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Monolithic 700V sensor power switch Precision fixed operating frequency: 250mW no-load power consumption at 130kHz 265Vac Burst mode down to 60mW plus bias Internal start switch Soft-start time tuned by external capacitor Under-Voltage Lockout (uvlo) with hysteresis Pulse-by-Pulse Current Limit Overload Protection (OLP) and Internal Thermal Protection Hysteresis Shutdown (TSD) Auto-Restart Mode No Auxiliary Bias Winding Required

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The FSQ500L is a low-cost linear power supply designed for replacement. This device combines a current-mode pulse width modulator (PWM) with a sensor. Integrated pwm controller features include: fixed oscillator, undervoltage lockout (uvlo) protection, overload protection (olp); leading edge blanking (LEB), optimized gate switch driver, thermal shutdown (TSD) protection with hysteresis and temperature compensation Precision current source for loop compensation. when? Compared to linear power supplies, the fsq500l device reduces overall size and weight while increasing efficiency, productivity, and system reliability. This device provides a basic platform for a cost-effective flyback converter.

Function description: 1. Start-up and VCC rules: At start-up, an internal high voltage current source provides internal bias and charges an external capacitor (CA) connected to the VCC pin as shown. An internal high voltage regulator (HV/REG) VCC pin located between D and VCC regulates VCC to 6.5V and provides supply operating current. Therefore, the FSQ500L does not require an auxiliary bias winding.

2. Feedback control: FSQ500L adopts current mode control, as shown in the figure. Optocouplers as FOD817A) and shunt regulators (eg KA431 ) are often used to implement feedback networks. Combining the feedback voltage with the voltage through the RSENSE resistor controls the switching duty cycle. When the reference pin regulator voltage exceeds the internal reference voltage voltage of 2.5V, the optocoupler LED current increases, pulling down the feedback voltage to shorten the duty cycle. This usually occurs when the line input voltage increases or the output load increases and the current decreases. 2.1 Pulse-by-Pulse Current Limiting: Because the current is mode controlled, the non-inverting input limit comparator (VFB*) is pulse-width modulated through the sensor, as shown. Assuming that the current source of 225 microamps only flows through the internal resistance (8R+R=12KΩ), the voltage of the cathode voltage diode d2 is about 2.7V. Because d1 exceeds 2.7V at the feedback voltage (VFB), max. The cathode voltage of d2 is clamped at this voltage, clamping VFB*. Therefore, the peak value of the current passing through the sensor is limited. 2.2 Leading Edge Blanking (LEB): When the internal sensor is turned on, a high current spike occurs through the sensefet, caused by the primary side capacitor and secondary side rectifier reverse recovery. Too high a voltage on the RSENSE resistor can cause erroneous feedback operation for current mode PWM control. To counteract this effect, the FPS employs leading edge blanking (LEB) circuitry. This circuit suppresses the time after the short-circuit sensefet of the PWM comparator is turned on (tleb=250ns).

3. Protection circuit: FSQ500L has two self-protection functions: Overload Protection (OLP) and Thermal Shutdown (TSD). The olp is implemented as an automatic restart mode, and the trigger is not switched during TSD. Once an overload condition is detected, the switch is terminated, the sensor remains off, and the HV/REG turns off. This causes VCC to drop. When VCC is lower than the under-voltage lockout (uvlo) stop voltage of 5.0V, the protection is reset and the startup circuit charges the VCC capacitor. When VCC reaches the startup voltage of 6.0V, the FSQ500L resumes normal operation. If the fault condition still does not exist after removal, sensefet and hv/reg remain off and VCC drops to VSTOP again. In this way, autorestart can alternately enable and disable switching until the fault state is eliminated, as shown. Because these protection circuits are fully integrated in the integrated circuit with no external components, reliability is improved without increasing cost.

3.1 Overload Protection (OLP): Overload is defined as due to unexpected abnormal events. In this case, the protection circuit should trigger to protect the switching power supply. However, even when the smps is operating under normal conditions, the overload protection circuit can trigger during load transitions. To avoid accidental operation in this situation, overload protection circuits are designed to trigger after a specified time to determine whether the situation is a temporary or a true overload. Due to the limiting capability of the pulse current, the maximum peak current flows through and therefore, the maximum input power is limited. Limited by a given input voltage. If the output consumes more than this maximum power, the output voltage (vo) drops below the set voltage. This reduces the current through the optocoupler LED, which also reduces the current through the optocoupler transistor, thereby increasing the feedback voltage (vfb). If VFB exceeds 2.7V, D1 is blocked and the 5µA current supply starts charging the circuit breaker slowly until VCC. Under this condition, VFB continues to increase until it reaches 4.5V, when the switching operation is terminated, as shown. The turn-off delay is the time it takes to charge the CB from 2.7V to 4.5V with 5µA. Generally speaking, a delay time of 10~50ms is a typical application for most people. This protection implements restart mode in auto.

3.2.Thermal shutdown ("TSD": The sensefet and the control IC in one package make the control easy. Detects abnormality in temperature sense when the temperature is over 140°C, thermally shuts down the flip-flop. When the flip-flop, the delay current is damaged, The switching operation is stopped and VCC is set to 5.7v from 6.5v by the internal high voltage current source, as Fig. Since the signal is disabled from the switch sensor, there is no switching before switching. The connection temperature drops enough if the connection temperature is lower than the typical 60 degrees signal is cleared, VCC is set to 6.5V again. Wheel is increased from 5.7v to 6.5v, the soft start function turns the senses to no voltage and/or current stress

4. Soft-start: Soft-start time is increased by external vcc capacitor (ca), non-inverting input voltage of pwm comparator and slow current after sensor start-up. At vStart when VCC arrives, the CA is charged by the current ICH-IStart, where ICH and IStart are shown in the figure. After VCC reaches vstart, all internal blocks are activated so that the current consumption inside the IC becomes the IOP. Therefore, CA is charged by the current ICH-IOP, making the rising slope of vcc slow. VCC is negatively shifted by 6.0V (performed in the soft-start block in Figure 2), then VCC-6.0V is an input terminal to a PWM comparator. The drain current follows vcc-6.0v instead of vfb* because of the low dominance characteristic of the pwm comparator. The soft-start time can be set long or shortened by selecting CA as shown. In TS/S, disable IDELAY to avoid unwanted OLP. Typically, ts/s is about 4.6ms with 27µf ca

The peak switching device of the power drain current is stepped up to establish the correct operating conditions of the transformers, inductors and capacitors. The output voltage capacitor is gradually increased to smoothly establish the desired output voltage. It also helps prevent transformer saturation and reduces stress on the secondary diode at startup. 5. Burst operation: Put standby mode, FPS into burst mode operation. During burst mode operation, ifb (burst) is reduced by half IFB (normal). When the load decreases, the feedback voltage decreases. As shown in the figure, the device operates when the feedback voltage is lower than VbUrl (750mV). At this point, switching stops and the output voltage begins to drop depending on the rate at which the backup current is loaded. This causes the feedback voltage to rise. Switching resumes once Vburh (800mV) is passed. The feedback voltage then drops and the process repeats. Burst Mode alternately enables and disables power switching sensefet, reducing switching losses in standby mode