Hi,

I want to make an discrete inverter to replace 74HC04. And, the discrete inverter can keep the supply current drawn both static and dynamic remains the same, no matter of the state of the inverter. How can I make it? Any circuits?

Thx!

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8899

 

CMOS logic dissipates more power as the frequency increases for two reasons. One is "shoot-through" current, and the other is due to the fact that it will always have a capacitive load that has to be charged and discharged at the switching frequency.
The shoot-thru current is caused by the fact that the pullup (Pchan) and pulldown (Nchan) transistors are on simultaneously during the transition between logic levels. This can possibly be alleviated somewhat by clever circuit design, probably at the expense of propagation delay.
The capacitor charging power cannot be eliminated. The capacitance is the sum of device output capacitance, package parasitic capacitance, wiring capacitance, and the capacitance of any devices which are being driven. The power dissipated by the logic device driving this capacitance is

P = F*C*V^2

Where F is the switching frequency, C is the aforementioned capacitance, and V is the supply voltage of the CMOS logic device.

Having explained all this, I gotta say I'm not sure this this addresses your question. :roll: Does it? What problem are you trying to solve?

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Ron

 

A CD4069 or 74C04 inverter also works with a 5V supply and has a much lower "shoot-through" current than a 74HC04 inverter. Its penalty is that it is much slower.

74HCxx ICs have such a high supply current when their output is "halfway" that their datasheet spec's a short max switching time for them.

Maybe you could use a Schmitt-trigger inverter like a 74HC14, CD74C14 or MC14584 if you have slowly changing inputs. Their "snap action" reduces power supply current considerably. :lol:

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Uncle $crooge

 

Ron H & audioguru,

Thanks for your replies!

Actually, in my design, I only need a single inverter. So, I want to use a discrete circuit (a single or 2 transistors) to make an inverter. I tried to search some sample circuits in yahoo.com, but got nothing. Could you all help on this?

Thx!

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8899

 

I think I've seen single Cmos inverters in a tiny 4-leg surface-mount package.

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Uncle $crooge

 

You don't mention what it's intended to do?, a single NPN transistor and two resistors is all you need for an inverter.

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Sorry! Yes, I'll use it to invert the clock signal at 100Mhz frequency.

__________________
8899

 

You don't perhaps think 100MHz was the most important thing you might have mentioned?.

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Naaaaaah! What's a little VHF among a bit of 2MHz logic?

And yes, there are manufacturers out there that are making single-function SMT logic, the idea being to place your logic physically where you need it without having to get the wiring run to a multiple-gate chip. It's the best way to keep it small and keep the specs high.

Dean

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Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

 

I'm guessing he does not understand the difficulty of designing a discrete 100MHz inverter.
I would use something like Fairchild's TinyLogic.

What was that stuff about constant current drain?

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Ron

 

This circuit will have constant current from the supply and switch at 100mHz:

Attached Images

inverter_140.jpg (100.3 KB, 464 views)

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Hey Russ,
Your circuit is exactly the same as I have written on my notepad but you beat me because I had to go out. As for your 2N2369 transistors, I have some brand new ones about 40 years old! :lol:

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Uncle $crooge

 

I have some 50 year old transistors, germanium, of course.

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AD149, AC128. Yeah, I have some too. :lol:

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Uncle $crooge

 

But NOT 50 years old, that's 1955, the year the transistor was invented (and the year I was born 8) ) - surely no coincidence?. Those transistors were 1960's, well after the OC71 series, which weren't that early either. There's not going to many 1955 transistors about (if any?).

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