Circuit Design of AC Inverter Power Supply Based on UC2525

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I. Design Requirements This power supply is applied to the front end of an AC voltage conversion. The input control signal is 4VAC (50HZ AC RMS variation range 2VAC-8VAC), and the input power supply is 350VDC (accuracy 0.5%). The output signal should be linearly proportional to the input signal (20 times magnification, accuracy 0.5%), and the phase error between the input control signal and the output signal is less than 20', and the power load is not less than 30VA.
Special requirements: The control signal input impedance is required to be greater than 500M.

Second, the design analysis The power supply model is an AC inverter power supply, but provides a control signal and requires linear proportional accuracy with the input signal requirements are quite high, and have the same phase requirements. Therefore, this power supply is an AC signal amplifier in a certain sense.
The input power is 350VDC, which needs to be converted into an AC signal. The conversion method is to generate a square wave by SPWM, and then become a standard sine through LC. To generate the SPWM, TI's UC2525 regulated pulse width modulator is used, and then the MOSFET is controlled to generate a square wave.
The input signal requires high impedance and can be isolated using an amplifier. Due to the output accuracy requirements, the amplifier's amplification factor needs to be adjusted to meet the design requirements. The processed signal is input to the UC2625 as a PWM duty control signal to obtain a correct output.
The design requirements have accuracy and phase requirements. In order to achieve the effect of closed-loop control, a small signal voltage transformer is added to the output as feedback.

Third, the implementation of the division
1 control signal input processing

Five, design regrets There is a place in the circuit I still have no calculation is the duty cycle control of UC2525, which is why I took this design out to the TI blog contest. In the circuit, from the control signal output to the feedback input, and then to the half-wave rectification, detailed design calculations can be made, but due to the uncertainty of the reference triangle wave of the UC2525 (for example, the peak-to-peak uncertainty, the initial voltage uncertainty) Etc.) There is no way to obtain a more accurate design calculation support for the accuracy of the sine wave. It can only be ensured by a small full-scale adjustment and feedback adjustment, which brings great inconvenience to mass production. If the TI staff saw the design, I hope to help.