NIKO dimmable PFC LED is designed for driving LED bulbs and tubes

In LED lighting applications, in LED driver circuits powered by AC-DC power supplies, isolated topologies and non-isolated topologies are common. These two topologies have their own characteristics. In comparison, the advantages of non-isolated topologies include smaller magnetic components, higher energy efficiency, fewer components, lower total bill of materials cost, and the ability to meet safety regulations with mechanical design. They are particularly suitable for LED bulbs and tubes with built-in drivers, and have become a trend in this type of LED lighting and are widely adopted. The isolated topology is more suitable for lighting applications where the driver and LED bulbs and tubes are separated due to safety requirements.

The LED driver non-isolated LED driver series provided by NIKO-SEM adopts peak current sampling plus average current sampling dual feedback control, so it can improve the lack of non-dimming in the single average current feedback control in high power factor applications. At the same time, the fast feedback characteristics can avoid the LED overcurrent damage caused by the input voltage conversion control delay, which can be applied to a variety of non-isolated LED driver high power factor and traditional non-high power factor application solutions. In the traditional pure resistance peak current sampling method, the inductor current flows through the sampling resistor. Because the peak voltage on the sampling resistor will immediately turn off the power transistor every time it reaches the internal reference voltage, the inductor current peak value will be the same in each switching cycle, and it cannot change with the input voltage sine wave amplitude, and the power factor cannot be effectively improved. NIKO-SEM uses a unique peak current sampling method of resistors in parallel with capacitors in non-isolated high power factor buck drive applications, so that the current flowing through the inductor can effectively change with the input voltage sine wave amplitude, thereby achieving the purpose of high power factor. The principle is: In the capacitor charge formula, Q=CV = IT, where the Q (charge) value, C (capacitance) value and V (sampling voltage) value of the parallel capacitor are all fixed values. The capacitor current I will change with the change of the conduction time T. As the input voltage sine wave amplitude increases, the current slope flowing through the inductor will increase, and the conduction time will be shorter to reach the internal reference voltage. Therefore, when the input voltage sine wave amplitude increases, the conduction time becomes shorter, and the capacitor current I will increase. At the same time, the inductor current will also increase. Therefore, it has a good high power factor performance. By adjusting the sampling resistor value, the LED load current can be changed at will. In addition, NIKO-SEM's LED driver provides a COMP pin specifically for input voltage and output load change compensation, so that the LED current change rate can be controlled at a 5% level. The following Figure 1 is a typical full-voltage non-isolated high power factor BUCK structure LED driver circuit provided by NIKO-SEM. In Figure 1, resistor R3 and capacitor C4 are peak current sampling elements, and resistor R4 connected in series with flywheel diode D1 is an average current sampling element. When the power transistor is turned off, the voltage of each working cycle of resistor R4 is integrated into a flat DC voltage value through resistor R5 and capacitor C5. When the LED load current is larger, the voltage value of resistor R5 and capacitor C5 is higher. At the same time, when the input voltage is higher, the voltage value of resistor R5 and capacitor C5 is also higher, thereby compensating for input voltage and output load changes. This voltage value is superimposed on the peak current sampling voltage when the power transistor is turned on again, generating peak current sampling plus average current sampling dual feedback control. The superimposed signal VLD and peak current sampling voltage VCS are shown in Figure 2. When dual feedback control is applied, the average current sampling resistor R4 is set first, the formula is R4 = ILED / 0.25, and then the peak current sampling resistor R3 is set, the formula is R3 = R4 / K, K = 3.75.

Figure 1 Typical full voltage non-isolated high power factor BUCK structure LED driver circuit

Figure 2 Voltage and current waveforms of high power factor BUCK LED driver circuit The constant current control of the LED driver series provided by NIKO-SEM adopts a fixed off-time control mode, so it can work in CCM or DCM mode in high power factor applications. In BUCK applications, operating in CCM mode has the advantages of smaller peak current and smaller frequency changes under high and low input voltages compared to CRM mode, which makes the conduction loss and switching loss smaller at high input voltages, so the efficiency is higher. In addition, when operating in CCM mode, it is necessary to consider the conduction loss between the power transistor and the flywheel diode caused by the diode reverse recovery current IRR generated at high input voltage. Therefore, when designing the inductance, it is necessary to consider that the valley current of the maximum inductor current should be less than 0.1A to avoid the reverse recovery current IRR loss affecting the overall efficiency and causing the power transistor and flywheel diode to have higher temperatures. 

The LED driver series provided by NIKO-SEM adopts source drive mode in driving power transistors, and is equipped with patented IC power supply in exchange working mode, which can effectively reduce the power loss of IC power supply and can supply IC power supply for normal operation without additional auxiliary windings and power supply components. Therefore, the energy storage inductor can adopt low-priced I-shaped inductors. In terms of protection function, the LED driver provided by NIKO-SEM has over-temperature protection, lamp short-circuit protection and lamp open-circuit protection. The lamp open-circuit protection uses the Zener diode to set the protection voltage to directly detect the LED output voltage. The open-circuit action voltage can be designed to be close to the normal lighting LED terminal voltage. Therefore, the parallel filter capacitor at the LED output end does not need to use a higher rated voltage, which can reduce the capacitor cost and volume.

The LED driver series provided by NIKO-SEM includes linear dimming, pulse dimming and TRIAC dimming. Figure 3 below shows the full voltage TRAIC dimming non-isolated high power factor BUCK structure LED driver circuit solution provided by NIKO-SEM.

Figure 3 Full voltage TRAIC dimming non-isolated high power factor BUCK structure LED driver circuit

The LED driver series provided by NIKO-SEM can support a variety of application solutions and provide very high energy efficiency. The circuit is simple and suitable for different medium and low power LED general lighting applications. The NIKO-SEM LED driver product series includes N3201M in SOT26 package and N3201V in SOP8 package. The N3101V and N3102V with built-in high-voltage MOSFETs are 1A and 2A respectively, and the SOP8 package is suitable for LED bulb applications below 8W. In addition, the LED driver series provided by NIKO-SEM can be used in other non-isolated BOOST and BUCK-BOOST topologies in addition to BUCK applications. In isolated topologies, it can be used in secondary feedback current regulation (SSR) applications.