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292 results found, displaying items 61 - 80
Sequence Generator Delays Bias Voltages To LCDs
Many graphic (passive/active (TFT)) LCDs require multiple positive and negative supply voltages. At “power on” and “power off,” these bias voltages must be sequenced properly, along with the LCD’s data and control signals, to prevent damage to the LCDs. Figure 1 shows a circuit that can provide the needed sequencing. The inverters are 74HC14 Schmitt types. The resistor-diode-capacitor...
Clamping Circuit Lowers Distortion, Improves Overdrive Recovery Time
Some amplifier applications require clamping or limiting due to large, sporadic signals appearing at the amplifier input. Clamping these errant signals protects the amplifier and other sensitive downstream circuitry. It also improves overdrive recovery time and can lower distortion. At the heart of the clamp circuit described here is the AD8099 high-speed, low-noise, externally compensated amplifier. The device consists of a single-stage amplifier followed by a unity-gain...
Germanium Dual-Boost Starts At 260 mV
No matter what portable power source you use, the lower the starting voltage your circuitry operates at, the better. A lower startup voltage also maximizes runtime. Furthermore, to completely discharge the power source, circuitry must run on ever-lower voltages and currents. Existing boost circuits can start up and drain a power source down to 1 V, but that still leaves too much unusable energy in a battery. Other power sources, like solar cells or micro-turbines,...
Pay Attention To Switch Arrangement To Improve PGA Performance
Programmable-gain amplifiers (PGAs) are often used in communication systems, such as basestations. Designers can select fully integrated, single-IC PGAs, which are now available with bandwidths over 500 MHz. But obtaining the low second- and third-order distortion that is critical in communication applications isn't easily achieved. Combine that with the desire for greater choice in the attenuation level and step size, and designers may opt to construct a PGA using a...
Lead-Acid Battery Charger Becomes A Subfunction In A Microcontroller
This design implements a charger for a lead-acid battery as a subfunction in a microcontroller whose main function can be any more complex task. Furthermore, the MCU gets its power from the same battery. The charging process is so slow and uses so little processor time that it doesn't jeopardize the MCU's primary task. The goal of the circuit (...
Digital Resistor Sets Operating Power For Laser Driver
Designers can use a photodiode in conjunction with a power-control feedback loop to compensate a laser driver circuit for temperature effects and the effects of the laser's aging. But a photodiode's response can vary by as much as 40%, so the system needs additional compensation. That can be achieved with a digital resistor that varies the power set-point in response to temperature. For example, the MAX3740 VCSEL laser driver and DS1859 dual temperature-controlled digital...
Self-Powered Eight-Channel Tester Checks Battery Discharge Rates
Nickel-metal-hydride (NiMH) batteries are made by many manufacturers and have different charge ratings. Also, with repeated use, the maximum charge that NiMH batteries will hold diminishes at different rates. Therefore, it's difficult to gauge the useful life and charge capacity of these batteries. To measure NiMH battery performance, a multichannel battery discharge unit was designed. The unit includes a serial interface through Windows Hyperterminal and is powered by the...
Minimize Input-Supply Ripple Current In LED Driver Applications
Consumer-based LED applications have really taken off. You now find them in home lighting, airplane cabin lights, automobile lights, MP3 players, and elsewhere. In the past, most LED drivers were based on some sort of charge pump, where the input voltage was multiplied by two and the LED voltage was post-regulated by an internal low-dropout regulator. But some high-power LEDs require much higher current before they start emitting light. Therefore, most of today's...
L-C High-Pass Filter Reduces Power Supply's Hum And Ripple
A previous Idea for Design described an R-C twin-tee circuit designed to reduce power-supply hum at 50 to 60 Hz ("R-C Twin-Tee Reduces Power-Supply Hum,"). This Idea for Design presents a new L-C high-pass filter that reduces both power-supply hum at 50 to 60 Hz and ripple at 100 to 120 Hz. The circuit is a relatively simple composite high-pass filter employing the classic design...
Charge Pump Extends Current-Sense Amplifier's Input Range Down To 0 V
In addition to the traditional lead-acid battery, modern electric/hybrid cars often include a large capacitor (40 F or more) as a backup power source. Located under the rear seat, this capacitor ensures an extra 10 to 15 minutes of driving time that allows you to reach the next charging station or gas station. Lead-acid batteries discharge down to only 8 V or so, but a capacitor can discharge all the way down to 0 V. This capability requires a current-sense amplifier that can...
Delay Circuitry Controls Supply-Voltage Startup Sequence
For some ICs, supply voltages should be applied in a particular sequence. One example is the subscriber line interface circuit (SLIC), which, depending on the application, may require several negative and/or positive voltages. The larger voltages are generally used to ring the phone, and the lower voltages power the phone while it's off-hook. As an example, consider a design that requires output voltages of 51 V, +60 V, and 27 V, all at load currents of several hundred...
Simplified AC Line Sensor Uses Few Parts, Little Real Estate
Typically, ac line sensors use comparators. But I had to design a power supply to be as low in cost as possible, be self-powered, use through-hole components, and take up as little space as possible on a small two-sided pc board. So I developed the simplest ac sensor possible. The resulting circuit senses the high-voltage dc bus (...
Supply Constant Power Level To A Varying Load Impedance
How do you deliver constant power when the load impedance isn't constant? That problem arises, for example, in trying to maintain a warm LCD display on an outdoor gas pump in cold climates. As the heating element changes temperature, its resistance changes as well. That variation is characterized by the temperature coefficient of the heating element. If you apply a constant voltage, power delivered to the load will vary inversely with the load resistance. In...
Lithium-Ion Battery System Upgrades Require Power-Management Analysis
As portable electronic systems become more sophisticated, selecting the optimum battery requires an intensive analysis of the entire power-management system. Many manufacturers now consider lithium-ion (Li-ion) batteries because they hold advantages over older battery technologies. However, upgrading from the older technologies to Li-ion isn’t possible as a one-to-one replacement. The first step in determining the feasibility of an upgrade is to fully describe the portable...
Ensure A Fixed Bias Current For Gain Blocks
RF gain blocks (amplifiers) are popular because they offer wide bandwidth, low noise, and ease of use. They're designed to operate with a fixed value of supply current because variations in supply current cause variations in the gain, compression point, and other crucial specifications. Typically, a series resistor sets the supply current to a value based on the known value of dc voltage at the RF choke. That voltage, however, can vary from part to part. For instance, the GALI-21...
Auto-Resetting Circuit Protects Auxiliary Outputs Against Shorts
Many products require an auxiliary dc output to power external devices or subsystems. If such subsystems are to be hot-connected, the auxiliary output must be protected against short circuits. Schemes using fuses are slow and will cause the internal dc-rail to drop, possibly affecting the main system. The circuit shown in the figure provides pulse current limiting at a very low cost. It can handle momentary or...
Give Your Projects Under- And Overvoltage Protection With Hysteresis
This circuit provides undervoltage and overvoltage protection for dc input supply voltages (see the figure). Its undervoltage cutoff is 6 V, and its overvoltage cutoff is 11.5 V. When VIN is less than about 6 V, Q1 and Q2 are OFF; Q3 (a series MOSFET switch) is also OFF and VOUT = 0. When VIN goes over about 6 V, Q1 turns ON, turning ON the series MOSFET. Then, VOUT =...
Dual-Phase Inverting Buck/Boost Supply Gets -5.2 V/15 A From 12 V
The most common use for a synchronous buck controller is high-efficiency conversion of a positive voltage to a lower positive voltage. But it can also produce a negative voltage from a positive voltage. In negative output applications, a buck controller can be configured as an inverting buck/boost device, where the negative output voltage has an absolute value either higher or lower than its positive input. To transform a buck converter to a buck/boost,...
Cascode Configuration Removes Miller Effect, Boosts PFC Performance
The power factor corrector (PFC) front end of an off-line power supply is subject to the operating frequency limitation caused by the Miller Effect of its associated power MOSFET. This effect is a property of any transistor configuration with a common source (MOSFET) or common emitter (bipolar transistor) configuration. Most PFCs employ a boost converter based on a configuration with a common source MOSFET or common emitter power bipolar transistor. ...
Single Solar Cell Trickle Charges 3- To 16-V Battery In-Circuit
Many battery-powered applications use very little power when idle and have short-duration operating periods. Thus, the total energy used is very small. It would be convenient to incorporate solar cells in these devices to charge the batteries. However, the number of cells needed to charge a given battery voltage is close to Vb/0.6, thereby necessitating an array of solar cells, series connected. The circuit in the figure addresses that issue by employing a...
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