Author Topic: Full Bridge rectifier using fast diodes  (Read 3574 times)

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Offline hussamaldeanTopic starter

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Full Bridge rectifier using fast diodes
« on: January 29, 2019, 06:37:51 am »
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 100KHz
which model of diodes shall I use ?
regards
 

Offline hussamaldeanTopic starter

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Re: Full Bridge rectifier using fast diodes
« Reply #1 on: January 29, 2019, 06:43:38 am »
Boost converter rectification with full bridge rectifier? Please tell me you are not on weed ;).
most schematics found are using single diode
but I want to use full bridge rectifier if possible
 
 

Offline hussamaldeanTopic starter

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Re: Full Bridge rectifier using fast diodes
« Reply #2 on: January 29, 2019, 07:25:40 am »
Can you show a schematic? I think we are talking about the same thing.
the schematic is attached
notice the diode which I want to replace it with full bridge rectifier
 

Online jbb

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Re: Full Bridge rectifier using fast diodes
« Reply #3 on: January 29, 2019, 07:45:18 am »
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.
 

Offline hussamaldeanTopic starter

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Re: Full Bridge rectifier using fast diodes
« Reply #4 on: January 29, 2019, 10:20:29 am »
That won't work. Your flyback converter's output is not symmetric, so half of your diodes won't conduct anyway.
ok
thx
 

Offline SiliconWizard

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Re: Full Bridge rectifier using fast diodes
« Reply #5 on: January 29, 2019, 07:11:57 pm »
The return of the full bridge rectifier! And it's veryy angry! ;D
 
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Offline hussamaldeanTopic starter

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Re: Full Bridge rectifier using fast diodes
« Reply #6 on: January 29, 2019, 07:13:08 pm »
The return of the full bridge rectifier! And it's veryy angry! ;D
a real man makes his own full bridge rectifier
 

Offline Doctorandus_P

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Re: Full Bridge rectifier using fast diodes
« Reply #7 on: January 30, 2019, 04:26:51 am »
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.
 

Offline Doctorandus_P

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Re: Full Bridge rectifier using fast diodes
« Reply #8 on: January 30, 2019, 07:27:32 am »
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.
 

Offline hussamaldeanTopic starter

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Re: Full Bridge rectifier using fast diodes
« Reply #9 on: January 30, 2019, 07:30:26 am »
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.
for study purpose to see the at which level of current when the primary of the transformer will be discontinues   
 

Offline Doctorandus_P

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Re: Full Bridge rectifier using fast diodes
« Reply #10 on: January 30, 2019, 07:36:20 am »
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.
 

Offline glarsson

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Re: Full Bridge rectifier using fast diodes
« Reply #11 on: January 30, 2019, 09:03:32 am »
Having a full bride rectum fire also leads to ...
Having a full what?
 

Offline timenutgoblin

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Re: Full Bridge rectifier using fast diodes
« Reply #12 on: February 05, 2019, 09:20:29 am »
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.
 

Offline Kleinstein

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Re: Full Bridge rectifier using fast diodes
« Reply #13 on: February 05, 2019, 12:16:38 pm »
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.
 

Offline Doctorandus_P

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Re: Full Bridge rectifier using fast diodes
« Reply #14 on: February 06, 2019, 03:37:23 am »
Having a full bride rectum fire also leads to ...
Having a full what?
The fun starts at 2:50
« Last Edit: February 06, 2019, 03:39:00 am by Doctorandus_P »
 


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