Category: LCD Television Repair and Service
Contents of this article
- FSQ0165 Details
- FAN 7530 Details
- Power supply schematic
A Valley Switching Converter generally shows lower EMI and higher power conversion efficiency than a conventional hard-switched converter with a fixed switching frequency. The FSQ-series is an integrated Pulse-Width Modulation (PWM) controller and SenseFET specifically designed for valley switching operation with minimal external components. The PWM controller includes an integrated fixed-frequency oscillator, under-voltage lockout, Leading-Edge Blanking (LEB), optimized gate driver, internal soft-start, temperature-compensated precise current sources for loop compensation, and self-protection circuitry. Compared with discrete MOSFET and PWM controller solutions, the FSQ-series reduces total cost, component count, size and weight; while simultaneously increasing efficiency, productivity, and system reliability. This device provides a basic platform for cost-effective designs of valley switching ﬂy-back converters.
SenseFET source terminal on primary side and internal control ground.
Positive supply voltage input. Although connected to an auxiliary transformer winding, current is supplied from pin 5 (Vstr) via an internal switch during startup. It is not until \/CC reaches the UVLO upper threshold (12V) that the internal startup switch opens and device power is supplied via the auxiliary transformer winding.
The feedback voltage pin is the non-inverting input to the PWM comparator. It has a 0.9mA current source connected internally while a capacitor and opto-coupler are typically connected externally. There is a time delay while charging external capacitor C“, from 3V to 6V using an internal 5pA current source. This delay prevents false triggering under transient conditions, but still allows the protection mechanism to operate under true overload conditions.
This pin is internally connected to the sync-detect comparator for valley switching. Typically the voltage of the auxiliary winding is used as Sync input voltage and external resistors and capacitor are needed to make delay to match valley point. The threshold of the internal sync comparator is 0.?Vf0.2V.
This pin is connected to the rectified AC line voltage source. At startu p, the internal switch supplies internal bias and charges an external storage capacitor placed between the Vcc pin and ground. Once the \/CC reaches 12V, the internal switch is opened.
The drain pins are designed to connect directly to the primary lead of the transformer and are capable of switching a maximum of 650V. Minimizing the length of the trace connecting these pins to the transformer decreases leakage inductance.
The FAN7530 is an active power factor correction (PFC) controller for the boost PFC applications that operates in critical conduction mode (CRM). It uses the voltage mode PWM that compares an internal ramp signal with the error amplifier output to generate MOSFET turn-off signal. Because the voltage mode CRM PFC controller does not need the rectiﬁed AC line voltage information, it can save the power loss of the input voltage sensing net- work necessary for the current mode CRM PFC control- ler. FAN753O provides many protection functions such as over voltage protection, open-feedback protection, over- current protection, and under-voltage lockout protection. The FAN7530 can be disabled if the INV pin voltage is lower than 0.45V and the operating current decreases to 65uA. Using a new variable on-time control method, THD is lowerthan the conventional CRM boost PFC lCs.
This pin is the inverting input of the error amplifier. The output voltage of the boost PFC converter should be resistively divided to 2.5V.
This pin is used to set the slope of the internal ramp. The voltage of this pin is maintained at 3V. If a resistor is connected between this pin and GND, current flows out of the pin and the slope of the internal ramp is proportional to this current.
This pin is the output of the transconductance error amplifier. Components for the out- put voltage compensation should be connected between this pin and GND.
This pin is the input of the over-current protection comparator. The MOSFET current is sensed using a sensing resistor and the resulting voltage is applied to this pin. An internal RC filter is included to filter switching noise.
This pin is the input of the zero current detection block. If the voltage of this pin goes higherthan 1.5V, then goes lowerthan 1.4V, the MOSFET is turned on.
This pin is used for the ground potential of all the pins. For proper operation, the signal ground and the power ground should be separated.
This pin is the gate drive output. The peak sourcing and sinking current levels are +500mA and -800mA respectively. For proper operation, the stray inductance in the gate driving path must be minimized.
This pin is the IC supply pin. IC current and MOSFET drive current are supplied using this pin.
POWER SUPPLY SCHEMATIC DIAGRAM
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