THVD8000: Power over RS485

The THVD8000 is used in systems where power and data are transmitted over the same two lines. The THVD8000 converts the RS-485 data into high frequencies. Power flows through low-pass filters; data flows through high-pass filters. See figure 9-1 for an example.

Hi Johnny,

The THVD8000 is called Powerbus which is OOK modulated RS-485. The THVD8000 doesn't carry power itself - it is purely data. However, why you use this in power line communication is that you can essentially place the data and power onto the same pair of wires with a proper coupling network - allowing power and data to be conducted over a single pair of wires between system nodes. 

The example Clemens shows is a good example where the power is an AC signal fed to a rectifier and LDO - however you don't need the LDO or rectifier in every example - this is just one example. A more generalized example is shown below:

Essentially the power supply and data are coupled onto the same pair of wires and are decoupled when they reach respective loads. 

C1 - C4 will allow higher frequency OOK data through without much attenuation but will block DC and greatly attenuate low frequency AC (50/60 Hz).

L1 - L4 will allow power signal through without much attenuation but will attenuate the higher frequency OOK data - it is assumed that there is bulk capacitance on the supply and power loads - if these are not present you may see OOK noise on the load/supply - for DC systems this usually isn't a problem because DC power supplies typically have bulk capacitance already - but AC supplies don't necessarily have that so some extra filtering may be needed in that case. 

One note is that you can have more than 2 nodes - the simple examples just typically show 2 nodes. 

If this device interests you and you would like to learn more I highly encourage you to look at the following three guides:

1. THVD8000 Design Guide --> This is the generic design guide for standard implementations of the THVD8000 and a great starting place to get a better understanding of how to use this device. 

2. THVD8000 Low Voltage (<= 36VAC) guide --> Since the AC source can add some complexity there are some possible tweaks needed

3. THVD8000 High Voltage/ Low Bus Impedance Guide --> Sometimes for higher voltages (generally > 50V) you need a more robust systems so this guide explains how to do higher voltage / lower bus impedance applications - I wouldn't use this unless you need to though because it is more complicated. 

Also we do have a THVD80x0 calculator that can help you quickly size the inductors and capacitors in the system. 

Calculator:

7737.THVD80x0_Design_Calculator.xlsx

Please note that the calculator has slightly different equations used for sizing of the inductors/capacitors than the design guide/datasheet - the reason for this is that the datasheet/design guide ignore the loading from other THVD8000 devices - which for lower node counts is fine - but as more nodes in the systems are added the datasheet equations are not as accurate as the design calculator.

This is just a very brief overview of the device - so please if interested look at our other guides or if you have any other questions please let me know. 

Best,

Parker Dodson