UC3876N

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The UC3876N is a versatile and highly efficient controller IC for AC-DC and DC-DC switching power supplies. It is a monolithic integrated circuit with built-in pulse width modulation (PWM) modulation, over-voltage protection, over-current protection and robust circuit designs that make it well suited for a wide range of applications, from telecommunication and computer grade power supplies to single-phase motor drive applications. This article will discuss the application field and working principle of the UC3876N.

Applications

The UC3876N can be used in a range of AC-DC and DC-DC switching power supply applications. It is well suited for telecommunication and computer-grade power supplies, and it can also be used in reduced-power applications, such as small power amplifiers and power conditioning modules. Its versatile design makes it an ideal choice for single-phase motor drive applications.

The UC3876N is also suitable for general purpose auxiliary power supply applications, such as providing isolated backup power or providing the means to phase shift audio or other low-frequency signals. Its robust circuit designs and PWM modulation capabilities are also great for variable-frequency switching mode power supplies, assuming the appropriate amount of external components and topology.

Working Principle

The UC3876N utilizes a fixed oscillator frequency, typically in the range of 250-400 kHz, to generate a PWM pulse train which is used to control the output current and voltage. The PWM pulse train is then converted to an analog signal using an external optocoupler for feedback control and current sensing.

The UC3876N also provides external inputs for over-voltage, overtemperature, and over-current protection. The over-voltage response is adjustable, allowing users to set the over-voltage limit that they want the regulator to trip at. The over-temperature response is programmable and can be used to shut down the regulator in order to protect it in the event of overheating.

In order to provide optimal output voltage regulation, the UC3876N incorporates phase shedding and peak current limit circuitry. The phase shedding limits the current density across the switching FETs and the peak current limit restricts the peak current in the event of an overload. Both of these features ensure a continuous and stable output voltage even in the event of an overload or transient load condition.

The UC3876N has a voltage mode current control loop which uses an external sense resistor to sense the current and adjust the output voltage to maintain a constant current in the output stage. This ensures a stable output voltage for both light and heavy load conditions.

Conclusion

The UC3876N is a highly-efficient controller IC for AC-DC and DC-DC switching power supplies. It is versatile, with a wide range of applications and built-in features, allowing users to design robust power supplies for single-phase motor drive applications or general purpose rigid power supplies. Its high-efficiency and PMW modulation capabilities make it an ideal choice for telecommunication and computer-grade power supplies.

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