, so that Q4 maintains the off state. At this time, even if SW is pressed, Q1 is turned on or off. Q4 is cut off, so Q3 is also cut off, and 3 LEDs have no current to pass through without being illuminated.

Led desk lamp

4, led desk lamp circuit - when the lead battery is fully charged

The measured +B voltage is 4.2V. In order to make Q1 maintain saturation conduction (self-protection) when in use. +B must be greater than Uce4+Uzd1+UD3+Ube1=0.2+2.5+0.6+0.6=3.9V; when the +B voltage drops below 3.9V in use. Not enough to make ZD1 reverse breakdown, so Q1 can not achieve self-protection. At this time, the phenomenon is that after the SW is pressed, the three LEDs are flashed or extinguished after a few minutes. Many people mistakenly believe that the lamp is broken. In fact, it should be charged at this time. Not a fault.

The above is the knowledge of the led desk lamp circuit shared by you, and I hope to help you. If you want to know more about led lamps , please continue to pay attention to the net. Get a quote for 10 seconds and get four sets of design solutions for free. You can also follow the whole process of decorating the housekeeper and take action!