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292 results found, displaying items 21 - 40
Redundant Power-Supply Diode Features Fanless Passive Cooling
A Schottky diode is an excellent way to connect multiple batteries or dc power supplies to a load. With a forward-biased “or” diode between each supply and the load, faults are isolated. Weak, low, or shorted supplies can’t sink current from the other supplies. Unfortunately, the heat produced by a diode can be difficult to remove in some applications. This circuit was created to reduce the heat dissipated by a power-supply “or” diode in a redundant 50-V...
Simple Technique Drives Multiple LEDs From One Processor Pin
Driving multiple LEDs with one microprocessor GPIO pin is a well-known technique. Typically, designs perform this task by issuing pulse widths and clocks of differing durations and employing multiple RC networks to distinguish between them. The design described here is much simpler. The microprocessor pin is connected to the clock of a multipleoutput sequential counter (see the figure). In its...
Step Down A Negative Voltage Without Using An Inductor
When you need to step down a negative voltage in a lowcurrent application, a non-inductor configuration offers two advantages: ease of use and a low number of external components. Such step-down converters can be implemented with two chargepump devices. The first produces a positive output by doubling and inverting the negative input voltage, and the second acts as an inverter to produce the desired negative output (...
Capacitor-Powered Electronics Is At The Core Of Green Design
The concept of using supercapacitors (also known as ultracapacitors, supercaps, etc.), and replacing the batteries in portable micropower applications,1 is gaining momentum. In fact, it has become one of the more noticeable technical trends of recent time. Supercapacitors, such as the BOOSTCAP ultracapacitors from Maxwell Technologies or DYNACAP from ...
Simulated Grounded Inductor Needs No External Capacitors
Inductors designed with active elements are very desirable to designers today because conventional spiral inductors are too big, too heavy, and too costly, and they require tuning. During the last few decades, various grounded inductors have been created using different high-performance active building blocks, such as operational amplifiers and operational transconductance amplifiers. But op amps suffer from a finite gain-bandwidth product (GBP) and GBP interdependence,...
"Unstable" Power Supply Simulates Solar Panel Behavior
This power supply may seem a bit strange, since it’s not stable in voltage or in current. However, it simulates the behavior of a solar panel and can be very useful if you’re working with a solar-powered device on a rainy day. A solar-panel circuit can be represented by a current generator and some diodes (Fig. 1a). The short-circuit current depends on the cell type and illumination. The open circuit...
Low-Power Logic Gate Protects Fluid Sensor From Leakage Current
Fluid-level sensing is very common in industrial applications and now is being used in domestic applications to sense water levels in overhead tanks. The greatest challenge for designers is to make these sensors operate with ultra-low power using battery voltages between 2 and 6 V, while making the device insensitive to potential damage from leakage current coming from mains power running pumps and valves. The design described here uses three sections of a...
Use Variable DC Voltage To Control 70-MHz Output Phase Shifter
In many situations, designers must control the phase of an output signal in order to make certain circuits work properly. At low frequencies, an op amp can be used to vary the phase. But as the frequency gets into the RF range, output phase control gets a bit more complex. The figure illustrates an example of how to control the phase at higher frequencies. I randomly chose 70 MHz for the circuit, but any ...
Power Control Circuit Limits On Time To Prevent MOSFET Burnout
A power control device that protects against MOSFET burnout was designed using a well-known gated-oscillator circuit. The circuit prevents excessive On time for the MOSFETs beyond a permitted limit. The R1-C1 time constant forms a timing circuit that limits the On-time pulse period and automatically generates its own maximum permitted On/Off duty cycle (Fig. 1). Without this timing circuit, if the input...
An Easy Way To Roll Your Own Programmable Power Supply
Adjusting the output voltage of a power supply is a feature typically reserved for highly integrated handheld power-management units (PMUs) with multiple integrated power supplies. You can implement this feature, however, with any power supply by adding a single resistor and an inexpensive digital-to-analog converter (DAC) (Fig. 1). While this technique isn’t new, the equations to select...
Tame Switching Supply Noise While Maintaining Efficiency
A number of situations could benefit from the high efficiency of a switched power supply, save for the supply’s intrinsically high noise level. For example, an optical communications application using a large number of laser diodes could employ a switched power supply to avoid the need for heat-removal techniques. However, the laser diodes require a noiseless environment. A hasty decision to use a switcher would not be rewarding ...
Controller Maps Auto's Electric Drive Voltage To Existing Thermal Fuel Gauge
While converting an older Volkswagen to electric power, we wanted to display the battery voltage on the existing fuel gauge. The gauge used an electromechanical regulator to resistively control the heating of a bi-metallic thermal strip. The regulator is periodically pulsed by the vehicle’s 12-V battery power. The conversion application provides a proportional control uniquely coded to synchronize and scale into the vehicle regulator’s proportionalcontrolled ...
Superior JFET Biasing Improves Amplifier Performance
An N-channel JFET has a low bias current when its gate is biased negative to the source. However, this requires either that the gate voltage be biased negative with respect to the source voltage or that source voltage be biased positive with respect to the gate voltage. For ac amplifier designs, gate biasing can be made self-biased by using an RC network at the source to hold the positive voltage for a period longer than the time period of the input pulse/frequency...
Design A Low-Cost 4- To 20-mA Receiver Circuit For Control Loops
Current-mode control loops (particularly the popular 4- to 20-mA controls) are used in many industrial applications because of their immunity to induced EMI from motors, contactors, relays, and other sources. Off-the-shelf process controllers often have 4- to 20-mA (sometimes 0- to 20-mA) output options for adjusting speed, pressure, temperature, or some other parameter in a closed-loop control system. The receiving circuit needed for the 4- to 20-mA control...
Simple Battery Monitor Works With Higher Battery Voltages
Battery-operated equipment often requires a low-voltage monitor to warn the user when the battery voltage is too low or to perform other functions, such as power-source switching or device shutdown. Many specialized ICs are available to satisfy this need, but most target applications that use fairly low-voltage lithium or NiCd batteries. Thus, they’re not directly compatible with applications using lead-acid batteries, which may go as high as 14 V during...
"Greener" Rectifier Loses The Diodes, Adds Power MOSFETs, Efficiency
A major cause of losses in a conventional power supply using a 50/60-Hz transformer is the bridge rectifier. This article shows how to build a “greener” rectifier, substantially reducing losses by eliminating the diodes in the bridge rectifier and substituting modern low-RDS(ON) power MOSFETs. The MOSFETs used are typically employed in high-frequency switch-mode power supplies. Aside from the power MOSFETs, the circuit uses only two...
Then, Now, And Beyond—System Design In The 21st Century
I remember the day it arrived. All of our design engineers gathered around the lab bench waiting for our technician to unpack the box. As it was slowly lifted from the protective cardboard packing and set on the bench, we all looked on in amazement— 5 Mbytes in a single hard drive that could fit in your hand! It was a Control Data Corporation ST-506-compatible hard-disk drive that weighed 4.5 lb and consumed around 40 W. Just about everyone made some...
Add Coordinated Overcurrent, Overvoltage Protection To PoE Equipment
POWER OVER ETHERNET (POE) enabled devices and their electronic components are designed for operation within specified current and voltage ratings. If these ratings are exceeded due to short-circuit or voltage transients, components may sustain permanent damage and the equipment may fail. Overcurrent and overvoltage protection devices are used to help protect both power-sourcing equipment (PSE) and powereddevice (PD) equipment. A growing...
Simple PWM Modulator Allows DC Control Signal To Drive LEDs
LED-driver circuits can be dimmed by applying a variable duty cycle (pulse-width modulation, or PWM) to the LED. PWM exploits LED behavior: At higher current levels, the LED’s light output is higher for a given level of power dissipation (temperature). Thus, applying PWM current to the LED yields an average power comparable to that of dc control, but with higher operating current and greater light output. Even if the...
Use A Boost Converter To Create An Auto-Dimmable LED Flashlight
Due to their light output and long life, high-brightness LEDs are well-suited for use in flashlights. Typically, the LEDs are driven with a constant current. So when the battery voltage drops, the flashlight just stops working. In some situations, this could be dangerous. It would be nice to have a flashlight that would automatically dim when the battery voltage drops. Just like a traditional flashlight, it would indicate a low-battery condition and...
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