Under normal operating conditions, the open-drain comparator output remains low, allowing a nominal current of 430µA to flow from the transistor's emitter through R2 to COUT1. The same current also flows through the collector and R1, generating a VGS voltage slightly above -6.4V, which drives the p-channel MOSFET into conduction.
This design is configured with a current limit of 900 mA. The MAX4373FESA was selected due to its ability to provide a 50V/V gain from the current-sense resistor to the output. When a 900 mA current flows through R6 (100 mΩ), it creates a voltage drop of 90 mV across the resistor. With a gain of 50, this results in an output voltage of 4.5 V at the OUT terminal.
To set the comparator’s threshold, a 6.5:1 resistor divider network is used. R4 is chosen as 68kΩ and R5 as 10kΩ, resulting in a load current threshold of approximately 936 mA, which is close enough to the target value of 900 mA.
When the load current exceeds this threshold, the comparator output transitions to a high-impedance state. This causes the transistor to enter the cutoff region, turning off the MOSFET. Once the fault condition is cleared, the circuit can be reset using the reset button to return to normal operation.
This circuit is suitable for high-voltage applications, such as those operating at +28V. It ensures that the voltage is at least twice the VCC level. Additionally, VCC is limited to a maximum of +5.5V, which stays within the operational range of the comparator. The difference between R1 and R2 introduces a certain gain, helping to increase the MOSFET gate drive voltage and reduce conduction losses.
Overall, this design provides a reliable and efficient way to manage current limits in high-voltage systems while maintaining stability and performance under various load conditions.
Outdoor Power Supply,Solar Lithium Battery,Portable Rechargeable Lantern,Power Solar Station Equipment
Sichuan Liwang New Energy Technology Co. , https://www.myliwang.com