Bicycle USB Charger

This circuit has been developed to add a USB charging port to a bicycle for charging a mobile phone. The input supply for the circuit is produced by a dynamo (6V, 3W dynamo) in the bicycle.

The circuit is based on LM2596-5.0. It is a 3A step down voltage regulator. LM 2596 are available in fixed output voltage of 3.3, 5, 12v and an adjustable output version. The LM2596 series operates at a switching frequency of 150 kHz, thus allowing smaller-sized filter components than what would be needed with traditional lower-frequency switching regulators. The IC provides all active functions for a step-down (buck) switching regulator, capable of driving a 3A load with excellent line and load regulation.

Circuit & Part list

  • C1        1000uf
  • C2        470 uf
  • D1-D2        1N5818
  • D5        1N5818
  • J        Dynamo 6v 3W
  • L        33 u
  • LED
  • R          1k
  • SW        1 on/off switch
  • IC        LM2596
  • USB-A Connector

How it Works?

The alternating voltage generated by the dynamo is converted to DC by a full-wave bridge rectifier comprising Schottky barrier rectifier diodes D1 through D4 and a filtering electrolytic capacitor (C1). The output of the bridge rectifier, which is charged to peak value of AC voltage (nearly 10V), is input to switching regulator LM2596-5.0 to provide a regulated 5V (DC) output, which is suitable for charging mobile devices using the USB connector.

The 5mm LED (LED1) in the circuit indicates output status. Feedback connection FB (pin 4 on IC1) is connected directly to output voltage at electrolytic capacitor C2. The 33μH inductor (L1) should be rated for a DC current of at least 1A. The dynamo output is connected to the circuit by switch S1.