T
treez
Guest
Hi,
The attached is a picture of the inductor current in a synchronous two transistor forward converter just after going from full load to no load. (its an LTspice sim)
As you can see the inductor current suddenly reverses to a badly high level due to the fact that the LT1681 has “malfunctioned”….the LT1681 holds the “catch” synchronous rectifier ON for far too long.
If the Vout had been higher, then this inductor current reversal would have been even worse, if not catastrophic.
The LT1681 is a $6 chip and for that price its amazing to see poor performance like this.
Do you know of other synchronous rectifier control chips which don’t allow this behaviour?
Attached is the LTspice schematic and the LTspice simulation of this part.
If we were to use this part in real life, we would have to buffer the SG output of the LT1681, (and add other circuitry) then take the buffered SG output high if it went low for more than one switching period.
LTC1698
https://www.analog.com/media/en/technical-documentation/data-sheets/1698f.pdf
LT1681
https://www.analog.com/media/en/technical-documentation/data-sheets/1681f.pdf
The attached is a picture of the inductor current in a synchronous two transistor forward converter just after going from full load to no load. (its an LTspice sim)
As you can see the inductor current suddenly reverses to a badly high level due to the fact that the LT1681 has “malfunctioned”….the LT1681 holds the “catch” synchronous rectifier ON for far too long.
If the Vout had been higher, then this inductor current reversal would have been even worse, if not catastrophic.
The LT1681 is a $6 chip and for that price its amazing to see poor performance like this.
Do you know of other synchronous rectifier control chips which don’t allow this behaviour?
Attached is the LTspice schematic and the LTspice simulation of this part.
If we were to use this part in real life, we would have to buffer the SG output of the LT1681, (and add other circuitry) then take the buffered SG output high if it went low for more than one switching period.
LTC1698
https://www.analog.com/media/en/technical-documentation/data-sheets/1698f.pdf
LT1681
https://www.analog.com/media/en/technical-documentation/data-sheets/1681f.pdf