Hello Tom,
most schoolbook class-E designs assume a DC feeding choke with
infinite inductance i.e. a huge inductor that keeps the DC current
constant without any RF ripple. This is of course totally impractical
(especially at VLF !)...
I'll try to find some class-E design documents that I have saved
somewhere. One of those documents has explicit design equations for
class E amplifiers with finite DC feed inductance.
If memory serves me, the reactance of the DC feed inductor can
be as low as the DC feed resistance (Vdc/Idc) but such a low value
would require a very large decoupling capacitance on the DC supply side
because of high RF ripple current flowing through the inductor.
I will send these pdf documents to you if you are interested.
73
Johan SM6LKM
Den 2018-10-07 kl. 19:51, skrev DK1IS:
Hello Group,
Planning a new
single-ended Class E PA for my activities on the Dreamers Band (8.27
kHz) two questions came up - perhaps someone can help me:
- Being interested only in on-off-keying I´m
concerned about the capacitor in parallel to the power FET which in my
case on VLF will be in the uF range. If the DC supply is on and without
gate drive this capacitor is charged to the DC supply voltage. At the
first positive gate pulse it discharges via the drain-source-path, the
current being limited only by parasitc
impedances - a poorly defined condition which usually has to be
avoided. Does this mean that I have to apply drive continously and key
the DC power supply only, perhaps synchronously to the next positive
drive pulse?
- Is there any rule of thumb for the inductance of
the rf choke in the drain-power supply path?
Thanks for any
idea!
73,
Tom, DK1IS
www.qrz.com/db/dk1is
.
