So, over the last couple days I have been again tinkering with my 555 timer based mosfet driver. This time I decided to see what would happen if I attached the drain pin of my mosfet in between a random ferrite donut connected to V+ and a SB560 Schottky diode hooked to a simple 120mm .46 amp rated computer box fan.
I set the frequency of the 555 timer's oscillator to around 25khz, turned down the duty cycle all the way via my voltage divider trimpot, set my resistance to around 18k going into pin 7 and hit the switch.
Amazingly the voltage on my output shot up from the ~9.35V out of my 2.5 amp rated SMPS wall wart to around 10.5v. Adjusting the duty cycle up resulted in a final output voltage of around 22v at which point the fan broke free from what I had propping it up from the force of the air it was moving. When the fan hit it got something on my desk caught up in the blades breaking one off. With the fan stopped the open circuit voltage shot up to around 68 volts.
I quickly proceeded to hit the oh shit cutoff button I rigged on my breadboard since my output caps were only rated at 50v. Luckily nothing blew up. A second attempt at driving another cheap recycled fan resulted in me achieving 30v with no signs of the toroid having reached its saturation point.
Still not satisfied, I fished around in my transformer pile and dug out a small 4 pin transformer maybe around the size of an ATX PSU 5v standby transfomer, just shorter and more rectangular. Realizing exactly the potential these things have from my donut experiences I decided to change my output filtering caps to a couple 200v caps also scavenged out of a PSU. Also, if the output of transformer went high enough I had to take precautions to protect myself from anything blowing up.
The idea was to use the transformer as a flyback. To do this I decided it would be best to rectify the output of the transformer into a capacitor and measure the voltage. I ended up using a BYV26C ultrafast sinterglass avalanche diode with a reverse breakdown voltage of 600v and reverse recovery time of 30ns as my rectifier, a .68uF nonpolarized 400v rated film capacitor as my tank, a 200v rated p6ke200 zener/transient diode connected to the positive pin in parallel with a beefy 180k resistor to safely bleed down the cap upon turning off the power or in the even the output of the transformer went overvoltage.
With my driver again turned all the way down I fired it up. ~750mv. Crap. Ok so I must have hooked it up to the primary... lets try it the other way around. Bingo... 100+ volts. So far so good... I remembered somewhere that SMPS transformers can be like wound and polarity biased so I reversed the output leads at which time I found out exactly what the little beast was capable of... imagine that 200+ volts out of a 9v PSU!
I set the frequency of the 555 timer's oscillator to around 25khz, turned down the duty cycle all the way via my voltage divider trimpot, set my resistance to around 18k going into pin 7 and hit the switch.
Amazingly the voltage on my output shot up from the ~9.35V out of my 2.5 amp rated SMPS wall wart to around 10.5v. Adjusting the duty cycle up resulted in a final output voltage of around 22v at which point the fan broke free from what I had propping it up from the force of the air it was moving. When the fan hit it got something on my desk caught up in the blades breaking one off. With the fan stopped the open circuit voltage shot up to around 68 volts.
I quickly proceeded to hit the oh shit cutoff button I rigged on my breadboard since my output caps were only rated at 50v. Luckily nothing blew up. A second attempt at driving another cheap recycled fan resulted in me achieving 30v with no signs of the toroid having reached its saturation point.
Still not satisfied, I fished around in my transformer pile and dug out a small 4 pin transformer maybe around the size of an ATX PSU 5v standby transfomer, just shorter and more rectangular. Realizing exactly the potential these things have from my donut experiences I decided to change my output filtering caps to a couple 200v caps also scavenged out of a PSU. Also, if the output of transformer went high enough I had to take precautions to protect myself from anything blowing up.
The idea was to use the transformer as a flyback. To do this I decided it would be best to rectify the output of the transformer into a capacitor and measure the voltage. I ended up using a BYV26C ultrafast sinterglass avalanche diode with a reverse breakdown voltage of 600v and reverse recovery time of 30ns as my rectifier, a .68uF nonpolarized 400v rated film capacitor as my tank, a 200v rated p6ke200 zener/transient diode connected to the positive pin in parallel with a beefy 180k resistor to safely bleed down the cap upon turning off the power or in the even the output of the transformer went overvoltage.
With my driver again turned all the way down I fired it up. ~750mv. Crap. Ok so I must have hooked it up to the primary... lets try it the other way around. Bingo... 100+ volts. So far so good... I remembered somewhere that SMPS transformers can be like wound and polarity biased so I reversed the output leads at which time I found out exactly what the little beast was capable of... imagine that 200+ volts out of a 9v PSU!
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