PWM Power Supply with Constant Current

Figure 1 

The purpose of this project is to control the current across a load by using pulse width modulation for maximum power efficiency while being constructed on a breadboard.

The project accommodates the need for constant current by utilizing NE555 chips to build this power supply that used for lighting an LED or powering a motor. To keep the load at a constant predetermined current, the circuit will be operated by the user by plugging the circuit into a power supply.

During the operation, when the circuit is connected to power supply, the astable mode will oscillate but falling at the edge of astable will trigger the monostable. It will stay high for a variable period which is modulated by the difference amplifier. The current is allowed to flow by the MOSFET switches and it is set using an LC circuit to smooth out the voltage into a DC flow.

The LED will turn ON when the output is high, making the load current too high. By changing its output, the difference amplifier attempts to make this as the reference. This will cause the output of difference amplifier to drop while monostable increases.

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