Can the 2 transistor forward work without the flyback?

[treez]

https://ac-dc.power.com/design-support/product-documents/data-sheets/hipertfs-2-data-sheet/

..in the above hyperTFS two transistor forward controller, can the two transistor forward work without the flyback? -it looks like the flyback clamp is used to provide the high side gate drive supply for the 2 transistor forward converter.
-It also looks like the flyback diodes on the 2 transistor forward also provide some of the high side bias supply. I appreciate that the flyback bias winding powers the chip but supposing this were provided by an external rail, then would the 2 transistor forward still be operable without the internal flyback?

 

[Warpspeed]

..in the above hyperTFS two transistor forward controller, can the two transistor forward work without the flyback?

Yes it can, provided you provide the chip with a low voltage external dc supply to run it.

The upper mosfet uses a bootstrap circuit, notice the capacitor between VDDH and HB. The bootstrap diode is hidden within the chip.

The two diodes in the forward converter are flyback voltage clamps, the whole topology is called "diagonal half bridge forward converter".

https://www.embedded.com/design/rea...ch-Forward-Flyback-Power-Converter-Topologies

 

[treez]

thanks

if you look at fig 15 page 16 of the datasheet, we see that the flyback diodes of the 2 transistor forward converter actually "empty" into the high side gate drive supply, nit into vin.....so are you sure that there is a bootstrap diode?

hyper TFS datasheet for 2 transistor forward smps
https://ac-dc.power.com/sites/default/files/product-docs/hipertfs-2_family_datasheet.pdf

 

[Warpspeed]

thanks

if you look at fig 15 page 16 of the datasheet, we see that the flyback diodes of the 2 transistor forward converter actually "empty" into the high side gate drive supply,

The figure 15 I am looking at, D2 and D3 empty into C1, which returns power to the main incoming B+ line via VZ1 and the resistor.

It has nothing to do with a bootstrap, if in fact there is a bootsatap. One is not shown.

 

[treez]

Thanks, but why not just take D2 cathode straight to B+ (ie why haven't they done that?)
(referring again to fig 15, page 16 of this...)

https://ac-dc.power.com/sites/default/files/product-docs/hipertfs-2_family_datasheet.pdf

 

[Warpspeed]

Thanks, but why not just take D2 cathode straight to B+ (ie why haven't they done that?)
(referring again to fig 15, page 16 of this...)

https://ac-dc.power.com/sites/default/files/product-docs/hipertfs-2_family_datasheet.pdf

I have no idea why they did that.
And reading their application notes does not help either.
It does not seem to have any useful purpose that I can see.
The conventional way is just to return D2 and D3 directly to the incoming B+ and recover all the flyback energy.

Its certainly a weird circuit, never seen anything like it before.

 

[treez]

I am guessing that they are providing the high side supply voltage from the energy from the discharging magnetising inductance.?

 

[Warpspeed]

That is a 150 volt zener !

If it was regulated down to twelve volts or something, I would tend to agree, but that circuit just sits there perched up on top of the B+ line with no connections going anywhere.

Its all a bit of a mystery...