push-push on/off switch

http://img20.imageshack.us/my.php?image=pushpushxo0.jpg


John

 

What? And what does it do ?

...Jim Thompson

 

Cool.

 

A sort of oscillator?

VLV

 

I think if you hold in the button, the negative feed back will bias
the mosfet half-on (destroying it if load is too heavy).

 

Is this an "I can't believe nobody else has thought of that yet"
moment?

Thanks,
Rich

 

No, but if someone holds the button long enough it'll be a "Phsssst -
pop - crackle - KABLOUIE" moment.

 

It works as a dimmer, too.

It's interesting to play with.

John

 

Why would it oscillate? No, it's a push-push on/off switch.

John

 

<Smirk>

...Jim Thompson

 

Bwahahahahaha!

...Jim Thompson

 

---
Not according to LTSPICE:

Version 4
SHEET 1 880 680
WIRE 208 -352 -272 -352
WIRE 208 -288 208 -352
WIRE -272 -176 -272 -352
WIRE 0 -176 -32 -176
WIRE 208 -176 208 -208
WIRE 208 -176 80 -176
WIRE 208 -112 208 -176
WIRE -32 -32 -32 -176
WIRE 32 -32 -32 -32
WIRE 160 -32 112 -32
WIRE 48 16 -176 16
WIRE -176 48 -176 16
WIRE -32 64 -32 -32
WIRE -272 160 -272 -96
WIRE -176 160 -176 128
WIRE -176 160 -272 160
WIRE -32 160 -32 128
WIRE -32 160 -176 160
WIRE 96 160 96 16
WIRE 96 160 -32 160
WIRE 208 160 208 -16
WIRE 208 160 96 160
WIRE -272 208 -272 160
FLAG -272 208 0
SYMBOL nmos 160 -112 R0
SYMATTR InstName M1
SYMATTR Value FDC637AN
SYMBOL res 192 -304 R0
SYMATTR InstName R1
SYMATTR Value 12
SYMBOL res 96 -192 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 1000
SYMBOL cap -48 64 R0
SYMATTR InstName C1
SYMATTR Value 1e-7
SYMBOL voltage -272 -192 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL voltage -176 32 R0
WINDOW 0 -53 5 Left 0
WINDOW 3 -242 110 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 1 2 1E-6 1E-6 1 2)
SYMBOL sw 128 -32 M270
WINDOW 0 32 15 Left 0
WINDOW 3 32 44 Left 0
SYMATTR InstName S1
TEXT -184 232 Left 0 !.model SW SW(Ron=1 Roff=10Meg Vt=0.5Vh=0)
TEXT -184 200 Left 0 !.tran 10


Or maybe I picked the wrong parts. Got some values that work?

 

My sincere apologies to LTSPICE, but it does work.

Try, say, 1M and 0.47 uF.


John

 

Yep, It will work for optimal button-press times. Then it will leak
one way or 'nother ;-)

It's fun that it works, but otherwise useless.

...Jim Thompson

 

Does everything that's fun have to be useful?

John

 

---
Tried it, it didn't work, and what about that floating gate when the
switch opens? (Yuck...)

Or maybe I'm misinterpreting your drawing.

I see a normally-open momentary switch, an N-channel enhancement
mode MOSFET, and an R and a C.

Am I missing something?

 

No. But a stable-state switch would be more interesting.

...Jim Thompson

 

Fry when it eventually drifts into the linear region?



Best regards,
Spehro Pefhany

 

Your sketch, for the permanent record,

,---/\/\----+----o LOAD o-- +V
| |
| |--'
| ___ ||<-,
+--o o--||--+
_|_ |
--- gnd
|
gnd

A 0.5-s time constant. Should work with most
modest pushbutton presses. My experiments show
modern power MOSFETs can hold their gate voltage
for days, if not weeks. But surely you remember
out long-running thread that completed the simple
circuit with a 2nd transistor making a flip flop.

 

The problem is that there is NO stable state to start from. A true
F-F is the only way to go.

...Jim Thompson