Power Management
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An overview of the voltages needed for this project:
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24V - Created by the Power Supply
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Motors
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Bed and Extruder Heaters
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5V - Created by LM7805
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UI display
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USB
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3.3V - Created by LM317/LM1117
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Microcontroller
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Bumper switches
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Memory IC and SD Card
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Motors
The stepper motors are driven through a stepper motor driver IC from TI that supports 24V and has current-limit sensing that will turn off the output to the motor and toggle a pin in the case of an error, which could be an object that impedes the motor and causes the current to spike.
The typical current of each motor will vary, due to the different loads that it is moving. For example, the X motor that moves the extruder will draw less current than the Y motor that moves the much heavier bed.
Heaters
We estimated that the heating elements would require up to 1A at 24V so the MOSFETs and gate drivers were chosen to meet these specifications and control that amount of power from a PWM module on the microcontroller.
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The NMOS MOSFETs chosen are rated for over 24V and 1A and require gate drivers in order to switch from the microcontroller's 3.3V signal. Also see Heater Control.
Motors and Heaters Together
Due to the quick demand for power from both the motors and the heaters, some bulk capacitance was added to the 24V line. The amount of bulk capacitance needed was not tested due to the project’s development being cut short.
The use of an eFuse, an IC that acts as a resettable fuse, was considered to act as a last resort protection element if the heaters or the motors consumed too much current as well as alert the microcontroller that such an event occurred.
5V and 3.3V
The current draw from the IC’s and circuits on these voltage rails is small and the voltage regulators chosen are both capable of 1.5A. Both of these regulators should be sufficient in bucking 24V to these respective voltages.