Just playing around with making a transformer, I don't need a lot of current, under 1 amp, basically I want to boost 7.4v (2 lithium cells) to around 12 to power a computer fan. I'm not fussy about the exact voltage, so I decided to just go for a 1:2 ratio which will give me more voltage and account for diode/load drop. 5 turns primary, 10 turns secondary originally but it's a bit more from playing around with it. The core is rather small, it's just a ferrite bead. That may be part of my issue too. About 0.08cm^2.
I'm driving it using a 555 timer which is driving a low side (can that be an issue?) N channel mosfet. Everything is fed from 5v.
Here is the wave form, the yellow is the output of the mosfet, the blue is the output of the transformer - I inversed it just to make it easier to read.
Note the volt/div. Getting 50 volts even on primary! I'm actually feeding it with 5. So it's almost like the transformer is causing back EMF or something, could that be? Or would back EMF be going the opposite way? I double checked that my probes are set correctly, ex: 10x and set 10x on scope, as that was my first suspicion.
I presume that what is happening is I'm saturating my core, does that sound right?
This is output of 555 timer in blue:
Circuit is rather basic, got some pull up/down resistors in some places such as mosfet to ensure it does not stay stuck on and the transformer secondary has a high value resistor to act as a basic load, I also put a diode to try to force the voltage to stay on the positive side and act as basic protection for the load. Not sure what good it's doing though as you can see in the scope it goes into the negatives a bit.
I can make a schematic if you want, but here is a pic of my setup:
Mostly just curious about the voltage spiking and the odd wave form, I presume it has to do with my transformer design but curious what I can try to improve it. Ex: if the core is too small, or if I need to use a normal E core etc.