switching Vss with a transistor

[[email protected]]

Total hobbyist here.

Is there anyway to wire a transistor so that it closes the Vss instead
closing the connection to ground?

I have a ciruit like this



Vss --------R1----+------------+
| |
3000 uF LED
| |
gnd --------------+-------------+


The capacitor provides a nice fade when Vss is switched off which is
much more cool than just blinking.

So i need to wire this into the output of a sound actuation circuit
(already done). But in order for the sound actuation circuit to
drive
the heavier load (100s of LEDs), I added a transistor.


Vss --------R1----+------------+
| |
3000 uF LED
| |
gnd---T1 ---------+------------+
|
+5V in


This is how I see it done in my books and online
(http://www.ectinschools.org/page.php?ps=2&p=45) but the problem is
that
the LED never gets the current bleed from the capacitor because the
transistor switched off connection to ground. The other way around
would work:

+5V in
|
Vss ----T1--R1----+------------+
| |
3000 uF LED
| |
gnd-----------------+------------+


But the transistor I'm using doesn't seem to want to work in this
configuration.

Any ideas?

 

[linnix]

Total hobbyist here.

Is there anyway to wire a transistor so that it closes the Vss instead
closing the connection to ground?
...

Use a load switch.

 

[Eeyore]

Use a load switch.

Eh ?

Graham

 

[Anthony Fremont]

Eh ?

I assume he means a high side driver. Something like this maybe:
http://www.st.com/stonline/products/literature/ds/7370/vn820.htm

Seems to me that if the circuit were wired as originally shown by the OP, it
should work fine. I suspect that the OP has the cap grounded somewhere
convenient and wasn't switching it's ground along with the LED's cathode.

 

[Eeyore]

I assume he means a high side driver. Something like this maybe:
http://www.st.com/stonline/products/literature/ds/7370/vn820.htm

Seems to me that if the circuit were wired as originally shown by the OP, it
should work fine.

I thought so too.

I suspect that the OP has the cap grounded somewhere
convenient and wasn't switching it's ground along with the LED's cathode.

I'm sure it must be something simple.

Graham

 

[John Fields]

Total hobbyist here.

Is there anyway to wire a transistor so that it closes the Vss instead
closing the connection to ground?

I have a ciruit like this



Vss --------R1----+------------+
| |
3000 uF LED
| |
gnd --------------+-------------+


The capacitor provides a nice fade when Vss is switched off which is
much more cool than just blinking.

So i need to wire this into the output of a sound actuation circuit
(already done). But in order for the sound actuation circuit to
drive
the heavier load (100s of LEDs), I added a transistor.


Vss --------R1----+------------+
| |
3000 uF LED
| |
gnd---T1 ---------+------------+
|
+5V in


This is how I see it done in my books and online
(http://www.ectinschools.org/page.php?ps=2&p=45) but the problem is
that
the LED never gets the current bleed from the capacitor because the
transistor switched off connection to ground. The other way around
would work:

+5V in
|
Vss ----T1--R1----+------------+
| |
3000 uF LED
| |
gnd-----------------+------------+


But the transistor I'm using doesn't seem to want to work in this
configuration.

Any ideas?

---
First, when you're drawing ASCII schematics, use a non-proportional
font like Courier and _never_ use the TAB key, use the space bar.

Second, try this: (View in Courier)


+V
|
[R]
|
+-----+
|A |+
[LED] [BFC]
| |
+-----+
|
C
ACT>--[R]--B NPN
E
|
GND


But, _hundreds_ of LEDs???

 

[John Fields]

I thought so too.


I'm sure it must be something simple.

 

[Michael A. Terrell]

Of course he will. Stuffed donkeys don't have much ground clearance!
;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[[email protected]]

Of course he will. Stuffed donkeys don't have much ground clearance!
;-)

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

That's not very nice or helpful, but thanks anyway. YFI, I'm
not stumped and none of you had the right answer anyway which was to
move the capacitor in front of R1. But I am extremely appreciative of
those who honestly tried to help.

 

[Michael A. Terrell]

That's not very nice or helpful, but thanks anyway. YFI, I'm
not stumped and none of you had the right answer anyway which was to
move the capacitor in front of R1. But I am extremely appreciative of
those who honestly tried to help.

Usenet has a lot of subject creep. Any thread over three messages is
at risk. You post through Goggle, so you're looking at it from a
different point of view where you can't see the big picture. At the
moment, there are 132,645 messages in sci.electronics.design, on the
Earthlink news server. There are people who are friends, enemies, and
lots of bad jokes. It isn't a classroom, and there is no handholding or
coddling. Things are tamer on sci.electronics.basics if you can't
handle this group. There are other newsgroups that make you think a war
has broke out. Its the nature of the beast. Like everyone else, its
time to love it, or leave it, because it won't change.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida