I have not had a lot of audio time for some time, but I have looked into the behavior of LT4320-1 which is the one I am using on Prasi THT boards.
LT4320 seems to have a well controlled turn on and turn off by having one mosfet turn on/off controlled by a square wave, while the other follows the sine wave of the AC from the trafo secondary.
There is a gap between the crossover of the positive and negative sine wave, so that any turn on/off artifacts of these are eliminated.
Q1 and Q4 is open when AC current flow is positive.
When Q4 is turned off by the square wave, the trafo secondary is disconnected from the circuit
and ist is irrelevant if Q1 has some turn on/off artifacts.
Here is a scope shot of the bases of Q1 and Q4 at 1A load
It basically does what it says on the box.
and here is a scope shot of the same at 30mA.
The only thing that changes is the width of the "hat" at the top of the sine wave; higher current, wider hat.
A little reminder of whar PRR said about this
It "stays on" when it should be OFF. It pulls the power rail the wrong way.
This should be eliminated with LT4032 with Q4 switching off the secondaries the way it does.
Please correct me if I missed something here.
LT4320 seems to have a well controlled turn on and turn off by having one mosfet turn on/off controlled by a square wave, while the other follows the sine wave of the AC from the trafo secondary.
There is a gap between the crossover of the positive and negative sine wave, so that any turn on/off artifacts of these are eliminated.
Q1 and Q4 is open when AC current flow is positive.
When Q4 is turned off by the square wave, the trafo secondary is disconnected from the circuit
and ist is irrelevant if Q1 has some turn on/off artifacts.
Here is a scope shot of the bases of Q1 and Q4 at 1A load
It basically does what it says on the box.
and here is a scope shot of the same at 30mA.
The only thing that changes is the width of the "hat" at the top of the sine wave; higher current, wider hat.
A little reminder of whar PRR said about this
It "stays on" when it should be OFF. It pulls the power rail the wrong way.
This should be eliminated with LT4032 with Q4 switching off the secondaries the way it does.
Please correct me if I missed something here.
I'd have to look where I have the communique with an LT-engineer in which I asked why it was that a 68 volts DC rectification could be done with equivalent FETs regarding their VDS. It was something along those lines written above. I'll see if I can find that email, hold on.
Can't find the email.
Vbg1 and Vbg2 are most of the time conducting, so the transformer isn't left floating. Done this way the Vds needed reflect the AC peak voltage of the transformer (not, as usual double the voltage). This is besides the advantages of only 1 side (Vtg1 & 2) being responsible for accurately following the input and the actual switching. I don't see how it would cross conduct or anything.
Vbg1 and Vbg2 are most of the time conducting, so the transformer isn't left floating. Done this way the Vds needed reflect the AC peak voltage of the transformer (not, as usual double the voltage). This is besides the advantages of only 1 side (Vtg1 & 2) being responsible for accurately following the input and the actual switching. I don't see how it would cross conduct or anything.