KA7553A

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KA7553A Application Field and Working Principle

The KA7553A device by Fairchild Semiconductor is a continuous pulse-width modulator controller designed for use in both DC-to-DC switching and AC-to-DC voltage regulator applications.

The KA7553A can adjust output voltage in tight regulation of a circuit or to reduce input voltage ripple on the rectified AC line.

Application Fields

The KA7553A is primarily used in high-current/low-voltage DC-DC converter applications but can also be used in AC-DC voltage regulator switching applications. Additionally, the device has found usage in such devices as high-current TV sets, video game consoles and laptop computers (for rechargeable batteries), and cellular telephones.

Working Principle

The KA7553A is a pulse-width modulator (PWM) controller with features that enable it to provide excellent performance in both DC-DC and AC-DC switching applications. The device is fabricated using a CMOS process with features that reduce power consumption and improve efficiency.

The core of the device consists of an oscillator and an error amplifier, which are both connected to a power-on reset (POR) circuit. The oscillator produces a rectangular wave that is fed to a comparator. If the comparator’s input voltage is lower than the reference voltage, then the PWM output will be high and when the voltage is higher, the PWM output will be low.

At the same time, the error amplifier compares the input voltage and the output voltage and produces a differential voltage that is used to adjust the duty cycle of the PWM signal. Depending on the requirements of the application, the device is capable of generating a linear or a saw tooth waveform, with frequency range limits of 300 Hz and 30 kHz.

In addition, the KA7553A offers a variety of protection features, such as current, thermal, and overvoltage protections. The device also has an integrated high-side output current sensing feature, allowing for precise pulse-by-pulse current limitation, as well as an overcurrent protection which shuts off the output when the current draw from the power source exceeds the pre-set value.

Conclusion

The KA7553A device is a versatile PWM controller capable of operating in both DC-to-DC and AC-to-DC voltage regulator applications. It is suitable for high-current/low-voltage devices such as TVs, video game consoles, laptop computers, and cellphones. The controller has an oscillator, error amplifier, POR circuit, and a variety of protection features. Additionally, it has a current sensing capability and a pre-set overcurrent protection.

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