Yes, it is possible, and your circuit should work. When you ground the input, the transistor should be in cut-off and the collector voltage should be at Vcc. When you apply Vcc to the input, the transistor should saturate and the collector voltage should be at zero.
Check all connections and check you transistor. If your ciruit still does not work, in what way is it not working? What type of transistor are you using? What value of Vcc?
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.
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...
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?
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 consulting
http://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
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.
Alan: Your transtor is saturating when on, and it is probably very slow to come out of saturation. Try putting a diode from base to collector; that will keep it from saturating. Here is the circuit:
| | GND --------------------------' (created by AACircuit v1.28.6 beta 04/19/05
formatting link
This trick is called a 'baker clamp' for some reason. The diode prevents the transistor from saturating, thereby increasing the speed at which it can turn off. This circuit probably won't do more than a few MHz, but you never know.
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 consulting
http://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
I tried out the circuit but it doesnt work in my application. What do you meant by "if you have enough drive"? I am driving the circuit with the output of a 74LS138. Does the 74LS138 have enough drive to unsaturate the transistor?
I am going to google the Zetex web site to get more info as suggested.
Hi, you're right! My copy of AoE does have a description on Baker Clamp on Page 584 and also a full chapter on the 8085 micro too. What a find! Looks like the book was sitting in my book shelf for toooooo long and I'm going to reread it from the begining again.
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.
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