Design Scheme of High Power LED Lighting Power Supply

Abstract: This paper introduces the solution of 350W high efficiency (> 90%) high power factor (> 0.95) led lighting power supply using PFC controller cm6807 and resonant half bridge controller cm6900. The scheme is suitable for up to 1kW power supply, and can be used for LED lighting, LED street lamps, large LED billboards and high-power sports venues lighting.

American "Energy Star" and other specifications require that the off-line LED lighting power supply at any power level has high power factor and high energy efficiency. For the low-power LED driving power supply for general lighting, the single-stage power factor correction (PFC) flyback circuit topology based on special controller IC is the most basic solution. This topology is characterized by the use of only one power switch without the use of high-voltage electrolytic capacitors. For 100 200W LED lighting power supply, PFC flyback two-stage circuit architecture is usually adopted. The characteristic of this topology is that PFC boost converter is placed in the front end of flyback converter, and PFC and flyback converter use a power switch respectively. For high-power LED lighting power supply above 200W, the above two topologies are not applicable. The effective solution is to choose the circuit architecture of PFC combined with its inductance inductance capacitance (LLC). In order to achieve high efficiency, the synchronous rectification scheme can be adopted at the secondary side of the main transformer. This paper introduces a design example of 350W LED lighting power supply using this scheme for readers' reference.

1 system technical specifications and basic architecture

1.1 technical specifications of 350W LED driving power supply

(1) Input specification

AC input voltage: 85 264 VAC;

AC maximum input current: 5A;

Line power factor PF: 0.95 (230VAC, full load);

AC power frequency: 47 63Hz;

Efficiency: 92% (230VAC, full load);

Operating temperature: 50 ℃;

Working environment: closed;

Heat dissipation mode: natural cooling without fan.

(2) Output specification

Output voltage uo: 36 40V;

Output Current IO: 5 10A;

Voltage ripple: ≤ 0.3V;

Current ripple: 0.1A;

Control mode: constant voltage / constant current.

1.2 system composition block diagram

The 350W LED lighting power supply is mainly composed of EMI filter, PFC boost converter based on continuous conduction mode (CCM) power factor controller cm6807, LLC resonant half bridge converter based on cm6900 and synchronous rectifier. Figure 1 is the basic architecture block diagram.

2 actual circuit

The 350W LED lighting power supply circuit based on cm6807 and cm6900 is shown in Figure 2. We briefly introduce each unit circuit in the system.

2.1 PFC boost converter and auxiliary power supply

The PFC boost converter and auxiliary power circuit of 350W LED lighting power supply are shown in Figure 2 (a).

(1) Input stage circuit

The input stage circuit consists of EMI filter and bridge rectifier. It is shown in Figure 2 (a) In, capacitors C3, C4, C5, C11 C14 and inductive elements T1 and T2 constitute input EMI filter; BR1 is bridge rectifier; fu1 is fuse; RT1 is NTC thermistor. EMI filter is used to limit and attenuate common mode and differential mode noise, and RT1 is used to limit surge current caused by charging large capacitor C7 during system startup.

(2) Active PFC boost converter

Power factor controller U1 (cm6807), power switch vt2, boost inductor L1, boost diode VD3, input capacitor C9 / C10, output capacitor C7, current sensing resistor R4, etc. form DC / DC active PFC boost converter. PFC level circuit works in continuous mode. Input current is detected through U1 pin ② through R5, R8 and R13. Output DC bus voltage (395v) It is sampled by voltage dividers R7, R10, R12 and R13 and fed to U1 pin FB. Pin ④ of U1 is the output of voltage error amplifier, and C17, C18 and C21 are compensation networks. The current through PFC stage is sensed by R4 and detected by U1 pin ③ through R11 and C20. The drive output on U1 pin ⑨ drives VT1 / VT3 and vt2. The function of PFC boost converter is to generate an AC output at the input of bridge rectifier BR1 The sinusoidal current whose input voltage tends to be in the same phase can meet the harmonic current limit requirements specified in iec61000-3-2 standard, the system power factor is much higher than 0.95, and can output a stable DC voltage of 395v within the AC input voltage range of 85 264v.

(3) Starting circuit and bias power supply

R5, R8, R6, R9, vt4, VD4 and C16 constitute the shoulder circuit on U1 pin ⑧. Once U1 is started, PFC enters the operating state, and U1 pin ③ is powered by the bias power supply composed of auxiliary windings between L1 pins ③ and ④, C1 and C2, VD1 and VD2, R15, VZ1, vT5 and C16.