260 results found, displaying items 1 - 20

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...

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...

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...

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...

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...

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...

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...

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...

This design shows how we combined four 36-V DeWalt DC9360 nanophosphate battery packs in a series-parallel configuration to create a robust, high-energy power source. Originally intended for the prototype Neodymics Cyclemotor electric bicycle kit, this power source may be used in other applications. Output power was at least 1.6 kW at 66 V, energy capacity was about 300 W-hr, and recharge time was one hour. Also, the claimed cycle life exceeds 2000. The...

This idea shows how to monitor input voltage and current consumption for telecommunications equipment powered by two independent feeds: -48 V (A) and -48 V (B). Each feed supplies at least -42.5 V to -56.5 V, and for redundancy the feeds are ORed on the module. For maintenance and support purposes, it’s important to monitor input voltage, the feeds’ presence, and the module’s power consumption. ...

High-brightness LEDs (HBLEDs) are making inroads into more traditional lighting applications that include a dc distribution system (for example, 24-V MR-16 track lights). HBLEDs are more efficient, and they have a potentially longer lifespan than do halogen or xenon lamps. Because hysteretic controllers are inexpensive, simplify lighting designs, and require no compensation networks, they’re well-suited for driving HBLEDs....

The converter described below, based on a silicon bipolarjunction transistor (BJT), can operate at as low as 250 mV, which is probably a record for a converter not based on a JFET or germanium transistor. How is this possible? The VBE threshold is not clear-cut, depending on current density and other factors. But 250 mV is way below the lowest accepted values. There has to be a trick and there is, sort of. The big difficulty is in the starting....

Designers of portable electronics such as cell phones, portable media players, and GPS devices are always pushing to squeeze every ounce of battery life out of the application. In particular, in the realm of power conversion, engineers aspire to ensure that every coulomb that leaves the battery finds its way to a point-of-load (POL) without being lost or dissipated as heat. The solution is not always straightforward, though, because as in...

Ballast-control ICs from International Rectifier and other similar half-bridge gate drivers feature an undervoltage lockout (UVLO) on the high-side output. This function protects the driven MOSFETs or insulated gate bipolar transistors (IGBTs) in the event that VB drops to potentially dangerous low levels. When designing an electronic ballast for operation off a 12-V dc (10.5 V to 13.6 V) battery, however, the UVLO creates a challenge ...

The well-known Kirchhoff’s current law is often used in linear circuit analysis. It’s also called Kirchhoff ’s first law, Kirchhoff ’s point rule, Kirchhoff ’s junction rule, and Kirchhoff ’s first rule. The law says that at any point in an electric circuit, the sum of currents flowing toward the point is equal to the sum of currents flowing away from the point. That is, the net current flow into the point is always zero. This article describes a new way of using...

In a typical automotive video application, the video digital-to-analog converter (DAC)—from a rear camera or DVD player, for example—is followed by a low-pass reconstruction filter and an amplifier that transmits a video signal to the LCD. This amplifier, and all such similar automotive circuits, must be protected from direct connection to the car’s battery voltage. Since these voltages range from 12 to 16 V, the minimum protection required is 16...

Care must be exercised when you try to “quickly” charge a nickel-cadmium (NiCd) cell or battery pack at a current density that approaches or exceeds one-third of its capacity (C/3). As the battery becomes fully charged, the high charging current raises both the internal cell pressure and temperature, which can quickly degrade the battery or destroy it. One way to avoid damage is to monitor the differential temperature (TDIFF) between the...

Performance under transient loads has become the most important specification of voltage regulators used to power a wide array of products whose current demands vary quickly during operation. Testing transient performance requires a load that can be programmed to change at different rates. Expensive electronic loads are available, but I found none that could supply a load that changes faster than 0.4 A/µs, which is too slow to...

One of our products uses a standard 1/10-W surface-mount resistor with a high-side current monitor to detect small load changes at the product’s output. Since this circuit is part of the device’s output, it’s vulnerable to field wiring mishaps. If the field installation results in a shorted output, the resistor, which can’t dissipate much power, will be destroyed. Protecting the resistor with a PTC (positive temperature coefficient) device is...

The output voltage of a voltage reference device can be adjusted using a digitally controlled potentiometer (DCP) without significantly changing the device’s temperature coefficient (TC), which describes how the output voltage changes as the operating temperature changes. Some voltage references include a trim pin for fine-tuning VOUT using a DCP. However, even parts without a trim pin can be adjusted using a DCP. First, consider the case of...

• Build A Smart Battery Charger Using A Single-Transistor Circuit
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• Easy-To-Build AC Power Meter
• Low-Dropout (LDO) Linear Regulators