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292 results found, displaying items 281 - 292
Supply circuitry selects main or backup voltage and disconnects load
A complete portable-equipment power supply, suitable for systems that can be plugged into a docking station, is presented in this circuit idea. When the main supply is removed or falls out of regulation, selector circuitry automatically switches the...
Simple soft-start circuit for switching regulators
In the early stages of development, one of the many issues circuit designers must evaluate is how the circuit behaves when power is first applied. Unexpected things can happen at startup. All capacitors must be charged and all ICs change from an...
DAC-powered charge pump varies negative rail
The circuit shown provides a low-current, adjustable negative supply rail suitable for use as a sensor bias, LCD-contrast bias, or a VCO tuning supply. By operating a charge-pump doubler from the output of a buffered DAC, it avoids the customary...
Simple switchers make simple pre-regulators
Linear regulators are used extensively because of their simplicity, low cost, quiet operation, and clean outputs. In applications where the output voltage must be adjusted over a wide range, however, they can dissipate considerable power and require...
Lead-acid battery charger also monitors terminal voltage
The three-IC power-supply system shown charges typical three-cell lead-acid batteries of the 6-V sealed D-cell type, and provides a manually activated check of the battery capacity. For charging, a conventional switch-mode controller steps down...
DC-AC inverter targets electroluminescent applications
Adc-ac inverter circuit generates the high-voltage ac signal required to drive an electroluminescent (EL) panel. An EL panel is a strip of plastic that’s coated with a phosphorous material. When a highvoltage ac signal, which is at least 40 V or...
Simple circuit shuts off system when supply voltage is low
Many low-cost and portable systems, including small consumer electronic products, operate from unregulated power supplies such as batteries or external, plug-in “power bricks.” These power sources sometimes produce lower-than-nominal output...
Low-cost, isolated 5-V supply for 3.3-V logic
Occasionally, a 3.3-V logic system will need an isolated supply for a peripheral function. There are some dc-dc converters available. However, if spare inverters are present in the circuit, a low-cost solution can be produced using only four inverters...
Constant power load needs only a few parts
Switching dc-dc converters are often used in portable or batterybacked projects because of their broad input voltage range and high efficiency. These converters present a constant-power load to the battery—their input current increases as the...
Dual-output voltage regulator converts 5V to 12V and 3.3V
Today’s microprocessors need a regulated 3.3-V supply that can provide several amperes of current. To obtain this, a synchronous switching regulator (LTC1266-3.3) using a 5-V supply is usually used with a p-channel top-side MOSFET and an n-channel...
Enhanced Varley Loop Locates Faults
Using the Varley-loop configuration to localize insulation faults in multipaired pulp-insulated cables has been practiced for quite some time. The standard configurations require precision potentiometers for manual nulling and calibration. However, modifying the Varley loop, and including a 3.5-digit digital panel meter chip (ICL 7106), eliminates the need for bridge balancing (...
Equalize Pad Power Dissipations
When an RF or microwave signal of excessively high power must be attenuated, one option is to use several cascaded pads. For example, an attenuation of 33 dB could come from a combination of 3 dB and 30 dB. But if the excessive power is really high, attention must be paid to the relative power dissipations of the two pads. In this case, the 3-dB pad would be put in first followed by the 30-dB pad, thus roughly equalizing the power dissipation burden placed on...
Dual VOUT DAC Takes Little Power
By using a combination of power-conserving tricks, a dual voltage-output DAC draws less than 20 æA from a 5-V supply (see the figure). The circuit suits a need for programmable voltage generation in slow or static applications, such as the nulling of offsets in a micropower instrument. Current-output DACs typically waste power by routing the complement of Iout to ground. In this setup, that waste is avoided by...
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