by Steven Keeping @ digikey.com
Switching DC-to-DC voltage converters (“regulators”) comprise two elements: A controller and a power stage. The power stage incorporates the switching elements and converts the input voltage to the desired output. The controller supervises the switching operation to regulate the output voltage. The two are linked by a feedback loop that compares the actual output voltage with the desired output to derive the error voltage.
The controller is key to the stability and precision of the power supply, and virtually every design uses a pulse-width modulation (PWM) technique for regulation. There are two main methods of generating the PWM signal: Voltage-mode control and current-mode control. Voltage-mode control came first, but its disadvantages––such as slow response to load variations and loop gain that varied with input voltage––encouraged engineers to develop the alternative current-based method.
Today, engineers can select from a wide range of power modules using either control technique. These products incorporate technology to overcome the major deficiencies of the previous generation.
This article describes voltage- and current-mode control technique for PWM-signal generation in switching-voltage regulators and explains where each application is best suited.
Voltage- and Current-Mode Control for PWM Signal Generation in DC-to-DC Switching Regulators - [Link]
An old but interesting app note (PDF) from Microsemi on resistorless current-sensing technique. [via]
This application note introduces a simple current-sense technique that eliminates that sense resistor, resulting in system-cost reduction, PCB space saving, and power efficiency improvement. Furthermore, the new current sensing mechanism allows higher dynamic tripping current than the static one (built-in low-pass filtering) to improve current-sense noise immunity.
A simple current-sense technique eliminating a sense resistor - [Link]
by Ryan Roderick, Intersil @ edn.com:
The fundamentals to translating the analog world into the digital domain reduces to a handful of basic parameters. Voltage, current, and frequency are electrical parameters that describe most of the analog world. Current measurements are used to monitor many different parameters, with one of them being power to a load.
There are many choices of sensing elements to measure current to a load. The choices of current sensing elements can be sorted by applications as well as the magnitude of the current measured. This write up is part one of a three part series that discusses different types of current sensing elements. The focus of this paper is evaluating current measurements using a shunt (sense) resistor. The paper explains how to choose a sense resistor, discuss the inaccuracies associated with the sensing element and the paper discusses extraneous parameters that compromises the overall measurement.
Sensing Elements for Current Measurements - [Link]
Kerry Wong built a DIY constant current/constant power electronic load. It can sink more than 200W of power:
A while back I built a simple constant current electronic load using an aluminum HDD cooler case as the heatsink. While it was sufficient for a few amps’ load under low voltages, it could not handle load much higher than a few dozen watts at least not for a prolonged period of time. So this time around, I decided to build a much beefier electronic load so it could be used in more demanding situations.
One of the features a lot of commercial electronic loads has in common is the ability to sink constant power. Constant power would come in handy when measuring battery capacities (Wh) or testing power supplies for instance. To accommodate this, I decided to use an Arduino (ATmega328p) microcontroller.
Building a constant current/constant power electronic load - [Link]
Paul over at Dorkbotpdx writes:
Recently I needed to actually “see” a current waveform in the 100 uA to 5 mA range with at least a couple MHz bandwidth. This extremely expensive probe would have been perfect, but instead I built something similar for about $30 using the amazing Analog Devices AD8428 amplifier.
Measuring microamps & milliamps at 3 MHz bandwidth - [Link]
FluxProbe is a test prod for measuring currents without touching the conductor it is flowing through. More acurately it is measuring the magnetic flux. This way you can measure currents on PCB traces without having to put a resistor in between. This test gear enables you to trace faults in your PCB (for example search for a short circuit). This is usefull for commissioning of you circuit for example.
FluxProbe – measure currents without touching the conductor - [Link]
Christian Aurich wanted a way to measure current on PCBs without having to cut the traces. He concluded building a probe able to measure current using a Hall Effect sensor. It’s on prototyping phase, so improvements are yet to come. He writes:
In the last weeks I followed an idea to measure current without the need to cut the wires or even open a pcb trace. The solution i came up with is a hall effect based measurement.
I wrote some more about it in an article here: http://avrs-at-leipzig.de/dokuwiki/en/prokekte/fluxprobe
Building a current / flux probe for contactless measurements - [Link]
Here is a PDF document from Linear Technology, featuring current sense circuits for different applications, including High side, low side, level shifting, high and low voltage, fault sensing, etc: [via]
Sensing and/or controlling current flow is a fundamental requirement in many electronics systems, and the techniques to do so are as diverse as the applications them-selves. This Application Note compiles solutions to current sensing problems and organizes the solutions by general application type. These circuits have been culled from a variety of Linear Technology documents.
Current sense circuit collection - [Link]
The INA230 is a current-shunt and power monitor with an I2C interface that features 16 programmable addresses. The INA230 monitors both shunt voltage drops and bus supply voltage. Programmable calibration value, conversion times, and averaging, combined with an internal multiplier, enable direct readouts of current in amperes and power in watts.
INA230 – Precision digital/current/voltage/power monitor - [Link]
This application note describes the use of current-sense amplifiers, differential amplifiers, and instrumentation amplifiers to measure battery charge and discharge currents in smartphones, tablets, computer notebooks, and USB accessories. It compares high-side current sense amplifiers with low-side differential amplifiers and recommends selection criteria for current-sense resistors. A high-voltage circuit breaker is described to provide system over-current protection due to faults and short circuits. Application circuits for a variable linear current source and a programmable 0–5A current source are included.
High-Side Current-Sense Measurement: Circuits and Principles - [Link]