Features: Avalanche Internal Sensor Precision Fixed Operating Frequency Advanced Burst Mode Operation <0.1w at 265VAC, no-load condition> Internal Startup Circuit Pulse Current Limit Overvoltage Protection Overload Protection Program: Mobile Phone Charger & Adapter White Goods Auxiliary Power, PC, C-TV & Monitor Related Application Notes: AN-4137, AN-4141, AN-4147 (AN-4134 (AN-4138 ("Charging")

illustrate

The fsdm311 consists of an integrated pulse width modulator (pwm) and sensor, specifically a minimum external power supply (SMP) component designed for high performance offline switch mode. This device is an integrated high voltage, sensor combined with vdmos' power switching regulator with a voltage mode PWM control block. Features of this integrated pwm controller include: a fixed oscillator, undervoltage lockout (uvlo) protection, leading edge blanking (LEB), optimized gate switch driver, thermal shutdown (TSD) protection, temperature compensation, precision current Source circuit for loop compensation and fault protection. When combined with discrete mosfet and controller or RCC switching converter solutions fsdm311 devices reduce total component count, and design size and weight; while increasing efficiency, productivity and system reliability. This device provides a basic platform ideal for designing cost-effective flyback converters.

Function description

1. Startup: During startup, the internal high voltage source provides the internal bias voltage MPC506AU to the external VCC capacitor, as shown in the figure. In the case of the fsdm311, when the vcc reaches 9v, the device starts the switch and the internal high voltage current supply stops charging the capacitor. The device is operating normally, provided that VCC is not lower than 7. After startup, provide bias from the auxiliary device. Transformer windings.

Calculated VCC capacitance is designed using FSDM311 . The maximum start-up current FSDM311Istart at initial start-up is about 100 μA, which supplies the current for the UV and VREF building blocks. The charging current ivcc capacitor of vcc is equal to Istr-Istart. VCC reaches the UVLO startup voltage and only the bias winding supplies the VCC device current. When the bias winding voltage is insufficient, the VCC level drops to the UVLO stop voltage and the internal current source is activated to charge the VCC capacitor again. To prevent this VCC from fluctuating (charging/discharging), a value should be chosen between 10uf and 47µf.

2. Feedback control: FSDM311 is a voltage mode control device, as shown in the figure. Typically, an optocoupler with a shunt regulator, such as the KA431, is used to implement the feedback network. The feedback voltage is compared to an internally generated sawtooth waveform, which directly controls the duty cycle. The KA431 reference pin voltage exceeds the internal reference voltage by 2.5V, the optocoupler LED current increases, the feedback voltage vfb is pulled low, and it reduces the duty cycle. When the input voltage increases or the output load decreases

3. Leading edge blanking (LEB): Instantaneously the internal sensor is turned on, and the primary side capacitor and secondary side rectifier diode reverse recovery usually passes through the sensory net. The RSENSE resistor voltage is too high resulting in incorrect pulse-by-pulse current limit protection. To avoid this, a leading edge blanking (leb) circuit disables the pulse-by-pulse current limit protection block for a fixed time after the inductor is turned on (TLEB). 4. Protection circuit: fsdm311 has several protection functions, such as overload protection (OLP); over voltage protection (ovp), under voltage lockout (uvlo) and thermal shutdown (tsd). Because these protection circuits are fully integrated in the integrated circuit with external components, increased reliability increases cost. In the event of a failure, the switchover ends and the sensor remains off. This causes VCC to drop. When VCC reaches the UVLO stop voltage Vstop (7V), the protection is reset and the internal high voltage current source charges VCC through the capacitor at the VSTR pin. When vcc reaches uvlo the starting voltage V starts (9V) and the device resumes normal operation. This way, auto-restart can alternately enable and disable the power sensor settings until troubleshooting.

4.1 Overload Protection (OLP): Overload is defined as due to unexpected events. In this case, the protection circuit should be activated to protect the SMPS. However, even when the SMPS is operating normally, the overload protection (OLP) circuit can switch the load. To avoid this undesired action, the OLP circuit is designed to determine whether it is a transient condition at a specified time or a true overload condition. If the output dissipates more than the maximum power determined by the ILIM, the output voltage (VO) drops below its rated voltage. This reduces the current through the optocoupler LED and also reduces the optocoupler transistor current, thereby increasing the feedback voltage (vfb). If VFB exceeds 3V, the feedback input diode blocks and a 5µA current source (IDELAY) begins to slowly charge the CFB to VCC. In this case, vfb increases to 4.5V when the switching operation is terminated as shown. This shutdown delay time is the time it takes to charge the CFB from 3V to 4.5V with a 5µA current source.

4.2.Thermal shutdown ("TSD": The sensefet and the control IC are integrated, making it easy to control the sensing sensor temperature. When the temperature excess is about 145°C, the temperature excess shutdown is activated. 5. Soft start: FPS has an internal soft The start-up circuit slowly increases the feedback voltage, sensing the current together, just as it starts. A typical soft-start time is 15ms, as shown, where the progressive increment of the sense current is ALOWED During the start-up phase. Soft The starting circuit gradually increases the current limit of the transformer operating condition capacitors, and switchgear It also helps to prevent transformer saturation and reduce voltage secondary diodes

6. Burst Operation: Minimize Power Consumption In standby mode, fsdm311 enters burst mode operation. When the load decreases, the feedback voltage decreases. The device automatically enters burst mode when the feedback voltage is lower than vburl (0.55v). At this point, switching stops and the output voltage begins to drop. This causes the feedback voltage to rise. Once it goes through Vburh (0.70V), it starts switching again. This feedback voltage drops and the process repeats. Burstmode operation alternately enables and disables the switch of the power mosfet to reduce switch losses in standby mode.

Application Tip: Methods to Reduce Audible Noise Switching power converters have electronic and magnetic components that generate audible noise when operating at frequencies between 20 and 20,000 Hz. Even though they operate at frequencies above 20kHz, they can be noisy under certain load conditions. Designers can use a variety of methods to reduce noise, including: Glue or varnish The most common method is to use glue or paint to tighten magnetic parts. Moving cores, spools, and coils; and jittering or magnetostriction of the core can cause audible noise in transformers. The use of hard glue and varnish helps reduce transformer noise, but can damage the core and glue due to sudden changes in ambient temperature causing the core and glue to expand or contract at different rates. Ceramic Capacitors Replacing ceramic capacitor shock absorbers with film capacitors is another noise reduction solution. Some dielectric materials exhibit a piezoelectric effect, which depends on the strength of the electric field. Therefore, a snubber capacitor becomes the most significant source of audible noise. Zener clamp circuit can be used instead of RCD snubber circuit for efficiency and lower audible noise. Tuning Audio AN-4137: Design Guidelines for Offline Flyback Using the Fairchild Power Switch (FPS™) to shift the noise fundamental out of the 2~4khz range is a third method. Generally speaking, humans are more sensitive to noise in the range of 2~4khz. When the fundamental frequency of the noise lies in this range, the noise is considered to be larger, despite the same level of noise intensity. See Figure Equal Loudness Curve. AN-4138: Battery Charger Design Considerations Using Green Mode Fairchild Power Switches (FPS™) AN-4140: Offline Transformer Design Considerations Flyback Converters (fps™) Using Fairchild Power Switches when fps is operating in burst mode and Burst operation is suspected to be the source of noise and this method may be helpful. If the frequency of burst mode operation is in the range of 2~4kHz, the adjustment feedback loop can move the frequency of burst operation. Reduce the burst operating frequency, increase the feedback gain capacitor (CF), optocoupler power supply resistor (RD) and feedback capacitor (CB); decrease the feedback gain resistor (RF) as shown.

feature

Passive PFC Auxiliary power supply for PC power supply 12.5W output DC input voltage 275V~375V (voltage doubler) 10W output DC input voltage 120V~375V (offline universal input) Isolated secondary output 5.1V/2.5A (maximum), 3.5A(peak)@vin=275~375VDC isolated secondary output 5.1V/2.0A(max), 2.5A(peak)@vin=120~375VDC non-isolated auxiliary output 15V(13~17V)/10mA(up to 20mA ) Regulation 5.1V ± 2.5% - Accuracy depends on reference (e.g. shunt regulator or precision resistor) Low no-load power consumption: <100MW@all input voltages <820mW@all input voltages, 0.5W output High efficiency: >80%@ 375VDC input, 12.5W output >79%@160VDC input, 10W output