A welding power supply apparatus configured to provide direct current welding power, comprising: a component disposed to output a DC bus voltage; a direct current-alternating current (DC-AC) power converter, the DC-AC converter disposed to receive the DC bus voltage and to output a primary alternating current voltage; an isolation transformer stage configured to receive the primary alternating voltage from the DC-AC power converter on a primary side of the apparatus; an active rectifier circuit, the active rectifier circuit arranged on a secondary side of the apparatus and coupled to the isolating transformer stage; and a controller coupled to the active rectifier circuit and the DC-AC converter, wherein the active rectifier circuit is configured to operate with zero current switching, ZCS, characterised in that the controller comprises: a first pulse width modulation system, wherein the first PWM system is configured to modulate a position of a lagging edge of a control signal; a second PWM system, wherein the second PWM system is configured to modulate a position of a leading edge of a control signal; a ZCS latch; an OR gate; and PWM latches (D115, D116), wherein the controller is configured to store a lagging edge PWM pulse in the ZCS latch in accordance with a signal from the OR gate, which is configured to sum set signals of the PWM latches (D115, D116) that are configured to generate switching signals for the active rectifier circuit, and wherein the controller is further configured to use a modulated version of an output of the ZCS latch in order to trigger outputs of PWM signals (D109, D110) supplied to the DC- AC power converter. a component disposed to output a DC bus voltage; a direct current-alternating current (DC-AC) power converter, the DC-AC converter disposed to receive the DC bus voltage and to output a primary alternating current voltage; an isolation transformer stage configured to receive the primary alternating voltage from the DC-AC power converter on a primary side of the apparatus; an active rectifier circuit, the active rectifier circuit arranged on a secondary side of the apparatus and coupled to the isolating transformer stage; and a controller coupled to the active rectifier circuit and the DC-AC converter, wherein the active rectifier circuit is configured to operate with zero current switching, ZCS, characterised in that the controller comprises: a first pulse width modulation system, wherein the first PWM system is configured to modulate a position of a lagging edge of a control signal; a second PWM system, wherein the second PWM system is configured to modulate a position of a leading edge of a control signal; a ZCS latch; an OR gate; and PWM latches (D115, D116), wherein the controller is configured to store a lagging edge PWM pulse in the ZCS latch in accordance with a signal from the OR gate, which is configured to sum set signals of the PWM latches (D115, D116) that are configured to generate switching signals for the active rectifier circuit, and wherein the controller is further configured to use a modulated version of an output of the ZCS latch in order to trigger outputs of PWM signals (D109, D110) supplied to the DC- AC power converter. a first pulse width modulation system, wherein the first PWM system is configured to modulate a position of a lagging edge of a control signal; a second PWM system, wherein the second PWM system is configured to modulate a position of a leading edge of a control signal; a ZCS latch; an OR gate; and PWM latches (D115, D116), wherein the controller is configured to store a lagging edge PWM pulse in the ZCS latch in accordance with a signal from the OR gate, which is configured to sum set signals of the PWM latches (D115, D116) that are configured to generate switching signals for the active rectifier circuit, and wherein the controller is further configured to use a modulated version of an output of the ZCS latch in order to trigger outputs of PWM signals (D109, D110) supplied to the DC- AC power converter.