With the development of technology, the world's environmental protection requirements are getting higher and higher, so lithium iron phosphate battery as a new environmentally friendly battery, began to gradually applied to electric vehicles, will become the head of the battery industry and become the trend of future development. Usually, due to the characteristics of lithium iron phosphate batteries, in the application of its charge and discharge process needs to be protected from overcharge and overdischarge or overheating, to ensure the safe operation of the battery. Lithium iron phosphate as a bit of new energy is used in our lives can not be separated from the electric bicycle industry, our understanding of the electric bicycle circuit structure and application characteristics is imminent, today the country's creation and everyone to hand over the electric bicycle circuit structure and application characteristics.
A simplified model of the discharge circuit of the LiFePO4 battery protection board for electric bicycles is shown in Figure 1. Q1 is the discharge tube, using an N-channel enhancement MOSFET, and in practice, depending on the application, multiple power MOSFETs are used to work in parallel to reduce on-resistance and enhance thermal performance. RS is the equivalent internal resistance of the battery, and LP is the battery lead inductance.
During normal operation, the control signal controls the MOSFET to turn on and the battery pack terminals P+ and P- output voltage for the load. At this time, the power MOSFET has been in the conduction state, the power loss is only conduction loss, no switching loss, the total power loss of the power MOSFET is not high, the temperature rise is small, so the power MOSFET can work safely. However, when the load is short-circuited, due to the circuit resistance is very small, the battery discharge capacity is very strong, so the short-circuit current from the normal operation of tens of amps suddenly increased to several hundred amps, in this case, the power MOSFET is easy to damage.
