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
.
