So I have been trying to design and build a boost converter which steps 5 V up to 12 V. More specifically, the output is to drive a fan which runs on 12 V, 70 mA (nominally).
As could also be seen in the image, the converter has an n-channel MOSFET, with the gate connected to a square wave oscillator that runs on 20 kHz with a 50% duty cycle and the source connected to ground.
The input is a 5 V-DC power source, with the negative side grounded and a 40 mH inductor between the positive terminal and the MOSFET's drain.
Also connected to the drain, is the anode of a diode (normally a Schotky diode is preferred for a boost converter, but I had none on hand so I used a more ordinary diode. LTSpice simulations indicated no problem with this discrepancy), with the cathode being connected to a 470 μf capacitor and a 171 Ω resistor (to emulate the load) connected in parallel to ground.
Although this setup is effective in LTSpice simulations, the test build is not functioning properly. The square wave oscillator and the MOSFET are functioning (at least on their own), as do all of the other components.
No matter what load or capacitor, the output voltage only hovers around 1.8 V. Changing the frequency of the oscillator and especially changing the inductance has not tangible effect. In fact, even putting all inductors I have in series or in parallel does not seem to effect it. Not matter the configuration, no step up voltage can be measured.
I simply do not know what is wrong, be it the inductors, the oscillator, or the MOSFET. Admittedly, LTSpice did not have the exact models for OPAMPs (used for the oscillator) and MOSFETs as I have in real life, but analogous substitutes were used in the simulation.