NCL30085FLYGEVB, NCL30088FLYGEVB 10 W High Power Factor Isolated LED Driver Evaluation Board www.onsemi.com User s Manual EVAL BOARD USERS MANUAL Overview This manual covers the specification, theory of operation, testing and construction of the NCL30085/88FLYGEVB evaluation board. The NCL30085/88 board demonstrates a 10 W high PF isolated flyback LED driver in a typical A19 outline. The 2 evaluation boards are nearly identical in construction except for the controller and Vcc bulk Table 1. SPECIFICATIONS capacitor. The NCL30088 controller is a nondimming Parameter Value Comment version while the NCL30085 supports 3 levels of step Input voltage (Class 2 Input, 90 265 V ac dimming. no ground) Key Features Line Frequency 50 Hz / 60 Hz As illustrated, the key features of this evaluation board Power Factor (100% Load) 0.9 Min include: THD (100% Load) 20% Max Wide Mains Class 2 Output Mains Low THD across Line and Load Isolated High Power Factor across Wide Line and Load Output Voltage Range 14 28 V dc Integrated Auto Recovery Fault Protection (can be Output Current 350 mA dc 2% latched by Choice A Version) Programmable Over Temperature Thermal Foldback Efficiency 85% Typical (NTC mounted on PCB) Start Up Time < 500 msec Typical Cycle by Cycle Current Limiting EMI (conducted) Class B FCC/CISPR Open LED and Shorted Output Protection Figure 1. Evaluation Board Picture (Top View) Semiconductor Components Industries, LLC, 2014 1 Publication Order Number: December, 2014 Rev. 0 EVBUM2287/DNCL30088FLYGEVB THEORY OF OPERATION Power Stage Auxiliary Winding The power stage for the evaluation boards is an isolated The auxiliary winding has 3 functions: flyback. The controller has a built in control algorithm that 1. CrM timing is specific to the flyback transfer function. Specifically: 2. Vcc Power Duty 3. Output voltage sense Vout Vin (1 Duty) CrM Timing In the off time, the voltage on the transformer/inductor This is applicable to flyback, buck boost, and SEPIC forward biases Dout and D9. When the current in the converters. The control is very similar to the control of the magnetic has reached zero, the voltage collapses to zero. NCL3008083 with the addition of a power factor This voltage collapse triggers a comparator on the ZCD pin correction control loop. The controller has a built in to start a new switching cycle. The ZCD pin also counts rings hardware algorithm that relates the output current to a on the auxiliary winding for higher order valley operation. reference on the primary side. A failure of the ZCD pin to reach a certain threshold also Vref Nps Iout indicates a shorted output condition fault. 2 Rsense Vcc Power Npri Nps The forward biases D9 to provide power for the controller. Nsec This arrangement is called a bootstrap. Initially the Cvcc, Where Npri = Primary Turns and Nsec = Secondary Turns is charged through R4 and R5. When the voltage on Cvcc We can now find Rsense for a given output current. reaches the startup threshold, the controller starts switching and providing power to the output circuit and the Cvcc. Cvcc Vref Nps Rsense discharges as the controller draws current. As the output 2 Iout voltage rises, the auxiliary winding starts to provide all the power to the controller. Ideally, this happens before Cvcc Line Feedforward R3 sets the line feedforward which compensates for discharges to the undervoltage threshold where the power stage delay times by reducing the current threshold as controller stops operating to allow Cvcc to recharge once the line voltage increases. R3 is also used by the shorted pin again. The size of the output capacitor will have a large detection. At start up the controller generates a current from effect on the rise of the output voltage. Since the LED driver the CS pin to check for a short to ground. If R3 is zero, the is a current source, the rise of output voltage is directly current sense resistor is too low a value and the controller dependent on the size of the output capacitor. will not start because it will detect a shorted pin. So R3 is There are tradeoffs in the selection of Cout and Cvcc. A required to make the controller operate properly. low output ripple will require a large Cout value. This requires that Cvcc be large enough to support Vcc power to Voltage Sense the controller while Cout is charging up. A large value of The voltage sense pin has several functions: Cvcc requires that R4 and R5 be lower in value to allow a fast 1. Basis for the reference of the PFC control loop enough startup time. Smaller values of R4 and R5 have 2. Line Range detection higher static power dissipation which lowers efficiency of The reference scaling is automatically controller inside the driver. the controller. While the voltage on Vs is not critical for the Output Voltage Sense PFC loop control it is important for range detection. The auxiliary winding voltage is proportional to the Generally the voltage on Vs should be 3.5 V peak at the output voltage by the turns ratio of the output winding and highest input voltage of interest. The voltage on Vs the auxiliary winding. The controller has an overvoltage determines which valley the power stage will operate at in limit on the Vcc pin at about 26 V minimum. Above that full load. At low line and maximum load, the power stage threshold, the controller will stop operation and enter a fault operates in the first valley (standard CrM operation). At the mode for overvoltage. This is the open load protection. higher line range, the power stage moves to the second In cases where the output has a lot of ripple current and the valley to lower the switching frequency while retaining the LED has high dynamic resistance, the peak output voltage advantage of CrM soft switching. can be much higher than the average output voltage. The auxiliary winding will charge the Cvcc to the peak of the output voltage which may trigger the OVP sooner than expected. www.onsemi.com 2