Load on or off when the power supply voltage,Its a mutation process ,for some appliances,the rapid change in current is too large,is likely to cause adverse effects,such as ranging from burned fuses,Power so incandescent moments damage phenomenon is also common.Through the redesign of the circuit,so that when you turn the power on and off the ladder to rise or fall stepped manner,and rise and fall times can be easily and arbitrarily changed,and thus the circuit protective devices play an effective role in cushioning .