Abstract: The system design for collecting AC voltage and load current signals using the built-in ADC of HCNR200 and TMS320F2812 is described in detail. The HCNR200 is a high precision linear optocoupler specifically designed for analog signal isolation sampling. Its use can effectively isolate the main circuit from the control circuit, and has high linearity and small detection error. The DSP built-in ADC is a 12-bit converter with high conversion accuracy, short conversion time (12.5 MSPS), and simple design.
Key words: HCNR200; TMS320F2812; analog isolation; AC sampling
0 Introduction In the design of three-phase variable frequency power supply, it is necessary to sample AC voltage and load current for double closed loop control and protection. Therefore, the design of AC voltage and current acquisition system is directly related to the performance of variable frequency power supply. The three-phase variable frequency power supply uses TMS320F2812 (referred to as F2812) as the control chip. The chip has a 16-channel 12-bit ADC. When using the F2812's built-in ADC for AC sampling, complex hardware design is avoided and cost is reduced. The power supply requires an output line voltage of 380 V and an output power of 3 kW. To collect the AC voltage and current signals and send them to the DSP chip, an isolation circuit must be designed to prevent high voltage and high current from being connected to the control system and burning the low voltage device. The HCNR200 is a dedicated high precision linear optocoupler for analog signal isolation. This article details the use of the F2812's built-in ADC, combined with HCNR200 for AC voltage and current sampling.
1 Introduction to TMS320F2812 built-in ADC
The TMS320F2812 chip is a 32-bit fixed-point DSP introduced by TI at the end of 2003. It is a high-performance controller that meets the real-time control requirements of the motor. It operates at up to 150 MHz and has a built-in 16-channel, 12-bit ADC. Two-channel sample-and-hold, one conversion unit for dual-channel simultaneous sampling with a minimum conversion time of 80 ns. The internal structure of the peripheral with built-in ADC is shown in Figure 1.
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