If you are installing an IRIG-B bus from the High Voltage (HV) MOSFET output on the ITR, and want to power the HV MOSFET circuit with a secondary isolated power supply, specific wiring is required for the circuit to work. This article describes how to correctly wire the ITR HV MOSFET circuit with a secondary power supply.
Figure 1 - Incorrect wiring of an IRIG-B bus using the ITR HV MOSFET circuit powered with a secondary isolated power supply
The HV MOSFET circuit on the ITR is polarity sensitive and will not work if the power supply is wired backwards. The circuit includes a diode across the HV-SW output, to ensure that the input power supply polarity is correct.
The positive terminal on the HV-SW output is connected to the MOSFET drain and the negative terminal on the HV-SW output is connected to the MOSFET source. In figure 1, the MOSFET drain is connected to the negative part of the power supply, meaning that the ITR HV MOSFET circuit is being supplied with -10V. Due to the backwards polarity of the input power supply, the HV MOSFET circuit will not work. Figure 2 highlights this issue.
Figure 2 - Diagram clarifying incorrect polarity for ITR HV MOSFET power supply input.
To make the HV MOSFET circuit work using a secondary isolated power supply, the following design changes should be made for the HV MOSFET wiring connections between the ITR and the IED, see figure 3.
- Move the fuse to connect to the HV-SW positive terminal on the ITR.
- Correct the HV MOSFET power supply to use the correct polarity.
- Move the load resistor so that it connects between the negative terminal on the power supply and negative terminal on the HV-SW.
Figure 3 - Correct wiring of an IRIG-B bus using the ITR HV MOSFET circuit powered with a secondary isolated power supply