12v to 400v boost converter - Page 1
Forum section: electronics / projects

author: alireza7
author_rank: Regular Contributor
timestamp: October 01, 2017, 08:54:37 pm
content: hii want to make 12v dc to 400v dc by a boost circuit in my circuit L=1900mH , C=33uF ,R=47k and i use 11n80 mosfet as switch and uf4007 diod.there is a formula (you can find it wikipedia) vout/vin=1/(1-D) which D is duty cycle of switch. so i need 97% duty cylcle to make 12 to 400i tryed range of 99% to 90% pwm duty cycle and also i sweeped the pwm frequency from 20khz to 50khz and the maximum voltage that i got is 270v.what do you think limit this voltage?don't you think maybe the switching speed of 11n80 limited the voltage?any suggestion?

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 01, 2017, 09:18:31 pm
content: I would suggest a "flyboost" topology, which is a flyback converter where the primary winding is also a boost converter choke, with the flyback output stacked on top of the boost output. In that way, the primary snubber would be "lossless".

author: Zero999
author_rank: Super Contributor
timestamp: October 01, 2017, 09:20:48 pm
content: Quote from: NiHaoMike on October 01, 2017, 09:18:31 pmIt sounds like you've described an autotransformer.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 01, 2017, 09:41:08 pm
content: Quote from: Hero999 on October 01, 2017, 09:20:48 pmJust one critical difference: in a flyboost, there's a diode and capacitor stage between the primary and secondary. In theory it will not make a difference, but in practice it acts as a snubber to counteract leakage inductance. It also gives two different output voltages if your application needs it.

author: Zero999
author_rank: Super Contributor
timestamp: October 01, 2017, 10:00:14 pm
content: Quote from: NiHaoMike on October 01, 2017, 09:41:08 pmLike this? I don't think I've seen that before.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 01, 2017, 11:17:55 pm
content: Quote from: Hero999 on October 01, 2017, 10:00:14 pmMove the start of the secondary to the other side of the diode. Then you'll see how the energy stored in leakage inductance gets transferred to the output.

author: alireza7
author_rank: Regular Contributor
timestamp: October 02, 2017, 05:25:13 am
content: Quote from: NiHaoMike on October 01, 2017, 11:17:55 pmdo you mean this?

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 02, 2017, 05:28:27 am
content: Take a flyback converter, then add a diode and capacitor so the primary winding is also a boost choke. Finally, take the secondary output and connect it in series with the boost output so the voltages add.

author: alireza7
author_rank: Regular Contributor
timestamp: October 02, 2017, 07:06:36 am
content: Quote from: NiHaoMike on October 02, 2017, 05:28:27 amis this your purpose?

author: Zero999
author_rank: Super Contributor
timestamp: October 02, 2017, 08:08:30 am
content: Quote from: alireza7 on October 02, 2017, 07:06:36 amThat makes much more sense.

author: CM800
author_rank: Frequent Contributor
timestamp: October 02, 2017, 01:05:06 pm
content: Dispite what a few people have said, It's certainly dooable. I've made one for a coilgun, so have several others:http://uzzors2k.4hv.org/index.php?page=450vboostconverterhttp://www.instructables.com/id/DC-DC-HV-Boost-Converter/Just dont' expect stunning efficiency, performance or reliability I guess.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 02, 2017, 02:01:52 pm
content: Something that the OP has not disclosed isthe load current.It is doable for small currents, but not for large ones.Why? Because of the Mosfet's switching current is roughly multiplied by the voltage transformation ratio.In this instance the transformation ratio is 33.33:1, but considering the losses, the actual switching to load current ratio would be closer to 40:1Edit; I know that in post #1 he discussed a 47k load resistor, but is that only for testing? or is that the actual load?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 02, 2017, 02:46:47 pm
content: The advantage you get in "flyboost" over straight flyback is very small: at 50% duty cycle (ideal, minimizes peak currents), the switch only sees 24V peak, or 6% of the total output. Nearly negligible.There can be good reasons for using a pure flyback topology, like isolation, multiple outputs, or reducing winding capacitance. It's not obvious if these are useful features, based on the vague OP.Tim

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 02, 2017, 02:54:11 pm
content: Quote from: T3sl4co1l on October 02, 2017, 02:46:47 pmIt gives you a lossless snubber if you don't need isolation.