Driving a MOSFET Full wave bridge rectifier

Thread Starter

IvyK

Joined Apr 7, 2012
15
Hi All,

I've developed a MOSFET full wave bridge rectifier. When the MOSFETs are fully on it rectifies beautifully. For my test conditions i used comparitors to turn them on when required. In real life MOSFET drivers are used. The reason for me using MOSFETs in the first place is because i wanted to rectify low AC voltage (1RMS to 12RMS). This is my system input voltage range. Turning these MOSFETs on are a problem at low voltages. I'm battling at high voltages as well.

The sine wave has a positive cycle and a negative cycle. During the postive cycle I wish to turn on two sets of MOSFETs, and during the 2nd half I wish to turn on the second set. This means that the driving signal needs to be synchronised with the input sinusiod. The input is a varying 1-12Vrms signal at 50Hz. Can anyone suggest a driving signal for the MOSFETs?

Looking at conventional MOSFET drivers, I don't think they will work.
Are there any suggestions?

Thanks
Ivy:)
 

wayneh

Joined Sep 9, 2010
17,153
I must say that I'm looking forward to the why-s of this circuit.
Active rectifiers are big in the alternative energy world, to reduce the diode voltage drop as a big source of loss at low AC voltage, and to rectify relatively large currents for not much cost.
 

Thread Starter

IvyK

Joined Apr 7, 2012
15
Yeah I can share it.

It's just getting drivers to drive the MOSFETs at the right time that's bugging me. I'm not a boffin on drivers, and i'm finding them quite complex. From what i understand is i'll need a DC input to drive the MOSFETs. Maybe I'm unclear on the operation. Also theres quite a few driver topologies for drivers.

I've tried to upload pics of the circuit and results.
 

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wayneh

Joined Sep 9, 2010
17,153
Yeah I can share it.
Thanks. You might be interested in this design presented by IR.

From what i understand is i'll need a DC input to drive the MOSFETs.
True, although rectifying the input and using a bootstrap capacitor can allow operation from the AC supply. But if the AC supply voltage is too low, a separate DC supply may be required. It'd be very low current, though, so even a 9V battery is a possibility.
 

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Thread Starter

IvyK

Joined Apr 7, 2012
15
Ok. Just to wrap my head around the driver circuit:

So the input of the driver is connected straight to the input line, and the output is connected to the gate of the MOSFET? What driver will you suggest?

The input voltage here varies at any time between 1Vrms and 12Vrms.
 

Thread Starter

IvyK

Joined Apr 7, 2012
15
WOW! just saw that circuit you posted. I'm going to take a deeper look into it. You actually got me excited *blush*... I'll keep you updated if i get it working :) :)
 

CDRIVE

Joined Jul 1, 2008
2,219
Active rectifiers are big in the alternative energy world, to reduce the diode voltage drop as a big source of loss at low AC voltage, and to rectify relatively large currents for not much cost.
Thanks for the enlightenment. Some old dogs don't stay very current. ;)
 

wayneh

Joined Sep 9, 2010
17,153
Well, this old dog can read and learn a new trick, but has been too lazy to actually DO the trick and build one of these. Maybe our OP will have the energy to make it happen.
 

Thread Starter

IvyK

Joined Apr 7, 2012
15
Hey Wayneh

I never check this thread for a while. I analysed that circuit and tried finding some info on the chip. I'll take a closer look at the presentation as well. I've looked at running the MOSFETs using IR2110 drivers. You'll need 2 ICs instead of 4. Come across some problems with it though. Some of sources on the bridge experience negative voltages that exceed he negative threshold of the chip.... sigh. In an ideal world things would work out so well. I have a solution for this but i'm not too sure about it. If you interested we can brainstorm it :)
 

wayneh

Joined Sep 9, 2010
17,153
If [you're] interested we can brainstorm it :)
I appreciate the notion but it's beyond my pay grade! The last time I looked around in this area , I was hoping to find an example circuit online that I could follow to make my own. But I never found one I felt comfortable with. Without an oscilloscope or any experience in this area, the details of setting the timing around the transitions, to prevent ringing and such, seemed intimidating for a DIY project.

What I wanted to find was an active rectifier with these properties:
1. Scalable by adding parallel MOSFETs. Minimum 5A initially, scalable to 30-50A. (I don't have a specific top end in mind, just more than 10A).
2. Max voltage up to 120V would be fantastic, but if it mattered, I could drop back to 50V or maybe even less.
3. Input frequency widely variable from maybe 5 Hz up to 500 Hz. This is the biggest design challenge?
Such a beast would find application to DIY windmills and other applications.
 

Thread Starter

IvyK

Joined Apr 7, 2012
15
If you working at those voltages, then what is the problem with using diodes? I see why you have a problem with frequency it varies quite a bit if you using MOSFETs, the switching becomes tricky. Are you trying to achieve maximum efficiency with MOSFETs?
 

wayneh

Joined Sep 9, 2010
17,153
Yes, it's all about eliminating the voltage drop and power loss that goes with it. The upper voltages are not the expected, normal operating voltage. They're the max expected, for instance from a windmill in high wind. High voltage would eliminate the problem (in terms of power percentage lost), but the rectifier would need to do its thing at much lower voltages, down where the diode drop would be significant.
 

Thread Starter

IvyK

Joined Apr 7, 2012
15
Oh I see, I'm truely no expert. Maybe you can look at techniques to stabalize the frequency to a narrower range then the IR1167 driver setup will work. Just an idea though. You've probably already looked at this.
 

crutschow

Joined Mar 14, 2008
27,895
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.
 

wayneh

Joined Sep 9, 2010
17,153
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.
Have you actually built one?
 
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