Enhanced PFC Controller NCL2801 Provides Higher Energy Efficiency and Better THD for Lighting Applications
“ON semiconductor‘s latest NCL2801 current mode critical conduction (CrM) power factor correction (PFC) boost controller IC for analog/pulse width modulation (PWM) dimmable LED drivers. The device’s market advantages are optimized Total Harmonic Distortion (THD) performance while maximizing system energy efficiency under wide load conditions, less over/undershoot during startup and dynamic loads, and linear level detection Optimized loop gain control, integrated error amplifier facilitates loop design and reduces power consumption. It adopts SOIC-8 small outline package and integrates a series of protection features to provide high system reliability. In addition, multiple Vc
ON semiconductor’s latest NCL2801 current mode critical conduction (CrM) power factor correction (PFC) boost controller IC for analog/pulse width modulation (PWM) dimmable LED drivers. The device’s market advantages are optimized Total Harmonic Distortion (THD) performance while maximizing system energy efficiency under wide load conditions, less over/undershoot during startup and dynamic loads, and linear level detection Optimized loop gain control, integrated error amplifier facilitates loop design and reduces power consumption. It adopts SOIC-8 small outline package and integrates a series of protection features to provide high system reliability. In addition, multiple Vcc enable thresholds increase design flexibility.
Key Features of NCL2801
Key features of NCL2801 include: innovative Valley Count Frequency Fold-back (or VCFF) method, THD enhancement technology, dynamic response enhancement, soft overvoltage protection (OVP)/fast OVP, linear feedforward, Wide Vcc range (10.5 V to 28 V)/multiple Vcc startup thresholds, transconductance error amplifier (OTA), high drive capability (-500/ +800 mA), and undervoltage protection, thermal shutdown, OVP, overcurrent protection, open/short circuit protection, etc.
NCL2801 has different versions. The optional features of each version are shown in the table below. The default version is NCL2801CDA DR2G. Designers can choose the appropriate version according to specific application needs, providing higher design flexibility.
Table 1: Optional Features of NCL2801 Versions
200 W PFC Grade Reference Design
Figure 2 shows the PFC grade reference design board designed with NCL2801 for 200 W output power. Linear voltage range 90 V to 305 V.
Figure 1: NCL2801 application block diagram
Figure 2: NCL2801 driven 200 W PFC grade reference design board
1. VCFF optimizes energy efficiency over a wide load range
Under heavy load current conditions, the NCL2801 operates in CrM mode, which counts as 1 valley switch. As the output power decreases, the frequency decreases, and when the VCTRL pin voltage falls below the threshold voltage, the controller enters discontinuous conduction mode (DCM) and begins to increase the valley switch count. After 6 valley switches, if the output power continues to decrease, add additional dead time. The total dead time should not exceed 36.5 us, and the minimum switching frequency should not be lower than 27.4 kHz. The switching frequency depends on the output voltage, input voltage, and boost Inductor value, and increases with load power. Threshold voltage can be set by Rcs, providing design flexibility. VCFF maximizes energy efficiency during DCM and under light load conditions and reduces standby power consumption. As with frequency clamped critical conduction type (FCCrM) controllers, internal circuitry keeps the power factor close to unity even as the switching frequency is reduced.
2. THD enhancement
THD performance is improved by adding a bias voltage at the output of the circuit multiplier to increase the on-time. As shown in Figure 3, the THD of the 200 W evaluation board at 305 Vac, full load
Figure 3: THD performance of the 200 W evaluation board at different Vac, load
3. Fast line/load transient compensation
Sudden changes in load or input voltage can cause significant undershoot or overshoot due to the slow loop response of traditional PFC stages. The NCL2801 uses dynamic response enhancement technology to reduce output undershoot; its soft OVP/fast OVP feature reduces output overshoot.
4. Linear level detection
By adjusting the gain value of the multiplier compared to the linear voltage state, the linear level detection circuit supports more optimized loop gain control and maintains stable operation under wide input conditions.
5. Transconductance Error Amplifier
The transconductance error amplifier has a typical transconductance gain of 200 us and a maximum current of +/- 20 uA. The output voltage of this PFC stage is reduced by a parallel resistor, and the bias current is minimized to support the use of a high impedance feedback network, which simplifies Loop design to reduce power consumption.
6. Totem pole output
The NCL2801 combines a -0.5/+0.8 A gate driver to provide the ability to drive power MOSFETs with high efficiency.
7. Rich protection features
NCL2801 continuously detects input and output voltage, MOSFET current and chip temperature by integrating a series of protection features, such as overvoltage protection, overcurrent protection, thermal shutdown, undervoltage detection, open/short circuit protection, etc., to protect the system from damaged, making the PFC grade extremely robust and reliable.
Layout and Anti-Noise Considerations
The NCL2801 is not particularly sensitive to noise, but the following points should still be considered when laying out the board to maximize system performance:
Ø Power loop area must be minimized
Ø The grounded power supply adopts a star configuration to provide a current return path
Ø The ground circuit adopts a star configuration
Ø Ground power supply and ground circuit should be connected through a single path, no loop can be used
Ø This path is best to connect the ground circuit and the ground power supply close to the ground end of the current sense resistor
Ø A 100 nF or 200 nF capacitor should be placed between the circuit Vcc and GND pins, and the connection length should be minimized
Ø It is recommended to place a filter capacitor on the FB pin to protect the pin from possible noise around it. But this filter capacitor must be small so as not to distort the voltage sensed through the FB pin.
The NCL2801 current mode CrM boost PFC controller IC utilizes ON Semiconductor’s THD enhancement technology to provide best-in-class THD performance over a wide load range, while the innovative VCFF method improves energy efficiency and reduces power consumption, and a range of protection features provide high reliability It is ideal for LED lighting applications and other PFC front-end applications that require high energy efficiency, low standby power consumption, low THD, and high reliability. The SOIC-8 package enables a compact design. Multiple different versions meet different design requirements and improve design flexibility.