Introduction

This article contains a preview of my work conducted on the DigiKey TechForum. I'm always looking for new ideas and challenges. Please leave a comment if you have a request for a specific topic or a friendly challenge. You can also leave your comments on the TechForum where a professional team and larger community are ready to assist.

04 Nov: What are Jellybean electronic components?

Today I wrote this little article exploring about Jellybean components. While researching the topic, I realized that there are two different definitions depending on who we are talking to. Here are the first few paragraphs to get you started. Please let me know what you think. Also, I could use your help to expand the list.

The educator’s task is challenging. For example, which components should you use in your introductory labs? On one hand, we want students to use the latest trending components. On the other, we need reliable components upon which to build lesson plans. Clear documentation is prioritized in the form of textbooks, datasheets, and application notes.

Your best bet is to use jellybean components. By definition, these jellybean components are well-established parts that have stood the test of time. They are popular, likely manufactured by multiple suppliers, often with derivatives for application-specific needs. Like jellybeans in a jar, you can reach in and select your favorite manufacturer and variations. The LM358 as pictured in Figure 1, is a prime example, DigiKey offers this gem from 10 different manufacturers, with packaging ranging from the classic metal can all the way to the latest BGA.

Continue reading at: What are Jellybean electronic components?

05 Nov: Implementing a Pulse Width Modulator in Verilog

Today was a vacation day — mostly. After performing my civic duty, I spent the day preparing for winter and cleaning the workshop; what should I do with these DigiKey bags?

While I have nothing new to share, I'd like to draw your attention to an older article regarding a Verilog implementation of a PWM.

Introduction

Does the world need yet another Verilog implementation of the Pulse Width Modulator?

There are dozens of examples on the web with various degrees of complexity. In this post we will explore a moderately complex example. More importantly we will explore some of the design decisions that accompany the construction of Verilog modules. This includes parameterization of the PWM width, bounds for the duty cycle, and strict operation within a given clock boundary for stability. In addition, we will explore a pragmatic design philosophy. Instead of exploring “what” we will also attempt to explain “why” a particular set of design decisions was made.

PWM Operation

At its core, a digital PWM module is constructed from three blocks. As shown in Figure 1, we need a counter, a comparator, and a register to hold the desired duty cycle. The counter continually counts from zero to the modulus defined by the number of bits in the counter’s register. The comparator block then compares the count register’s value with the desired duty cycle. If the count is greater than or equal to D, the PWM output is set high otherwise it is low.

Figure 1 contains additional circuitry to bound the duty cycle to a given minimum and maximum value. This is a desirable feature in certain applications. For example, assume the PWM is used to control the upper MOSFET in a bridge circuit. A MOSFET in this position is typically powered by a bootstrap circuit. Extended operation at full duty cycle (always on) can discharge the bootstrap capacitor, causing undesirable operation as the MOSFET slides into a linear mode causing overheating. Consequently, it is desirable to place limits on the duty cycle.

Continue reading at: Implementing a Pulse Width Modulator (PWM) in Verilog

06 Nov: Circuit Myths: Current Takes the Path of Least Resistance

It was a busy Wednesday. I've been working to expand the Jellybean concepts - more to follow soon. Until then, you may be interested in this material I wrote last week exploring circuit myths.

This "current follows the path of least" resistance is a challenging concept. It's one of those things that people internalize early in their study of electronics. It takes some effort to dislodge the concept.

Introduction

We have been told that the current takes the path of least resistance.

Wrong!

Actually, it’s worse than wrong! It’s a dangerous way to think about electricity and the flow of current.

When I was teaching, my students would go out of their way to say, “current takes the path of least resistance.” They knew that I was sure to quickly respond with a scolding side lecture (yes, it is a pet peeve – and they knew it!). My revulsion to this myth reflects the painful electrical shocks I’ve received. One incident occurred when I was a young man. I’ll never forget the electrifying pain associated with stripping wax from a floor while standing in a pool of wax remover. Something broke inside the machine. Believe you me, I knew it was electrical!

Safety ground

To understand why, consider the power connection as shown in Figure 1.

Continue reading at: Circuit Myths: Current Takes the Path of Least Resistance

07 Nov: Meet the Jellybeans: 2N7000 and 2N7002 Logic Level Switching MOSFETs

This was fun! Researching and then writing about electronics is always rewarding, but this jellybean 2N700X was especially enjoyable. I hope you enjoy reading it as much as I enjoyed writing it. Thank you to the DigiKey team for the side conversations that help inform the article.

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.

Continue reading at: Meet the Jellybeans: 2N7000 and 2N7002 Logic Level Switching MOSFETs - Semiconductor

08 Nov: Meet the Jellybeans: The 2N3904 and 2N3906 General-Purpose Transistors

The day started out easy with an article exploring Substitutions for the NTE123. It was smooth writing as the topic has been on my mind for a few days. The second article showcasing the 2N3904 family was considerably harder. It was challenging to stay focused on the core message, as there we some many ideas to explore in the old datasheets.

The 2N3904 (NPN) and the complementary 2N3906 (PNP) are classic jellybean transistors, approaching 60 years of age and still going strong. Without exaggeration, DigiKey has over 10 million of these devices and variants in stock. See for yourself by searching “3904 BJT” and “3906 BJT”.

They don’t get more ubiquitous than that!

In relative terms, the 2N3904/06 aren’t the most powerful or highest performing transistors. In many respects, the jellybean 2N2222 and its complementary 2N2907 are better devices. However, there is a “horses for courses” consideration where the lower cost 2N3904 family members continue to perform admirably in their market niche. One reason for the continued momentum is the all-plastic TO-92 packaging while the 2N2222/2907 were originally offered in the older TO-18 metal can. This cost advantage certainly led to its early adoption.

Continue reading at: Meet the Jellybeans: The 2N3904 and 2N3906 General-Purpose Transistors

09 Nov: Stay tuned!