Do PWM-Based AC Control Circuits Using MOSFETs Require ZCD Circuits?

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There are two common types of zero-crossing detection (ZCD) circuits: operational amplifiers and passive circuits comprising resistors, capacitors, etc. ZCD circuits are used for detection of zero voltage reference point in an AC signal or in a sinewave signal. A typical zero-crossing detection of the AC signal is shown in Fig. 1.

Many PWM-based AC control circuits such as inverters use MOFETs and ZCD circuits. MOSFET devices such as CS1501, AOZ5311NQI, AOZ5237QI and CS1601H have dedicated pins for ZCD and related functions. ZCD circuit is used to initiate the MOSFET switching cycle for monitoring and controlling actions such as synchronisation of the signals.

The ZCD circuit is used in many applications including controlled voltage rectifiers, resonant power supplies, AC motor speed controllers, AC power controllers, among others.