feature

Avalanche Internal Sensor Precision Fixed Operating Frequency (67khz) Operating Mode Internal Start-Up Circuit Pulse Double Pulse Current Limit Overload Protection (OLP) Internal Thermal Shutdown Function Self-Recovery Mode Voltage Lock Under Diaphragm (UV) Soft Start Secondary Side Regulation Applications for Mobile Phones Chargers and Adapters White Goods Auxiliary Power Monitor Related Application Notes AN-4137 Offline Feedback Design Guidelines Converter Use Issues and Design Fairchild Power Switch (FPS & Flyback Applications) AN-4147 RCD Snubber Flyback AN-4134 Offline Forward Design Guidelines Switch Design Considerations Using a Green Mode Power-Down Switch Using a Battery Charger

describe

The fsq211 consists of an integrated pulse width modulator (PWM) and sensor specifically designed for high performance offline switching power supplies with minimal external components (SMP). This device is an integrated high voltage power supply combined with a vdmos sensor switching regulator with a voltage mode pwm control block. Features of the integrated pwm controller include a fixed oscillator, precision in voltage lockout (uvlo) protection, leading edge blanking (LEB), an optimized gate on/off driver, thermal shutdown (TSD) protection, and temperature compensation Current source loop compensation and fault protection circuits. When combined with discrete mosfet and controller or rcc switching converter solutions, the fsq211 device reduces component count and design size and weight while improving efficiency, productivity and system reliability. This device provides a basic platform ideal for cost-effective flyback converters.

1. Leading edge blanking (LEB): that is, when the internal sensor is turned on, the primary side capacitor and the secondary side rectifier diode reverse recovery usually passes the SSESFETRSENSE resistor voltage too high resulting in incorrect pulse-by-pulse current limiting protection. To avoid this, a leading edge blanking (leb) circuit disables the pulse-by-pulse current limit protection block for a fixed time (tleb) after the sensefet is turned on. 4. Protection Circuits: The fsq211 has several protection functions such as Overload Protection (OLP); Under Voltage Lockout (uvlo) and Thermal Shutdown (TSD). Because these protection circuits are integrated inside the integrated circuit, there are no external components, improving reliability without increasing cost. Once a fault condition occurred, the switch terminated and the Sensefet remained off. This causes VCC to drop. when? The vcc reaches the uvlo stop voltage vstop (7v), then the protection is reset, and the internal high voltage current supply charges the vcc capacitor through the vstr pin. when? When VCC reaches the UVLO start voltage Vstart (9V), the device resumes normal operation. In this way, auto-restart can alternately enable and disable switching power sensors until the fault condition has been eliminated.

2.1 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, the overload protection (OLP) circuit can switch under load even when the SMPS is functioning properly. To avoid this undesired operation, the OLP circuit is designed to determine whether this is a transient condition or an overload condition as specified. If the output consumes more than the maximum power as determined by the ILIM, the output voltage (vo) is lower than its rated voltage. This reduces the current through the optocoupler LED, which reduces the optocoupler transistor current, thereby increasing the feedback voltage (VFB). If VFB exceeds 3V, the feedback input diode is blocked and the 5µA current source (IDELAY) begins to slowly charge CFB up to VCC. In this case, vfb increases until it reaches 4.5V, when the switching operation is terminated, as shown. The shutdown delay is the time required to charge the CFB from 3V to 4.5V with a 5µA current source.

3.2 Thermal crack (TSD): The sensor is integrated with the thermal crack control IC, making it easy to control the temperature of the detected sensor. When the temperature excess is about 145 °C, the temperature excess shutdown is activated. Five Soft-Start: The FPS has an internal soft-start circuit that slowly increases the feedback voltage, together feeling right now, right when it starts. A typical soft start time is 15 mm, as shown, where progressive increments of sensory current are approved during the starting phase. Increasing Current Limit of Soft Start Circuits Working Conditions for TransformersInductors, Capacitors, Switchgear. It also helps prevent transformer saturation and reduce stress on secondary diodes

4. Burst operation: Minimize power consumption In standby mode, the fsq211 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 passes Vburh (0.70V), the switch starts again. The feedback voltage drops and the process repeats. Burst Mode operation alternately enables and disables the switching of the power mosfet to reduce switch losses during standby mode.

Application Tips

Methods of reducing 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 depending on the load. Designers can use several methods to reduce noise. The most common method of glue or varnish is to use glue or paint to tighten magnetic parts. Moving cores, spools, and coils, as well as jitter 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. This is because sudden changes in temperature of the environment cause the core and glue to expand or contract at different rates. Ceramic capacitors Replacing ceramic snubber capacitors with film capacitors is another noise reduction option. Some dielectric materials exhibit a piezoelectric effect, which depends on the strength of the electric field. Therefore, the A-snubber capacitor becomes the most important source of audible noise. Zener clamp circuit can be used instead of RCD snubber circuit for efficiency and lower audible noise. Adjusting the sound frequency to move the noise fundamental frequency out of the 2~4khz range is the third method. Generally speaking, humans are more sensitive to noise in the range of 2~4khz. When the fundamental frequency of the noise is in this range, the noise is considered to be larger, despite the same noise intensity level (see the equal loudness curve in the figure). This method may be helpful when the fps is working in burst mode and burst operation is suspected to be the source of noise. 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), reduce the feedback gain resistance (RF).

Other Reference Materials AN-4134: Design Guidelines for Offline Forward Converters Using Fairchild Power Switches (fps) AN-4137: Offline Flyback Design Guidelines for Converters Using Fairchild Power Switches (FPSμ) AN-4138: Design of Battery Chargers Consider Using Green Mode Fairchild Power Switches (FPSμ) AN-4140: Offline Transformer Design Considering Flyback Converter Switches Using Fairchild Power Supplies (FPS 8482 ;) AN-4141: Troubleshooting and Design Tips for Fairchild Power Switch (FPS™) Inverters Exciter Applications AN-4147: RCD Shock Absorber Design Guidelines Flyback AN-4148: Sound Noise Reduction Technology FPS™ Application