292 results found, displaying items 121 - 140

In multiple-output-voltage power supplies, the topology may place restrictions on the startup sequence. This can be particularly troublesome in an isolated power supply, where a lower output voltage must be present before a higher output voltage. Typically, the higher voltage is the source of power for the lower voltage output. Consider a system with an isolated ­48-V input supply with a 3.3-V/9-A output and a 1.8-V/3-A output. The 1.8-V output must be present at the load before the...

Recently, white LEDs have made sizable performance gains by squeezing extreme luminous density into ultra-compact packages. The latest white LEDs hold numerous advantages over more conventional lighting, including improved spectral characteristics, shorter response time, greater luminescence, greater durability, longer life, and decreased size. The Lumileds Luxeon V, for instance, boasts up to 50 times the flux, and at least 20 times the luminous density, of a standard...

Reliable system operation often depends on the quality of the power supplied. Supply voltages that are too low can cause faulty operation as the microcontroller, FPGA, or ASIC begin to send bad data to memories or peripheral devices. Too high a voltage can damage a device permanently. In addition to providing protection in the event of a voltage fluctuation, users may want to identify the source of the failure. The application must use a voltage regulator plus a pair of FETs...

Switched-capacitor blocks are easily configured to be integrators. When configured as an integrator, a switch-capacitor block can function as an op amp. Closed-loop stability is achieved by parametrizing the capacitor values and sample frequency, which allow for precise gain-bandwidth control. Adding an external pass transistor and current-setting resistor enables easy construction of a programmable current source. Figure 1 shows...

In telecom power systems, the positive rail is usually grounded. This forces designers to place a shunt resistor on the system's negative rail to measure current. Yet there are other ways to sense the system's current. Some methods even use a transducer, like Hall-effect or magnetic inductance current transducers, instead of a shunt resistor. These transducers are made for only certain current values (50, 100, or even 200 A). Although effective, such solutions are more...

Designing a power supply that meets the demands of Power over Ethernet (PoE) and Voice over Internet Protocol (VoIP) applications can be challenging. The low component-count power supply depicted in the figure meets these specifications without the need for complicated circuitry. The circuit shows a typical converter for a powered device (PD) as defined by the PoE standard. The schematic includes the necessary circuitry for "discovery" and "classification," along with a...

Using standard circuits and no auxiliary voltage generators (such as charge pumps or inductive dc-dc converters), it's difficult to build a precision, rail-to-rail ramp generator that operates on a single supply and resets to a well-defined level. Figure 1 implements such a circuit using a bootstrapped series reference and an op amp with rail-to-rail I/O and very low bias current. The ramp is generated by a constant charging current into capacitor CRAMP. This is...

In many computing and communication applications, the intermediate bus architecture (IBA) with non-isolated point-of-load (niPOL) converters continues to displace conventional distributed and centralized power solutions. Key drivers of this trend include the increasing number of system voltages, their higher output currents, tighter regulation requirements, and lower total system cost. While meeting these needs, many IBA/niPOL solutions don't include certain protection mechanisms that come...

The circuit that's shown in Figure 1 implements a programmable 0- to 20-mA precision current source. The REF192 low-headroom 2.5-V voltage reference (U1) can source up to 30 mA. An AD5280 digital potentiometer (U2) controls the voltage-divider ratio of the reference voltage. U3, an OP1177 op amp, closes the loop by forcing VL = VW. At the digital pot's zero scale, where VWB ≈ 0 V, the voltage across RSET will approach zero and...

Read about one experience from the twentieth annual Applied Power Electronics Conference and Exhibition that took place in Austin, Texas, last month.

Lithium-based batteries are becoming standard in portable equipment. They have desirable characteristics, but lead times may be long unless you have a preferred-customer status with the battery manager. A backup alternative is desirable, especially for smaller companies. It should (ideally) provide the same performance, size, and cost as a lithium-type battery. Nickel-metal-hydride (NiMH) batteries are still in wide use. They're much cheaper than lithium batteries, and they...

Camera shops usually will give disposable flash units away for free. The flash capacitor, output rectifier, and transformer are de-soldered easily for use in the new circuit.

The circuit shown in Figure 1 implements a programmable 0- to 20-mA precision current source. The REF192 low-headroom 2.5-V voltage reference (U1) can source up to 30 mA. An AD5280 digital potentiometer (U2) controls the voltage-divider ratio of the reference voltage. U3, an OP1177 op amp, closes the loop by forcing V_L = V_W...

When a circuit requires reverse-voltage protection on the power input, the usual approach is a series diode (see the figure, a). But if the input voltage input is low—say, two or three AA batteries—the 0.5-V loss of a Schottky diode may represent a significant loss in useful battery life. An FET can serve as a series diode with significantly less voltage drop (see the figure, b). A dual IRF7342 FET was used (p-channel,...

Many systems require a low-power supply in addition to the main supply. A typical example is when an analog front-end amplifier needs ±5 V, while the main digital circuitry requires +5 V only. For reasons of cost, inventory management, electromagnetic compatibility, and so on, a separate —5-V converter may not be appropriate. So, some means must be found to provide extra power rails from the main supply. Implementing a step-down IC converter's switching action may...

Power-supply margining is a technique commonly used to test circuit boards in production. By adjusting power-supply output voltages, electrical components are tested at the upper and lower supply-voltage limits specified for a design. In addition to its usual task of tracking multiple power supplies, the LTC2923 power-supply tracking controller can be used to margin supplies. The LTC2923 employs the simple tracking cell shown in ...

The Point Of Load Alliance (POLA) and the Distributed-power Open Standards Alliance (DOSA) have both endorsed Power Management Bus (PMBus), the brainchild of Artesyn and Astec Power. An open architecture for power systems, PMBus employs I2C for digital control and monitoring. Power-One's Z-One Digital IBA uses I2C with a proprietary chip that talks to Power-One's POLs over a custom interface. PMBus takes a different approach, envisioning an...

This design modifies a simple first-order, low-pass filter into a slewing-voltage control that is programmable for its slope and amplitude through a PC's LPT port. These control parameters are typically required for metallurgy studies like corrosion of materials using a potentiostat. (A potentiostat, which is a standalone device, sets the required potential/second for the electrode under corrosion studies.) Figure 1 shows a circuit that supplies...

See associated figure Low-voltage halogen lighting for decorative and architectural use continues to gain in popularity. Due to the comparatively short lifetime and low reliability of halogen bulbs, however, high-power LEDs are emerging as the preferred solution. The circuit in the figure offers a novel approach to high-power white LED driving—using a standard boost-converter IC in a voltage-reducing or "buck" mode. This solution...

Polar-array systems are becoming a very important energy source. Today, they're being used in numerous applications where mains power isn't available or clean energy generation is preferred. To determine the electrical and physical characteristics of the whole system, it's a good idea to use an experimental setup. It comes in handy when defining the solar-panel model and checking the power-conditioning system while its main parameters are varied. The circuit...

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