GP9303 and GP8101 Circuit Review: Analog Signal Isolation

zjqmyron

GP9303 and GP8101 Circuit Review: Analog Signal Isolation [Copy link]

1. The sampling method using optocoupler isolation is as shown below

Both GP9303 and GP8101 are powered by 12V, and the PWM frequency of GP9303 is 10KHz. PC817 optocoupler is used for isolation in the middle. Tests show that the optocoupler PC817 has a serious tailing phenomenon, and the rising edge is very poor, and the falling edge is not ideal. Reducing the pull-up resistor on the secondary side of the optocoupler will make the PWM waveform better, but it is not suitable as a waveform for sampling and transmission after observation by an oscilloscope. The test waveform is as follows

The yellow waveform of channel 1 is the PWM waveform after the optocoupler

The blue waveform of channel 2 is the waveform sent by GP9303, and the two are very different.

Conclusion: So using ordinary optocouplers for isolated sampling is not ideal. (Here it is speculated that using high-speed optocouplers should be possible)

2. Use digital isolation

Digital isolation uses the digital isolation chip π121U (this chip is domestically produced, the original secondary side voltage resistance can reach 3000Vrms, which is enough to meet the isolation voltage resistance requirements). The circuit is as follows

The power consumption of the π121U chip is very low, and it can be directly powered by the 5V power supply of GP9303 and GP8101. There is no tailing phenomenon in the digital chip. Although there is a delay in the transmission of PWM, the duty cycle does not change. The test waveform is as follows

From the tested waveform, we can see that the duty cycle is basically not lost, so the measurement result will be more accurate.

The actual measurement of the linearity and accuracy of the input analog voltage and the output analog voltage.

By testing multiple sets of data, the linearity can be found out very well.

It can be concluded that GP9303 and GP8101 chips can be used as isolated sampling solutions. The specific use is based on cost and accuracy.

GP9303_cn_V1.9.pdf (527.97 KB, downloads: 113)

2020-1-7 09:01 上传

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GP8101_cn_V1.9.pdf (419.68 KB, downloads: 145)

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This content is originally created by EEWORLD forum user zjqmyron . If you want to reprint or use it for commercial purposes, you must obtain the author's consent and indicate the source

gynijun

Great, no need to use RC to convert PWM analog voltage signals!

hanzhen91

gynijun posted on 2020-5-15 11:22 Very good, no need to use RC to convert PWM analog voltage signals!

Using RC filtering to obtain DC is slow, and the benchmark depends on the high level of PWM. It is not suitable for high-precision application scenarios. Therefore, we launched the PAC series for this market, which can effectively solve some of the user's pain points.