Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Styx said:Optikon said:Styx said:is there any particular reason you have to use a FET?
if not use an IGBT (those rating you state are starting to enter IGBT territory)
they dont have any anti-parallel diode, unless you get one like that - rare in distrete form
IGBT will have too high a saturation voltage. My application needs bi-directional controlled current flow.
If I could get one off the shelf, I'd use it but since it seems to be exotic (at best), I'll just use 2 mosfets in series with sources tied together.
Well the thing is BJT's have the lowest Vsat and they also dont have a intrisnic diode. Only limitation with them are that they are current-driven and are slow
are BJT's a possibility?
Oznog said:The body diode is not always such a bad thing. It depends on your app.
For example. if you want to build a cool and efficient FWB rectifier, you would orient the MOSFETs so the body diodes act just like a normal diode FWB when the gate drivers are turned off. So turning on the gate driver just brings the vds down from 0.7v to millivolts but otherwise it works either way.
Styx said:YOu are going to get shoot-throughs with that arrangement unless you have interlock logic
Styx said:YOu are going to get shoot-throughs with that arrangement unless you have interlock logic
the frequency of the generator as it stands is 100 HZOznog said:Styx said:YOu are going to get shoot-throughs with that arrangement unless you have interlock logic
Yes, that problem exists with any implementation regardless of the number of transistors or whether they're MOSFET or bipolar.
The problem is lessened due to the presence of the body diodes in a functional FWB implementation- the diodes will catch the turn-off spikes and continue to function as a rectifier, so prematurely turning off one transistor to make a clearance before turning on the other leg will not have very negative consequences.
From what I can tell, a hand-cranked generator will not be a really high frequency job so generous latentcies between turning off one and turning on another would not constitute a whole lot of the waveform. Switching losses from charging and discharging gates are also not very big.
Oznog said:Styx said:YOu are going to get shoot-throughs with that arrangement unless you have interlock logic
Yes, that problem exists with any implementation regardless of the number of transistors or whether they're MOSFET or bipolar.
The problem is lessened due to the presence of the body diodes in a functional FWB implementation- the diodes will catch the turn-off spikes and continue to function as a rectifier, so prematurely turning off one transistor to make a clearance before turning on the other leg will not have very negative consequences.
From what I can tell, a hand-cranked generator will not be a really high frequency job so generous latentcies between turning off one and turning on another would not constitute a whole lot of the waveform. Switching losses from charging and discharging gates are also not very big.
williB said:styx , i dont want to use any diodes at all..
i think i am going to try my origional schematic..
williB said:Oznog , have you ever simulated your schematic..
that body diode really effs things up..
i have been trying to simulate it since last night, and it isnt going well..
Styx said:williB said:styx , i dont want to use any diodes at all..
i think i am going to try my origional schematic..
ok fiar enough, however for anyone else running inot intrisic diode problems ill post this
Oznog said:Styx said:williB said:styx , i dont want to use any diodes at all..
i think i am going to try my origional schematic..
ok fiar enough, however for anyone else running inot intrisic diode problems ill post this
Congratulations in coming up with the world's most convoluted example of a FWB.
Now the original point was to make a FWB without the 1.4v diode dropout. This circuit leaves the diode drops in place, but adds transistors for no reason whatsoever. Nor do I understand how it's going to perform a blocking function, the diode parallel diode will conduct one way, the MOSFET will conduct if going the other way, so I don't see how it functions as a FWB anymore.