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Re: LF: Iron dust toroids and heating/H bridge

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Subject: Re: LF: Iron dust toroids and heating/H bridge
From: DK7FC <[email protected]>
Date: Tue, 30 May 2017 15:36:07 +0200
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Am 30.05.2017 15:04, schrieb Graham: question the choice of a half bridge , over that of the full version?
A half bridge is easier to build because both sources of the FET are at GND level. So you are not forced to use a decoupling transformer for driving the FETs. I would recommend to use one anyway, and it works quite well and it is an advantage to pull the gate of the non conducting FET to a negative voltage. The H bridge has an advantage when mains voltage is used directly, i.e. 320 V DC switching voltage.
There are 1000 V FETs however, meanwhile.

Oh i just see the point, a half bridge has two FETs in series and the other half are capacitors. I was talking about the other circuit which uses the lower two FETs not the left two FETs of the H bridge :-)
I would not recommend a hlaf bridge at all.

Its tempting to link the harmonic content , with the high loss rate of devices , In your 136 vk experiments, with the H , did you loose fets , other than by loss of tune ?
I only lost FETs in the beginning, until i discovered that i made an error when building up the driver. After correcting this i didn't loose any FETs. I passed several kWh through one pair of FETs. No problems in WSPR, OP32, CW, even slow hell (which actually is for linear PAs only!). I have a fan blowing on the heat sink whos speed is controlled by the temperature of the heat sink. So i always get an impression of the temperature (when listening to the speed :-) ). When the antenna was not spot on the resonance, the fan blew a bit faster, so the losses must have been somewhat higher. But it never cost the FETs (IRFP460A).
Is there a  ferrite , that  is  comfortable  in 136  and  477 service ?
Several, almost any.
but worth consideration for a driver, having no transformer
The standard FET drivers (ICL7667, TC4422, IXDD614CI...) are switching between Vss and GND. It is however saver to pull the FETs gate voltage to a negative value when OFF. This is given by the transformer. Since the voltage of the opposite winding must be negative when the other one is positive, it is impossible that both FETs are conducting, what ever the driver and transients does.
effectively all  band from  audio up ?
From DC up :-) Yes, but not with some high/low side drivers like IR2110. I built a second bridge for VLF some years ago and used it down to 100 Hz...
73, Stefan

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