What are the safety standards required for photocouplers?

When photocouplers are mounted in equipment as a means of "isolation" for assuring safety such as protecting the human body against an electric shock, they may be restricted by safety standards. Including standards and criteria for assuring safety, a broad range of items related to electricity have been standardized as standards. The safety standards are divided into equipment standards, which apply to end products, and component standards, which apply to individual photocouplers.

Each country has its own safety standards based on the International Electrotechnical Commission (IEC) standards. The typical standards include UL in the U.S, VDE in Germany and BSI in Britain. The UL standards in the U.S. and the VDE standards in Germany, both of which are applicable to photocouplers, have completely different definitions of test methods for measuring input-output insulation performance and of acceptance criteria.

• UL: Using the Dielectric Strength Test method, this test judges the insulation performance by whether or not dielectric breakdown occurs when a high voltage is applied.
• VDE: By using the Partial Discharge Test method, this test judges the insulation performance by checking that an electric charge produced by a partial corona discharge is of 5pC or less.

For details, also refer to Toshiba Application Note "Safety Standards for Photocouplers", Chapters 1 to 3.
(https://toshiba.semicon-storage.com/ap-en/semiconductor/knowledge/application-note.html)