Introduction to the characteristics of monolithic switching power supply
(1) The internal components of TOpSWitch II include an oscillator, error amplifier, pulse width modulator, gate circuit, high-voltage power switch transistor (MOSFET), bias circuit, overcurrent protection circuit, overheat protection and power on reset circuit, and turn off/automatic restart circuit. It completely isolates the output terminal from the power grid through a high-frequency transformer, ensuring safe and reliable use. It belongs to the 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 terminal S, and drain terminal 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 are multifunctional output terminals, realizing one foot multi-purpose. Taking the control terminal as an example, it has three functions: ① The voltage VC at this terminal provides bias voltage for the on-chip parallel regulator and gate driver stage; ② The current IC at this end can adjust the duty cycle; ③ This end also serves as a connection point between the power supply branch and the automatic restart/compensation capacitor, which 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 used as 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 should be reduced by 40%. The input frequency range of a switching power supply is 47-440Hz.
(4) The typical switching frequency is 100KHz, and the duty cycle adjustment range is 1.7% to 67%. The power efficiency is around 80%, with a maximum of 90%, which is nearly twice as high as that of linear integrated voltage regulators. The 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 optocoupler feedback circuit causes Ic ↑ → error voltage Vrt → D ↓ → Vo ↓, keeping Vo constant. vice versa.
(6) The peripheral circuit is simple and cost-effective. Only rectifier filters, high-frequency transformers, primary protection circuits, feedback circuits, and output circuits need to be connected externally. The use of such chips can also reduce electromagnetic interference generated by switching power supplies.
