Re: Simple transistor NOT gate
- From: Allen Bong <allenbsf6502@xxxxxxxxx>
- Date: Wed, 13 Feb 2008 06:05:08 -0800 (PST)
On Feb 4, 1:55 pm, Tim Wescott <t...@xxxxxxxxxxxxxxxx> wrote:
On Sun, 03 Feb 2008 17:46:02 -0800, Allen Bong wrote:
On Feb 4, 9:19 am, Tim Wescott <t...@xxxxxxxxxxxxxxxx> wrote:
On Sun, 03 Feb 2008 16:54:44 -0800, Allen Bong wrote:
On Feb 4, 2:29 am, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris
<cfoley1...@xxxxxxxxx> wrote:
On Feb 3, 1:52 am, Allen Bong <allenbsf6...@xxxxxxxxx> wrote:
Hi,
Is it possible to construct a simple inverter gate using 1 or 2
transistors and resistors?
I tried the circuit below but it doesn't work at all.
VCC
+
|
|
.-.
| |
| |4K7
'-'
|
+------o OUTPUT
|
1K_ |/
INPUT o-|___|----+---|
| |>
.-. |
| | |
4K7| | |
'-' |
| |
| |
=== ===
GND GND
Allen
(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
You've described a perfect transistor inverter, that should work
for logic level inputs. A couple of things to check:
* Make sure you're using an NPN transistor instead of a PNP, a
MOSFET, or something else.
* Recheck your wiring, looking particularly at the pinout of the
transistor. It's easy to assume EBC when it's ECB, or vice versa..
* Use a voltmeter to actually measure the voltage at the input. If
you're driving the input from an open collector transistor or gate
output, no current will be injected into the base of your
transistor when your logic level is "high".
If you run through these three, the transistor has to be defective.
Replace it.
You've got the right answer right in front of you. Make it work.
Cheers
Chris
Classic RTL gate: should work.
But if you used this to drive another such gate, the second gate
would serious load down the output voltage of the first one. You
could juggle the resistor values to reduce this effect. Like
maybe...
VCC
+
|
|
.-.
| |
| | 1K
'-'
|
+------o OUTPUT
|
10K |/
INPUT o-|___|----+---|
| |>
.-. |
| | |
open| | |
'-' |
| |
| |
=== ===
GND GND
John- Hide quoted text -
- Show quoted text -- Hide quoted text -
- Show quoted text -
Thanks very much Richard, Randy, Chris & John,
The gate was used to replace a 74LS04 TTL inverter used between the
output of 74LS138 and the LE input of a 74LS373 latch. The clock was
about 1.8Mhz. During a high the transistor conducts fine but during
a low input of short duration, I would not be able to get a high with
my logic probe nor the LE is triggered. The Vcc is 5V and the
transistor is a Japanese 2SC945 general purpose transistor.
I checked with google for a transistor NOT gate and it used 1K at
collector and 10K for the base and input. There was no resistor
between Base and Emitter. And I tried that circuit, it doesn't work
too. Where can I get the schematics for a RTL or DTL not gate?
TIA and regards,
Allen
Plain 'ol transistor circuits can be slooow if you aren't careful. You
should either use a smaller (220 ohm?) resistor on the base, or you
should use a 220 in series with a 1k in parallel with a cap --
something between 100pF and 1nF should do, but I refuse to go through
the math in my head.
You can get Tiny Logic inverters -- I assume you are purposely avoiding
surface mount parts?
--
Tim Wescott
Control systems and communications
consultinghttp://www.wescottdesign.com
Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html-Hide
quoted text -
- Show quoted text -
Is this the circuit you have in mind?
VCC
|
.-.
| |
| |1K
'-'
|
10k +------o
___ |/
o-|___|-+ -|
| |>
.-. |
| | |
220| | ===
'-' GND
|
+---+
| |
.-. |
| | ---
1k| | ---1n
'-' |
| |
+---+
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
Yes, this is just a hobby & fun project and I dont have the gears to
solder a SMD. I am constructing the circuit on a breadboard and if it
works, I would solder it onto a stripboard.
I saw the inverter SMD on the back of the databook. It was made by
Toshiba and part number is TC4S69F. It was a 1989 databook.
Allen
No no! You want the capacitor in the path from the drive to the gate, to
speed up the current into and out of the base:
470pF?
___ .----||-----.
o---|___|--+ ___ +--- to base of xistor
220 '---|___|---'
1k
If you have enough drive this will even forcibly de-saturate a transistor
-- look around on the Zetex web site & you'll find some app notes on this.
--
Tim Wescott
Control systems and communications consultinghttp://www.wescottdesign.com
Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html- Hide quoted text -
- Show quoted text -
Hi Tim,
I've found the application notes on the zetex web site. It was on P2
& P4 of the pdf file which explains the speeding up of switching, both
the capacitor speedup and baker clamp methods are described.
http://www.zetex.com/3.0/appnotes/apps/an22.pdf
Allen
.
- References:
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- From: Allen Bong
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- Re: Simple transistor NOT gate
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- Re: Simple transistor NOT gate
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