Shielded Optocouplers Prevent Offline Switching Power Supply Upset

摘要

Switching power supplies, operating directly from input power lines, are generally required to have their outputs galvanically isolated from the input, in order to reduce the danger of electrical shock to the end user. A high frequency power transformer typically performs this isolation function. Since most switching power supplies are controlled on the primary side of the isolation transformer, but sense the output voltage on the secondary side, a means must be provided to relay the voltage sensed on the secondary side back across the isolation boundary to the control circuit on the primary side.