1195 results found for Ideas For Design, displaying items 1 - 20
July 10, 2008 Create A 250-MHz Bandwidth Digital Potentiometer For Video Level Control
A circuit used to control the level of a video signal should have a 3-dB cutoff frequency of greater than 5 MHz for a television application or 100 MHz for a monitor application. CMOS-based digital potentiometers typically cannot be used as video devices because their frequency responses barely exceed 1 MHz. For such applications, a good choice would be a variable-gain amplifier (VGA) with analog or digital gain control. VGAs are offered...
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Oleg Ayranov
, et al.
July 10, 2008 VHDL Code Offloads LED Blinking Task To A CPLD
An earlier Idea For Design (“Hardware-Based LED Blinking Control Eliminates Software Overhead,” Sept. 27, 2007, p. 52) described a very interesting way to offload the software overhead required for a microcontroller to drive LEDs that indicate operating states to the user. That article discussed the use of memory-mapped LED control registers, buffers, and a clock source, all used to blink an LED without burdening the microcontroller code with...
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Philip Warren
July 10, 2008 VHDL Code Listing
IFD2303code.txt library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity LED_Driver is port ( clk: in std_logic; -- Clock input por: in std_logic; -- Power-On Reset a_bus: in std_logic_vector(3 downto 0); -- 4-Bit Address Bus d_bus: inout std_logic_vector(7 downto 0); -- 8-Bit Data Bus led_out: out std_logic); -- Output to...
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Philip Warren
June 26, 2008 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....
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Jim Christensen
June 26, 2008 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....
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Louis Vlemincq
June 12, 2008 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...
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Peter Khairolomour
June 12, 2008 Control Camera Time Exposure Through A Computer's Serial Port
A computer’s serial port is a convenient source of low-speed dc control signals that are easy to set from software. For example, the RTS (request-to-send) line outputs about +9 V when “on” and -9 V when “off.” This idea shows how to use this signal to control the shutter of a Canon EOS 40D camera for a computercontrolled time exposure. An ordinary cable release for this camera contains two switches, mechanically linked so that as you press the...
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Michael Covington
June 12, 2008 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 ...
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T.A. Babu
May 22, 2008 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...
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Anshi Chen
May 22, 2008 Use PWM To Maintain Motor Speed And Phase While Eliminating Loop Filter
In designing a simple spectroscopy setup, we needed to synchronize the speed of a small, inexpensive dc motor precisely to 6000 rpm (100 Hz). Our first idea was to take a phase-frequency detector type of phase-locked loop (PLL), the CMOS 4046, to maintain not only the speed, but also the phase to the reference signal. 1 In the classical approach, the motor’s speed is modeled as a firstorder time delay over time. Some math is done to obtain a good ...
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Richard Heming
May 22, 2008 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...
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Ron Koo
, et al.
May 8, 2008 "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...
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Joseph Diecidue
, et al.
April 24, 2008 Circuit Transfers Resistance Value Through Isolation Barrier
The circuit shown in the figure can monitor resistance in a noisy or otherwise hostile environment. A 1:1 transformer provides isolation and a good common-mode rejection ratio (CMRR). The resistance across the secondary winding is reflected to the primary, where it forms a voltage divider with resistor R1 (see the figure). This divider produces a reducedamplitude clock signal that's coupled through C2, rectified by ...
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Leo Sahlsten
April 24, 2008 Novel Switch Interface Scheme Reduces Microprocessor Pin Count
The most common method for interfacing multiple switches—multiplexing— allows for the connection of (N/2)2 switches with N microcontroller IO lines. The method described below, which has its roots in an LED interface technique commonly known as “Charlieplexing,” makes it possible to interface N*(N – 1) switches with N IO lines. In conventional multiplexing of an N-by- N matrix with 2N IO lines, half of the lines are configured for input and...
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Kartik Joshi
April 24, 2008 Electronic Birthday Candles “Blow Out” One At A Time
This circuit creates a set of LED-based electronic birthday candles that are just as much fun as blowing out wax candles, but are also reusable, scalable, and even eco-friendly. It uses a thermal sensor that’s maintained at a temperature above the ambient temperature. When you blow air over the sensor, the resistance changes. The circuit detects this change and turns off the eight LEDs. When you stop blowing, all but one of the LEDs turn on. This cycle...
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Abhijeet Deshpande
April 10, 2008 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...
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Chester Simpson
April 10, 2008 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...
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Bob Urman
March 27, 2008 LMC555 Timers Delay Hardware Reset To Collect Debug Data
Most microprocessors have some type of hardware watchdog that can be used to reset the microprocessor and the surrounding hardware to a known state if firmware inadvertently stops executing code. But it may be advantageous to record the watchdog-overflow event in nonvolatile memory (NVM) for debug purposes prior to resetting the hardware. The circuit in Figure 1 uses two LMC555 timers that delay a hardware...
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Ken Turocy
March 13, 2008 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...
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Dipti Desai
March 13, 2008 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. ...
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Nick Allen-Rowlandson
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