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HiperTFS operation questions

Posted by: treez on

Hi,
These questions concern the HiperTFS Two Transistor Fwd controller by Power.com
Please advise. Just while I am reading the HiperTFS datasheet, please advise on the following.?
1…Can I disable the Flyback part and just use the two transistor forward? I wish to use an external TNYswitch for the bias power in one particular design.
2….I see the datasheet shows the R pin being supplied by both the Flyback leakage reset current, and also the Two tran fwd magnetising current reset. Is it necessary to do both?. For example, can I just use the flyback leakage reset current only? I would rather recycle 2TranFwd magnetising reset current to the input capacitors.
3….If I am using both flyback and forward, is it possible to temporarily disable the two tran fwd part?
4….isn’t a bootstrap diode also needed?, in order to more quickly charge up the VDDH pin capacitor in cases of no load to full load transient?
5…Can I feed the R pin just with an isolated winding from the flyback?
6…Could I feed the R pin from a combo of a bootstrap diode, and also the Flyback leakage reset current? (not the two tran fwd magnetising reset current)

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

Comments

Submitted by PI-Wrench on 07/16/2020

You can disable the internal flyback controller on the Hiper-TFS2, but it is more cost-effective to use that controller rather than a separate TinySwitch outside. The internal flyback is equivalent to a TinySwitch, anyway.

You want both the flyback and forward sharing the same snubber for cost reasons. The forward uses the information from the R pin to control max duty cycle, so it is a really bad idea to disconnect the forward from the R pin.

You can separately disable the forward converter in the TFS by cutting off the bias supply to the BP pin using an optocoupler. This is shown in the example schematic (Figure 30) in the TFS-2 data sheet.

The diode from primary bias (D9 in Figure 30 of the data sheet) is sufficient to supply the VDDH capacitor at 66 kHz operation. If you choose 132 kHz, you will likely need to gap the transformer to lower the magnetizing inductance sufficiently to allow the primary to ring down far enough for D9 to do its job. A very small gap is generally sufficient - we used tape with a substrate thickness of 0.5 mil (0.013 mm) to gap the core for our 132 kHz design example, and that was sufficient.
I am deleting the two redundant posts to avoid confusion.