Re: op amp controlling a mosfet


John Popelish wrote:
kell wrote:
Imagine you have a vehicle that receives up to ten amps from a
generator, and with the generator off you need a blocking rectifier to
keep the 12 volt battery from discharging into the generator windings,
so you decide to use the body diode of mosfet as the blocking
rectifier; during charging you can have the mosfet turned on to reduce
dissipation. The blocking has to occur in the positive rail because
ground consists of the vehicle chassis.
What is the best way? I was thinking about something along these
lines:

generator
|
,------------+
| |
| _ _|D
'--|-\ | STP80PF55
LF412| >-+-|| p-channel
,--|+/ | |_ mosfet
| | |S
| 100K |
| | |
| | |
'-------+----+
|
|
battery

Somebody told me the LF412 works with common mode inputs at the
positive rail, but if I should be looking at some other op-amp let me
know.
http://www.national.com/ds/LF/LF412.pdf

I doubt this simple circuit will do. The concept is to drive the gate
negative (down to ground) with respect to the source any time the
battery is more negative than the generator. So it gets real
important what powers the opamp, and that it (both the supply pins and
inputs) is protected from voltage spikes. Are you going to power the
opamp at all times from the battery?
I expect to power the op-amp from the generator.
I didn't indicate power pins, bypass caps, input resistors and such on
the circuit diagram. I was more interested in the concept, the utility
of the LF412 and and the like so I didn't flesh out the circuit like I
guess I should have.
So are you saying that conceptually it's ok, but that actual
implementation is impractical? I get the impresson you don't like the
idea of powering the op-amp from the generator.

.

Relevant Pages

  • Re: pro user 850w generator opinions?
    ... | would be OK to plug into the van mains input and charge the battery / ... the van powered up, you should give either method several days to ... The power from a wind generator varies as the *cube* of the windspeed, ...
    (uk.rec.caravanning)
  • Re: Portable inverter/generator questions
    ... probably a very long cord to locate the generator elsewhere {:-). ... And add a bit more because inverters cost power any way) ... If you only want to run the generator say once every four days, then you need 400+ AmpHours in battery storage. ... j) solar panel regulator so it doesn't pump too much charge into the battery. ...
    (misc.survivalism)
  • Re: Redox batteries
    ... When you say that charging will use a fraction of the power of the generator because most of it is used by the propulsion, you are right when you consider riding at nominal speed. ... In this case, what I need is having the generator run for one hour at full power, then quietly ride using the batteries only for ten hours. ... You do not need to modify the charger itself - it bases lowering the current on voltage only, and "relaxing" will make sure that battery voltage will not go high enough to start throttling down the current. ... it does not matter how to charge it as long as you do not cause ...
    (sci.chem.electrochem.battery)
  • Re: Onan Genset: soon to be owner, need a little help
    ... The Model of the genset matter a lot. ... Should have been enough to crank over, ... DC generator to provide control and battery charging voltage. ...
    (rec.outdoors.rv-travel)
  • Re: Onan Genset: soon to be owner, need a little help
    ... I tried both the remote switch and the one on the genset - all it ... Should have been enough to crank over, ... DC generator to provide control and battery charging voltage. ...
    (rec.outdoors.rv-travel)
Quantcast