| Compared to conventional linear regulator power supply, switching mode power supply has a lot of advantages such as much smaller in size, has higher efficiency, and could provide stable output voltage without cumbersome power frequency transformers, etc. which made it becoming the mainstream of the stable power supply.An off-line, multi-mode controlled AC/DC switching mode power supply with line voltage feed-forward is analyzed and designed in this paper, this economic, highly integrated switching mode power supply is consisted by several blocks on a monolithic chip: a 700V power MOSFET, high voltage current source, PWM controller, oscillator, OTP(Over Temperature Protection),FP(Fault Protection) and other control logic circuit. This monolithic chip can be widely used in spot-light, TV and portable electronics products. An novel multi-function pin is added, which can introduce feed-forward or adjust the current limiting. Dynamic response of the new power supply is faster and efficiency is higher compared to the traditional design.In this paper, first, the key specification of this switching power supply chip is introduced. Then fly-back light emitting coupled topology, feedback method and working principle of this chip is given and analyzed. Three sub-circuits: bandgap reference block, compensation circuit block, line voltage block and frequency jitter block are designed and simulated using HSPICE. Error correction option strategy is realized by adding trimming option on adjust the current of biasing circuit and charge-discharge current of the oscillation circuitThis chip is laid out and taped out on a co-developed BCD process. Key performance parameters of the fabricated chip is tested and measured, which validated the correction of this design and the specification requirement is met. |
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