Thursday, February 28, 2013

Non-inverting Amplifier Using op-amp

When PiezoDrive PDX 150 amplifier that I used to drive a piezoelectric actuator was damaged, I need to find a way to use an existing spare amplifier. The spare amplifier shown in the following figure has input voltage -2 V to 12 V and output voltage -20 V to 120 V. Its gain is only 10 while the damaged one is 20. Therefore, I decided to design and use an additional preamplifier with gain 2.

The input to that amplifier is -1 V to 6 V and its output shold be -2 V to 12 V. Since I need non-inverted output, I have used an op-amp with non-inverting configuration. I have also used a trimmer so that it is possible to fine tune the gain. Readily available LM358N op-amp IC is arbitrarily picked up. The schematic circuit diagram and resulting amplifier using available components in our lab is shown below. Since the non-inverting amplifier has very high input impedance, I have used additional 56k resister to prevent it from floating.

When tuning the amplifier to get exact gain of 2, it looked unreliable to use peak to peak readings from oscilloscope. That was why, I had to think of an alternative way to achieve it. I set channel 1 which was connected to output of the amplifier to 10 V per division and I set channel 2 which was connected to input of the implifier to 5 V per division. After that, I calibrated the trimmer to get identical waves at the screen :P

Wednesday, February 6, 2013

TRIAC Power Control Circuit

My vacuum cleaner was faulty. I thought the reason might be blown fuse and I tried to fix it. Unfortunately, I could not find any fuse either in machine or connector. I then thought that the reason might be the faulty power control circuit. Therefore, I tried to bypass the control circuit by directly connecting power and motor. But it did not work. Finally, I successfully solved the problem by throwing the old one and buying a new vacuum cleaner :P I kept the power control circuit and tried to trace it when I was free. It uses a simple RC circuit and a DIAC to make a phase lag in firing the TRIAC. The circuit is quite simple and it is shown below.