Driving a MOSFET Full wave bridge rectifier

wayneh

Joined Sep 9, 2010
17,155
Nope.
Just have the simulation.
I'll add a caveat about that in the writeup. :oops:
One reason I never built one is I realized that the switching timing – the absolute requirement of avoiding shoot-through, but also the issue of gate ringing – was not something I could fix if it didn't work out of the box. So I wimped out.
 

#12

Joined Nov 30, 2010
18,223
There is a lot of demand for DC supplies below 20 volts. I wouldn't be surprised if this became available as a single chip like a 4 diode bridge rectifier. I hope your piggy bank gets full.
 

crutschow

Joined Mar 14, 2008
28,207
There is a lot of demand for DC supplies below 20 volts. I wouldn't be surprised if this became available as a single chip like a 4 diode bridge rectifier. I hope your piggy bank gets full.
Well, any addition to my piggy would be fine, but that's unlikely from this circuit. :rolleyes:

I came up with the design for hobbyists who might want to roll their own using a common IC.

There already is a single custom chip (the LT4320) that does this (albeit with external MOSFETs), and is better because it uses all N-MOSFETs.
I posted a simulation of that chip here (post#33), near the bottom of the page.
(Still haven't figured out how they readily generate a gate voltage higher than the peak sine voltage). :confused:
 
Last edited:

crutschow

Joined Mar 14, 2008
28,207
Bootstrap capacitor.
That's the obvious answer. :)
But where's the large bootstrap capacitors needed to drive the large MOSFET gate capacitance?
I don't think they can squeeze two of those inside the IC package. :confused:

Edit: Found a description of the circuit here.
It has a charge-pump to generate the gate voltage and the on-chip capacitance is obviously sufficient to drive the gate capacitance.
 
Last edited:

k7elp60

Joined Nov 4, 2008
562
Well, any addition to my piggy would be fine, but that's unlikely from this circuit. :rolleyes:

I came up with the design for hobbyists who might want to roll their own using a common IC.

There already is a single custom chip (the LT4320) that does this (albeit with external MOSFETs), and is better because it uses all N-MOSFETs.
I posted a simulation of that chip here, near the bottom of the page.
(Still have figured out how they readily generate a gate voltage higher than the peak sine voltage). :confused:
Thanks for the information...of this post, I am really interested in mosfet rectifier cks.
Ned
 

crutschow

Joined Mar 14, 2008
28,207
I realized that the switching timing – the absolute requirement of avoiding shoot-through, but also the issue of gate ringing – was not something I could fix if it didn't work out of the box
My circuit doesn't have any shoot-through issues, since the N-MOSFETs change state at the zero crossing when the P-MOSFETs are off.

Gate ringing is generally not an issue with such a slow circuit.
 

ronv

Joined Nov 12, 2008
3,770
My circuit doesn't have any shoot-through issues, since the N-MOSFETs change state at the zero crossing when the P-MOSFETs are off.

Gate ringing is generally not an issue with such a slow circuit.
It is curious how they develop the gate voltage in the LT part. Very low drive current. I was thinking of a friend who builds high output alternators, but a big old fet wouldn't work.
 

srinath99

Joined Jun 30, 2017
6
I know this is an old thread and I'm guilty of necro-posting, but I wanted to add my circuit in case someone runs into this thread from a search for MOSFET Bridge Rectifiers and might want to consider this relatively simple approach.
My write up on the circuit is here.
Hi, continuing with the necro-posting trend...
I looked at your circuit and the OP's circuit and i have a thought... (I am just an electronics noob)
In the OP's circuit, if the bottom-mosfets of the H-bridge are P-type, couldn't a single Op-Amp comparator, drive the gates ?
 

ghulands

Joined Apr 1, 2016
1
Hi,
Sorry to raise a dead thread again. I'm a novice when it comes to electronics so please be gentle. I'm looking at getting a 1.8kw wind turbine and wanted to try an active rectifier to eek out as much power as i can.

I've been looking at the Linear 3 phase demo board referenced in post #31 and can't work out why the board is rated for 25A. The MOSFETs are rated for 100A. Could someone explain why? If I were to replace them with 300A rated ones, would the rated amperage be 75A? Is there a linear relationship between the rated current of the FET and the rated current of the circuit?

Any help is greatly appreciated.
 

crutschow

Joined Mar 14, 2008
28,207
can't work out why the board is rated for 25A. The MOSFETs are rated for 100A.
It depends upon the on-resistance of the MOSFET which determines its heating, and efficiency.
At the rated current the dissipation from the on-resistance may cause overheating of the MOSFET without a large heat-sink and/or reduce the efficiency by a significant amount.
So you want a MOSFET with a low enough on-resistance so that's not a problem. Likely, such a MOSFET will be operated well below its maximum current.
Is there a linear relationship between the rated current of the FET and the rated current of the circuit?
There is a relationship between the MOSFET's practical operating current and its max rating, but it may not be linear.
 

srinath99

Joined Jun 30, 2017
6
It depends upon the on-resistance of the MOSFET which determines its heating, and efficiency.
At the rated current the dissipation from the on-resistance may cause overheating of the MOSFET without a large heat-sink and/or reduce the efficiency by a significant amount.
So you want a MOSFET with a low enough on-resistance so that's not a problem. Likely, such a MOSFET will be operated well below its maximum current.
There is a relationship between the MOSFET's practical operating current and its max rating, but it may not be linear.
I want to use the synchronous rectifier to charge a battery (most probably LiPo)
I understand that battery chargers need to balance cell voltages and prevent overcharging.
So
1) Is there a reference design for a balanced LiPo charger ? Is there a writeup that explains it better ?
2) Would it be possible to interface it with the 3 phase synchronous rectifier mentioned in the threads above without having another DC-DC conversion stage ?
3) How does Battery chemistry play a role in design of the charger (LiPo, versus Li-ion vs Ni-Cd... etc)
 
Top