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Thursday, March 20, 2008

Design Ideas test circuits under load

To discover potential power-supply problems, you must run dynamic and static tests. The simple current sink in Precision voltage-controlled current sink tests power supplies tests low- to medium-power supplies and voltage sources. The current sink can draw current of 0 to 1.5A for an input-voltage range of 0 to 5V with a supply voltage as high as 20V.

Ordinary red LEDs normally function as light emitters, but they can also function as photosensors. In Red LEDs function as light sensors a single LED can even function as both a light emitter and a light detector in the same circuit . The basic idea is to pulse the LED, using the on-time to light it and the off-time to sense the photovoltaic current from the ambient light that the LED sees. The Design Idea presents two circuits: a night light and a day light.

In the noise-generator circuit of White-noise generator has no flicker-noise component, a MAX4238 amplifier has no flicker-noise component in its input-voltage noise. It amplifies its own input-voltage noise with a feedback network comprising low-value resistors to avoid adding noticeable flicker-component noise from either the resistors or the amplifier's input-noise current.

Analog voltage controls digital potentiometer describes an analog voltage that controls a digital potentiometer through the device's I2C interface. An ADC in the Microchip PIC12F683 microcontroller converts the analog voltage to the I2C stream that controls the Maxim DS1803 digital potentiometer and. Of the microcontroller's six general-purpose I/O pins, two control the SDA (system-data) and SCL (system-clock-line) output signals, one controls an LED, and one accepts the analog input. SDA and SCL connect directly to the digital potentiometer's SDA and SCL pins with 4.7-kΩ pullup resistors to VDD.

Energy-harvesting, or "scavenging," systems extract energy from the ambient environment. Unfortunately, these power generators supply much less energy than do standard batteries. However, thanks to the decreasing size and low-power requirements of today's wearable devices, it is feasible to replace batteries in some low-power systems with power generators that capture energy from the user's environment, such as the vibration energy a user produces during walking or running. Harvest energy using a piezoelectric buzzer uses the piezoelectric effect of a standard and easy-to-find piezoelectric buzzer to turn mechanical vibrations into electrical energy.

Universal power supplies must work from mains power lines ranging from 90 to 264V ac at 50 or 60 Hz. Directly rectifying the input voltage charges the filter capacitor to 120 to 370V dc. Such voltages present a serious threat to personnel who are prototyping or repairing the power supply. It is desirable to discharge the filter capacitor when mains power is off so workers can safely deal with the power supply. Retriggerable monostable multivibrator quickly discharges power-supply capacitor presents a solid-state alternative to an energy hungry relay.

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