Precision Optocoupler (v2.0)

An optocoupler is used to isolate a voltage source from the process (or experiment) by creating a optical link between the two using an LED-photodiode combination. A digital optocoupler can output only digital signals (high or low), while an analog optocoupler faithfully reproduces the input voltage into the same output voltage but now produced by an independent power source. This device provides good electrical isolation of the power source (typically, an analog output card of a computer) from potentially harmful processes that might occur on the experiment side (eg: voltage spikes during fast switching of magnetic fields).

The circuit and the board is a replica of a project by Todd Meyrath which can be found here. The central optocoupler circuit was inspired by fig. 17 of the datasheet of the HCNR200.

The original project required two independent +/- power supplies. This revamped version (2024) can be powered from a single +/- power supply by utilizing an isolated DC-DC converter (plus sophisticated filtering) to power the secondary side. If signal quality is absolutely important and any kind of residual noise introduced by the DC-DC converter (<1 mV) one can power the device as before from two independent (linear) +/- power supplies.

• Mechanical compatible with standard 160x100mm EuroCard slot (can be powered by backplane)
• Bandwidth is roughly 200-250 kHz (step-response: 4 µs delay)
• RMS ripple on the output should be around 2-3 mV

Project date (v2.0): July 2024

About 10 almost fully populated boards have been ordered by VLBAI of which ~3-4 will be used.

Klaus Zipfel (VLBAI)

The project is developed and managed by VLBAI at the VLBAI gitlab instance. Access can be granted by VLBAI members, if you need to develop on the project. A mirror is available IQ Gitea

• The schematic in PDF-Format
• The production files (gerber, cpl, bom)
• The Layout in HTML format (ibom)

Input and output signals should ideally match 100% (offset and amplitude). If not, adjust via the three trimmers until they match.

Then apply a step-function (e.g. 1V, 50% duty at 1 kHz) to the input and observe the output. If you see oscillations/harsh transients, you might have not populated capacitor C11, C14 (missed out by first JLCPCB batch → Place 4.7 pF).

Additional components required per board (not populated by JLCPCB)

Was für die nächste Version zu tun ist: (: verworfen, : in Arbeit, : im Schaltplan, aber noch nicht im Layout, : erledigt)