The 2N700X jellybean family includes the 2N7000 (TO-92 through-hole) as well as the 2N7002 (SOT23 surface mount) devices. They are considered jellybean components because they are popular, have stood the test of time, are inexpensive, and are available from many different manufacturers. These components have been used for decades and are likely to be used for many more.
The 2N7000 is an old part; if I’m reading my datasheet correctly, it has roots extending back 50 years to Siliconix (Vishay). It was advertised as a MOSPOWER FETlington with a “logic-to-load design 5 Volts in - 100 mA” out as shown in Figure 1. The term FETlington is a delightful play on words, combining FET with Darlington. This would have helped the designers of the era who would have been familiar with Darlington transistors, but not necessarily the emerging MOSFET technology. For reference, the transistor itself was only 30 years old, and you could still test vacuum tubes at the local drugstore.
This was a big deal 50 years ago. It emerged within years of the classic microcontroller such as the Zilog Z80 and the General Instruments (Microcontroller) PIC1650. It allowed these 5 VDC devices to directly control class loads. Modern parts like the Vishay 2N7002K-T1-GE3 are direct descendants.
Figure 1: The older Siliconix (Vishay) datasheets described the 2N7000 as a MOSPOWER FETlington.
Tech Tip: Jellybean parts represent a logistics paradox. We aren’t looking for a needle in the haystack; instead, we are looking for the haystack itself using a DigiKey system purpose-built and optimized to find the needle. We will introduce a few techniques later in this article to overcome this hurdle. TL;DR: search using “2N700 MOSFET”.
2N700X Characteristics
The 2N700X family members are generally described using the following metrics. Note that we err on the conservative side to include manufacturer and part variations. Refer to individual datasheets for the complete specifications.
- N-channel MOSFET
- Logic level drive (see precautions below)
- ESD protection via gate-to-source clamping diodes
- V_{DS (max)} = 50 VDC
- I_D approximately 300 mA (continuous) for the 2N7000 and about 200 mA (continuous) for the 2N7002
- R_{DS(on)} in the 2 to 5 Ω range (drive voltage dependent)
- P_D approximately 350 mW (continuous) for the 2N7000 and about 150 mW (continuous) for the 2N7002
Tech Tip: Conservative design is a corollary of the jellybean concept. If we assume any jellybean parts will suffice, we should design conservatively to accommodate the full range of potential options.
2N700X Applications
As implied in the playful MOSPOWER FETlington name, the 2N700X are often used in switching small loads. Today, we designate the 2N700x family members as logic-level MOSFETs. They are attractive as the gate can be directly driven by a microcontroller thereby minimizing the total parts count.
To better understand the performance of the 2N7000, assume a 24 VDC load. If we drive a conservative 150 mA load, we calculate that the MOSFET can control a 3.6 W load. This capacity is useful for applications such as relay drivers.
We also see the 2N700x used for level shifting applications. The open drain example in Figure 2 shows the potential. For example, we could easily change the lightbulb voltage from 5 VDC to anywhere between 3.3 to 50 VDC with a reasonable safety margin.
Figure 2: Schematic for wired NOR featuring open drain devices.
MOSFET Precautions
Lack of gate drive voltage is perhaps the largest design mistake. This is especially true when the MOSFETs are driven by 3.3 VDC systems. To better understand the situation, consider Figure 3 showing the V_{DS} and I_D relationships for the Vishay 2N7002K-T1-GE3.
As an example, let the 2N7002 drive a 200 mA load (highlighted in red). We see an immediate problem if 3.3 VDC is used. There simply isn’t enough gate voltage to turn on the MOSFET. Instead of operating as a switch, the MOSFET will enter a quasi-constant-current condition, with excessive power dissipation. The result will sound like popcorn popping as the MOSFET explodes.
The solution is to use a 5 VDC source. The resulting operating point is identified by a green dot in Figure 3. With a 0.5 V_{DS} voltage and a current of 200 mA, we calculate a 100 mW power dissipation which is well within range for the SOT-23 package.
There may also be problems with insufficient gate current if the MOSFET is used in high frequency applications. Please refer to this engineering brief for additional information about gate current and drive voltage.
Figure 3: Output characteristics of the Vishay 2N7002K-T1-GE3 showing the relationship between V_{DS} and I_D as a function of V_{GS}.
How can we locate the 2N700x in DigiKey’s system?
We could simply enter 2N7000 or 2N7002 in the DigiKey search bar. This will return several exact matches which may meet your needs. However, this fails to capture the essence of the jellybean part as it’s too specific. Instead, we want a wider search to find all related parts.
From DigiKey Specific to General Searches
There are two ways to expand your DigiKey search from the specific to the general.
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Hacking Substrings: The DigiKey search tool is built to handle conjunctions e.g., “Arduino Shield.” In this example, the space between words is interpreted as AND operation e.g., “Arduino&Shield.” It also operates on substrings. We can use this to our advantage by truncating the part number and then adding a description e.g., “2N700 MOSFET”. At the time of this writing, it returns 221 unique devices that are currently sold by DigiKey.
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Reverse parametric search: If you have already located a specific DigiKey component, use the reverse search tool as shown in Figure 4 with a starting position based on the OnSemi 2N7002. This search identifies 28 OnSemi components with the root 2N7002 part number.
Figure 4: Initiate a reverse search for manufacturer specific components with the 2N7002 part number.
Tech Tip: Manufacturing trends have changed over the years. One important consideration is lead free components. Many of the new part numbers reflect this shift to RoHs compliance.
2N700X Variants
The utility of the 2N700X family has expanded into other areas outside of the TO-92 and SOT-23 packaging. A good example is the Nexperia 2N7002KQBZ with the SOT-8015 packaging as shown in Figure 5. There are also dual 2N700X arrays. An example is the Diodes Incorporated 2N7002DW-7-F.
These variants allow you to reduce board size and part counts. They may also be useful to reduce total cost.
Figure 5: Image of a 2N700X product in a SOT8015 package.
Parting Thoughts
The 2N700X has been with us for half a century. This family of parts is a friend to generations of engineers and has been featured in millions of products. Time will tell, but this family and its variants are likely to be around for several more generations. Will they become the next 6L6 vacuum tube, which is approaching 100 years of continuous production?
And that’s the beauty of jellybean parts.
What’s your favorite jellybean?
Best wishes,
APDahlen
Related Information
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About This Author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.