[Zenith Monitor]
> Using LED as a reference? That is poor idea to do that! It should
> have put the sense line on that heavy current line to work.
I think you misunderstood me. It does sample the output of the PSU. But it
compares it to the 2V-ish across the power-on LED rather than using a
zener or something similar.
[Boschert 2-stage]
> > 1) Rectify/double the AC mains input to give 340V DC
> > 2) Feed that into a non-isolated 'flyback' converter to step it down to
> > 150V.
> hi frenquency ac or dc at that point?
DC. It's smoothed by a smallish capacitor.
[...]
> > 1) The chopper (2) shorts. The output of that stage now leaps to 340V
> > (since there's a DC path through the shorted transistor and the inductor)
>
> Ah! Not a transformer just a giant inductor driven by that chopper?
Absolutely...
> :) that would be a biggest OUCHIE! Why not jerryjig a design to
> clamp down based on voltage level when exceeding 150v at this point
> when chopper went so it will blow the fuse instead?
I'm not sure you could. The voltage at that point rises as the PSU is
loaded (to compensate for losses in the transformer and oscillator). I
suspect the crowbar would still kill the oscillator transistors and cause
a lot of other damage before the overvoltage trip did a darn thing.
>
> > 2) The oscillator (3) continues running, so the 5V line leaps to about 12V
> > 3) The crowbar trips, shorting the output to ground
> > 4) The overcurrent trip tries to work, but as the chopper (2) is shorted,
> > it doesn't do a darn thing.
>
> Other option, Why not use this output of this crowbar to trip other
> clamper at the 340vdc output to blow the fuse instantly?
> You want to blow the fuse first before the last 2 trans dies
> resulting in expensive heap of smelly stuff. :)
That would have meant an extra optoisolator at least. And would you trust
a thyristor to short a 340V line at essentially unlimited current?
> Jason D.
--
-tony
ard12_at_eng.cam.ac.uk
The gates in my computer are AND,OR and NOT, not Bill
Received on Tue Jun 24 1997 - 08:47:38 BST