App note: High-power emitters for illumination applications

App note from OSRAM on High-power LEDs and their special requirements. Link here (PDF)

In general high power emitters can be driven with DC currents in the range of 1 Ampere whereas most low power products like 5 mm Radials are limited to 100 mA.

As the light output increases with driving current the optical power is raised by a factor of ten compared to standard devices. At the same time much less board space is occupied as fewer devices are needed. On the other hand a careful thermal management is absolutely mandatory because the thermal power dissipation is increasing in the same way as the optical output power. To keep the junction temperature of the chip as low as possible a low thermal resistance is needed and the standard FR4-PCB has to be replaced by a metal core PCB. By this a high optical efficiency of the IRED can be achieved.

App note: Analog switch lowers relay power consumption

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Clever way of starting-up relays discussed in this app note from Maxim Integrated. Link here

Relays are often used as electrically controlled switches. Unlike transistors, their switch contacts are electrically isolated from the control input. On the other hand, the power dissipation in a relay coil may be unattractive for battery-operated applications. You can lower this dissipation by adding an analog switch that allows the relay to operate at a lower voltage.

App note: Ferrite bead demystified

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App note from Analog Devices hinting for proper selection of ferrite bead for you applications. Link here (PDF)

An effective method for filtering high frequency power supply noise and cleanly sharing similar supply rails is the use of ferrite beads. A ferrite bead is a passive device that filters high frequency noise energy over a broad frequency range. It becomes resistive over its intended frequency range and dissipates the noise energy in the form of heat. The ferrite bead is connected in series with the power supply rail and is often combined with capacitors to ground on either side of the bead. This forms a low-pass filter network, further reducing the high frequency power supply noise.

App note: Silicon Labs’ TS3004 VS. the CMOS 555 – Determining lowest supply current for battery-powered applications

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Good read on this app note from Silicon Labs comparing their low power but obsolete timer. Link here (PDF)

The 555 timer is the workhorse of ICs, with close to a billion of them manufactured every year. Introduced in 1972, the 555 is still in widespread use because of its ease of use, reasonable price, and good stability. It can be found in a wide variety of applications for oscillation, timing and pulse generation. But what if you need a timer IC for ultralong life, low-frequency battery-powered/portable applications where a low supply current is a requirement? Is the CMOS555 timer your best option?

App note: Single-cell regulated Q-pump draws low quiescent current

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Q-pump an alternative to inductor charge pump boost regulator for low power and sleepy microcontroller from Silicon Labs. Link here (PDF)

In the switch-mode power supply world, capacitor-based charge pumps (or Q-pumps) generally aren’t useful for heavy lifting, but work well in niche micropower applications where space is at a premium. They work best in applications where the output voltage is an integer multiple of the input voltage, which are operating points that result in peak efficiency. However, they can also shine when powered from a variable input like a battery, particularly when quiescent battery drain is more important than heavy-load efficiency. This might be the case when powering a microcontroller that spends most of its life sleeping.

App note: Core independent voltage window signal detection using a single comparator

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Presenting the usage of Core independent paripheral of PICs in this app note from Microchip. Link here (PDF)

It is possible to find out whether a measured signal is below or above a certain value/reference using a single comparator. But, what if the desired interval is between two values, the undervoltage and overvoltage protection?

The most convenient and fastest solution is to use two comparators and two references. The results are analyzed to decide which of the three intervals houses the measured signal. Using an Analog-to-Digital Converter (ADC) and core post-processing will yield the same result, but the process is slower and dependent on core availability.

App note: Power supply rejection ratio of low dropout voltage regulators

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Here’s an app note about PSRR of LDO from Microchip. Link here (PDF)

The Power Supply Rejection Ratio is the ability of a device, such as a Low Dropout Voltage regulator, to reject the various perturbations that can be found in its input supply rail by providing a greatly attenuated signal at the output. Generally, the main source of the perturbation will be the output ripple of the DC/DC converters that typically power LDOs.

High PSRR LDOs are recommended for powering line ripple sensitive devices such as: RF applications, ADCs/DACs, FPGAs, MPUs, and audio applications.

One important clarification must be made: PSRR is NOT the same with output noise. PSRR is a measure of rejection. It shows what the part will output based on the given input.

App note: Comparison of LED circuits

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Another application note from OSRAM on different LED circuit design failure mode. Link here (PDF)

In recent years, Light Emitting Diodes (LEDs) have become a viable alternative to conventional light sources. The overriding advantages long life, high efficiency, small size and short reaction time have lead to the displacement, in ever increasing numbers, of incandescent bulbs. One of the markets where this change has become most evident is Automotive, where LEDs are used now not only for backlighting dashboards and switches, but also for exterior illumination in Center High Mounted Stop Lights (CHMSL), Rear Combination Lamps (RCL), turn signals and puddle lighting.

Despite the long life and low failure rates of LEDs, cars can be found, on occasion, with failed LEDs in their CHMSL. Most often this is due to a flawed circuit design wherein the LEDs were allowed to be overdriven. It is with that supposition in mind that this application note is written: to identify, characterize and comment on LED behavior and failure modes in serial and matrix circuits.

App note: Dimming LEDs with respect to grouping current

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App note from OSRAM describing the behaviour of LEDs in respect to brightness by varying the current and to suggest solutions for avoiding negative influence for the application. Link here (PDF)

In the design of a driving circuit for LEDs, the dimming behaviour is an important topic to fulfill the end customer requirements. The behaviour of the LEDs in respect to brightness is investigated by varying the current and solutions for avoiding negative influence for the application are suggested.