April 04, 2020

Isolated LED driver scheme based on NCL30000 PF greater than 0.95

For low-power AC-DC LED power conversion, different topologies such as isolated flyback or non-isolated buck can be selected. The so-called "isolation" refers to the electrical isolation between the input and output using a transformer or the like. Both of these topologies have their own characteristics. In comparison, the non-isolated topology design and circuit board configuration are simple, the board size is small, the number of components is small, and the energy efficiency is higher. The isolation topology is easy to meet the safety requirements, but the magnetic design is complicated and requires a large circuit. Board size. This article will focus on the AC-DC LED driver solution in an isolated topology.

LED driver application requirements

For LED general lighting applications, the current cost is relatively high, so high-performance LED drivers will undoubtedly be more popular. In addition, LED drivers should also have high energy efficiency (low loss), high reliability, compliance with electromagnetic interference (EMI) and harmonic content or power factor (PF) standards, flexibility, adapt to wide environmental conditions, and can be retrofitted to existing Application, support for traditional control mode work (compatible with traditional dimming).

Among them, in terms of power factor requirements, the US ENERGY STAR project solid-state lighting standard has mandatory requirements for PFC (regardless of the power level), applicable to specific products, such as recessed lights, cabinet lights and table lamps. Wait. The standard requires a power factor greater than 0.7 for residential applications and a power factor greater than 0.9 for commercial applications, while integral LED bulbs require a lamp power factor greater than 0.7 for input power greater than 5W. Of course, not all countries absolutely mandate improved power factor in lighting applications, but some applications may have this requirement. For example, utilities may strongly promote the commercial use of products with high power factor in utilities.

NCL30000 isolated LED driver solution with high power factor

To provide a high power factor while meeting other application requirements, it is necessary to use a high power factor circuit architecture. As a result, the traditional two-stage architecture (PFC boost + pulse width modulation (PWM) flyback conversion) can not meet the requirements. Advantageously, such as the ON Semiconductor NCL30000 power factor correction dimmable LED driver with a single-segment architecture (see Figure 1), can provide a power factor of 0.9 or higher. The device is packaged in a compact 8-pin surface mount package that uses a critical conduction mode (CrM) flyback architecture to provide a high power factor of greater than 0.95 in a single-segment topology, eliminating the need for dedicated DC-DC conversion power sections. Reduce component count and reduce total system cost.

Comparison of traditional two-stage architecture with improved single-segment architecture

Figure 1 Comparison of traditional two-stage architecture with improved single-segment architecture

The constant on-time CrM operation of the NCL30000 is especially suitable for isolated flyback LED applications because

High-voltage 110~220KV XLPE Cable

A. Brief introduction of the 110~220KV XLPE high-voltage cable products

1. The cross-linkage PE insulated and wrinkled aluminum wrapper waterproof PVC Sheathed Power Cable.

Type: YJLW02/YJLLW02

Specification: 240mm²--300mm²

Voltage: 110--220KV

Usage: Suitable for damp areas and the places with a lower underground water level and to be used underground, in tunnels or pipes. Such cables bear a bigger pulling force and pressure.

2. The cross-linkage PE insulated and wrinkled aluminum wrapper waterproof PE sheathed power cable.

Type: YJLW02/YJLLW02

Specification: 240mm²--300mm²

Voltage: 110--220KV

Usage: Suitable for damp areas and the places with a lower underground water level and to be used underground, in tunnels or pipes. Such cables bear a bigger pulling force and pressure.

B. Specific property for usage of 110KV~220KV XLPE high-voltage cable

1. Cable`s conductor highest working temperature is allowed up to 90℃, and overload when meet an emergency is 130℃ ,When short circuit (in ≤5 seconds) the highest temperature is 250℃

2. When installing or laying cable, the ambient temperature should be less than -20℃, and have to give a preheat to cable.

3. The minimum bending diameter:

After laying: 30D0

During laying: 40D0

4. Allowed biggest axial traction force to outer diameter when laying cable (not consider the radial lateral

pressure at bent section) T=K×core NO. ×section (kg), in formula, the coefficient K value should be: the copper core get 7, the aluminum core get 4.

5. Allowed biggest lateral-press P, when cable is being bent

The single core cable is required P≤500kg/m.

P=T/R (T is indicated axial traction force; R is indicated radius of bent-wheel), Knowing from above formula, as the traction force is made up by length and weight of cable. So it lets P to applying requirement as above. Then the diameter of bent-wheel should be widened.

6. Cable laying is not being restricted by drop.

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