RadioBanter - View Single Post

February 23rd 04, 09:45 AM

On 22 Feb 2004 15:50:35 -0800, (Tom Bruhns) wrote:

But in reply to Paul, I'd ask: Do you understand how the "full-wave
rectifier doubler" works, basically? (Ideal waveforms and all that.)

IFAIA, pretty much the same as a full-wave rectifier in a PSU. All the
negative going half-cycles are converted to postitive going
half-cycles that 'slot in' between the unmodified positive half
cycles. The resulting waveform is twice the original frequency and
subsequent signal processing can restore this half-wave signal back to
a full sine wave of the desired output frequency.

Do you have a data sheet for the 1N4148?

I could get one off the good old 'net. Aw, **** it; I'll get one. Hang
on a minute..... Got it!

What items from the data
sheet do you suppose might limit the useful frequency?

Primarily junction capacitance, I guess. In this instance, 4pF.
There's also something called transit time, IIRC, which is relevant,
but for some reason it's not mentioned on the DS.

Can you make
an estimate, based on the data sheet numbers?

Nope. Maybe from the graphs, though...

What would you do in a
design to extend the frequency range for a given diode characteristic?
For example, what does diode capacitance do to circuit operation?

More slows it down.

What does reverse recovery do?

Slower recovery the same, I guess. I'm not totally familiar with this
parameter but it would make sense.

In the full-wave frequency doubler
circuit, what does the input impedance look like, assuming an ideal
transformer, when one diode is forward biased and the other is
reverse-recovering? Can you think of parts to add to cause that to
not be so much of a problem (assuming it is a problem)?

Totally beyond me at this stage, I'm afraid!

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