# Low side MOSFET switch
* Fits a AO3400, 2301V or similar SOT23-3 N-MOS transistor
* Lets you control a 5A load from a 3.3V logic pin
* Designed at ELAB, bare PCBs and matching transistors can be found in the SMD drawers


# Basic configuration
![Basic configuration](images/basic.png)
* Only the transistor needs to be populated, all other components are optional
* This configuration is suitable for RESISTIVE loads for example:
	* LEDs with suitable resistors
	* Heating elements
	* Incandescent bulbs
* *small* inductive loads should ok OK like a tiny < 0.5A DC motor


# Notes and tips
* 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
* At 5A the transistor will get hot. Ventilation might be necessary
* Use wires thick enough for the current. AWG24 or better for 5A
* Remember that max 5A 30V does not mean it's ok to do 30A 5V! But you knew that, right?

## To use with inductive loads (DC motors, coils, speakers, etc)
* Populate the FLYBACK DIODE
* It protects the transistor from flyback voltage, caused by switching inductive loads
* Recommended diode: SS34 in SOD-123 package
* Note the direction of the diode - stripe towards VCC

## Proportional "analog" control
* To control the power of the load (instead of just ON/OFF operation), use PWM
* The "analogWrite()" of an arduino produces a suitable PWM output
* Do not use a potentiometer at the gate! The FET will not enjoy that at all

# Other optional components
![Full configuration](images/full.png)

## Gate pull-down resistor
* Strongly recommended
* Ensures safe operation when a controlling MCU is booting / sleeping / disconnected
* Allows use with simple pushbutton as source of control signal
* Can be anything between 1k and 100k, in 0603 package

## LED and its resistor
* LED shows status of control line - shines when switch is ON
* Recommended resistor: 330 - 2700Ohms, depending on MCU voltage and LED
* Both the resistor and LED are in 0603 package

## Bypass capacitor
* Only useful when intending to PWM the load at higher frequencies (>10kHz)
* Reduces electromagnetic interference emitted by the input cables
* Might somewhat improve performance of switched device
* 1-100uF, must be rated for at least VIN * 1.5
* Footprint for 0603 package, but an 0805 might fit as well.


# Other options
* 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)
* 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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Made at [ELAB](http://elab.kth.se) by Marek Baczynski. Find him on the ELAB slack if you have any questions