TOP253PN

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The TOP253PN is a control IC for flyback and forward converters that is aimed at use in external ac dc switch mode power supply (SMPS) which have an ac input voltage from 90Vac to 264Vac. It is designed primarily for use in electronic equipment that is powered from the mains. In particular, the TOP253PN is suitable for battery charging, medical, home and office applications.

The TOP253PN works with voltage, current and frequency control loops to achieve stable operation, smooth and continuous power output and low noise. It is a synchronous rectification and burst mode control with current mode control. This consists of an internal power MOSFET, a transistor driver and a DC-DC converter.

The TOP253PN has integrated protection functions such as under voltage lock out (UVLO) and over temperature protection (OTP). It is also equipped with short circuit protection (SCP) which cuts off the output if the load current exceeds a certain limit.

The internal power MOSFET switch is driven by an internal oscillator which uses a voltage mode controller to regulate the output voltage. The pulse width modulation (PWM) signal is generated from the error amplifier and its frequency is determined by a range of external resistors and capacitors. The PWM signal then controls the power switch which regulates the output voltage. The transformer secondary current is sensed by the current sense circuit. The TOP253PN features soft-start and cycle-by-cycle current limiting to reduce start-up stress on the system components and to prevent overloading during continuous operation.

To ensure the power supply\'s effective regulation capability, the TOP253PN has four loop control systems. The voltage loop, the current loop and two frequency control loops. These four control systems interact to provide a constant voltage, current and frequency under all environmental conditions.

The voltage loop is used to maintain the output voltage. It is based on an error signal created between the feedback signal taken directly from the output voltage and an internal reference voltage. The error signal is then amplified to provide a control signal for the power MOSFET switch.

The current loop is used to regulate the peak output current. This is achieved by sensing the current from the transformer secondary winding and the controller turning off the power MOSFET switch if the sensed current exceeds the predetermined limit.

The two frequency control loops are used to control the switching frequency of the power MOSFET switch. The first frequency control loop is based on an external PWM frequency and the second is based on an internal frequency. The two frequencies are then compared to give a control signal for the power Mosfet switch that maintains a constant frequency.

These features, combined with a wide input voltage range, precise output control, low noise and low input/output ripple, make the TOP253PN ideal for off-line switcher applications. It is possible to use the TOP253PN in various applications including chargers, switched mode power supply, led lighting, and industrial control systems.

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