Improved Mosfet switching circuit for powering Hydrogen fuel system

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Improved Mosfet switching circuit for powering Hydrogen fuel system

MOSFET switch for hydrogen generator systems

A Simple Switch

MOSFETs are really easy to “saturate”, which just means that they are fully open, and they are dead reliable for very fast switching between their saturation and cut-off regions (fully on and fully off regions). This makes them wonderful switches, especially for high power applications like motors, lamps, etc. In most cases, you can use the same power supply that you are using for your high power device to operate the MOSFET as well, using a mechanical switch to apply the gate voltage. The image below shows exactly that type of application

Build:
For this project wewill use N channel MOSFET only

Place the N-ch MOSFET on the board. Connect the 1kΩ resistor between the gate and GND. Connect the switch between the gate and +9V. Place the 220Ω resistor and LED in series between +9V and the drain. Tie the source pin directly to GND. See image below.

Push the button and the LED should light up. The 1kΩ resistor acts as a pull-down resistor, keeping the voltage at the gate at the same potential as the negative battery terminal until the button is pushed. This puts a positive voltage at the gate, opening the channel between the drain and source pins and allowing current to flow through the LED. Note that the gate voltage is +9V and there are no negative side effects.

 

Step 3: Motor Drivers  – not applicable or necessary configuration for Hydrogen electrolysis circuits

Improved Mosfet switching circuit

Building off of Step 1, we can use the ZVN as a DC motor driver. To avoid over-current damage to the ZVN, I’m using a small 6V DC hobby motor, much like the kind you find inside of small hobby servos. With a higher current N-ch MOSFET, you can drive larger motors with larger current needs.

Looking at the schematic below you’ll see two diodes placed backward (reverse biased) across the motor contacts and across the MOSFET drain/source pins. Any electrical component that has a coil in it (inductors, relays, solenoids, motors, etc.) can generate a very large voltage spike in the reverse direction when it is turned off. (This is a common problem in airsoft, and it can lead to premature wear on the trigger contacts that turn on the motor. An easy fix for this is to add an “airsoft MOSFET”, and this is a similar example. It should be noted that the parts used here are nowhere near capable of handling the voltage/current needs of an airsoft motor, so don’t use this specific example.) The diodes give that spike a place to go so that the components are not damaged.

Improved Mosfet switching circuit

Build: Place the ZVN on the board. Connect the 1kΩ resistor between the gate and GND. Connect the switch between +6V and the gate. Connect the source to GND. Connect the drain to the negative motor lead. Tie the positive motor lead to +6V. Place one diode between the drain and source pins, with the stripe on the diode facing the drain pin. Put the other diode across the motor leads, with the stripe toward +6V. See image below.

Once everything is connected, double check it. And again. It’s really easy to get things switched and even though it probably won’t matter with this circuit, it’s a good habit to already have when it does matter. Then push the button and your motor should run in one direction.

Improved Mosfet switching circuit

Conclusion

As you can see MOSFETs are extremely useful. They are arguably the most important electronic component in use today when you look at how much we rely on them for our everyday electronic devices. There isn’t a day that goes by that you don’t use several million transistors just to do something simple, like look at what time it is. Or make your coffee, check your email, watch a movie, listen to music, or read this I’ble.

You may have noticed that there is no mention of MOSFETs as amplifiers here. I did that on purpose, but that isn’t to say that they can’t be used as such. My experience has been that analog signal amplification duties are best handled by BJTs, and fast, high current switching is best done by MOSFETs. I realize that is a generalization, as there are plenty of examples for both transistor types working both ways very well. I encourage you to do the research yourself if you wish to learn more on those applications.

 

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