UC3867N

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The UC3867N belongs to the family of Pulse-Width Modulation (PWM) controllers which are used in the production of efficient switched mode power supplies (SMPS). The primary application of the device is to provide the gate drive signals to an external switch from an isolated DC source. The device does not have an internal power switch, so an external switch is required for the SMPS.

Overview of the UC3867N

The UC3867N has an operating supply voltage range of 4 V to 20 V, a wide input voltage range of up to 24 V, and requires a minimum of 350 mV to turn on. It has a burst mode operation which allows it to minimize the output power consumption while producing a continuous output voltage. It also has a built-in oscillator and enable pin to provide additional features. It features over-voltage and over-current protection, and over-temperature protection. The device includes an open drain output to provide a logic-controlled enable function.

Output Rectification and Regulation

The UC3867N features an output rectification circuit and a feedback loop that controls the output regulation of the device. The rectification circuit includes an internal full-wave bridge rectifier and a voltage reference that sets the output voltage level. The output rectification is controlled by the error amplifier, which senses the output voltage and feeds back the error signal to the internal oscillator, which adjusts the output current accordingly. The back-EMF voltage, generated by the external power switch and the inductor, is fed back to the internal error amplifier, and the error amplifier regulates the output voltage.

Power Switch Signalling

The UC3867N provides a dual-level gate drive output, which provides independentrise and fall times for the external power switch, allowing for better efficiency andreduced electrical stress on the power switch. The device also includes a low-side voltage detection circuit, which can be used to provide under-voltage protection and shut down of the SMPS in case of a fault. The device also includes a fault flag output, which can be used to shut down the SMPS in case of an over-temperature or over-current fault.

Advantages of Using the UC3867N

The UC3867N provides a cost-effective and readily available solution for SMPS applications. The device is able to minimize the power consumption, while providing a stable regulated output voltage. The device includes a low-side voltage logic control input, which can be used to shut down the SMPS in case of an under-voltage fault. The device also includes several protection features to protect against over-temperature, over-current, and over-voltage faults. Finally, the device includes a dual-level gate drive output, which allows more efficient power switch operation.

Conclusion

The UC3867N is an economical solution for SMPS applications. It features a bursemode operating, low-side voltage logic control input, over-temperature, over-current, and over-voltage protection, and a dual-level gate drive output to maximize efficiency. The device enables the production of high efficiency SMPS designs in a variety of applications.

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