Vout Lo in LM324

- M
- Marte Schwarz
  
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posted
12 years ago

Mon, Dec 12, 2011 1:11 PM

Hi Joerg,

I don't make a switcher here, just a chopper. So ton and toff is not any problem at all. 4.5 kHz is also quite low. We did it before with BSS89 FET also no problem, it is quite similar to 2N7000.

Shure, never use typical value! The devices must do their job not only typical :-) This is the very first thing my students learn.

No problem here. I don't need the minimal Rdson. It only has to be quite small against 100 ohms, may be I should multiply the resistors of the divider by 10. I#ll test it in the next minutes. Also the specs is about

3 V.

I'm very shure you would be satisfied.

Marte

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- Joerg
  
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posted
12 years ago

Mon, Dec 12, 2011 3:52 PM

[...]

Good! You would not believe how often I had to flag a design with a 600V or 800V FET in there that was driven with 6-7V at the gate. While the datasheet only spec'd them at 10V.

[...]

Only if there's enough bagels. Or in Germany, Marzipan candy or Mettbroetchen with onions on top.

--
Regards, Joerg

http://www.analogconsultants.com/

- C
- Charlie E.
  
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posted
12 years ago

Mon, Dec 12, 2011 6:53 PM

Of course, there was the buddy I worked with many years ago that would come in on Monday morning telling us about his weekend taking his jeep off road into the boonies, barely clearing rocks, having to use his winch to get out of tight scrapes, etc. Then, you would go out and look at his jeep, with the pretty light blue paint job without a single scratch or dent... ;-)

Charlie

- F
- Fred Bloggs
  
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posted
12 years ago

Mon, Dec 12, 2011 7:18 PM

The MOSFET drive is marginal on both ends. You can add a few parts to rail the drive: Please view in a fixed-width font such as Courier.

. . . . +5V . | . +-------------------------. . | | . | | . | |< . +--[10K]--------+-------| 5V . | | |\ ---- . | | | | | . | |/ | | | . +--[56K]--+---| | | | . | | |> +----> out | | . | [39K] | | | | . | | | | | | 0V . |\ | -+- [1K] [1K] --- ---- . | \ /// | | . | \ | -+- . | > -----+-------' /// . | / | . | / | . |/ | . | . | . | . FB

- D
- dagmargoodboat
  
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posted
12 years ago

Mon, Dec 12, 2011 10:37 PM

g

h

=A0 =A0 |

=A0 |<

=A0 =A0 =A0 =A0 5V

|\ =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0----

=A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0| =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0+----> out =A0 =A0 | =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0| 0V

=A0 =A0 =A0 =A0 --- =A0 =A0 =A0----

=A0-+-

- J
- Joerg
  
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posted
12 years ago

Mon, Dec 12, 2011 10:38 PM

My colleague was different. Since our company was almost adjacent to a Home Depot store he'd sometimes drive over during lunch and get lumber, sheet rock and whatever else he needed. All in the bed of his trusty

1956 Chevy truck.

--
Regards, Joerg

http://www.analogconsultants.com/

- F
- Fred Bloggs
  
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posted
12 years ago

Mon, Dec 12, 2011 11:39 PM

ing

ith

=A0 =A0 |

=A0 |<

=A0 =A0 =A0 =A0 5V

=A0 |\ =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0----

=A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0+----> out =A0 =A0 | =A0 =A0|

| =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0| 0V

=A0 =A0 =A0 =A0 --- =A0 =A0 =A0----

|

=A0-+-

Even then the high side pull-up is marginal. And it's only a student project. His circuit has a lot of skew, maybe better to make the astable for 10KHz then drive a CMOS toggle FF with built-in schmitt trigger clock to get a more accurate 50% duty and this drives the chopper FET directly.

- G
- George Herold
  
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posted
12 years ago

Tue, Dec 13, 2011 2:34 AM

ing

ith

=A0 =A0 |

=A0 |<

=A0 =A0 =A0 =A0 5V

=A0 |\ =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0----

=A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0+----> out =A0 =A0 | =A0 =A0|

| =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|

=A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0| 0V

=A0 =A0 =A0 =A0 --- =A0 =A0 =A0----

|

=A0-+-

Oh I agree, (as if my opinion matters) and they come it 8 pin dips too. And if it's for students, they should be shown that opamps are best for amplifying and comparators for comparing. (they can try switching things around later, .. and being disappointed with the results.) I wanted a slow comparator once, and tried an opamp... an LM393 with a bit of C hanging on the output was better.

George H.