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A Low Cost Discrete Digital Isolator Circuit

Thomas Conway

Abstract

This work presents a fully discrete, low cost digital isolator requiring no specialized ICs and implemented entirely with general purpose transistors and a two layer PCB embedded air core transformer. The design avoids vendor lock in and long term component obsolescence risks, while providing >1 kV isolation, ~200 ns propagation delay, and validated NRZ data rates of 1 Mbps. A modified dual oscillator architecture enables inherent hardware lockout suitable for half bridge gate driver applications. Measured performance and PCB layout guidelines are provided.

A Low Cost Discrete Digital Isolator Circuit

Abstract

This work presents a fully discrete, low cost digital isolator requiring no specialized ICs and implemented entirely with general purpose transistors and a two layer PCB embedded air core transformer. The design avoids vendor lock in and long term component obsolescence risks, while providing >1 kV isolation, ~200 ns propagation delay, and validated NRZ data rates of 1 Mbps. A modified dual oscillator architecture enables inherent hardware lockout suitable for half bridge gate driver applications. Measured performance and PCB layout guidelines are provided.
Paper Structure (8 sections, 6 figures, 1 table)

This paper contains 8 sections, 6 figures, 1 table.

Table of Contents

  1. Galvanic Digital Isolation
  2. Discrete Circuit Implementation
  3. Transmitter Side
  4. Receiver Side
  5. PCB Implementation with Copper Trace Transformer
  6. Prototype Measured Performance
  7. Low and High Side Signalling for Half Bridge Driver
  8. Conclusions

Figures (6)

  • Figure 1: Schematic of Digital Isolator using Discrete Components
  • Figure 2: Layout of transmitter (top side) and receiver (bottom side) for 2 layer PCB
  • Figure 3: Measured logic transfer for the prototype PCBs with a 1 Mbps NRZ random data signal
  • Figure 4: Corresponding Eye Diagram for 1 Mbps NRZ random data
  • Figure 5: High/Low Side Isolation for Half Bridge Application
  • ...and 1 more figures