EMRFD Message Archive 4293

Message Date From Subject
4293 2010-02-19 07:20:02 k5nwa (no subject)
A generic design question to Dan Tayloe but others feel free to chime in.

On the transmitter circuitry you are using a CA3086 device to
implement from oscillator, buffer, to driver to the finals. The
devices are running on 12V which on a freshly charged battery is
13.8V yet that device has a rating of 15V guaranteed Vce and a
typical Vce of 40V. I always believed that the transistor in RF use
must have at least 2X the power supply rating due to inductor voltage
swing more on some due to either high Q or special class like class E finals.

I'm I wrong on that or are you depending on the "typical" 40V rating to get by?


www.softrockradio.org www.qrpradio.com

"Blessed are the cracked, for they shall let in the light."
4294 2010-02-19 08:03:08 Paul (no subject)
I'm pretty new to this, so I could be quite wrong. But isn't the 2x supply rating guideline for when you are actually getting a swing up to +2x at the collector?

I'm not familiar with the actual circuit, so I don't know what the AC output voltages are for the buffer and driver.

But if the buffer and driver don't actually swing past +15v you then wouldn't a 15v rating would be OK, regardless of supply voltage?

I'm definitely interested hearing a better explanation.


4295 2010-02-19 08:07:22 Tayloe Dan-P26412 Re:
In the current version, of the five transistors in the array, the
transistor that sees the highest voltage level is the driver for the
finals. The drive to the finals is 4v pk-pk, which is a 2v peak on top
of the DC voltage. With a supply voltage of 13.8 and a diode drop
(diode protected input), we have a peak voltage on the driver of 13.8 -
0.7 + 2 or 15.1v.

Yes that is a hair above the spec limit, but with a typical of 40v, I
think all is well.

- Dan, N7VE