Re: [TCML] op amp wiring

[Gabriel Cardona <cardogab7341@xxxxxxxxx>]

Scott,

Driving a power MOSFET from an op-amp is not recommended. Power MOSFET's require about 10V higher voltage at the gate than the source to be fully turned on, and there is a significant amount of stray capacitance on the gate that needs to be charged before the gate voltage will get to that 10V above Vsource. Op-amps typically cannot supply the instantaneous current required to drive a power MOSFET gate. You can use the op-amp to drive a MOSFET driver. It looks like you are using the op-amp as a comparator, you may want to look at a stand-alone comparator such as the LM111 or Linear Tech LT1011. You will still need a MOSFET driver after the comparator.

Regards,

Gabe Cardona




________________________________
From: Scott Bogard <sdbogard@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Thursday, January 15, 2009 11:22:08 AM
Subject: Re: [TCML] op amp wiring

I'll put a schematic up someplace later it may be some time as I don't
have internet in my apartment and school internet frowns on uploading
files; but basically this will be a modification of the single
transistor feedback winding schematic, the op amp will have a steady 6
volt fed the the non-inverting pin? and the sinusoidal output (which
would normally be the base for the 3055 transistor) will go to the
inverting pin?.  The idea is to have the op amp flip between 0 and 12
volts to drive a mosfet for a square wave output, when the mosfet is
on, it will choke the input to the inverting pin (via the feedback
winding) until the op amp switches off, and then the cycle begins
again when the field in the feedback winding dissipates.  This is
probably an over complicated system, but I want something that is
square wave and self resonant (the standard 3055 circuit seems to
never utilize the full 12 volts input unless I'm reading the
oscilloscope wrong, and I don't like the 555 timer circuits as they do
not dynamically adjust to load.)  Also as best I can tell nobody does
it this way and I wanted to make something original; then again maybe
they done do this because it won't work, I don't know.  Any help would
be appreciated.

Scott Bogard.

On 1/15/09, Gabriel Cardona <cardogab7341@xxxxxxxxx> wrote:
> Scott,
>
> Can you explain what you're trying to do?
>
> 1. What will the output of the op-amp be connected to and what voltage
> levels are needed at the op-amp output?
> 2. What voltage levels will be at the input to the op-amp?
> 3. What is the op-amp you're using (manufacturer and part number)?
>
> With this information, it will be easier to help.
>
> Regards,
>
> Gabe Cardona
>
>
> ________________________________
>
>
>
>
> ________________________________
> From: Scott Bogard <sdbogard@xxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Wednesday, January 14, 2009 1:17:51 PM
> Subject: [TCML] op amp wiring
>
> Hey guys,
>      I am in need of some assistance, I am doing an experiment with
> flyback drivers, and the circuit I designed uses a Op-amp in a
> comparator configuration.  The only problem is I know nothing about
> actually wiring an Op-amp except for the extreme basics (inverting
> pin, non-inverting pin, output) which I learned in school.  I do not
> know how to connect it to the power supply, if I need negative
> voltage, what the "offset" pins are for, what Vcc or Vss is, etc.  Any
> help would be appreciated, there are 8 pins and I only know for sure
> what 3 of them do, thanks.
>
> Scott Bogard
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla