Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Diode-less Power MOSFETS

Status
Not open for further replies.
Oznog said:
williB said:
the reason i'm using two mosfets is the single diode approach just doesnt work
I think that's because, again, you're driving it incorrectly.
i ment single mosfet ,but i guess you understood though.. :lol:

How should i be driving it..??
driving the gates?
I'm pretty sure that the H-bridge single mosfet rectifier setup does not work..
The H-bridge Mosfet rectifier setup with P-channel Mosfets Ron proposed last night works better than a full wave bridge rectifier using the best shottkey diodes in the library..
it outputs close to 7A peak rectified current into a 2.4 V battery with a 12V p-p sine wave as input..
 
williB said:
How should i be driving it..??

At least one half the rectifier must be driven by an amp, rather than by AC polarity. That's absolutely essential if there is any energy storage in the load such as battery or capacitor that would allow current to flow back into the source. A mosfet with its gate turns on conducts current in either direction unlike a diode and thus polarity of the AC signal alone cannot be used to switch the transistors.

Vpp can be like -0.05v. Compilcated to generate but you need it.

The amp on the nmos will turn them on when the ac voltage is less than gnd. Actually I don't think the circuit will work as-is because there's a triggering issue, after a zero crossing the ac source is floating. The pmos won't turn on until the nmos pulls down the pmos's gate, but the nmos amp can't turn on with the other leg floating like that. Impossible to read a voltage when the other pole is floating. Not sure of the best way to remedy this, an opto can do it, maybe there's a simpler scheme there.
 

Attachments

  • sync.jpg
    sync.jpg
    24.1 KB · Views: 742
i've managed to eliminate those pesky little 500mA dips (down to 100mA), with some common source inductance..
if ya play with values i bet we eliminate it compleatly..
 

Attachments

  • mosfet_rect2.jpg
    mosfet_rect2.jpg
    76.4 KB · Views: 690
  • mosfet_rect2_output2.jpg
    mosfet_rect2_output2.jpg
    57.6 KB · Views: 682
williB said:
why go through that much trouble , just to save four mosfets..

Willie, the amps aren't there to compensate for the loss of the extra 4 mosfets. Those serve no purpose and don't fix your central flaw in any way- that you have no control over current direction.

It looks like the only reason you can get an output is you're using the threshold voltage of the mosfets to sort of coincidentally control the current flow. This is not very reliable, threshold voltage is inconsistent and you should be design it to be a bit more versatile than this. Here you're mostly limited to having the battery voltage less than the threshold voltage. That's the only thing preventing the battery from discharging into the source- the source will have to be higher than 2.4v before the threshold voltage is exceeded making the mosfets turn on.

You're not actually only trying to charge a 2.4v battery with a 12v source, are you? If that's the case there's already plenty of voltage available and the standard fwb makes a lot more sense here.
 
As far as the inductors are concerned it was just an idea..
You're not actually only trying to charge a 2.4v battery with a 12v source, are you?
umm no,
i am trying to charge a battery(1.2v OR 2.4v doesnt matter really), with a few .22 F caps tacked on to absorb some of the power..
the "source" is a model for a generator with 20V p-p no load output..
but under load it looks more like a 12Vp-p sinusoid , hence the use of the 12V source in simulation..
the generators internal resistance is 1.3 ohms..
these are som numbers i hav collected from the generator..
5.2W measured output with Just a FWB into a resistive load ..


8.75W simulation output w/diode(single) in output leg & .44F cap feeding 2.4V battery..
9.38W simulation output w/out diode into a 2.4V battery & .44F cap..
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top