T
treez
Guest
Hello,
We are doing an isolated 120W, 26Vout, Two Transistor Forward converter. Vin = the 220VDC output of a Boost PFC.
I’ve always just used heatsunk diodes on the output in the past, but this time synchronous rectifiers are required.
There are not many options using offtheshelf controllers for doing it with sync rects as I see…
The best options seem to be from linear.com…..
These are …..
1…LTC3781 with LTC1698 sync rect controller
2…LT1681 with LTC1698 sync rect controller
3…LTC3705 with LTC3706 sync rect controller
4…LTC3705 with LTC3726 sync rect controller
…..all of these would need the primary side driver to be “hacked” to make it work with a gate drive transformer for the hi-side fet.
I must admit the LTC3705/LTC3726 option looks best……this is because it actually senses the current in the “drive” sync rect. Also, it treats light load by staying in CCM and just making the inductor current shuffle back and forward, which looks far safer than other methods which go into DCM, and where when in light load, there is a danger of ringing noise causing cross conduction.
With all of the solutions above though, it looks like there is no “timeout” overload/short cct output protection…so that will have to be implemented externally.
Do you know of any other vendors with solutions for Two Transistor forward with sync rects?...i must admit, with high-ish current outputs being common I am surprised not more people do chips for this.
We are doing an isolated 120W, 26Vout, Two Transistor Forward converter. Vin = the 220VDC output of a Boost PFC.
I’ve always just used heatsunk diodes on the output in the past, but this time synchronous rectifiers are required.
There are not many options using offtheshelf controllers for doing it with sync rects as I see…
The best options seem to be from linear.com…..
These are …..
1…LTC3781 with LTC1698 sync rect controller
2…LT1681 with LTC1698 sync rect controller
3…LTC3705 with LTC3706 sync rect controller
4…LTC3705 with LTC3726 sync rect controller
…..all of these would need the primary side driver to be “hacked” to make it work with a gate drive transformer for the hi-side fet.
I must admit the LTC3705/LTC3726 option looks best……this is because it actually senses the current in the “drive” sync rect. Also, it treats light load by staying in CCM and just making the inductor current shuffle back and forward, which looks far safer than other methods which go into DCM, and where when in light load, there is a danger of ringing noise causing cross conduction.
With all of the solutions above though, it looks like there is no “timeout” overload/short cct output protection…so that will have to be implemented externally.
Do you know of any other vendors with solutions for Two Transistor forward with sync rects?...i must admit, with high-ish current outputs being common I am surprised not more people do chips for this.