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In-Reply-To: <4D22026B.7070908@iup.uni-heidelberg.de>
References: <4D22026B.7070908@iup.uni-heidelberg.de>
Date: Mon, 3 Jan 2011 17:29:40 +0000
Message-ID: <AANLkTiky2PFxCs=0erxbbOJUhJsY9_5AiyGZGYGwKYhf@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: Re: VLF: DK7FC's "big" VLF PA
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Or you could use opto couplers in the input.   There are plenty with built
in logic level converters

Andy
www.g4jnt.com
http://www.g4jnt.com/137tx.pdf

2011/1/3 Stefan Sch=E4fer <Stefan.Schaefer@iup.uni-heidelberg.de>

> Dear group,
>
> Since a long time i wanted to publish the circuit of my "big" VLF PA. It=
 is
> titled as a 600W PA since it has never handled more power so far, due to=
 the
> power limit of my /p generator. In fact i think it will handle at least=
 1
> kW, probably even 2 kW. As announced i will try a 2 kW generator in my=
 next
> VLF experiment and i am not afraid to use this PA for the first test.
>
> The circuit is nothing new or very special. The mains voltage is rectifi=
ed
> and stabilized by a 2.2 mF capacitor. A H bridge using *4x IRFP 460* FET=
s
> is switching at the desired frequency. To achieve an accurate 50% duty
> cicle, a *CMOS4013* is used in front of the MOSFET driver. It is switche=
d
> as a frequency divider (/2), thus the input frequency has to be 2x the
> actually wanted frequency (17.94 kHz > 8.97 kHz). The driver(s) are *2x
> IR2110*. The operating frequency is about *0.1...20 kHz* (320 VDC) or
> 0.1...150 kHz (100 VDC). It is designed to work properly below 9 kHz. Th=
e
> input waveform has to be a 12Vp rectangular waveform, ideally. The wavef=
orm
> is not very critical, e.g. a sinusoidal or triangular waveform is no pro=
blem
> as well.
> A small transformer is used to generate a local 15V supply for the drive=
rs,
> ICs and LEDs.
> There are several methods how the input signal can be applied. Either
> directly (please use an audio transformer to decouple the PC from the
> circuits ground which has mains potential!), as shown in the circuit or=
 via
> a fiber optic cable, as i do it. The fiber optic solution is a special=
 and
> (for some) strange method so i prefer to show the usual way to do it...
>
> If the mains is used to supply the PA (much lower output impedance), a
> resistor has to be used to charge the 2.2 mF capacitor. A 100 W/230V lam=
p
> might be used. If the capacitor is charged, this resistor should be bypa=
ssed
> by a relay.
>
> One has to *take care* about the output: There is no isolating transform=
er
> used so the *output has main potential!* Thus, a galvanic isolated
> coupling winding has to be used for applying the RF to the loading coil.=
 No
> ferrite output transformer is needed!
>
> This PA is still using *the first pair of FETs, there was no fault so fa=
r*.
> It was received in several countries that it is no problem to transmit=
 a one
> hour carrier at P > 500 W. Here, the heat sink gets not even hand warm!=
 So
> the efficiency can be assumed to be almost 100%.
> The design can handle pretty much reactive power. It was no problem to
> drive an antenna that is totally out of resonancy (kite lying on the gro=
und
> or wire suddenly disconnected due to strong pull).
>
> The actual (active) output power can be regulated continuously by adjust=
ing
> the resonance.
>
> So, if one of the new VLF TX stations want to change from an audio PA to=
 a
> high power switching mode PA, this well proven design may give some idea=
s.
> Just ask if something is not understood.
>
> See once again one of my very amateur like ugly hand drawings ;-) at *
> http://www.iup.uni-heidelberg.de/schaefer_vlf/pic/DK7FC_600W_VLF_PA.pdf*
>
> Vy 73, Stefan/DK7FC
>
> PS: Once again i explicit want to say that one has to take care about th=
e
> parts that are on mains potential! If you are not sure about the handlin=
g,
> add an isolating transformer at the 230V AC input!
>

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<div>Or you could use=A0opto couplers in the input.=A0=A0 There are plenty=
 with built in logic level converters</div>
<div>=A0</div>
<div>Andy</div>
<div><a href=3D"http://www.g4jnt.com/">www.g4jnt.com</a></div>
<div><a href=3D"http://www.g4jnt.com/137tx.pdf">http://www.g4jnt.com/137tx=
.pdf</a><br><br></div>
<div class=3D"gmail_quote">2011/1/3 Stefan Sch=E4fer <span dir=3D"ltr">&lt=
;<a href=3D"mailto:Stefan.Schaefer@iup.uni-heidelberg.de">Stefan.Schaefer@=
iup.uni-heidelberg.de</a>&gt;</span><br>
<blockquote style=3D"BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8e=
x; PADDING-LEFT: 1ex" class=3D"gmail_quote">
<div text=3D"#000000" bgcolor=3D"#ffffff">Dear group,<br><br>Since a long=
 time i wanted to publish the circuit of my &quot;big&quot; VLF PA. It is=
 titled as a 600W PA since it has never handled more power so far, due to=
 the power limit of my /p generator. In fact i think it will handle at lea=
st 1 kW, probably even 2 kW. As announced i will try a 2 kW generator in=
 my next VLF experiment and i am not afraid to use this PA for the first=
 test.<br>
<br>The circuit is nothing new or very special. The mains voltage is recti=
fied and stabilized by a 2.2 mF capacitor. A H bridge using <b>4x IRFP 460=
</b> FETs is switching at the desired frequency. To achieve an accurate 50=
% duty cicle, a <b>CMOS4013</b> is used in front of the MOSFET driver. It=
 is switched as a frequency divider (/2), thus the input frequency has to=
 be 2x the actually wanted frequency (17.94 kHz &gt; 8.97 kHz). The driver=
(s) are <b>2x IR2110</b>. The operating frequency is about <b>0.1...20 kHz=
</b> (320 VDC) or 0.1...150 kHz (100 VDC). It is designed to work properly=
 below 9 kHz. The input waveform has to be a 12Vp rectangular waveform, id=
eally. The waveform is not very critical, e.g. a sinusoidal or triangular=
 waveform is no problem as well.<br>
A small transformer is used to generate a local 15V supply for the drivers=
, ICs and LEDs. <br>There are several methods how the input signal can be=
 applied. Either directly (please use an audio transformer to decouple the=
 PC from the circuits ground which has mains potential!), as shown in the=
 circuit or via a fiber optic cable, as i do it. The fiber optic solution=
 is a special and (for some) strange method so i prefer to show the usual=
 way to do it...<br>
<br>If the mains is used to supply the PA (much lower output impedance),=
 a resistor has to be used to charge the 2.2 mF capacitor. A 100 W/230V la=
mp might be used. If the capacitor is charged, this resistor should be byp=
assed by a relay. <br>
<br>One has to <u>take care</u> about the output: There is no isolating tr=
ansformer used so the <u>output has main potential!</u> Thus, a galvanic=
 isolated coupling winding has to be used for applying the RF to the loadi=
ng coil. No ferrite output transformer is needed!<br>
<br>This PA is still using <u>the first pair of FETs, there was no fault=
 so far</u>. It was received in several countries that it is no problem to=
 transmit a one hour carrier at P &gt; 500 W. Here, the heat sink gets not=
 even hand warm! So the efficiency can be assumed to be almost 100%.<br>
The design can handle pretty much reactive power. It was no problem to dri=
ve an antenna that is totally out of resonancy (kite lying on the ground=
 or wire suddenly disconnected due to strong pull).<br><br>The actual (act=
ive) output power can be regulated continuously by adjusting the resonance=
. <br>
<br>So, if one of the new VLF TX stations want to change from an audio PA=
 to a high power switching mode PA, this well proven design may give some=
 ideas. Just ask if something is not understood.<br><br>See once again one=
 of my very amateur like ugly hand drawings ;-) at <b><a href=3D"http://ww=
w.iup.uni-heidelberg.de/schaefer_vlf/pic/DK7FC_600W_VLF_PA.pdf" target=3D"=
_blank">http://www.iup.uni-heidelberg.de/schaefer_vlf/pic/DK7FC_600W_VLF_P=
A.pdf</a></b><br>
<br>Vy 73, Stefan/DK7FC<br><br>PS: Once again i explicit want to say that=
 one has to take care about the parts that are on mains potential! If you=
 are not sure about the handling, add an isolating transformer at the 230V=
 AC input!<br>
</div></blockquote></div><br>

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