feature

internal avalanche

Species only 0.8w at 230 vac&0.5w load with start mode operation Precision fixed operating frequency, 100khz internal start circuit and soft start pulse side current limit and self sustain

Fashion

Overload Protection (OVP) Internal Thermal Shutdown Function Under-Voltage Lockout (UVLO) Low Operating Current (3MA) Adjustable Peak Current Pole yy

application

Auxiliary power supplies for PCs and servers Switching power supplies for VCRs, SVRs , set-top boxes, DVD and DVCD players, camera adapters for printers, fax machines and scanners ) Converters AN-4137: Offline Flyback Design Guidelines for Converters Using Fairchild Power Switches (FPS™)

AN-4141: Troubleshooting and Design Tips for Fairchild Power Switch (FPS™) Flyback Applications AN-4147: RCD Damper Design Guidelines AN-4148: For FPS™ Applications

report an error

illustrate

The fsq0170rna, fsq0270rna, fsq0370rna include an integrated current mode pulse width modulator (PWM) and avalanche rugged 700V sense FET. It is an external component designed for high performance offline switching power supplies (SMP). Integrated pwm controller features include: fixed frequency generating oscillator, undervoltage lockout (uvlo) protection, leading edge blanking (leb), an optimized gate on/off driver, thermal shutdown (TSD) protection, and precision temperature compensation Current source loop compensation and fault protection circuits.

Compared to discrete mosfet and controller or rcc switching converter solutions, FSQ0170RNA , fsq0270rna, fsq0370rna reduce total component count, design size and weight while increasing efficiency, productivity and system reliability. These devices provide a basic platform ideal for designing auxiliary power supplies for cost-effective flyback converters.

Application Diagram

output power meter

Note:

1. The maximum output power is limited by the junction temperature.

2. 230 VAC or 100/115 VAC with frequency multiplier.

three. Typical continuous power supply in a non-vented enclosed adapter with adequate cooling mode ambient at 50°C.

4. Maximum practical continuous power in an open frame design, at 50°C, with sufficient thermal mode ambient.

Internal block diagram

Function description

1. Entrepreneurship: In previous generations of Fairchild Power

switch (FPS™), VSTR pin requires external

Resistor for DC input voltage line. In this generation,

The startup resistor is replaced by an internal high voltage current source and a switch that turns off for 10ms

When the power supply voltage VCC is higher than 12V. If VCC drops below 8V, the power will turn back on

Above: High Voltage Current Source

2. Feedback Control: The 700V FPS series adopts current mode control as shown in the figure. Optocouplers (such as h11a817a) and shunt regulators (such as KA431 ) are often used to implement feedback networks. Comparing the voltage across the feedback voltage sensor resistor, plus the offset voltage, causes the control to switch the duty cycle. When the reference pin voltage of the parallel regulator exceeds the internal reference voltage of 2.5V, the optocoupler LED current increases, and the feedback voltage vfb is pulled down, thereby shortening the duty cycle. This usually occurs when the input voltage increases or the output load decreases.

three. Leading Edge Blanking (LEB): When the internal sensefet is turned on, the primary side capacitor and the secondary side rectifier diode reverse recovery normally passes through the sense net. The RSENSE resistor voltage is too high causing incorrect feedback operation in current mode PWM control. To counteract this effect, fps employs leading edge blanking (LEB) circuitry. This circuit suppresses the pulse width comparator for a short time.

4. Protection Circuits: The FPS has several protection circuits with 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 (usually 8V), the protection resets the internal high voltage current source to charge VCC through the capacitor at the VSTR pin. When vcc reaches uvlo start voltage, V starts (usually 12V) and FPS resumes its normal operation. This way, auto-restart can alternately enable and disable power switch sensing until the fault is resolved.

4. 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 switching power supply works normally, the OLP circuit can be activated during load transitions. To avoid unwanted operation in this situation, the OLP circuit is designed to activate after a specified time to determine if a transient condition or a true overload condition is present. When connected with the IPK current limit pin (if used), the current mode feedback path is limited 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 and also 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 the CFB to VCC. In this case, the VFB increase operation is terminated when switching to 6V, this shutdown delay time is the time it takes to charge the CFB from 3V to 6V with a current source of 5µA.