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]
by Deivaraja Ramasamy @ www.edn.com:
This Design Idea is able to turn off inductive loads at a very fast rate. When connected to a load (here 15mH + 10Ω), the modified freewheeling path in the clamping circuit based around M2 reduces the turn off time to 450µs. A simple freewheeling diode in place of the clamping circuit takes about 4ms to turn off the load.
Low-side switch with fast turn-off for inductive loads - [Link]
Juan Ignacio Cerrudo @ ssihla.wordpress.com writes:
The design is based on some of the various diy electronics loads out there (like the one from Dave Jones). The mosfet is a P45N03LT , most likely I took it from some of the PC power supply I’ve “recycled”. I’m using two 25k potentiometers, one for coarse adjustment and the other for fine adjustment (10 turn pots are kind of expensive…). The control voltage varies between 0 and 5 volts and is divided by two with a couple of 10k resistors. The op-amp is an OPA2336, It has rail to rail output so the load can sink roughly up to 2,5. The op amp is powered with a 7805.
Constant Current Electronic Load - [Link]
Dave grabs a few junkbox parts and builds a useful constant current load for switch mode power supply, battery testing, and other applications.
EEVblog #102 – DIY Constant Current Dummy Load for Power Supply and Battery Testing - [Link]
Jasper @ jasper.sikken.nl writes:
I designed an electric load. Using an Arduino Nano, the load can be programmed, and the voltage and current are measured. You can set a constant current (CC), a constant power (CP), or a constant resistance (CR) load by simply typing it in to the Arduino Serial Monitor. The circuit is designed for up to 30V, 5A, and 15W. An opamp, a mosfet, and a small sense resistor form the constant current circuit. The current is set using a DAC. Two other opamps measure the power supply voltage and the current. The circuit is powered from the Arduino USB voltage. I reflow soldered the board using the hacked toaster oven at the hackerdojo. Here are pictures of the reflow soldering process
Arduino based programmable load - [Link]
Here’s an interesting open source project on Kickstarter the Re:Load Pro by Nick Johnson of Arachnid Labs:
A constant current load for testing your projects. 6 amps, 60 volts and 25 watts in a workbench-friendly package with a USB interface.
The Re:Load Pro is an active load. It acts as a current sink, always drawing the same amount of current regardless of the voltage across it.
Active loads are incredibly useful for all sorts of electronics testing requirements. You can use one to see how a power supply performs under load, check if a battery lives up to its manufacturer’s specifications for capacity or current draw, test motor drivers, or a variety of common constant-current tasks, such as testing LEDs, or even doing electroplating. With computer control of the load, you can even do your own IV-curve tracing.
Re:Load Pro – A DC active load - [Link]
Super cheap way to make a dummy load for testing high power PSUs.
Dummy load in a bucket - [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]
Anthony H Smith writes:
The circuit in Figure 1 lets you switch high-voltage power to a grounded load with a low-voltage control signal. The circuit also functions as a submicrosecond circuit breaker that protects the power source against load faults. Power switches to the load when you apply a logic-level signal to the output control terminal. When the signal is lower than 0.7V, transistor Q3 is off and the gate of P-channel MOSFET Q4 pulls up to the positive supply through R6, thus holding Q4 off. During this off condition, the circuit’s quiescent-current drain is 0A.
Inexpensive power switch includes submicrosecond circuit breaker - [Link]
Debraj built an electrical dummy load to test his power supply:
Recently, I purchased a power supply that claimed a max current of 2A and 0~15V. So I wanted to test it. I had a 36 watts bulb (used in motor cycles), but that was too much. Then, I thought of the dummy load that is explained by Dave in his video blog. My version is similar, but I changed certain components to my liking (and what ever was already available with me)
Dummy electrical Load - [Link]