Tag Archives: app notes

App note: How to select the Triac, ACS, or ACST that fits your application

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Choosing the right AC switch for your application based on specification like current rating, voltage rating and triggering quadrant. Here’s an app note from STMicroelectronics to guide you on selecting the right part. Link here (PDF)

This document gives basic guidelines to select the AC switch device according to the targeted application requirements. These guidelines will allow the appropriate Triac, ACS or ACST to be selected, for most of the applications. Some very specific cases could require a higher level of expertise to ensure a reliable and efficient operation.

App note: A logic-level transient-voltage protected AC switch

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STMicroelectronics’ AC switch directly controlled by microcontroller. Link here (PDF)

Home appliances such as washing machines, refrigerators and dishwashers employ a lot of low power loads such as valves, door lock systems, dispensers or drain pumps. Since these loads are powered by the mains in ON / OFF mode, they were initially controlled by relays. Recently, relays have been replaced by triacs, due to their smaller size and lower driving energy. Nevertheless triacs don’t fulfill alone the new requirements that users now need and are used with others components.

Power switches must now be directly driven by a microcontroller unit (MCU) and must be robust to withstand the A.C. line transients so that systems may fall into line with electromagnetic compatibility (EMC) standards. ACSs (for Alternating Current Switches) have been designed with this goal mind, i.e. to offer logic level and more robust semiconductor devices.

App note: Low-power battery temperature monitoring

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Low current consumption temperature battery monitoring TMP303 from Texas Instruments. Link here (PDF)

Charging a battery cannot be independent of temperature. In fact, most batteries specify a range of temperatures where charging is permitted. Charging outside these bounds risks damage, failure or worse. To prevent charging when the temperature is too hot or too cold, a temperature sensor and corresponding circuitry are required to disable the charging circuit accordingly. Some temperature sensors like TMP303 already incorporate this functionality. TMP303 monitors the local temperature and asserts its output when the temperature rises above or falls below factory-programmed trip points. This output signal is used to disable the charging circuit.

App note: Stopping reverse current flow in standard hot swap applications

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Application report from Texas Instruments about a simple circuit that blocks reverse currents. Link here (PDF)

The proposed circuit uses an inexpensive operational amplifier to sense the condition of the output voltage exceeding the input voltage, and subsequently disable the hot swap controller, stopping the flow of reverse current (current flow from the output (load) into the input (supply)). The device used for testing this method is the LM5069, configured to provide hot swap control of input voltages from 11V to 22V to a load capacitor of 220 µF. A schematic of the solution and results are provided.

App note: Fast Rail-to-Rail operational amplifiers ease design constraints in low voltage high speed systems

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Migration to lower rail voltages considerations on operational amplifier designs an Application note from Analog Devices. Link here (PDF)

Movement towards lower power supply voltages is driven by the demand that systems consume less and less power coupled with the desire to reduce the number of power supply voltages in the system. Lowering power supply voltages and reducing the number of supplies has obvious advantages. One such advantage is to lower system power consumption. This has the additional benefit of saving space. Lowering overall power consumption has a residual benefit in that there may no longer be a need for cooling fans in the system.

However, as the traditional system power supply voltages of ±15 V and ±12 V give way to lower bipolar supplies of ±5 V and single supplies of +5 V and +3.3 V, it is necessary for circuit designers to understand that designing in this new environment is not simply a matter of finding components that are specified to operate at lower voltages. Not all design principles used in the past can be directly translated to a lower voltage environment.

Reducing the power supply voltage to a typical op amp has a number of effects. Obviously, the signal swings both at the input and output are reduced. The required headroom between signal and rail (typically 1 V to 2 V in conventional amplifiers), which is of lesser importance with power supplies of ±15 V, now drastically reduces the usable signal range. While this reduction does not normally increase noise levels in the system, signal-to noise ratios will be degraded. Because the designer can no longer use techniques such as increasing power supply voltages and signal swings in order to “swamp” noise levels, greater attention must be paid to noise levels in the system.

App note: Resolution enhancements of digital potentiometers with multiple devices

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An old application note from Analog Devices about configuring multiple digital potentiometers to improve resolution, accuracy and programming complexity might add-up to the mix though. Link here (PDF)

Digital potentiometers usually come with standard resistance values of 10k, 100k, and 1MW at a given number of adjustable steps. If an application requires a resistance range that falls between these values, users will most likely apply a part with a resistance larger than needed scarifying resolution. Fortunately, users can parallel, stack, or cascade multiple digital potentiometers to optimize the resolution for a given application. In this article, we will share some of the ideas that may solve the challenge.