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254 results found, displaying items 1 - 20
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...
Nanophosphate Batteries Create High-Energy, Rechargeable Source
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...
Add On-Board Power Measurement Capability To Telecom Equipment
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. ...
Adapt DC Voltage To Perform PWM DImming Of High-Brightness LEDs
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....
Trick A BJT-Based Converter Into Starting At Only 250 mV DC
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....
Maintain Power-Conversion Efficiency While Saving PCB Space
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...
Switch Tricks Electronic Ballast ICs Into Working On Low Voltages
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 ...
New Way To Use Kirchhoff's Current Law Simplifies Circuit Analysis
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...
Simple Circuit Uses FET To Protect Car's Video Driver From Overvoltage
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...
"Intelligent NiCd Charger Avoids Battery Damage From High Currents
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...
Fast Load Transient Tester Circuit Features Adjustable Slew Rate
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...
Unconventional Use Of An Output Driver Protects Current Monitor
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...
Use Digitally Controlled Potentiometer To Adjust Voltage Reference Output
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...
Two AA Cells Power Class D Amp To Produce Huge Audio Volume
Class D audio amplifiers like the MAX9704 offer almost 90% efficiency, but they need 10 V to operate. For battery-operated systems, that would require a large number of batteries wired in series. You can avoid bulky battery packs by incorporating a switched-mode boost converter like the MAX1771, which generates 12 V from inputs as low as 2 V and delivers output currents up to 2 A. A battery-operated class D amplifier can then run off a pair of AA cells. ...
Add Fail-Safe Shoot-Through Protection To Power MOSFET
MOSFETs are widely used as power switching elements in regulators and motor controllers. They can be either discrete devices or integrated into ICs in various H-bridge configurations. A common arrangement uses a high-side (HS) power MOSFET, M1, and a low-side (LS) MOSFET, M2, to drive an inductive load (Fig. 1). When the HS FET is switched on and LS FET is switched off,...
Use "Extra" LED Driver Channel To Provide Constant-Voltage Source
LED applications are booming: backlighting for LCD TVs, projectors, and computer displays, camera flashes, and vehicle brake lights and taillights are just a few. All require constant-current LED drivers that offer a high dimming ratio, high efficiency, precise adjustable current, and low cost. To save space, some LED drivers can handle multiple strings of LEDs. For instance, the LT347drives four LED strings, totaling 100 W. If all of the driver channels aren’t...
Protect Current-Sense Amplifiers Against Overvoltage Transients
Certain current-sense amplifiers have to contend with frequent overvoltages. For example, a current-sense amplifier that monitors batterydischarge currents in an automobile must withstand high-voltage "load dump" pulses produced when loads are disconnected from the battery. This causes inductive spikes and overvoltages at the output of the alternator. If these pulses exceed the amplifier's common-mode voltage, the amplifier requires external...
Simple Circuit Additions Power A Microcontroller Through Its Load
Many small microcontrollers require so little power that often they can draw what they need through their loads. This can simplify a system, reduce its cost, increase its reliability, and provide unexpected benefits. One example is an automotive check system that monitors a car's brake lights and indicates any faults through an incandescent bulb in the instrument cluster, LMP1 (Fig. 1)....
Microcontroller Interface Delivers Standard 4- To 20-mA Output
Voltage-to-current converters that feed grounded loads are common in industrial measurement and control applications. The conventional "textbook" circuit uses both positive and negative supply rails. An earlier article by this author titled "Voltage-To-Current Converter Works From A Single Supply Rail" (Electronic Design, Feb. 17, 2003, ED Online 2985) described a circuit that could power grounded loads and needed only a positive ...
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