The invention relates to a primary side feedback (FB) 
switching power supply controller and a 
switching power supply 
system. The 
switching power supply 
system comprises a 
transformer, a 
voltage-dividing circuit, a main switch tube, an output circuit and the primary side FB switching power supply controller, wherein the 
voltage-dividing circuit is connected to the 
transformer; the power supply endof the primary side FB switching power supply controller is connected with the primary side first input end of the 
transformer; the FB control end of the primary side FB switching power supply controller is connected to the 
voltage-dividing point of the voltage-dividing circuit; the input end of the primary side FB switching power supply controller is connected with the grid of the main switch tube; the control end of the primary side FB switching power supply controller is connected to the source of the main switch tube; and the primary side FB switching power supply controller comprises an FB waveform detection module, a 
triangular wave generating circuit, a first comparer, a narrow pulse generating circuit, a second comparer and an RS (Reset-Set) trigger. Due to the implementation of the primary side FB switching power supply controller and the switching power supply 
system, provided by the invention, the 
system stability can be effectively improved, the complexity of a 
peripheral system can be lowered, the quantity of 
peripheral elements can be reduced, and the cost of a product can be reduced.