which parameter is vital for mosfet driver selection for two-transistor flyback ?

[s.manikandan]

hi ,

i m designing 60w smps with input range 170-450VDC. multiple output. due to high voltage stress i chosen two-transistor flyback topology to reduce the voltage stress across the switch. Now i m in selection part of pwm controller and driver for the above topology.

1) how to select pwm controller ?
2) which parameter is vital for mosfet driver selection for two-transistor flyback ? i chosen the mosfet. what are all the parameters that i should take from the mosfet datasheet in order to select driver (high side and low side driver)
3) That is, how to determine sink and source current ? switching times ?

pls if possible, give some guide for above and explain with some example.

 

[varunkant2k]

1) how to select pwm controller ?

PWM Controller Depends on output voltage level and error amplifier gain.
First model your complete design in linear model. (google! Buck regulator design.)

2) which parameter is vital for mosfet driver selection for two-transistor flyback ? i chosen the mosfet. what are all the parameters that i should take from the mosfet datasheet in order to select driver (high side and low side driver)
pls if possible, give some guide for above and explain with some example.

MOSFET driver is nothing but buffers, depend on the size of MOSFET switches. They can be of cascade of transistors that can follow rise/fall time constraints.

3) That is, how to determine sink and source current ? switching times ?

Current source/Sink is your design parameter depend on your system efficiency/Inductor/Load capacitor sizes.
And these are well related with output ripple. Try to google! again?
As a starting point
1.first devide how much power you can invest in switches. and then decide your MOSFET sizes.
2. Then decide your L/C value with respect to ripple voltage and Inductor current sweep from Load current.

Hope this may give some idea.

 

[s.manikandan]

hi sir,

i completed mosfet selection and transformer design for two-switch flyback topology (primary is same as TWO-switch forward converter ,since secondary is flyback transformer ). so i need to select pwm controller and integrated both high side and low side driver for 600V mosfet (two mosfet).
THE spec is given below.

Qg = 76 nC
rise time = 35 nS
fall time = 20 nS
Td(on) = 45 nS
Td(off) = 122 nS
Vgs = 10 V

By using above parameters how to select driver and pwm controller. i searched in Google ,i found some papers but i cant understand clearly due to different procedures used in various papers.

And for driving dual switches which type is most preferable.
1) Bootstrap
2) galvanic isolation using opto couplers
3) Using transformer isolation.

 

[grizedale]

There are no bootstrap drivers for 2 switch flyback.............at least very few, and if you pick one and it goes obselete, then youre in a bad position. I think powerint.com do a specific bootstrap pwm controller for 2 transistor forward which can be used for 2 transistor flyback, but i think its the only one of its type in the world.

So you have to use transformer drive for the top fet.

This post gives you all the nice problems of transformer isolated gate drive..................

https://www.edaboard.com/threads/231931/

.......is your smps for a smart meter?

 

[s.manikandan]

hi,

K. i agree your apoints. now pls find the document from FAIRCHILD semiconductor for TWO-transistor flyback with high side and low side driver.

links to:

https://www.fairchildsemi.com/support/referencedesign/docs/RD-353.pdf

https://www.fairchildsemi.com/support/referencedesign/docs/RD-351.pdf

https://www.fairchildsemi.com/support/referencedesign/docs/RD-352.pdf

they used dual side driver for the above topology. its a simple one compared with transformer isolation driver.
Why i chosen this topology-- due to high voltage stress across device when we choose singly switch flyback . and also for 60W power supply with multiple outputs ,flyback topology is the best choice.

pls,give your suggestion to complete this project ASAP

---------- Post added at 14:32 ---------- Previous post was at 13:36 ----------

hi,

K. i agree your apoints. now pls find the document from FAIRCHILD semiconductor for TWO-transistor flyback with high side and low side driver.

links to:

https://www.fairchildsemi.com/support/referencedesign/docs/RD-353.pdf

https://www.fairchildsemi.com/support/referencedesign/docs/RD-351.pdf

https://www.fairchildsemi.com/support/referencedesign/docs/RD-352.pdf

they used dual side driver for the above topology. its a simple one compared with transformer isolation driver.
Why i chosen this topology-- due to high voltage stress across device when we choose singly switch flyback . and also for 60W power supply with multiple outputs ,flyback topology is the best choice.

pls,give your suggestion to complete this project ASAP