feature

Internal Avalanche Rugged Sensor: 650V Precise Fixed Operating Frequency: 67kHz Unbiased 265Vac No Load < 150mW Winding; <25mW with Bias Winding No Auxiliary Bias Winding Required Frequency Modulation Lines to Attenuate EMI Voltage protection (LUVP) pulse-by-pulse current limiting Low under-voltage lockout (UVLO) Ultra-low operating current: 300 microamps Built-in soft-start and start-up circuit Various protections: overload protection (OLP); over-voltage protection (ovp), thermal shutdown ( TSD), abnormal overcurrent protection (AOCP) automatic restart mode for all protections.

application

Switching Power Supplies Auxiliary Power Switching Power Supplies for Set Top Boxes, DVD and DVCD Players

describe

The fsl206mr integrated pulse width modulator (pwm) and sensefet is designed for high performance offline switching power supplies (smps) using minimal external components. This device is an integrated high voltage power regulator with a current mode avalanche rugged sensor PWM control block. Integrated pwm controller includes: 7.8v regulator for unbiased winding, under voltage lockout (uvlo) protection, leading edge blanking (LEB), optimized gate on/off driver, EMI attenuator, thermal shutdown (TSD) Protection, temperature compensation Precision current sources for loop compensation, and fault protection circuits such as overload protection (OLP), overvoltage protection (ovp), abnormal overcurrent protection (AOCP) and line undervoltage protection (luvp). During startup, the fsl206mr provides good soft-start performance. Power dissipation in standby mode with internal high voltage start switch and burstmode operation at very low operating current. So it is unbiased which can reach 150mw of power loss at no load with a 25mw winding with bias winding at 265 VAC input voltage.

Function description

During startup, an internal high voltage current source provides internal bias and externally charges a capacitor (CA) connected to the VCC pin as shown. An internal high voltage regulator (HV/REG) is located between the VSTR and VCC pins to regulate VCC to 7.8V and provide operating current. Therefore, the FSL206MR does not require an auxiliary bias winding.

oscillator block

Oscillator frequency is set internally, FPS 8482 ; with random frequency fluctuation function. Switching frequency fluctuating power supplies reduce EMI by dispersing energy measured by EMI test equipment over a wider frequency range than bandwidth. Quantitative EMI reduction and frequency variation. The frequency range is fixed internally; however, the choice is a random combination of external feedback voltages and an internal free-running oscillator. This randomly chosen switching frequency effectively extends the EMI noise around the switching frequency, allowing the use of a cost-effective inductor instead of an AC input line filter to meet global EMI requirements.

feedback control

fsl206mr adopts current mode control, as shown in the figure. Optocouplers (such as the FOD817A) and feedback networks are typically implemented using shunt regulators (such as the KA431 ). Comparing the feedback voltage to the voltage across the sensor resistor makes it possible to control the switching load cycle. When the reference pin voltage of the parallel regulator exceeds the internal reference voltage of 2.5V; the optocoupler LED current increases, the feedback voltage VFB is pulled down, and the duty cycle decreases. This usually occurs when the input voltage increases or the output load decreases. Leading Edge Blanking (LEB) Primary side capacitance and secondary side rectifier diode reverse recovery typically cause high currents to pass through the sensor mesh when the internal sensor is turned on. Over-voltage RSENSE resistor causes incorrect feedback operation in current mode pwm control. to counteract this effect. The FPS employs a leading edge blanking (LEB) circuit that suppresses the PWM sensor from being set up for a short time after the comparator is turned on. Protection circuit fsl206mr protection functions, including overload protection (OLP), overvoltage protection (ovp), undervoltage lockout (uvlo), line undervoltage protection (luvp), abnormal overcurrent protection (AOCP) and thermal shutdown (TSD). Because these protection circuits are fully integrated in the integrated circuit with no external components, reliability is improved without increasing cost. In the event of a fault, the switch is terminated and the sensor remains off. This causes VCC to drop. The stop voltage Vstop (7V) when vcc reaches uvlo, the protection resets the internal high voltage current source to charge VCC through the capacitor at the VSTR pin. When the vcc reaches the uvlo, the startup voltage V starts (8V), and the FPS resumes normal operation. This way, auto-restart can alternately enable and disable the power sensor settings until troubleshooting. Abnormal Over Current Protection (AOCP) When the secondary rectifier diode or transformer pins are shorted, the current is steep and the di/dt is extremely high and can flow through the sensor within the LEB time. Even though the FPS has overload protection, it is not enough to protect the FPS in this abnormal situation, because severe current stress is placed on the sensor until the OLP triggers. The FPS includes internal AOCP (Anomalous Over Current Protection) circuitry such as when a gate open signal is applied to power sensing, enabling the AOCP block and monitoring the current through the sense resistor. The voltage is compared to a preset AOCP level through a resistor. If the sense resistor voltage is greater than the AOCP level, the set signal is applied to the latch, causing the SMPS to turn off. The thermal shutdown (TSD) sensor is integrated with the control chip, which makes it easier to detect the SSESFET when the junction temperature exceeds about 135°C, and the FPS restarts after the thermal shutdown is initiated to cool down to 60°C. Over Voltage Protection (ovp) If the secondary side fails the feedback circuit or is caused by a welding defect, the current through the optocoupler transistor is almost zero, then VFB rises in a manner similar to an overload condition, forcing a preset maximum current to be supplied to the SMPS until the overload protection is activated. Because excess energy is supplied to the output, the output voltage may exceed the rated voltage before the overload protection is activated, resulting in failure of the secondary side equipment. To prevent this, overvoltage protection (ovp) circuits are used. Generally speaking, VCC is related to the output voltage and fps using vcc instead of monitoring the output voltage directly. If VCC exceeds 24.5V, the ovp circuit is activated, resulting in switching operation. To avoid accidental activation during normal operation, VCC should normally be designed below 24.5V.