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Registered Member #1951
Joined: Sun Feb 01 2009, 01:59PM
Location:
Posts: 105
hi,
i have build a sstc off off a ne555 design i pulse the primary via a mosfet, that get it's signal from a ne555.
but the strange thing is when i crank up the voltage to about 30-40 volts it stops and shorts the mosfet, and meens the ne555 is to hot to touch.
what could be the reason this is happening? i have build a sstc from steve's site, the mini sstc, but that project was a long time ago beside's i could get it to work, and now i want to go back to basic's so i build a sstc with a ne555 i have not many ne555's left so :S
any idea why?
if you need a picture of my setup i'll make one :)
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Pictures and schematics would be helpful.
If it is just a 555 timer controlling a single switch then a possibility is that your FET is dying and shorting your 555's output to ground. Another possibility is that there is noise feeding into your 555 causing it to latch up or something silly like that, making the 555 die stick the FET high, taking the FET down with it.
The NE555 doesn't have a great max frequency rating, so that could be to blame, also. Fres?
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
The 555 has a maximum voltage of about 15V IIRC, though it works up to about 25V. The mosfet's gate must not be more than about 20V away from the source, and maybe that is why it dies when you crank up the voltage.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Scope the waveform on the mosfet gate and drain. You *do* have an oscilloscope right? IMO a scope is a mandatory tool for any sort of SSTC or high power SMPS development.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Grenadier wrote ...
The 555 has a maximum voltage of about 15V IIRC, though it works up to about 25V. The mosfet's gate must not be more than about 20V away from the source, and maybe that is why it dies when you crank up the voltage.
Use a 555 and a high side gate driver IC.
I would agree with this, also the 555 has no were near enough current to drive a MOSFET like this, you need a dedicated gate drive.
Registered Member #1951
Joined: Sun Feb 01 2009, 01:59PM
Location:
Posts: 105
schematic's? i don't have sorry, it's just a ne555 switching a mosfet :) well i calculated my coil about 480khz fres.
yes i have a scoop! lol i have build sstc's before, it's just so long ago i don't really know my stuff anymore :) i'll scoop the wave form, i'll post pictures of it :)
and if i don't have a drive ic? can i make my own? i have some fets from a lot of tv sets, that be usefull?
edit: i forgot to ask, scoop with or without load?
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killing ne555's (sstc back to basics)
