Step 4: The Enable Circuit

The first thing we have to tackle is the Enable Transistor.  The schematic shows that all you need is one N-channel MOSFET to be the enable.  That, however, is an ideal MOSFET.  An ideal MOSFET is a symmetrical device that can switch currents in both directions.  The 2N7000* is not an ideal MOSFET, there is a small diode built into it that is parallel with the actual FET.  This means that current can be switched on and off when flowing in one direction, but it will flow freely through the other direction whether the FET is on or off. I don't know why the MOSFETs are made that way, it is probably a manufacturing thing.  My guess is that for some reason, it is easier to make MOSFETs with a diode than without.

To counter this, we put 2 FETs together with their diodes facing opposite directions. That way, current can't flow in either direction freely UNLESS the MOSFET is switched on.  This is why our SRAM will need 8 transistors instead of 6.

*It should be noted that most discrete MOSFETs have a body diode, as its called, in them.
<p>i like your INSTRUCTABLE but i disagree on some fact you tell correct one is,</p><p>1. SRAM is static while DRAM is dynamic<br> <br>2. SRAM is faster compared to DRAM<br> <br>3. SRAM consumes less power than DRAM<br> <br>4. SRAM uses more transistors per bit of memory compared to DRAM<br> <br>5. SRAM is more expensive than DRAM<br> <br>6. Cheaper DRAM is used in main memory while SRAM is commonly used in cache memory (L1,L2,etc in processor).</p>
im not sure why you have so many transistors? also, you didnt really explain how it works. <br> <br>i played around with sr latches last weekend, which is essentially what sram is. <br>you could make a simple 'bit ram' with 2 npns and 4 resistors, if you had a static output (as in, the load on the output will always be the same..led, motor, transistor etc..) <br> <br>all it is, is 2 nand gates with crossed i\o. since 0-0 is a bad state, iv added a simple transistor inverter on each input (in=1 out =0; in=0 out=1) as to set it to a neutral state. added a transistor on each output so they both have an equal load. the output(s) are coming from the resister-Collector junction. <br> <br>one of them is a 2bit stack with master reset. <br> <br>http://postimage.org/image/ekiyoa3cl/ <br>http://postimage.org/image/6jwmqod81/ <br>hope it helps someone here <br> <br>not sure if this belongs here, im kinda high
What types of ICs could I use in place of this project?
Has anyone seen these price of these transistors for less than 20 cents for the BS250 and 8 cents for the 2N7000 in smallish quantities? I have wanted to make mosfet logic circuits using discrete transistors but I heard that they had to be &quot;matched&quot; so I am glad this instructable came along with a p and n channel that apparently work together in a circuit..
I really like http://ledcalc.com/ for resistor calculations. Also, for Android there is an app called &quot;ElectroDroid&quot; that I use all the time for my electronics project. Just letting people know about it.
The LED calculator that I provided is just one that I've seen in a few other instructables, so whatever works for you is great. ElectroDroid looks really cool though! I just got it this morning after seeing the comment, and so far, I really like it.
A picture is worth 10million 32-bit words. I love it! Great instructable, and keep the puns coming.
Thanks man!<br><br>Just wait until core memory...
Cool. Can i make like this 10mb memory to my project?
Well if you've got a few million spare transistors laying around, and heaps of spare time I don't see why not.
Dear santa...

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Bio: I like to make things that move, sense, calculate, compute, blink, and make noise. I like making things that create high voltages, electrical arcs, and ... More »
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