Can the ST8500 be used for communication on a 140V DC cable?

闰土 · ‎2025-10-13

Is it feasible to use the ST8500 + STLD1 configuration for modulating, demodulating, and amplifying signals, then coupling them via high-voltage film capacitors onto a cable powered by DC140 for communication? Are there any better solutions or suggestions? Thank you.

*This post has been translated from Chinese to comply with the ST Community guidelines.

Didier HERROUIN · ‎2025-10-14

Dear Visitor,

For optimal performances, you can keep the differential mode with a transformer as in the AC design.

You can also connect the STLD1 in single ended mode, removing the transformer : only PA1_OUT signals are connected to the coupling circuit. The coupling circuit being the capacitance (in series with a coil, depending on your resonant frequency bandwidth) + protection diodes. PA2_OUT stay not connected.

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Didier HERROUIN · ‎2025-10-14

Dear Visitor,

Yes, this is feasible, the PLC design based on ST8500+STLD1 works on AC and DC networks.
You can optimize the coupling to the powered cable, meaning that the coupling capacitor and the transformer can be adapted to your DC network characteristics as you do not have the same constraints as in an AC network.

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闰土 · ‎2025-10-14

Hello, do you have any recommended circuits or design considerations for using capacitively coupled DC cables? The STLD1 outputs a differential signal. Is it correct that the two differential signals are directly coupled via capacitors to the 140V and 140V GND lines of the DC cable?

*This post has been translated from Chinese to comply with the ST Community guidelines.

Didier HERROUIN · ‎2025-10-14

Dear Visitor,

For optimal performances, you can keep the differential mode with a transformer as in the AC design.

You can also connect the STLD1 in single ended mode, removing the transformer : only PA1_OUT signals are connected to the coupling circuit. The coupling circuit being the capacitance (in series with a coil, depending on your resonant frequency bandwidth) + protection diodes. PA2_OUT stay not connected.

In order to give better visibility on the answered topics, please click on 'Accept as Solution' on the reply which solved your issue or answered your question.

闰土 · ‎2025-10-14

Hello, your previous reply mentioned single-ended mode. Is it acceptable to continue using differential mode? PA1_OUT and PA2_OUT are capacitively coupled to the 140V and 140V GND lines of the cable, respectively, then received by the ST8500's receiver. Subsequently, TVS protection and common-mode chokes are implemented.

*This post has been translated from Chinese to comply with the ST Community guidelines.