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foreword
At present, many peripherals are USB interface, but the power consumption is not low, especially some devices have a large current at instant start, such as some brands of lidar, only the power supply of 3.0 USB interface can barely support, and due to The instantaneous start-up current is very large, and it may damage the USB interface of the machine. In order to deal with this kind of situation, I will share with you a pre-charging power supply circuit.
1. Schematic diagram
2. Schematic Analysis
The overall principle is to provide sufficient starting current for the device through capacitor precharging, but it is not so simple to directly connect two capacitors at the output. The overall circuit is divided into three parts:
1. The pre-charge control circuit charges the energy storage capacitor before the power supply is output, and needs to control the charging current, which cannot be too large, otherwise it is easy to burn out the USB port. In addition, when the output is turned on, it must be charged at full speed, otherwise the capacitor discharge current is large, the charging current is small, and the output voltage will be pulled down immediately.
2. For energy storage capacitors, it is best to choose solid capacitors, because the internal resistance of general farad capacitors is relatively large, and it is easy to pull down the voltage when a large current is discharged. When the output capacity is not enough, you can combine several.
3. The output control circuit. This part is based on the voltage judgment made by the reset detection chip. When the capacitor voltage meets certain requirements, the output signal controls the total output switch and releases the limitation of the charging current. The actual one used is MAX809MEUR.
During the actual test, you can observe the voltage change on the energy storage capacitor and leave a little more threshold.
Summarize
This circuit is suitable for peripherals with large startup current, but only for a short time. If the power consumption is very large when it is running, this circuit cannot solve it.