Characteristics of Single Chip Switching Power Supply
(1) The internal components of TopSwitch II include an oscillator, error amplifier, pulse width modulator, gate circuit, high-voltage power switching transistor (MOSFET), bias circuit, overcurrent protection circuit, overheat protection and power on reset circuit, and shutdown/automatic restart circuit. It completely isolates the output end from the power grid through a high-frequency transformer, making it safe to use. It belongs to a current controlled switching power supply with open drain output. Due to the use of CMOS circuits, the power consumption of the device is significantly reduced.
(2) There are only three output terminals: control terminal C, source pole S, and drain pole D, which can be comparable to a three terminal linear regulator and can form a flyback switching power supply without a power frequency transformer in the simplest way. To achieve various control, bias, and protection functions, both C and D belong to multifunctional lead out terminals, achieving one foot for multiple purposes. Taking the control end as an example, it has three functions: ① The voltage VC at this end provides bias voltage for the on-chip parallel regulator and gate drive stage; ② The current IC at this end can adjust the duty cycle; ③ This end also serves as the connection point between the power supply branch and the automatic restart/compensation capacitor, and determines the frequency of automatic restart through an external bypass capacitor, and compensates for the control circuit.
(3) The range of input AC voltage is extremely wide. When using a fixed voltage input, 220V ± 15% AC power can be selected. If equipped with AC power with a wide range of 85-265V, the maximum output power needs to be reduced by 40%. The input frequency range of a switching power supply is 47-440Hz.
The typical value of the switching frequency is 100KHz, and the range of duty cycle adjustment is 1.7% to 67%. The power efficiency is around 80%, with a maximum of 90%, which is nearly twice that of a linear integrated voltage regulator. Its working temperature range is 0-70 ℃, and the highest junction temperature of the chip is Tjm=135 ℃.
(5) The basic working principle of TopSwitch II is to use feedback current IC to adjust the duty cycle D and achieve voltage stabilization. For example, when the output voltage VOT of a switching power supply is caused by some reason, the error voltage Vrt D ↓ Vo ↓ is maintained constant through the optocoupler feedback circuit, keeping Vo unchanged. The opposite is also true.
(6) The peripheral circuit is simple and the cost is low. Externally, only rectifier filters, high-frequency transformers, primary protection circuits, feedback circuits, and output circuits need to be connected. The use of such chips can also reduce the electromagnetic interference generated by switching power supplies.
