Transient loads are also known as high di / dt dynamic loads. Which is characterized by transient changes in the load current, and the load current change rate (di / dt) is very large. For example, the rate of change in current for high-speed logic and RF / microwave transmitters may exceed 100 A / ps. The current production of low-voltage microprocessors in different modes of operation between the fast switching, will also have an impact on the switching power supply in a few nanoseconds time can make the switching power supply output current changes several orders of magnitude. Again, many computers have switching power supply voltages of + 3.3V, and when switching data from the database, the switching power supply is required to respond to a 30A / us load current transition. Assume that the load current is changed from zero to 5A for a time of 1us. If the bandwidth of the switching power supply is 25 kHz, the time required to complete the above change is 1/25 kHz = 40 μ. Assuming that the current is linearly rising, the amount of charge missing is (5A / 2) X40us = 100uC. If the allowable +3.3 voltage fluctuates by 50mV and the instantaneous energy is supplied by the output filter capacitor, a capacity of 100 uC / 50 mV = 2000uF is required to prevent the voltage from falling below the specified value. It should be noted that a nominal capacitor can not be used to achieve the above purpose, but should use a few small capacity capacitor parallel to 2200uF. Since the total output filter capacitor is equivalent to the series resistance R'esr = 50mV / 5A = 10mΩ, the equivalent series resistance of each small-capacity capacitor should be R'esr = 10mΩ / n, and n represents the number of shunt capacitors. When n = 4, R'esr = 40mΩ. This can greatly reduce the requirements of the output filter capacitor.