Hello Group,

I have been playing around with a 4046 Phase lock loop!
I am using it to drive two mosfet drivers one inverted and the other non
inverted which then drive a gate transformer connected to a Half Bridge.

Now when I view the square wave output with a scope from the PLL vcoout it
appears slightly un-equal.
The negative portion of the wave appears slightly shorter than the positive
portion. This is exaggerated even more when viewing the output(s) of the
mosfet gate driver (tc4421 / tc4422). I believe this is causing one side of
the half bridge to work harder which creates much more heat in one mosfet
than in the other (Well that's what I think is happening as one mosfet
becomes much hotter than the other) .

Additinal info :-
I am using a current sense transformer located around a parallel tank
circuit to send the correct phase signal to the Phase Lock Loop. This
appears to lock the PLL / VCO at the self resonant frequency of the tank
circuit, which should then drive the Half Bridge mosfets at ZCS / ZVS
causing the desired affect of soft switching.

The output on the scope suggests that soft switching is almost taking place
all though there is slight ringing which at this point I am unable to
minimalise any further and which may be connected to the above waveform
issue?

Does anyone have any idea why the initial waveform could be un-even even
when just running from the fixed VCO (ie with no PLL feedback)?

Hope this makes some degree of sense! ;-)

Regards
Steve.

SRG wrote:
Hello Group,

I have been playing around with a 4046 Phase lock loop!
I am using it to drive two mosfet drivers one inverted and the other non
inverted which then drive a gate transformer connected to a Half Bridge.

Now when I view the square wave output with a scope from the PLL vcoout it
appears slightly un-equal.
The negative portion of the wave appears slightly shorter than the positive
portion. This is exaggerated even more when viewing the output(s) of the
mosfet gate driver (tc4421 / tc4422). I believe this is causing one side of
the half bridge to work harder which creates much more heat in one mosfet
than in the other (Well that's what I think is happening as one mosfet
becomes much hotter than the other) .

Additinal info :-
I am using a current sense transformer located around a parallel tank
circuit to send the correct phase signal to the Phase Lock Loop. This
appears to lock the PLL / VCO at the self resonant frequency of the tank
circuit, which should then drive the Half Bridge mosfets at ZCS / ZVS
causing the desired affect of soft switching.

The output on the scope suggests that soft switching is almost taking place
all though there is slight ringing which at this point I am unable to
minimalise any further and which may be connected to the above waveform
issue?

Does anyone have any idea why the initial waveform could be un-even even
when just running from the fixed VCO (ie with no PLL feedback)?

Hope this makes some degree of sense! ;-)

Regards
Steve.

Can you run the PLL 2 times as fast and use a divide by 2 to get the
original frequency with perfect duty cycle?
GG

"Glenn Gundlach" wrote in message
oups.com...


SRG wrote:
Hello Group,

I have been playing around with a 4046 Phase lock loop!
I am using it to drive two mosfet drivers one inverted and the other non
inverted which then drive a gate transformer connected to a Half Bridge.

Now when I view the square wave output with a scope from the PLL vcoout
it
appears slightly un-equal.
The negative portion of the wave appears slightly shorter than the
positive
portion. This is exaggerated even more when viewing the output(s) of the
mosfet gate driver (tc4421 / tc4422). I believe this is causing one side
of
the half bridge to work harder which creates much more heat in one mosfet
than in the other (Well that's what I think is happening as one mosfet
becomes much hotter than the other) .

Additinal info :-
I am using a current sense transformer located around a parallel tank
circuit to send the correct phase signal to the Phase Lock Loop. This
appears to lock the PLL / VCO at the self resonant frequency of the tank
circuit, which should then drive the Half Bridge mosfets at ZCS / ZVS
causing the desired affect of soft switching.

The output on the scope suggests that soft switching is almost taking
place
all though there is slight ringing which at this point I am unable to
minimalise any further and which may be connected to the above waveform
issue?

Does anyone have any idea why the initial waveform could be un-even even
when just running from the fixed VCO (ie with no PLL feedback)?

Hope this makes some degree of sense! ;-)

Regards
Steve.

Can you run the PLL 2 times as fast and use a divide by 2 to get the
original frequency with perfect duty cycle?
GG

Thanks for the feedback!
Not sure if that would work I could be wrong ofcourse as this is the first
time I have played with a PLL.

The VCO on the 4046 is currently set to around 150khz with a shift allowance
from aprox 100 - 200 khz. The output drives a parallel tank circuit
consisting of 1.5uh inductor and 564nf worth of capacitors giving a
frequency of around 171khz. Additionally the output of the inverter is
connected to DC blocking cap then a 45uh inductor in series(for impedance
matching though having trouble finding the correct value for this!) this
then connects to the aforementioned Parallel tank circuit.
I have connected a ferrite (Clip on type) with aprox three turns which acts
as a current sense transformer (CT) which passes its output to the PLL
input. I then tune the VCO until I get a perfect phase alignment (well
almost) for both current and voltage so as to achieve the golden Zero
Current Switching for the mosfets in the inverter (half bridge). That's the
plan anyway ;-)

So in effect the VCO (on the 4046) acts as a starting frequency to drive the
inverter which in turn feeds the tank circuit AC that acts like a filter ie
only producing significant power when the inverter is tuned to the tanks
resonant frequency. The current transformer feeds back voltage and phase to
the PLL which follows any resonant frequency change that's produced from the
tank circuit thus theoretically keeping everything running sweetly in tune
and consequently soft switching mosfets at ZCS / ZVS which should make them
run cooler and more efficiently with the exception of inherent mosfet
losses.

So I guess by upping the frequency would not help in this case?
I still am at a loss why the square wave output from the VCO and gatedriver
is not evenly spaced for the positive side compared to the negative side of
the waveform?

My God did I just type that? LOL scratching head......

SRG wrote:

Hello Group,

I have been playing around with a 4046 Phase lock loop!
I am using it to drive two mosfet drivers one inverted and the other non
inverted which then drive a gate transformer connected to a Half Bridge.

Now when I view the square wave output with a scope from the PLL vcoout it
appears slightly un-equal.
The negative portion of the wave appears slightly shorter than the positive
portion. This is exaggerated even more when viewing the output(s) of the
mosfet gate driver (tc4421 / tc4422). I believe this is causing one side of
the half bridge to work harder which creates much more heat in one mosfet
than in the other (Well that's what I think is happening as one mosfet
becomes much hotter than the other) .

Additinal info :-
I am using a current sense transformer located around a parallel tank
circuit to send the correct phase signal to the Phase Lock Loop. This
appears to lock the PLL / VCO at the self resonant frequency of the tank
circuit, which should then drive the Half Bridge mosfets at ZCS / ZVS
causing the desired affect of soft switching.

The output on the scope suggests that soft switching is almost taking place
all though there is slight ringing which at this point I am unable to
minimalise any further and which may be connected to the above waveform
issue?

Does anyone have any idea why the initial waveform could be un-even even
when just running from the fixed VCO (ie with no PLL feedback)?

Hope this makes some degree of sense! ;-)

Regards
Steve.


MosFet's have Capacitance on the gate verses what you normally
see on bipolar, you maybe current sinking ?
you may want to test the output unloaded to see if you are
still getting the problem? if not, then the problem is most likely
current sinking due to external cap.
you could try a current driver Tansistor (emitter flower)? or
some high speed switching device to output more current with much
less input current and capacitance.

the ringing you see may just be the effects of your scope that is
common, also you may want to experiment a bit with your scope probe
in 1:1 mode and 1:10 mode, you may not hage the cap set correctly in the
probe.