New Product: LED Drivers for Dimmable Bulbs

The iW3606 and the iW3608 are single-stage, solid-state lighting (SSL) LED drivers. The iW3606 (8-W output power) and the iW3608 (15-W output power) feature configurable over-temperature protection (OTP) and derating functionality to provide predictability and reliability of bulb operating life.

Designed for all retrofit bulbs, including candle and GU10 lamp replacements used in existing phase-cut dimmer installations, the LED drivers manage poor dimming performance (e.g., pop-on, popcorning, dead travel, drop-out, and flicker) and short bulb lifetime or failure. Both drivers meet or exceed global regulations for power quality and efficiency with less than 0.92 power factor (PF) and less than 20% total harmonic distortion (THD).

The LED drivers’ OTP and derating feature addresses the thermal issues caused by the high and unpredictable operating temperatures in dimmable SSL applications. iWatt’s OTP derating monitors the temperature inside sealed SSL bulbs. When thermal conditions reach a point set by the system designer, the LED drivers automatically reduce the current drive to the LEDs, lowering the power dissipation and resulting in a cooler overall operation.

The iW3606 and the iW3608 feature a wide, flicker-free dimming range from 100% to 1% of measured light to closely match incandescent bulbs’ dimming performance. This enables smooth “natural” dimming with no light drop-out at the low end of the dimming range and virtually no dead travel where the light turns off before the dimmer control reaches the bottom of its travel.

The LED drivers’ low internal power consumption enables them to start at less than 5% of light output, which is a very low dimming level. This virtually eliminates pop-on, in which the light does not turn on at low dimmer levels and, as the dimmer level is raised, the light suddenly turns on. The low power consumption also helps eliminate popcorning effects, in which various bulbs in multiple-light installations on the same dimmer circuit can turn on at different dimmer-setting thresholds.

The iW3606 costs $0.46 and the iW3608 costs $0.51, both in 1,000-unit quantities.

 

iWatt, Inc.

www.iwatt.com

Test Equipment: What to Consider

Editor’s Note: Ian Broadwell, a postdoctoral fellow at the Department of Chemistry at Ecole Normale Superieure in Paris, wrote the following review of test equipment for circuitcellar.com readers. He is pursuing additional articles about making the right choices in equipment.


Whether you are setting up your own electronics workbench or professional design company, you certainly will be thinking about the test gear you should buy. With big-name brands such as Agilent, Fluke, Keithley, Tektronix, and LeCroy (to name a few) aggressively marketing their latest products, it’s easy to think you’ll have to start earning a pro soccer salary and work until you’re 150 to own some of these high-end products. But this is not necessarily true—if you’re prepared to wait and buy used equipment (I will revisit this point later).

The diverse spectrum of Circuit Cellar readers will have a wide variety of test and measurement requirements. In this first article about “making the right choice,” I want to introduce myself, the variety of test equipment available, and, finally, the rules I follow in buying test equipment for my electronics lab.

Introducing Myself

As a teenager, I had ambitious dreams of setting up an electronics laboratory. My journey started when I became involved with the local ham radio club, G4EKT, in Great Britain’s East Yorkshire County. At 17, I became a fully licensed A-class radio amateur and started to build some of my own equipment, such as a shortwave valve RF power amplifier (a tube amplifier in the US) and a dual-function standing wave ratio / power meter.

After joining G4EKT, I found flea markets and radio rallies a source of electronic and mechanical parts for constructing my own equipment. Money was tight as a teenager, so I could only dream of owning an oscilloscope; having a spectrum analyzer would be like standing on the moon (a very remote possibility). I came to realize it takes years to collect the equipment to set up your lab—and successful people rarely tell you this.

After my schooling, I followed the traditional university route—graduating with a BSc in Physics, MSc in Exploration Geophysics, and a PhD in Physical Chemistry. My professional experience has taken me from being a quality-control technician in an analytical chemistry lab to an offshore field geophysicist in northwest Australia. Eventually, I came full circle—back into academia with several postdoctoral positions in England, China, and now France. The diversity of working environments, locations, and multidisciplinary subjects has provided a unique window for viewing the tools-of-the-trade in different disciplines. My fascination with scientific instruments encompasses all domains.

Currently, I work in the Department of Chemistry at Ecole Normale Superieure in Paris as a Marie Curie Postdoctoral Fellow. My research interests include instrumentation and development of microfluidic tools for use at the interface between physics, chemistry and biology.

A Diversity of Available Equipment

Today we take test equipment for granted. We have testers for just about anything imaginable. Where there is something to be measured, there will be a machine to do so—along with 100 patents claiming rights to all the varied ways to measure what you want to quantify. There has never been a better time to find test equipment in the used market, a result of the global economic slowdown and the turnover and exploitation of new technologies. Consider the computer you bought last year; it’s already old, technologically speaking.

Technological progress has not always been this rapid. Historically, war or military endeavours have driven technological leaps. Remember the Cold War, the nuclear arms race between the US and USSR from 1947-1989? This period of sustained technological development spurred the Internet and the abundance of test equipment we see today. My favorite test-equipment manufacturer was Hewlett-Packard (HP), which produced a vast range of scientific and laboratory equipment from 1939 until 1999, when the company was restructured. Agilent Technologies continues to develop the company’s former test and measurement product lines, while the new HP primarily focuses on computer, storage and imaging products. Most of HP’s equipment is well-documented, with downloadable manuals. Meanwhile, Web-based user groups are continually contributing to online document repositories. And HP’s equipment was built to last, using military-grade components. That is why 20- or 30-year vintage test equipment is often found in working order.

At the high end, test equipment comes in many different forms—from stand-alone, high-precision single benchtop units to dedicated chassis and multifunction rack-mount instrument arrays. HP was one of the first companies to use instrument arrays. This has been further developed by companies such as National Instruments (NI), with its range of chassis and stand-alone data acquisition (DAQ) cards that fit into a desktop PC and form a virtual instrument using NI’s LabVIEW software. Industries often prefer to use modular measurement systems because of the inherent flexibility to tailor the functionality to meet their own specifications. They also conserve space and allow the test stand engineer to automate select tests.

At the low end, every electronics enthusiast should aim to have a basic handheld multimeter and an oscilloscope. This is essential equipment to start your hobby. Fluke, B&K Precision, and Extech Instruments are but a few of the established brands. Although company headquarters are usually located in Europe or the US, many companies have design and manufacturing units in Taiwan and mainland China (Hong Kong and Shenzhen). My experience working in China showed me that the mainland Chinese prefer electronic components and instruments made in Taiwan because of its longer history of Western investment. This is not to say mainland products are poor—Rigol is an excellent brand with top-quality components in its products.

The message is that you get what you pay for. So, whatever basic equipment you intend to buy, try to purchase it from an established brand that you know will provide at least a one-year guarantee and some sort of manufacturing quality control in its products. A Fluke 115 multimeter, for example, has the essential functions you’ll need and costs around $200. For this price, you should feel confident that the meter will last a very long time if used as intended.

Some of the best information sources for those interested in electronics are subscription electronics magazines such as Elektor, Circuit Cellar, Everyday Practical Electronics and Nuts and Volts. Article technical levels vary widely between the magazines, ranging from absolute beginner to seasoned professional. General magazines are a great introduction for beginners and offer a relatively cheap route into the electronics field or more focused areas. Specialized electronics areas such as audio or industrial have their own publications, including audioXpress, IEEE Industrial Electronics, and the free-subscription online EDN Network (www.edn.com).

Speaking to people can be better than wading through magazine pages. Local electronics or ham radio clubs are a rich knowledge source. In fact, they can be more informative than large professional-equipment suppliers who have commercial agreements or little knowledge of different test platforms. In Europe, a number of small equipment brokers survive. They can offer excellent advice on a wide range of equipment issues and projects, because their employees must multitask. Such companies have small profit margins, so their employees often work on projects outside their normal expertise. Brokers also tend to be professionals who have worked in the industry for 20 to 30 years before heading out on their own.

Rules I Use for Buying Test Equipment in My Electronics Lab

After determining your future test equipment needs and drawing up a short list of essential features, it’s time to focus on the brands, models, and vintages that will meet your minimum specifications. Some less obvious things to consider are: the physical volume and weight of the equipment and cooling and power requirements. My lab is situated in a 2-by-3-m room with minimal space and ventilation. Large rack-mounted instruments are heavy and take up a lot of space, which requires careful arrangement to accommodate all the equipment. Additional considerations include: electrical power ratings (daisy chaining too many instruments together from the same socket is a fire risk); sufficient room ventilation to remove hot air from the instruments’ cooling systems; and smells generated by aging, phenolic printed circuit boards.

In recent years, I have been collecting a wide range of instruments. My objective has been to build up a general-purpose electronics lab where overall functionality (i.e., the breadth of measurements I’m able to make) is more important than high resolution and cutting-edge accuracy (this is what calibration labs are for). General-purpose semi-professional labs should, in my opinion, be able to tackle a range of projects—be it RF, audio, or control.

One of the most expensive pieces of test equipment an RF lab should have is a spectrum analyzer. Recently, I spent a lot of time considering spending my money and realized that such a purchase could require remortgaging my house and would, at minimum, need the boss’s (wife’s) permission. In preparation to achieve the “minimum,” I drew up a series of feel good factors” to give weight to my case.

These factors amount to a list of things you should consider before a purchase (see Table 1). They can serve as a yardstick for reviewing a spectrum analyzer or other pieces of equipment.

 

Table 1

Feel good factor Description
a) Space utilization Keithley source meters have five instruments in one unit (i.e., one box replaces four or five boxes of its predecessors). This is efficient space utilization.
b) Connectivity Does the equipment come with all the latest LAN, Wi-Fi, GPIB, USB, and RS-232 protocols as standard?
c) Portability Is the equipment your lab doorstop, or is it small enough to be used in remote locations such as up a cellular phone mast?
d) Ease of use Is the equipment intuitive and easy to use, or do you need the latest version of the user guide and service manual (which may not be available) to get going?
e) Special features and add-ons/expansions Include extended memory depth or high-speed data streaming, automated test stand, hardware upgrades, and powerful proprietary software-analysis functions (i.e., modifications that allow uses with MATLAB or LabVIEW).
f) Resolution/accuracy How much resolution is required and what level of calibration/traceability?
g) Price vs. functionality You are either buying the latest feature-packed instrument or used equipment from a broker or eBay. Generally, money will be tight and buying high-end new equipment isn’t an option. Clearly, the used market can offer some good deals. You find two instruments that have nearly the same functionality and both are tempting. Which do you buy? At first, you may reply the more modern one, as there may be less risk of failure.Let’s now consider buying a 20 GHz vector network  analyzer. The Agilent 8510c is about half the price of the slightly more modern Agilent 8720a.  Both have nearly the same specifications. The 8720a is more compact. The 8510c is definitely larger, more modular (requiring an external signal generator and S-parameter test set), and better built. The latest versions of the 8510c are similar in vintage to the 8720a and differ by only a few years. Agilent repairs are prohibitively expensive for both. The modular nature of the 8510c and abundance of eBay modules translate into increased self-servicing of repairs. If 8510c spares were hard to find, then it would be a good reason for choosing more modern equipment (i.e., 10 years old rather than 25).
h) Disposal and small print issues Are there any toxic materials used in the instrument’s manufacturing that will cause future disposal issues? Is it going to cost you more to dispose of it than it did to buy it?EBay dealers only cover equipment faults detected within the initial weeks of a purchase. The buyer will be responsible for any repairs costs that fall outside of this guarantee period.
i) Overall value for money Does the equipment have a reputation for being reliable and consistently doing what is written on the packaging, year after year? What’s included with your purchase? Probes? Extended warranty? On-site maintenance? Service contracts?Often, eBay purchases come without peripherals (e.g., probes) and these need to be found elsewhere. Sometimes, there are lucky buys to be had. Generally, most traders only want to maximize their profits, so beware of this.
j) Deal or no deal 1) Does the equipment fit your test requirements?2) Is it within your budget?3) And finally, do you really need it?

 

Rules for reviewing equipment are often best understood by offering an example. To foster understanding, I have made a comparison between two spectrum analyzers—a used Agilent 8591a and a new Rigol DSA815-TG. Both have very similar specifications in terms of maximum frequency, dynamic range, and resolution. While the Rigol offers the latest color LCD, portability, and connectivity, the HP provides the reassurance that it still works after all these years. When new, the HP was a very high-end instrument (costing $18,000 in the 1980s). But evolving technology has enabled us to purchase entry-level spectrum analyzers, such as the Rigol DSA815-TG, with virtually the same specifications. This is really mind-blowing.

When considering instrument performance by comparing marketing data, you should keep in mind manufacturers will try to legitimately report best values for important parameters. Although the two analyzers appear identical, the phase noise performance of the HP is better than the Rigol. The phase noise represents the short-term stability of the frequency reference and the analyzer’s ability to distinguish weak signals next to a strong carrier. With my preference for high performance, value for money, and a hint of nostalgia, I would buy the HP 8591a rather than the Rigol DSA815-TG.

For a “feel good factor” comparison of the HP 8591a and Rigol’s DSA815-TG, see Table 2.

Table 2

Feel good factor Instrument 1: HP 8591a Instrument 2: Rigol DSA815-TG
a) Space utilization 163 mm x 325 mm x 427 mm 399 mm × 223 mm × 159 mmThe Rigol is approximately half the volume of the HP.
b) Connectivity GPIB, serial port, and analogue monitor output USB interface allows connection to PC and memory stick; LAN
c) Portability Not very portable at 15 kg and has no battery feature. It will accept 86-127/195-250 VAC; 47-66 Hz. Very portable at 7.5 kg including battery and also accepts 100-240 VAC, 45-440 Hz.
d) Ease of use Although the instrument is old, the menu system is easy to use. ROM updates for the software are available but no longer updated. The Rigol also has an excellent indexed menu system with hot keys on the side of the screen. The operating system can be switched instantly to a range of different languages
e) Special features and add-ons/expansions 004 precision frequency reference, 010 tracking generator, 101 fast time domain sweeps, 102 AM/FM demodulation Optional USB to GPIB; tracking generator and preamp are not standard features.
f) Resolution/accuracy Frequency resolution bandwidth 3 kHz to 3 MHz in a 1, 3, 10 sequence; 10 MHz frequency reference with option 4 has 0.2 ppm drift/year. The phase noise sidebands at 10 kHz offset from the carrier is <-90 dBc/Hz. Signal amplitude dynamic range of −115 dBm to 30 dBm from 1 MHz to 1.8 GHz and 0.01 dB resolution 100 Hz to 1 MHz in 1-3-10 sequence. Frequency reference has 2 ppm drift/year10 kHz offset from the carrier is <-80 dBc/Hz.−115 dBm to 20 dBm across 1 MHz to 1.5 GHz without preamplifier and 0.01 dB resolution
g) Price vs. functionality 9 kHz–1.8 GHz spectrum analyzer with tracking generator. This unit was originally sold from 1978 to 1990 for $18,000 including options. Today a good uncalibrated unit on eBay will fetch $1,750. 9kHz–1.5GHz spectrum analyzer with tracking generator currently sells for $2,000, including tax, from both eBay and directly from a Rigol supplier. With this, you are buying the latest instrument 2012 production date.
h) Disposal and small print issues Has beryllium oxide RF components inside, which could be a problem for disposal Repairs are only carried out by the manufacturer in Beijing. In 2010, I remember this was the situation.
i) Overall value for money Reliable and time-honored equipment made of excellent quality components and built to be repairable. Boasts 8″ WVGA 800 × 480 pixel screen. Has all the bells and whistles that your portable lab needs. Not really built to be repaired by the broker or individual, with all the FPGA and surface-mounted components.
j) Deal or no deal Personally, I would buy the used equipment, as there is more margin to negotiate the price and it is built to last. The product will not substantially depreciate, as with a new model such as the Rigol. This excellent equipment built from Analog Devices components is a budget spectrum analyzer and offered at the lowest price in the Rigol range.

The Key Questions

Always remember, making the right choice doesn’t have to be painful and costly. Just ask yourself the key questions:

1) Is the equipment a fit for your test requirements?

2) Is it within your budget?

3) Do you really need it?

If you manage to convince your line manager (or your spouse) that the answer to all three is “yes,” then you’re likely to get the thumbs up to make that important purchase.

Circuit Cellar’s New Look

Circuit Cellar has a new look and more content! The September issue will feature CC’s new logo, layout, and magazine sections. Here’s a quick peek.

The new CC logo:

The new CC layout:

The new CC content and features:

  • QR codes and direct links to code, project files, parts lists, videos, and more
  • A “CC Community” section that spotlights people, happenings, and news in the CC, Elektor, and greater embedded systesms community
  • Ayse Coskun’s “Green Computing” column

The issue will hit newsstands in late August.

 

Ayse Coskun and Green Computing

Green computing can mean different things to different people—and interests.

Environmental organizations tend to embrace the definition of green computing that stresses practices that lead to efficient and eco-friendly use of computing resources.

But businesses are also interested in green computing, particularly when it creates energy efficiencies that reduce their costs.

So, the topic is a hot one. And with that in mind, next month Circuit Cellar will introduce a bimonthly Green Computing column written by Ayse Coskun.

Coskun, who has MS and PhD degrees in Computer Science and Engineering, is an assistant professor in the Electrical and Computer Engineering Department at Boston University. Her research interests include temperature and energy management, 3-D stack architectures, computer architecture, and embedded systems. You can find out even more about her by checking out our interview published in July 2012.

Coskun will address a wide range of topics in her columns. “I will be writing about energy-efficient software and hardware design strategies, opportunities for electricity cost savings and battery-life extension, system-level policies for energy and thermal management, and smart infrastructures for improving efficiency,” she says.

Her September column focuses on energy-efficient cooling strategies for servers, which require striking a balance between cooling energy and leakage power. “You can reduce the cooling energy used by enabling the processor temperatures to rise within safe limits, “ she says.  “However, leakage power increases at high temperatures and can cause excessive energy waste. “

Her column explains how  to experimentally analyze the trade-off between a server’s cooling and leakage and how to use that analysis to design energy-efficient cooling strategies—not only for servers, but for computing systems in general.

For more details, be sure to check out her debut column in the September issue.

An experimental setup for enabling customized fan control for a commercial server.

 

 

Jon Chapman Wins the CC Code Challenge (Week 9)

We have a winner of last week’s CC Weekly Code Challenge, sponsored by IAR Systems! We posted a code snippet with an error and challenged the engineering community to find the mistake!

Congratulations to Jon Chapman of Ohio, United States for winning the CC Weekly Code Challenge for Week 9! He’ll receive a CCGold Archive on USB drive.

Jon’s correct answer was randomly selected from the pool of responses that correctly identified an error in the code. Jon answered:

Line 24: bgcolor tag is misspelled as ‘bgoclor’. It needs to be corrected to ‘bgcolor’

You can see the complete list of weekly winners and code challenges here.

What is the CC Weekly Code Challenge?
Each week, Circuit Cellar’s technical editors purposely insert an error in a snippet of code. It could be a semantic error, a syntax error, a design error, a spelling error, or another bug the editors slip in. You are challenged to find the error.Once the submission deadline passes, Circuit Cellar will randomly select one winner from the group of respondents who submit the correct answer.

Inspired? Want to try this week’s challenge? Get started!

Submission Deadline: The deadline for each week’s challenge is Sunday, 12 PM ESTRefer to the Rules, Terms & Conditions for information about eligibility and prizes.

Microcontroller-Based, Cube-Solving Robot

Cube Solver in ActionCanadian Nelson Epp has earned degrees in physics and electrical engineering. But as a child, he was stumped by the Rubik’s Cube puzzle. So, as an adult, he built a Rubik’s Cube-solving robot that uses a Parallax Propeller microcontroller and a 52-move algorithm to solve the 3-D puzzle.

Designing and completing the robot wasn’t easy. Epp says he originally used a “gripper”-type robot that was “a complete disaster.” Then he experimented with different algorithms–“human memorizable ones”—before settling on a solution method developed by mathematician Morwen Thistlethwaite. (The algorithm is based on the mathematical concepts of a group, a subgroup, and generator and coset representatives.)

Nelson also developed a version of his Rubik’s Cube solver that used neural networks to analyze the cube’s colors, but that worked only half the time.

So, considering the time he had to spend on project trial and error (and his obligations to work, family, and pets), it took about six years to complete the robot. He writes about the results in the September issue of Circuit Cellar magazine. 

Here, he describes some of the choices he made in hardware components.

“The cube solver hardware uses two external power supplies: 5 VDC for the servomotors and 12 VDC for the remaining circuits. The 12-VDC power supply feeds a Texas Instruments (TI) UA78M33 and a UA78M05 linear regulator. The UA78M05 regulator powers an Electronics123 C3088 camera board. The UA78M33 regulator powers a Maxim Integrated MAX3232 ECPE RS-232 transceiver, a Microchip Technology 24LC256 CMOS serial EEPROM, remote reset circuitry, the Propeller, a SD/MMC card, the camera board’s digital output circuitry, and an ECS ECS-300C-160 oscillator. The images at right show my cube solver and circuit board.
“The ECS-300C-160 is a self-contained dual-output oscillator that can produce clock signals that are binary fractions of the 16-MHz base signal. My application uses the 8- and 16-MHz clock taps. The Propeller is clocked with the 8-MHz signal and then internally multiplied up to 64 MHz. The 16-MHz signal is fed to the camera.

“I used a MAX3232 transceiver to communicate to the host’s RS-232 port. The Propeller’s serial input pin and serial output pin are only required at startup. After the Propeller starts up, these pins can be used to exchange commands with the host. The Propeller also has pins for serial communication to an EEPROM, which are used during power up when a host is not sending a program.

“The cube-solving algorithm uses the coset representative file stored on an SD card, which is read by the Propeller via a SparkFun Electronics Breakout Board for SD-MMC cards. The Propeller interface to the SD card consists of a chip select, data in, data out, data clock, and power. The chip select is fixed into the active state. The three lines associated with data are wired to the Propeller.

“The Propeller uses a camera to determine the cube’s starting permutation. The C3088 uses an Electronics123 OV6630 color sensor module. I chose the camera because its data format and clocking speed was within the range of the Propeller’s capabilities. The C3088 has jumpers for external or internal clocking.”

To read more about Epp’s design journey—and outcomes—check out Circuit Cellar’s September issue. And click here for a video of his robot at work.

 

NXP LPC800 Microcontroller Challenge

Attention microcontroller users around the world! Ready to enter NXP Semiconductor’s LPC800 Challenge? Getting started is straightforward.

Elektor and Circuit Cellar have partnered with NXP Semiconductors to promote the Challenge. Once you have your LPC800 mini-board and code, you simply register and start working. The rules and complete details are listed on the LPC800 Challenge webpage.

The entry deadline is August 30, 2013. Once all the entries are received, NXP will select the most unique, interesting and funny submissions to receive a LPC800 LPCXpresso development kit.

The LPC800 is an ARM Cortex-M0+-based, 32-bit microcontroller operating at CPU frequencies of up to 30 MHz. The LPC800 supports up to 16 KB of flash memory and 4 KB of SRAM. The peripheral complement of the LPC800 includes a CRC engine, one I2C-bus interface, three USARTs, two SPI interfaces, one multi-purpose, state-configurable timer, one comparator, function-configurable I/O ports through a switch matrix, and up to 18 general purpose I/O pins.

Need design ideas? Check out these microcontroller projects with NXP parts.

Issue 276: EQ Answers

Problem 1
Suppose you have an ordinary switch mode buck regulator. The input voltage is 100 V, the switch’s duty cycle is exactly 50%, and you measure the output voltage as 70 V. Is this converter operating in continuous conduction mode or discontinuous conduction mode? How can you tell?

Answer 1
If a switch mode buck converter is operating in continuous conduction mode, then the output voltage is the fraction of the input voltage as defined by the duty cycle. 100 V × 0.5 would equal 50 V. Therefore, this converter is operating in discontinuous conduction mode.

Note that continuous conduction mode includes the case in which synchronous (active) rectification is being used and the current through the coil is allowed to reverse direction when the output is lightly loaded. The output voltage in relation to the input voltage will still be defined by the switch duty cycle.

Therefore, we also know that the regulator in question is not using synchronous rectification, but rather is using a diode instead.

Problem 2
Since a diode can be placed in a High-Impedance state (reverse-biased) or a Low-Impedance state (forward-biased), they are sometimes used to switch AC signals, including audio and RF. What determines the magnitude of a signal that a diode can switch?

Answer 2
When diodes are used for signal switching, there are two considerations with regard to the magnitude of the signal relative to the DC control signal:

  • In the Blocking state, the reverse bias voltage must be greater than the peak signal voltage to prevent signal leakage. Also, a high-bias voltage reduces the parasitic capacitance through the diode. PIN diodes are often used for RF switching because of their ultra-low capacitance.
  • In the On state, the forward DC control current through diode must be greater than the peak AC signal current, and it must be large enough so that the current doesn’t approach the diode curve’s “knee” too closely, introducing distortion.

Obviously, the diode needs to be rated for both the peak reverse voltage and the peak forward current created by the combination of the control signal and the application signal.

Problem 3
What common function does the following truth table represent?

A B C X Y Z
0 0 0 ? 0 0 0
0 0 1 ? 0 0 1
0 1 0 ? 0 1 0
0 1 1 ? 0 0 1
1 0 0 ? 1 0 0
1 0 1 ? 0 0 1
1 1 0 ? 0 1 0
1 1 1 ? 0 0 1

Answer 3
The truth table implements a form of priority encoder:

Z is set if C is set, otherwise
Y is set if B is set, otherwise
X is set if A is set

In other words, C has the highest priority and A has the lowest. However, unlike conventional priority encoders that produce a binary output, this one produces a “one hot” encoding.

Problem 4
Write the equations for the logic that would implement the table.

Answer 4
The logic is quite straightforward:

Z = C
Y = B & !C
X = A & !B & !C