Type B RCD with a simplified magnetic modulation/demodulation method

In this paper, a type of Type B RCD applying a simplified magnetic modulation/demodulation method is designed to detect residual currents of sinusoidal AC, pulsating DC and smooth DC to protect person against indirect/direct contact and fire hazards. A modulation method based on RL self-oscillation circuit is applied to modulate AC and DC residual current with square-wave pulse signal. A simplified demodulation method, involving a 2^nd-order LPF (Low Pass Filter) circuit, is designed to easily measure AC and DC residual current. Type B RCD presented in the paper fulfills the AC and DC residual current protections complying with IEC60947-2 Annex B and IEC60755. Furthermore, this Type B RCD characterizes a simple structure, small size and low cost.