Two-switch logic-level LS/HS MOSFETs driver

Hello,

Recently, I've been playing with flyback SMPS topology for fun but also
to make a reference design for eventual future use in commercial products.

Specifically, what I am experimenting with is a capacitor charger (those
things for which one usually uses a LT3750 or LT3751) and I want to charge
the biggest possible cap in the shortest possible time. Power and efficiency.

One thing I learnt is that when you need higher output voltage, and you
don't have a suitable transformer, ie. when you need high duty cycles, you
start finding that leakage inductance and other problems play a bigger
role. Consider also that I pretend to do all the experiments in software,
on a EF PIC32, and when you use a transformer with 10uH primary inductance,
you are very short in time, especially during the discharge phase of a high
duty cycle when you want to do things like zero-voltage (valley) switching.

Anyhow, experimenting brought me towards the implementation of a two-switch
topology of flyback SMPS, something I had overlooked before. I now understand
the beauty and usefulness of this topology. This way, the transil/snubber is
gone, the MOSFETs can be much lower voltage, and I have a chance (not verified
yet) to measure discharge current with much higher precision and ease (while
measuring discharge current is not necessary, I think I can do some interesting
things if I can measure it).

To experiment (but always with eventual, future, production design in mind)
with it I need a low side and high side driver for the 2 MOSFETs, which do
turn ON and OFF simultaneously albeit on two different "rails", and I want
to drive them directly via a MPU pin, ie. logic level (for my ease and for
containing noise even in imperfect PCB), but I can't find any suitable IC
for this task.

Is there one, or can any of you suggest some smart/clever solutions to drive
with as few components as possible (also to reduce board space and interference
as I'll be switching tens of Amperes, maybe in continuous mode, not even
discontinuos) both MOSFETs simultaneously, considering the ~12V difference
between them?

One a side note: I noticed that the "primary" part of two-switch flyback and
two-switch forward converters are identical, the only difference is on the
secondary side. What are the benefits of implementing a type of secondary
(flyback) or the other (forward)?

Thank you.

Chers,
lchplsnw

PS: I just realized that the discharging current I will see is only of the primary leakage inductance, not the one happening on the secondary.

Returning to the main topic: is there an IC, or a good design made of discrete components, to make a gate driver with one logic level input, and two outputs, one of ground + needed gate1 drive, and the other of Vcc + needed gate2 drive?

Something like (assuming 12V Vcc, a gate drive of 10V and that the gate can go +/- say 20V):
Input Output1 Output2
0V 0V 0V or 12V, it doesn't really matter
3.3V 10V 22V

Thanks.

Hi,

is there an IC, or a good design made of discrete components, to make a gate driver with one logic level input, and two outputs, one of ground + needed gate1 drive, and the other of Vcc + needed gate2 drive?

Click to expand...

It seems you are looking for the very common and widly used MOSFET drivers.

Did you ever do a search for MOSFET drivers?
The most common are the IR2110 and it´s family..
Do a parametric search at a distributor or a manufacturer internet page.

If this is not what you are looking for, could you please give the information what´s wrong with them?

Klaus

Thank you for your reply. While the IR2110 looks interesting (and may be useful for some other project), I just realized that I cannot use a two-switch flyback converter for my project, as this topology imposes a limit on the duty cycle that prevents high voltages to be generated (unless one acts on the turns ratio, of course).

So I am back to classic flyback..

Sorry and thanks for the answer, it will be useful anyway for some other project.

Your post above appears to be self contradictory, unless you are making a distinction between the 2sw flyback and the "classic" single ended. While the 2sw fwd has a duty limit - so does the 2sw flyback, as, if you apply Vcc = 100V to a core for 5uS, the flyback volts are now clamped by the input Vcc to 100V and so you require the same amount of time to reset the core, i.e. 5uS. In the single ended flyback - there is no such limitation, the flyback volts can go as high as you require - ditto for the single ended fwd.

There is another trap for the newbie with the 2sw flyback, the turns ratio must be such that at the lowest Vcc, the flyback output volts can be reached, else the energy will simply be returned to Vcc and you will not get your desired Vout... (possibly you were alluding to this above?)