Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

does it possible get greater than 0.5 duty ratio using SG3525A

Status
Not open for further replies.

Maloth Ramesh

Junior Member level 2
Joined
May 31, 2015
Messages
20
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
i am designing dc dc converter, is it possible to get more than 0.5 duty ratio using SG3525A

thank you........
 

Warpspeed

Advanced Member level 5
Joined
May 23, 2015
Messages
2,213
Helped
756
Reputation
1,514
Reaction score
734
Trophy points
113
Location
Melbourne, Australia
Activity points
17,766
Yes, you can get almost 100% but not quite, due to the dead time limitation.

The trick is to ground both the output pins 11 and 14, as well as pin 12.
Then fit a 1K pullup resistor to pin 13 that normally supplies power to the output section.

As each output tries to turn on, because it is directly shorted to ground, it pulls down pin 13 almost to ground. You get twice the output frequency doing this, but the duty cycle can then go from 0% to maybe 95%.

This is all a bit odd, but if you read the application notes for the chip, it is a recommended method.

You will need an inverting gate drive buffer to drive your mosfet gate, because connecting the 3525 like this, its output at the pullup resistor now goes logic low when you want your mosfet gate to go logic high.
 

schmitt trigger

Advanced Member level 5
Joined
Apr 17, 2013
Messages
2,727
Helped
859
Reputation
1,722
Reaction score
847
Trophy points
1,393
Activity points
18,440
The reason for the 50% duty limitatation in a 3525 is because it was designed for push-pull or bridge stages. Two nonoverlapping outputs are required in those topologies.

The method that warpspeed recommends combines the two outputs to a single output. Is that what you want? Or do you want both outputs to go above 50%?
 
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top