292 results found, displaying items 101 - 120

IC temperature sensors generally are preferred in data-acquisition systems when the accuracy demands aren't extreme. Sensor, signal-processing, and data-conversion electronics are all integrated in the IC along with an easy to use digital-I/O interface, all at low cost. Such ICs require a supply voltage in the range of +3 V to +5 V, negative to common. Also, they usually draw very low supply current. But biasing the sensor is more difficult in a telecom system, where the only...

Short ac powerline dropouts can cause incomplete power-on resets, leaving the microcontroller and logic circuits in an indeterminate state. This susceptibility can be tested using a very low-cost eight-pin microprocessor and a solidstate relay (SSR). Operation of the reset circuit under test is accomplished by varying the number of half-cycle powerline dropouts. The dropout simulator, an ATtiny11 MCU, detects the line frequency zero crossing using level shifter Q1 and its...

Demand for voltage-controlled current sources (VCCSs) and multipliers in a wide spectrum of electronics and communication devices always seems to exist. The multipliers employed in circuits like the Gilbert Cell, however, produce outputs proportional to the product of two voltages. Research, as well as commercial applications, perpetually confronts the problem of implementing a single-ended multiplier with an output that's produced from the differences of two pairs ...

For white LEDs to maintain constant luminosity, they're typically driven with a constant dc current source. In portable applications with a single-cell lithium-ion (Li-ion) source, the sum of the voltage drop across the white LED and the current source can be lower or higher than the battery voltage. This means that whereas a single-cell Li-ion battery can directly power a red LED, a white LED sometimes requires a boosted battery voltage. The easiest way to boost the voltage is via a...

A recent project required an inexpensive microprocessor that could be battery operated and indicate if the batteries were low. I chose Microchip's PIC16LF84A for the microprocessor because it was simple to program and could operate between 2.0 and 5.5 V dc. However, the PIC16LF84A doesn't have analog or comparator inputs. To meet the design criteria for a battery monitor, I went with Microchip's inexpensive MCP100315 Microcontroller Supervisory Circuit. It costs $0.33 each in...

Ken Yang was working at Maxim when he submitted this Design Brief. (He's since moved to the power group at a network equipment company.) The circuit turns on emergency lighting (in the form of a string of white LEDs) and turns them off again after about 10 minutes. The objective is to give personnel time to safely exit the building when a power outage occurs and then to shut off the emergency light to conserve battery power. Yet unlike the emergency lights most of us are used to,...

For decades, and continuing today, the fluorescent lamp has been the cheapest way to produce white light with the minimum amount of energy taken from the mains (lumens/watt). As such, hundreds of millions of compact fluorescent lamps (CFLs) are sold every year, with an ever-increasing demand for higher reliability. Today's lighting systems need ballast control functions to drive compact fluorescent lamps, adding cost and requiring more design time. Also, these functions must often be...

Electronics lab experiments often use low-power control cards that can fail even in expert hands. These cards contain ICs that fail if the supply voltage exceeds a certain value or has an unsuitable polarity. Also, current must be limited to avoid damage to the card. Therefore, protection against inverted polarity, overvoltage, and overcurrent is needed. In our case, the control card that we wanted to protect consumed less than 50 mA, a negative input voltage wasn't allowed, and a sensitive...

This power supply is ideal for the circuitry that drives high-side p-channel MOSFET switches often found in motor controllers. It's especially useful for designs where the motor's positive supply voltage exceeds the typical 20-V gatesource breakdown voltage of the power p-channel MOSFET. There are three notable advantages to the design: It will always track the motor's positive supply voltage, which can be especially useful if the positive supply...

Why not take advantage of the micro-controller included in many systems these days? This design uses microcontroller feedback to produce a ?50-V, 1-W power supply (see the figure). It leverages an unused analog-to-digital converter (ADC) input and a pulse-width-modulation (PWM) output to close the loop on a basic inverting single-ended primary inductance converter (SEPIC) topology. Varying the duty cycle of the...

To minimize the electromagnetic interference (EMI) and video noise caused by different signal frequencies inside the same piece of equipment, it's sometimes necessary to synchronize the switching frequency of the power supply (such as for tuner compatibility). Generally, using a fixed-frequency controller with an external oscillator, or at least an adjustable frequency, solves this. But instead of designing a different specific— and often...

I was using a thermoelectric cooler for a camping trip and discovered the next morning that my car battery was dead from the load. I never expected a 3.5-A load to drain the battery in eight hours. So I went about making a circuit that could be contained in a standard automotive plug (MPD APP-001). The plug houses a fuse and an LED that's also used in the circuit shown in the figure. The main problem was getting enough drive on the MOSFET to achieve the lowest RDS(ON). High-side...

Medical and industrial applications often require galvanic isolation of 2500 V ac or higher for the safety of patients and equipment operators. The isolation barrier conveys not only power to the sensing element, but also data to or from that element. Each data signal crossing the barrier-requires isolation. Consequently, designers can typically save costs in these applications by choosing a serial bus rather than a parallel bus. Serial buses include SPI, I2C, and the...

Solenoids and relays used in electronic control applications consume lots of power. The current required for activation is typically three to 10 times higher than the minimum needed to hold the relay or solenoid in the ON position. Thus, reducing the driver's operating current after the solenoid or relay is switched ON will save power and reduce thermal loading. The technique presented here substantially reduces power dissipation when the device is ON. The circuit employs an op...

Originally, the venerable three-terminal linear regulator featured a bipolar junction transistor emitter-follower output that exhibited very low output impedance. Many of today's applications demand dropout voltages lower than that of the first-generation regulators (1.5 V). Most modern regulators, therefore, include a common-source MOSFET as the pass element. One compromise that's associated with the common-source (or common emitter) output is an intrinsically high output...

It's certainly easy enough to buy a switcher off the shelf, but what do you do if you need a little extra voltage with a little more control? A programmable switcher would be nice. The following design is a very simple attempt at providing a little extra voltage with flexible control, while requiring very little hardware overhead. A basic voltage-feedback boost converter design is chosen with a vastly simplified feedback circuit. The feedback circuit requires only a comparator,...

The semiconductor industry’s rapid move toward a 90-nm process node to achieve performance and cost benefits puts enormous pressure on power budgets. Decreasing transistor sizes lead to increased leakage current and, as a result, static power. Dynamic power also rises with system speeds and higher design density, but in a more linear fashion. Today, many designs have 50-50 static and dynamic power dissipation. According to International Technology Roadmap for Semiconductors (ITRS)...

Designers of high-sensitivity, low-noise preamplifiers recognize the benefits of galvanic isolation to reduce noise. Besides the noise benefits of isolation, some preamps have further requirements, such as the ability to float at a large dc offset voltage. Accommodating this requirement with off-the-shelf solutions may result in high cost and the addition of large components. Designers can craft a high-isolation micropower dc-dc converter using a telecom transformer. The design...

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