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Recently, frequent Design Idea (DI) author Christopher Paul showcased an innovative and high performance true-two-wire current source using a depletion mode MOSFET as the pass device in “A precision, voltage-compliant current source.”

In subsequent comments the question arose whether similar performance is possible using a bipolar junction transistor instead of Christopher’s FET in a similar (looking) topology?

Wow the engineering world with your unique design: Design Ideas Submission Guide

It posed an intriguing design problem for which I offer here a possible (if implausible) solution. Bizarrely, it’s (roughly) based on the classic discrete transistor model of an SCR, shown in Figure 1.

Figure 1 SCR positive feedback loop suggests an unlikely basis for a BJT current source.

Figure 2 shows the nonlinear positive feedback loop of the thyristor morphing into a linear current source.

Figure 2 Q1 and Q3 current mirror, regulator Z1, and BJT Q1 comprise precision 2-wire current source. The source current is 1.05 * 1.24/R1, or 1.30/R1. * = 0.1% precision resistor

Shunt regulator Z1 and pass transistor Q2 form a very familiar precision current source circuit. In fact, it looks a lot like the one Christopher Paul uses in his MOSFET-based design. Negative feedback from current sense resistor R1 makes shunt regulator Z1 force Q2 to maintain a constant emitter current of 1.24v/R1.

Also, similar (looking) to Christopher Paul’s topology, bias for Z1 and Q2 is provided by a PNP current mirror. However, unlike the symmetrical mirror in Christopher Paul’s design, this one is made asymmetrical to accommodate Z1’s max recommended current rating.

Significant emitter degeneration (~2.5 volts) is employed to encourage accurate current ratios and keep positive feedback loop gain manageable so Z1 can ride herd on it.

Startup resistor R3 is needed because the bias for the transistors and regulator is provided by the SCR-ish regenerative positive feedback loop. R3 provides a trickle of current, a few hundred nanoamps, sufficient to jumpstart (trigger?) the loop when power is first applied.

To program the source for a chosen output current (Io).

 If Io > 5 mA, then:
R1 = 1.30/Io
R2 = 49.9/Io
R4 = 2.40/Io

 If Io < 5 mA, then:
R1 = 1.55/Io
R2 = 8/Io
R4 = 2/Io

Minimum accurate Io = 500 µA.  Maximum = 200 mA.

And for a finishing touch, frequent commentator Ashutosh points out that it’s good practice to protect loads against erroneous and possibly destructive fault currents. Figure 3 suggests a flexible and highly reliable insurance policy. Wire one of these gems in series with Figure 2 and fault current concerns will vanish.

Figure 3 Accurate, robust, fast acting, self-resetting, fault current limiter where Ilimit = 1.25/R1.

In closing, I leave it to you, the reader, to decide whether Figure 2’s resemblance to Christopher Paul’s design is merely superficial, truly meaningful, outright plagiaristic, or just weird.

Stephen Woodward’s relationship with EDN’s DI column goes back quite a long way. Over 100 submissions have been accepted since his first contribution back in 1974.

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• A precision, voltage-compliant current source
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The post SCR topology transmogrifies into BJT two-wire precision current source appeared first on EDN.

Have you ever had a duty-cycle resolution issue in your digitally controlled power supply?

In a digital pulse width modulation (DPWM)-controlled power supply, the duty-cycle adjustment is not continuous, but has a minimum step. This is one significant difference between digital control and analog control.

In order to really understand the resolution issue, let’s look at the exaggerated DPWM waveform in Figure 1.

Figure 1 An exaggerated DPWM waveform where the DPWM is acting as the output by comparing its clock counter with a preset comparison value. Source: Texas Instruments

DPWM is acting as the output by comparing its clock counter with a preset comparison value; when the counter equals the comparison value, it will generate a trigger signal, and flip the PWM outputs. When you adjust the comparison to different values, the flipping edge will act earlier or later. Because the counter value can be the only integer, the minimum adjustment step of the duty cycle is expressed by Equation 1:

Oscillation caused by low duty-cycle resolution

The duty-cycle resolution of DPWM brings a disturbance to power-supply control. If the duty-cycle resolution is too low, it may bring limit cycle oscillations (LCOs) to the control loop and cause output voltage ripple. This problem is more serious in high-switching-frequency systems.

Let’s take a 48-V to 5-V synchronous buck converter as an example, as shown in Figure 2.

Figure 2 A 48-V to 5-V synchronous buck converter example. Source: Texas Instruments

Assuming a 500-kHz switching frequency when using 120-MHz PWM frequency, recalling Equation 1, the minimum duty-cycle step is . The minimum duty-cycle adjustment brings the voltage difference with , which means 4% voltage ripples of the output, shown in Figure 3. This is obviously unacceptable.

Figure 3 A low-resolution duty cycle causes output voltage ripple. Source: Texas Instruments

Increase duty-cycle resolution

The most direct way to resolve this duty-cycle resolution issue is to use high-resolution PWM (HRPWM). HRPWM is a powerful peripheral that can reduce the adjustment step significantly—to the 10ps level—but it is typically only available in high-performance MCUs, which may be too powerful or expensive for the design.

Is there a simple method to resolve the duty-cycle resolution issue without extra cost? Can you increase the duty-cycle resolution by using software, or an algorithm?

Looking again at the DPWM waveform, the duty cycle is generated by two variables: the comparison value and the period value, which Equation 2 calculates as:

The common method of adjusting the duty cycle is changing the comparison value and keeping the ‘Period’ value in constant; in other words, the buck converter is operating in fixed switching frequency. What happens if you adjust the duty-cycle by varying the switching frequency? Mostly, a small variation of the switching frequency is not harmful but helpful to power converters, it will reduce the electromagnetic interference and help to pass the EMI regulations.

If you keep the comparison value unchanged, but adjust one count to the period value, how much is the duty-cycle variation? Is it larger or smaller than adjusting the comparison value? Please look into the Equation 3:

Keeping in mind that, the duty-cycle variation by adjusting the comparison value is , because D is always smaller than 1, and  is nearly equal to , you can see that  will be always smaller than .

Which means, adjusting the period value will generate smaller variation to the duty-cycle than adjusting the comparison value.  The improvement is more significant when the duty cycle is much smaller than 1. If you point out the duty-cycle values on one numerical axis with varying the period value, you will clearly see that, when you adding the period value with fixed comparison value, the duty cycle will reduce with a smaller step, as shown in Figure 4.

Figure 4 Duty-cycle values when varying both period and comparison. Source: Texas Instruments

Varying the frequency

Based on the analysis above, it is possible to generate a higher resolution by adjusting the period value. But, in power converter, the switching frequency generally can’t vary much, otherwise the magnetic component design will become very challenge. So, the next question is, how to generate the expected duty cycle with the combination of these two variables?

The method is, first, decided the comparison value with a preset period value, and then, finetune the period value to get the closed duty cycle. The fine tune process either can by increasing the period value with the larger the comparison value, or by reducing the period value with the smaller the comparison value. Figure 5 shows the flowchart of the software by increasing the period value with the larger comparison value, the decreasing method will be similar to this, just need reverse the calculate direction.

Figure 5 Software flowchart for adjusting both the comparison and period values simultaneously. Source: Texas Instruments

At last, I need to figure out that, this software method is principally independent of HRPWM hardware technology, such as a micro-edge positioner. So it is applicable to a digital control loop with HRPWM peripherals same.

Improvement results

Let’s return to the example of the 48-V to 5-V synchronous buck converter in Figure 2. After adopting this software method, it’s possible to reduce the duty-cycle resolution too; the output voltage ripple drops tremendously to <40 mV, as shown in Figure 6. This is acceptable to most of the electrical appliance.

Figure 6 Improved output voltage ripple using the software method. Source: Texas Instruments

This method doesn’t need to use HRPWM to solve the duty-cycle resolution problem, but slightly increasing the duty-cycle resolution with a software algorithm can make your product more competitive by enabling the use of a low-end MCU.

Furthermore, this method is a purely mathematical algorithm; in other words, it is not limited to low-resolution PWM only but also works for HRPWM. So it can be used in some extremely high requirement conditions to further increase the duty-cycle resolution with HRPWM.

Desheng Guo is a system engineer at Texas Instruments, where he is responsible for developing power solutions as part of the power delivery industrial segment. He created multiple reference designs and is familiar with AC-DC power supply, digital control, and GaN products. He received a master’s degree from the Harbin Institute of Technology in power electronics in 2007, and previously worked for Huawei Technology and Delta Electronics.

Related Content

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The post Power Tips #148: A simple software method to increase the duty-cycle resolution in DPWM appeared first on EDN.

Got a table saw recently so I went a little overboard with the French cleats. I also made a scope cart from the remains of my last desk. Fume extraction is a work in progress and I think I need a bigger flare on the hood. Next steps are better parts storage and filling out the relay rack with test gear. If anyone has any test lead/ cable storage suggestions, I’d love to hear them submitted by /u/jellzey [link] [comments]

From ancient compasses to modern smartphones, magnetometers have quietly shaped how we sense and navigate the world. Let us explore the fundamentals behind these field-detecting devices.

Magnetic fields are all around us, yet invisible to the eye. Magnetometers turn those hidden forces into measurable signals, guiding everything from navigation systems to consumer electronics. Well, let us dive into the principles that allow a simple sensor to translate invisible forces into actionable data.

A magnetometer is a device that measures magnetism: the direction, strength, or relative change of a magnetic field at a given location. Measuring the magnetization of a magnetic material, such as a ferromagnet, is one example. A compass is a simple magnetometer: it detects the direction of the ambient magnetic field, in this case the Earth’s.

The Earth’s magnetic field can be approximated as a dipole, offset by about 440 kilometers from the planet’s center and inclined roughly 11 degrees to its rotational axis. At the surface, its strength averages around 0.4 to 0.5 gauss, about 40–50 microtesla, which is quite small compared to laboratory magnetic fields.

Only a few types of magnetometers are sensitive enough to detect such weak fields, including mechanical compasses, fluxgate sensors, Hall-effect devices, magnetoelastic instruments, and magneto resistive sensors.

One of the landmark magnetoresistive sensors from the 1990s was KMZ51 from Philips. Released in 1996, it offered high sensitivity by exploiting the magnetoresistive effect of thin-film permalloy. At its core, the device integrated a Wheatstone bridge structure, which converted changes in magnetic resistance into measurable signals.

To enhance stability and usability, Philips added built-in compensation and set/reset coils: the compensation coil provided feedback to counter drift, while the set/reset coil re-aligned the sensor’s magnetic domains to maintain accuracy. These design features made KMZ51 particularly effective for electronic compasses, current sensing, and detecting the Earth’s weak magnetic field—applications where precision and reliability were essential. KMZ51 remains a classic example of how clever sensor design can make the invisible measurable.

Figure 1 Simplified circuit diagram of KMZ51 illustrates its Wheatstone bridge and integrated compensation and set/reset coils. Source: Philips

On a related side note, deflection, compass, and fluxgate magnetometers represent three distinct stages in the evolution of magnetic sensing. The deflection magnetometer, essentially a large compass box with a pivoted needle, measures the Earth’s horizontal field by observing how an external magnet deflects the needle under the tangent law. The familiar compass magnetometer, in its simplest form, aligns a magnetic needle with the ambient field to indicate direction, a principle that has been carried forward into modern electronic compasses.

Fluxgate magnetometers, by contrast, employ a soft magnetic core driven into alternating saturation; the resulting signal in a sense coil reveals both the magnitude and direction of the external field with far greater sensitivity. Together, these instruments illustrate the progression from basic mechanical deflection to precise electronic detection, each expanding the engineer’s ability to measure and interpret the invisible lines of magnetism.

Tangent law and Tan B position in compass deflection magnetometers

In the Tan B position, the bar magnet is oriented so that the magnetic field along its equatorial line is perpendicular to the Earth’s horizontal magnetic field component. Under this arrangement, the suspended magnetic needle deflects through an angle β, and the tangent law applies:

Tanβ= B/BH

B is the magnetic field produced at the location of the needle by the bar magnet.

BH is the horizontal component of the Earth’s magnetic field, which tends to align the needle along the geographic north–south direction.

This relationship shows that the deflection angle β depends on the ratio of the magnet’s equatorial field to the Earth’s horizontal field. This simple geometric relationship makes the Tan B position a fundamental method for determining unknown magnetic field strengths, bridging classroom demonstrations with practical magnetic measurements.

Figure 2 The image illustrates magnetometer architectures—from pivoted needle to fluxgate core—across design generations. Source: Author

Quick take: Magnetometers on the workbench

Magnetometers range from fluxgate arrays orbiting in satellites to quantum sensors probing in research labs—but this session is just a quick take. The spotlight here leans toward today’s DIY enthusiasts and benchtop builders, where Hall-effect sensors and MEMS modules serve as practical entry points. Think of it as a wake-up call, sprinkled with a few lively detours, all pointing toward the components that make magnetometers accessible for everyday projects.

Hall-effect sensors remain the most approachable entry point, translating magnetic fields into voltage shifts that DIY-ers can easily measure with a scope or microcontroller. MEMS magnetometers push things further, offering compact three-axis sensing in modules that drop straight into maker projects or wearables.

These devices not only simplify experimentation but also highlight how magnetic sensing has become democratized—no longer confined to aerospace or geophysics labs but are available in breakout boards and low-cost modules.

For the benchtop builder, this means magnetometers can be explored alongside other familiar sensors, integrated into Arduino or Raspberry Pi projects, or used to probe the invisible magnetic environment around everyday circuits. In short, the practical face of magnetometers today is accessible, modular, and ready to be wired into experiments without demanding a physics lab.

Getting started with magnetometers is straightforward, thanks to readily available pre-wired modules. Popular options often incorporate ICs such as the HMC5883L, LIS3MDL, and TLV493D, among others.

Although not for the faint-hearted, it’s indeed possible to build fluxgate magnetometers from scratch. The process, however, demands precision winding of coils, careful core selection, stable drive electronics, and meticulous calibration—all of which can be daunting for DIY enthusiasts. These difficulties often make home-built designs prone to noise, drift, and inconsistent sensitivity.

For those who want reliable results without the engineering overhead, ready-made fluxgate magnetometer modules are a practical choice, offering calibrated performance and ease of integration straight out of the box. A good example is the FG-3+ fluxgate magnetic field sensor from FG Sensors, which provides compact and sensitive measurement capabilities for hobbyist and applied projects.

FG-3+ is a high-sensitivity fluxgate magnetic field sensor capable of measuring Earth’s magnetic field with up to 1,000-fold greater precision than conventional integrated IC solutions. Its output is a stable 5-volt rectangular pulse, with the pulse period directly proportional to the magnetic field strength.

Figure 3 The FG-3+ fluxgate magnetic field sensor integrates seamlessly into both experimental and applied projects. Source: FG Sensors

Closing thoughts

This marks the end of this quick-take post on magnetometers, presented in a deliberately unconventional style. We have only scratched the surface; the field is rich with subtleties and deflections that deserve deeper exploration. If this overview piqued your interest, I encourage you to experiment with sensor modules, study fluxgate designs, and share your findings with the engineering community.

And while magnetometers probably will not help you track UFOs, at least not yet, they remain a fascinating gateway into sensing the invisible forces all around us. The more we build, test, and exchange ideas, the stronger our collective understanding becomes. Onward to the next signal.

T. K. Hareendran is a self-taught electronics enthusiast with a strong passion for innovative circuit design and hands-on technology. He develops both experimental and practical electronic projects, documenting and sharing his work to support fellow tinkerers and learners. Beyond the workbench, he dedicates time to technical writing and hardware evaluations to contribute meaningfully to the maker community.

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The post Magnetometers: Sensing the invisible fields appeared first on EDN.

Що відкрили для себе студенти КПІ в Національному музеї літератури України kpi ср, 12/31/2025 - 13:00

Space Forge of Cardiff, UK (which has operations on Florida’s Space Coast) has generated plasma aboard its ForgeStar-1 satellite, marking a world-first for commercial in-space manufacturing and a step toward producing a new class of high-performance semiconductor materials on orbit...

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