Thus single-phase full-wave circuits can only be used for h.v. applications if the h.t. winding of the transformer can be earthed at its midpoint and if the d.c. output is single-ended grounded. More commonly used are single-phase voltage doublers, a circuit of which is contained in the voltage multiplier or d.c. cascade of Fig. 2.6, see stage 1. Although in such a circuit grounding of the h.v. winding is also not possible, if asymmetrical d.c. voltages are produced, the potential of this winding is fixed. Therefore, there is no danger due to transients followed by voltage breakdowns.