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Posted by Artemus on June 24, 2008, 4:18 pm
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>
> > This circuit is not a good design.
> >
> > 1. There is the obvious problem of the capacitor polarity being
> > reversed.
> >
> > 2. The snubbers (D1-R2 & D2-R1) are suitable for a flyback
> > circuit but not a push-pull circuit like this one is.
> > Consider: When Q1 is saturated, Q2 is cutoff. Q1 pulls the
> > voltage on the right primary connection to 3V (Ic=10A). The
> > voltage on the left primary connection will be +21V.
> > But D1-R2 shunts this to the 12V CT. 9V / 10ohms = 0.9A of
> > wasted current. Good designs use RC combinations for snubbers.
> >
> > 3. C2 charges to 19.5V (21V - 1.5Vbe). When Q1 switches off
> > this places -16.5V on it's base. The max spec for Vbe is -7V so
> > the design far exceeds the 2N3055's ratings.
> >
> > 4. A collector current of 10A requires a base current of around 3A.
> > Yet R4 limits it to (12V -1.5V) / 180ohms = 58mA.
> >
> > 5. There is no provision for a dead time. During switching Q2 must
> > turn on before the base drive can be removed from Q1 to turn it off.
> > This causes collector currents of both transistors to spike very high
> > for
> > a short time and is just piss poor design for high power inverter
> > circuits.
> >
> > Art
>
>
> Is that why this was posted in the comments section of that site?
>
> "I built this and it immediately exploded the tantalum caps. They were
> the exact value and voltage rating as those listed."
>
>
I didn't read the comments, but yes all polarized caps don't take kindly
to having reverse voltage applied to them.
art
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>
> 1. There is the obvious problem of the capacitor polarity being
> reversed.
>
> 2. The snubbers (D1-R2 & D2-R1) are suitable for a flyback
> circuit but not a push-pull circuit like this one is.
> Consider: When Q1 is saturated, Q2 is cutoff. Q1 pulls the
> voltage on the right primary connection to 3V (Ic=10A). The
> voltage on the left primary connection will be +21V.
> But D1-R2 shunts this to the 12V CT. 9V / 10ohms = 0.9A of
> wasted current. Good designs use RC combinations for snubbers.
>
> 3. C2 charges to 19.5V (21V - 1.5Vbe). When Q1 switches off
> this places -16.5V on it's base. The max spec for Vbe is -7V so
> the design far exceeds the 2N3055's ratings.
>
> 4. A collector current of 10A requires a base current of around 3A.
> Yet R4 limits it to (12V -1.5V) / 180ohms = 58mA.
>
> 5. There is no provision for a dead time. During switching Q2 must
> turn on before the base drive can be removed from Q1 to turn it off.
> This causes collector currents of both transistors to spike very high
> for
> a short time and is just piss poor design for high power inverter
> circuits.
>
> Art