Full Bridge rectifier using fast diodes  - Page 1
Forum section: electronics / projects

author: hussamaldean
author_rank: Unknown
timestamp: January 29, 2019, 06:37:51 am
content: Hi all,I want to use fast diode for my flyback boost converter (DC-DC )which is using high frequency (~100KHz), the output is AC and I want convert it to DC using the rectifier, the RMS voltage is about 300V and the frequency is about 100KHzwhich model of diodes shall I use ?regards

author: hussamaldean
author_rank: Unknown
timestamp: January 29, 2019, 06:43:38 am
content: Quote from: blueskull on January 29, 2019, 06:42:21 ammost schematics found are using single diodebut I want to use full bridge rectifier if possible

author: hussamaldean
author_rank: Unknown
timestamp: January 29, 2019, 07:25:40 am
content: Quote from: blueskull on January 29, 2019, 07:09:29 amthe schematic is attachednotice the diode which I want to replace it with full bridge rectifier

author: jbb
author_rank: Super Contributor
timestamp: January 29, 2019, 07:45:18 am
content: Yep, that’s a flyback converter. The diode placement is very deliberate, and a full bridge is inappropriate.Note that a flyback works by loading energy into the inductor core while the switch is on. Then when the switch is off the energy is transferred to the output via the diode. So there’s no real reason to even want a full bridge rectifier.

author: hussamaldean
author_rank: Unknown
timestamp: January 29, 2019, 10:20:29 am
content: Quote from: blueskull on January 29, 2019, 07:46:55 amokthx

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 29, 2019, 07:11:57 pm
content: The return of the full bridge rectifier! And it's veryy angry!

author: hussamaldean
author_rank: Unknown
timestamp: January 29, 2019, 07:13:08 pm
content: Quote from: SiliconWizard on January 29, 2019, 07:11:57 pma real man makes his own full bridge rectifier

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 30, 2019, 04:26:51 am
content: 100kHz is not a "high frequency" for an SMPS. Using a MHz or more is not uncommon nowaday's.Using a full bridge rectifier can only be usefull if the inductor carries current in both directions.This would also imply using an H-bridge on the primary side to drive the transformer.With this you can transfer twice as much energy with a transformer core because more of the B-H curve is used.Alternatively, the same can be done by using (grounded) center taps on the transformer windings. This needs less electronics (only 2 drive transistors and 2 diodes) but the disadvantage is a smaller "copper fill factor", which probably leads to a (slightly) larger transformer core to make room for the extra copper.Having a full bride rectum fire also leads to 2 diode drops of loss on the secondary side, which reduces efficiency. This can be overcome by synchronous rectification, but you will need 4 synchronous rectifiers, which leads to extra complexity and still need the drive the primary side both ways.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 30, 2019, 07:27:32 am
content: Sensible switching frequencies als depend on the amount of energy / current you want to convert.This is #12 and OP has not bothered to tell us how much current his mystery diodes need to switch nor has anybody else bothered to ask...So, What are the power levels you're thinking of, how much current do your diodes need to switch? Is it for a nixi tube display, or is it for a 100kW power supply.My best guess is that it's probably somewhere in between those 2.

author: hussamaldean
author_rank: Unknown
timestamp: January 30, 2019, 07:30:26 am
content: Quote from: Doctorandus_P on January 30, 2019, 07:27:32 amfor study purpose to see the at which level of current when the primary of the transformer will be discontinues

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 30, 2019, 07:36:20 am
content: This thread is also relevant:https://www.eevblog.com/forum/projects/1kw-200400v-dcdc-converter-design-tip/It also mentiones bridge rectum fires and has some nice fotage of a 50 year old power converter working at 30kHz.

author: glarsson
author_rank: Frequent Contributor
timestamp: January 30, 2019, 09:03:32 am
content: Quote from: Doctorandus_P on January 30, 2019, 04:26:51 amHaving a full what?

author: timenutgoblin
author_rank: Regular Contributor
timestamp: February 05, 2019, 09:20:29 am
content: hypothetically if the single diode was replaced with a full wave bridge rectifier then the input voltage could be either positive or negative and the output capacitor would still charge up. with the schematic in its existing configuration the diode will only conduct unless the input voltage is positive and not negative. yes it is possible to use a full wave bridge rectifier in this circuit but it would be impractical and inefficient.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 05, 2019, 12:16:38 pm
content: With a full wave rectifier the DCDC converter would be a combination of a forward converter and flyback. It may make sense, but could also cause trouble. At best the other polarity does not conduct at low load and at high load (or at start up), when the output voltage drops the other half wave kicks in as a forward converter to deliver extra power - but without much regulation.At 300 V the extra drop from a second diode would not be so bad for efficiency.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 06, 2019, 03:37:23 am
content: Quote from: glarsson on January 30, 2019, 09:03:32 amThe fun starts at 2:50