LED driver switch power circuit and components illustrated

2019-12-26 17:46:03

 

I. introduction to LED drive switching power supply

 

The core of the LED driver in the LED lamp, the quality directly affects whether the LED works normally. LED driver also belongs to the switching power supply. The typical circuit of LED driver switching power supply is single-ended flyback type. The so-called single-terminal means that the core of the high-frequency converter (7) only works on one side of the hysteresis loop. The so-called flyback means that when the switch tube (6) is switched on, the induction voltage of the primary winding of the high-frequency transformer (7) is positive and negative, and the secondary rectifier diode (10) is in cut-off state, storing energy in the primary winding. When the switch tube (6) is cut off, the energy stored in the primary winding of the transformer (7) is filtered through the secondary winding and the rectifier tube (10) and the electrolytic capacitor (11) to output dc voltage to the LED lamp.

 

The output power of single-ended flyback LED driver switching power supply is generally 0.5-100w, which can output different voltages at the same time, and has a good voltage adjustment rate.

 

The main circuit of switching power supply for LED driver is composed of safety tube pressure sensitive resistor, electromagnetic interference LC filter (also known as EMI), rectifier filter circuit, pulse width modulation PWM controller circuit, output rectifier filter circuit, output sampling feedback constant current circuit and so on.

LED driver switching power supply circuit component surface diagram

Three: electronic components corresponding to the role of digital label explanation

1. Input circuit surge proof and lightning proof short circuit

In section L wire series insurance tube and negative temperature coefficient (NTC) thermistor, models such as the NTC 8 d - 9 (10 Ω, 9 mm in diameter), thermistors are generally low resistance of a few Europe to 10, and mainly plays a role of storm surge, also can need not. Safety tube is generally tubular, the above power supply due to limited space, so choose a small volume of the box safety tube. Generally behind insurance tube in electric blue varistor in parallel on the road, such as 7 d471 (7 mm in diameter, voltage 470 v), 10 d471 (10 mm in diameter, voltage 470 v), etc., instant surge voltage to appear when the thunder and lightning, exceeds the breakdown voltage of varistor, low impedance change of the pressure sensitive resistance to a few ohms around, make insurance tube over-current fuse, so as to protect and disconnect the circuit. Safety tube, pressure sensitive resistance in safety certification is an important control device, use to choose a safety certificate.

 

2. Electromagnetic interference LC filter (also known as EMI)

 

 

By two yellow safety capacitance (also called X2 capacitor, metallized polypropylene film interference film capacitor), filtering inductance type PI filter network, mainly of the input power of electromagnetic noise and the clutter signal is suppressed, to prevent the power interference, but also prevent power itself produces high frequency noise interference of power grids. Safety capacitor is an important control device in safety certification. It should be used with safety certification certificate. In the test certification, a better filter design can pass the conducted interference in EMC EMC.

 

 

Change the positive and negative alternating current into a unidirectional direct current. The rectifier bridge is used in the figure above, such as KBP307 (3A1000v).

 

 

Smooth the changing voltage waveform into the less fluctuating dc voltage waveform. Generally, electrolytic capacitors are used. The power source in the figure above is a unipolar PFC circuit. CBB polypropylene capacitors, such as 104/630v, are used.

 

 

At the moment of high speed switching cut-off of the field effect tube (MOS tube), the resonance between the primary inductance of the transformer and the distributed capacitor is formed, and the primary inductance will also generate the reverse electromotive force, and the energy accumulation will produce a high spike pulse, which may break down the effect tube switch tube. The function of RCD peak pulse absorption circuit is to prevent and suppress higher peak pulse and protect the safety of effect tube switch tube.

Circuit diagram of switch power supply for LED driver

 

 

The LED driver switching power supply controls the field effect tube (MOS tube) to conduct high-speed on-off and cut-off through the control chip, and converts the direct current into the high frequency ac to supply the transformer for voltage conversion, thus generating the required safety isolation voltage. The maximum reverse voltage of the field effect tube (MOS) as a switching tube is twice the operating voltage of the circuit and the operating frequency is between 20 and 200kHz. When the input voltage is 220V, the withstand voltage of the switch tube is generally greater than 650V or above.

 

 

The electrical clearance between the two stages of the transformer is ≥8.0mm or more. The design of winding and shielding layer of transformer has great influence on the radiation interference in EMC.

 

 

The main role in the LED driver switching power circuit is to play the switching power transformer between the primary and secondary voltage control signal photoelectric transmission, and the primary PWM control chip to achieve photoelectric isolation signal feedback. High pressure and low pressure are not directly connected, realizing safety isolation and protecting personal safety. In the safety certification is an important control device, use to choose a safety certification certificate. In practical application, the general model of optoelectronic coupler is PC817.

 

 

Generally connected at high and low pressure, 101-682 (100p-6800p) is used. The function is to suppress high-frequency interference. Y2 capacitor is helpful to improve the radiation interference in EMC EMC, especially for the 100MHZ frequency band.

 

 

Change the positive and negative alternating current into a unidirectional direct current.

 

Smooth the changing voltage waveform into the less fluctuating dc voltage waveform

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The output voltage and current changes are fed back to the control circuit in the form of voltage drop for identification and processing. The resistance value is selected according to the constant current.

 

Such as L6561, UC3842, UC3843 and so on.

14. Represents complete isolation between high voltage and low voltage, and the circuit realizes voltage transmission by magnetoelectric coupling. High voltage (primary side) low voltage (secondary side) electrical clearance (

 

Also called spatial distance). If safety requirements are specified, primary side to secondary side ≥6.4mm.

LED driver switching power supply circuit copper foil diagram