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
