switching mosfet fully

Dimmer circuit for dc?


12v
|
|
,---------------------+------------+-------+
| | | |
| 10K 1K Rload
10K | | |
| 0.1 | | |
| ,-----||-------|---10K------|-------+
| | | | |
/ | ,--1M------+ | |-
\ | | | ,--+----||
/ | | |\ | | |-
\<-----|---+--|+\ | /c |
1K/ | | >----+-------| npn |
\ +---+--|-/ \e |
/ | | |/LM2903 | |
| | | | |
| - 100K | |
| ^ | | |
| | | | |
| | | | |
| +---+--------------------|----------+
| | |
| | Rs
| | |
'-------------------------------+----------'
|
|
gnd


It does okay running a very light load (like a car taillight bulb), but
even driving a load of an amp or two, the mosfet gets warm. It
oscillates too fast, so the mosfet never turns full on or off. At
least I think so lol.

I actually want to use this circuit topology to run a 25 amp load, so I
have somehow to get the circuit to do hard switching (also I have to
get rid of the transistor/pullup resistor combo and replace it with a
proper inverting fet driver).
I don't have any drivers on hand but I do have a pile of 555's. I can
make a 555 into an inverting driver, by tying pin 6 high and using pin
2 as the input for example. I only need very low frequency switching
so a 555 should do it.
Still figuring out how to make the circuit do hard switching. I
thought instituting a delay in the signal between the comparator and
the fet driver, or within the driver itself might accomplish it. This
dimmer should switch pretty slow, between 10 Hz and 1 kHz. I'd
appreciate any ideas how to slow it down.

.

Relevant Pages

  • Re: switching mosfet fully
    ... even driving a load of an amp or two, ... I think you want to make the positive feedback AC only and low pass the negative feedback. ... proper inverting fet driver). ... Still figuring out how to make the circuit do hard switching. ...
    (sci.electronics.basics)
  • Re: Bally Solenoid Driver Test Board
    ... Load wise, you are correct, this is why the factory Bally solenoid driver ... tester has a full complement of actual coils to energize. ... in mind to properly test a solenoid circuit, ...
    (rec.games.pinball)
  • Re: Bally Solenoid Driver Test Board
    ... in mind to properly test a solenoid circuit, ...  I had a lamp ... driver once that did not work 100% in my machine, ... and under a normal load would fail. ...
    (rec.games.pinball)
  • Re: 5V switching IC
    ... >>>the inductor, causing the output voltage to increase. ... >>>its magnetic field collapses, but eventually stops, allowing the load ... the output voltage eventually falls. ... >> end of the circuit. ...
    (sci.electronics.design)
  • Re: 5V switching IC
    ... This circuit costs the least of any design that I know of, ... on load, and this has strange effects on the oscillator. ... the inductor, causing the output voltage to increase. ... the output voltage eventually falls. ...
    (sci.electronics.design)