Sunday, March 20, 2016

Square and Triangle Opamp Oscillator

Here is the circuit of a Op-Amp based Square Wave Generator. One of the main application of this is in a Simple PWM circuit and Triangle Opamp Oscillator. The Slope of the Triangle wave is compared with a DC Level to derive a pulse width or On-Time proportional to a Voltage.

Tutorials on Basics and Instrumentation Electronics

This On-Time proportional to voltage is for a fixed oscillation rate based on C2-C3 and R15. The C2-C3 form a Unpolarized cap, This type is also used in crossover networks in speaker boxes. This is because, a plastic 4.7 uF (2 * 10uF series) is big and costlier, but a plastic cap is very stable and closer to an ideal cap.

Square and Triangle Opamp Oscillator

First you need to know that most opamps in such circuits can give a square wave, but very few can swing to the rails (+/-5). For designing take 75% of Vcc. CA3130 is one that can swing to rails like a CMOS gate.

Assuming the swing of output is around +/- 4V, the pin 10 + input will be at +/- 2V. When the cap is discharged at 0 V, let us take that the output is +, the cap charges to a little above +2, - input becomes dominant, so output swings negative. This discharges the cap to 0 and then charges it negatively upto -2. This in turn flips the output to + as pin 10 turns dominant. Hence this continues as a oscillation, with a nice triangle across the cap for the PWM comparator.

Dominant means more +, 0 is positive compared to -2V. Also -2.5 is negative compared to -2.2.

Related Reading - Op Amp Triangle-Wave Generator

Friday, March 11, 2016

Tubelight Electronic Choke

This is an electronic choke for a Conventional Fluorescent Lamp. This was an application note of MJE13005 a High Voltage Switching NPN Power Transistor. I Might have modified it. This was very popular in the early days, The Coil Winding and Ferrite is very Critical design.

Emergency Light with Fluorescent Tubes

Tubelight Electronic Choke

The diodes, npn transistor and caps are high voltage 350V-1KV, The tubelight is 40W-60W 5 feet long. This circuit replaced the choke and starter in an existing frame.

Low Cost Simple CFL lamp

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Hobby DIY Electronics