feature

Internal avalanche rugged sensor: 650V 50MW or less Standby power consumption 265V AC, no-load condition in burst mode Precision fixed operating frequency FM attenuating electromagnetic interference Internal start-up circuit Built-in soft start: 15ms pulse-by-pulse current limiting (ovp), Overload Protection (olp), Output Short Circuit Protection (OSP), Abnormal Over Current Internal Thermal Shutdown Protection (AOCP) Hysteresis Function (TSD) Auto Restart Mode Under Voltage Lockout (UVLO) Low Operating Current: 1.8MA Adjustable Peak Current limit

application

Skim milk powder adapters for SMPS home appliances for VCR, STB, DVD and DVCD players Related resources AN-4 137 - Offline Flyback Design Guide Using FPS 8482 ; Converters AN-4141 - Troubleshooting and Design Tips Fairchild Semiconductor Power Switching (FPS™) Flyback Converter

application

AN-4147 - RCD Damper Design Guidelines for Flyback Converters

describe

The fsl106mr integrated pulse width modulator (pwm) and sensefet is designed for high performance offline switching power supplies (smps) using minimal external components. The FSL106MR includes an integrated high voltage power switch combined with an avalanche voltage regulator sensor with a current mode PWM control block. Integrated pwm controller features include: under voltage lockout (uvlo) protection, leading edge blanking (leb), frequency generator attenuation for emi, optimized gate switch driver, thermal shutdown (TSD) protection for loop and temperature compensated precision current source compensation and fault protection circuits. The FSL106MR has good soft-start performance. when? Compared to discrete mosfet and controller or rcc switching converter solutions, the FSL106MR reduces total component count, design size and weight; while improving efficiency, productivity and system reliability. This device provides a very suitable basic platform for designing cost-effective flyback converters.

Overload Protection (OLP) Overload is when the load current exceeds a pre-set level due to unexpected events. In this case, the protection circuit should be activated to protect the SMPS. However, even if smps are functioning properly the overload protection (OLP) circuit can be activated during load transition or startup. To avoid this undesired operation, the OLP circuit is designed to activate after a specified time to determine whether it is a temporary or real overload condition. Together with the IPK current limit pin (if used), the current mode feedback path limits when the maximum PWM duty cycle is reached. If the output consumes more than this maximum power, the output voltage (vo) drops below the rated voltage. This reduces the current through the optocoupler LED, which also reduces the optocoupler transistor current, thereby increasing the feedback voltage (VFB). If VFB exceeds 2.4V, the feedback input diode is blocked by 5µA current SOURCEIDELAY starts to slowly charge CFB. Under this condition VFB increases to 6V, and the switching operation is terminated, as shown in the figure. The shutdown delay time is to charge the CFB from 2.4V to 6V with a 5µA current source.

Abnormal Over Current Protection (AOCP) When the secondary rectifier diode or transformer pin is shorted and the current is too large, very high DI/dt can flow through the sensor time during LEB. Even if the fps has an OLP (overload protection), it is not enough to protect against abnormal conditions because severe current stress is applied until the OLP triggers. The FPS includes an internal AOCP (Abnormal Over Current Protection) circuit as shown. When the gate open signal is applied to the power sensor, the AOCP block is enabled and monitors the current through the sensed resistor. The voltage across the resistor is compared to the preset AOCP level. If the sense resistor voltage is greater than the AOCP level a signal is applied to the latch, causing the SMPS to shut down.

Thermal Shutdown The sensefet and the control IC are integrated, making it easy to detect the temperature. When the temperature of the Sensefet is over 137 degrees, the thermal shutdown activates. Overvoltage protection In the event of an accident on the second side of the feedback circuit or the open feedback loop solvent defect, the current through the optocoupler transistor becomes zero. Paste in a similar overload condition, forcing the current maximum current supply until the overload protection is activated. Because excess energy is supplied to the output, the output voltage may exceed the rate at which the voltage overload protection is activated, resulting in a rupture of the intermediate equipment. To prevent this, an overvoltage protection circuit is used. Generally speaking, VCC is equivalent to the output voltage and the FPS directly uses VCC to monitor the output voltage. If the VCC Exceeds 24VtheOVP circuit is activated, the result is a switching operation to avoid undesired activation. During normal operation, VCC should be ready in advance. Set at 24V below. Output Short-Circuit Protection (OSP) If the output is short-circuited, a steep current high di/dt can occur at the Leber time. Such large currents produce high voltage stress on the sensor drain when shutting down. That protects equipment from abnormal conditions, including outsourced service providers. It is detected and sensed by the vfb on time. When VFB is higher than 1.6V and the SENSEFET turn-on time is lower than 1.0m, FPS regards this situation as an abnormal error and closes the PWM switch VCC to reach VStart again. The exception output is shown in the figure.

The soft-start FPS has an internal soft-start circuit to increase the feedback voltage, as well as the induced current, after startup. A typical soft-start time is 15 ms, as shown, where sensor current is allowed to increase during the start-up phase. The pulse width switching device of the power is stepped up to establish the correct operating conditions of the transformer, inductor and capacitor. The output voltage capacitor is gradually increased to smoothly establish the desired output voltage. It also helps prevent transformer saturation and reduce stress on the secondary diode.

Burst Operation To minimize power consumption in standby mode, the FPS™ enters burst mode. As the load decreases, the feedback voltage decreases. When the feedback voltage drops below Vburh. Switching continues until the feedback voltage drops below vburl. At this point, switching stops and the speed at which the output voltage begins to drop depends on the backup current load. This causes the feedback voltage to rise. Once it passes vburh, the switch continues. The feedback then drops the voltage and the process repeats. Burst Mode alternately enables and disables sensing in standby and reduces switching losses.

Adjusting the peak current limit As shown, the combined 6KΩ internal resistor is connected to the PWM comparator. The external resistor current limit pin on Rx forms a parallel resistor with a 6KΩ source of 400µA when the internal diode is biased by the mains current. For example, the fsl106mr has a typical sensor peak current limit (ILIM) of 0.55A. ILIM can be via the IPK pin and ground. The value of rx can be given by the following equation: 0.55A: 0.4A=6KΩ: XKΩX=Rx 6kΩ where x represents the resistor network of parallel lines.