k so i just finished building i guess what could be called a single switch forward converter. Pretty simple stuff, the only problem is that the voltage stresses on the transistor are pretty high. Now, i've posted the schematic i'm using at the bottom.
the PWM is coming from this circuit here:
**broken link removed**
i've used the circuit before on a motor and it seems to work pretty good.
using some simulations (since i don't have a scope), the pulse duration (on time + off time) is 20.15µS...i don't know what frequency that is...but the cap i use is pretty close to the 800pF i used in my simulations. i think its like 832pF or something on the timer?
now here's where the problem comes in..i was testing out the switching supply on the transformer (which i wound myself from a core taken from a 400watt PSU), and at 12vdc, it was drawing 3.14A! not good if i'm gonna eventually want to use this with mains voltage! but i believe all that happened after the mosfet broke...cause before the mosfet broke, i had 6vdc (pulsed with the 555) on the primary and i was getting around 0.5vac on the secondary (yah i know i still have to tweak the transformer turns ratios)....i shorted the secondary and was able to get around 600mA, so atleast i could draw current
...then i started turning up the voltage and that's when the problems started..I heard something go "click" and then the mosfet started to heat up rapidly and the transformer core started vibrating with a 60hz hum....i then stopped everything, disconected the mosfet and checked for any shorts....I found that the Gate-Drain resistance was at 12 ohms. That's not supposed to happen! So...does anybody have some ideas as to what went wrong??
the PWM is coming from this circuit here:
**broken link removed**
i've used the circuit before on a motor and it seems to work pretty good.
using some simulations (since i don't have a scope), the pulse duration (on time + off time) is 20.15µS...i don't know what frequency that is...but the cap i use is pretty close to the 800pF i used in my simulations. i think its like 832pF or something on the timer?
now here's where the problem comes in..i was testing out the switching supply on the transformer (which i wound myself from a core taken from a 400watt PSU), and at 12vdc, it was drawing 3.14A! not good if i'm gonna eventually want to use this with mains voltage! but i believe all that happened after the mosfet broke...cause before the mosfet broke, i had 6vdc (pulsed with the 555) on the primary and i was getting around 0.5vac on the secondary (yah i know i still have to tweak the transformer turns ratios)....i shorted the secondary and was able to get around 600mA, so atleast i could draw current