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62 lines
2.8 KiB
62 lines
2.8 KiB
# Low side MOSFET switch
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* Fits a AO3400, 2301V or similar SOT23-3 N-MOS transistor
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* Lets you control a 5A load from a 3.3V logic pin
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* Designed at ELAB, bare PCBs and matching transistors can be found in the SMD drawers
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# Basic configuration
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* Only the transistor needs to be populated, all other components are optional
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* This configuration is suitable for RESISTIVE loads for example:
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* LEDs with suitable resistors
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* Heating elements
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* Incandescent bulbs
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* *small* inductive loads should ok OK like a tiny < 0.5A DC motor
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# Notes and tips
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* This is a LOW side switch. OUT+ is always connected to VCC, only OUT- is switched. Because of this, this board is not recommended for switching modules that have more connections than just VCC and GND
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* At 5A the transistor will get hot. Ventilation might be necessary
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* Use wires thick enough for the current. AWG24 or better for 5A
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* Remember that max 5A 30V does not mean it's ok to do 30A 5V! But you knew that, right?
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## To use with inductive loads (DC motors, coils, speakers, etc)
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* Populate the FLYBACK DIODE
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* It protects the transistor from flyback voltage, caused by switching inductive loads
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* Recommended diode: SS34 in SOD-123 package
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* Note the direction of the diode - stripe towards VCC
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## Proportional "analog" control
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* To control the power of the load (instead of just ON/OFF operation), use PWM
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* The "analogWrite()" of an arduino produces a suitable PWM output
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* Do not use a potentiometer at the gate! The FET will not enjoy that at all
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# Other optional components
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## Gate pull-down resistor
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* Strongly recommended
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* Ensures safe operation when a controlling MCU is booting / sleeping / disconnected
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* Allows use with simple pushbutton as source of control signal
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* Can be anything between 1k and 100k, in 0603 package
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## LED and its resistor
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* LED shows status of control line - shines when switch is ON
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* Recommended resistor: 330 - 2700Ohms, depending on MCU voltage and LED
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* Both the resistor and LED are in 0603 package
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## Bypass capacitor
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* Only useful when intending to PWM the load at higher frequencies (>10kHz)
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* Reduces electromagnetic interference emitted by the input cables
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* Might somewhat improve performance of switched device
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* 1-100uF, must be rated for at least VIN * 1.5
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* Footprint for 0603 package, but an 0805 might fit as well.
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# Other options
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* For bi-directional motor control, use a motor driver or H-bridge, [like this one](https://git.elab.kth.se/marek/pcb-hbridge-cp2119l/src/branch/main/README.md)
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* For digital modules, like an ADC or OLED module, use a HIGH-SIDE switch. A high side switch module based on a CH217 is coming to elab "soon".
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---
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Made at [ELAB](http://elab.kth.se) by Marek Baczynski. Find him on the ELAB slack if you have any questions |