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Subject: Re: Can I make an inverter out of diodes or alternative means?

Date: 11/02/01 at 12:40 PM
Posted by: David Ashby
E-mail: dashby@quin.co.uk
Message Posted:

In Reply to: Can I make an inverter out of diodes or alternative means? posted by Teddy Allan on 10/30/01 at 11:16 AM:

Hi Teddy,You certainly can make an inverter using a discrete transistor - but if switching speed is critical, it won't work as fast as the gates in your logic chip. And if current consumption is critical, it won't be as economical. If the foregoing doesn't put you off, and assuming you are using CMOS (CD4000 family or 74HCxxxx), all you do is:1) Take almost any small signal NPN transistor2) Connect it's emitter to the 0V supply rail3) Connect the signal you wish to invert to it's base via a 10K resistor4) Connect it's collector to your positive supply rail via a resistor. The value of this resistor depends on your supply voltage, and whether you prefer to optimise for speed or low power operation. As a starting point, try 4.7K.If you are interfacing to TTL, you may need to add a diode in series with the 10K resistor connected to the base of the transistor. This raises the switching threshold of your D.I.Y. inverter. The cathode of the diode goes towards the transistor base.Hope this helps.David Ashby.

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