Wiring Schematic diagram

Although a simple crystal oscillator may be built from one comparator of an LT1720/LT1721, this will suffer from a number of inherent shortcomings and design problems. Although the LT1720/LT1721 will give the correct logic output when one input is outside the common mode range, additional delays may occur when it is so operated, opening the possibility of spurious operating modes. Therefore, the DC bias voltages at the inputs have to be set near the center of the LT1720/LT1721’s common mode range and a resistor is required to attenuate the feedback to the non-inverting input. Unfortunately, although the output duty cycle for this schema is roughly 50%, it is affected by resistor tolerances and, to a lesser extent, by comparator offsets and timings.

Comparator Based Crystal Oscillator Circuit Diagram

If a 50% duty cycle is required, the schema shown here creates a pair of complementary outputs with a forced 50% duty cycle. Crystals are narrow-band elements, so the feedback to the non-inverting input is a filtered analogue version of the square-wave output. The crystal’s path provides resonant positive feedback and stable oscillation occurs. Changing the non-inverting reference level can vary the duty cycle. The 2k-680Ω resistor pair sets a bias point at the comparator + (Comparator IC1a) and – (Comparator IC1b) input. At the complementary input of each comparator, the 2k-1.8k-0.1µF path sets up an appropriate DC average level based on the output.

IC1b creates a complementary output to IC1a by comparing the same two nodes with the opposite input. IC2 compares band-limited versions of the outputs and biases IC1a’s negative input. IC1a’s only degree of freedom to respond is variation of pulse width; hence the outputs are forced to 50% duty cycle. The schema operates from 2.7V to 6V. When ‘scoping the oscillator output signal, a slight dependence on comparator loading, will be noted, so equal and resistive loading should be used in critical applications. The schema works well because of the two matched delays and rail-to-rail outputs of the LT1720.

Source by : Streampowers

This schema is basically a 8W inverter schema. The  schema continues to be intended to drive an 8W fluorescent lamp from a 12V power supply, utilizing an cheap inverter primarily based on a ZTX652 transistor.

The inverter will operate from supplies in the variety of 10V to 16.5V, obtaining efficiencies up to 78% as a result causing it suitable for use in on-charge devices like as caravans / mobile homes / RVs and also periodically charged devices like as roadside lamps, camping lights or outhouse lights etc. Other capabilities on the inverter are that it oscillates at an inaudible 20kHz and that it contains reverse polarity protection.

This lamp schema using ultra-bright white LEDs provides sufficient light for reading purposes while consuming approximately 3 watts of power. In the case of AC mains failure, the battery backup schema instantly lights up the LEDs. When the power resumes, the battery supply is automatically disconnected and the lamp schema again works off AC mains.

The power supply schema consists of 0-7.5V, 500mA step-down transformer X1, rectifier diodes D1 through D4 and filter capacitor C1. Regulator IC 7805 (IC1) provides regulated 5V to LEDs, so there is no variation in the intensity of the lamp light even if the mains power supply fluctuates. A total of ten white LEDs (LED1 through LED10) are connected in parrallel across the 5V power supply. Resistors R1 through R10 (each 56 ohms) are connected in series with the white LEDs to limit the current. To increase the intensity of the lamp light, you can add more LEDs in the same manner; a maximum of 15 LEDs can be used for the lamp.

LED-Based Reading Lamp Circuit Diagram

When power switch S1 is closed, relay RL1 energises to disconnect the 6V, 4Ah battery (connected across N/C contact of relay RL1) from input to regulator IC1 if battery switch S2 is closed. When power switch S1 is open, relay RL1 de-energises and connects the battery to the input of IC1 via N/C contacts of the relay.

Diodes D5 and D6 are reverse-current protection diodes that don’t allow the battery current to flow towards the power supply section. Diode D7 is for reverse polarity protection of the battery. Before connecting the battery, make sure that it is fully charged.

The schema can be assembled on a general-purpose PCB. Arrange all white LEDs (LED1 through LED10) on the PCB. Now remove the bulb holder from the lamp and fix the PCB (where bulb holder was mounted) such that LED light falls on your book properly. No separate reflectors are required for LEDs as the LEDs have inbuilt lens reflectors. Use a heat-sink for IC1 as indicated in the figure.

Caution. Though you can read for hours without eye strain in this lamp light, don’t directly look at white LEDs for long.


Sourced By: EFY Author:  Pranab Kumar Roy