Sine wave inverter  - Page 1
Forum section: electronics / beginners

author: NASK
author_rank: Contributor
timestamp: June 15, 2018, 09:00:00 am
content: i need to utilize sine wave inverter, here i go with 50Hz/ Vp=4V sine wave and 500Hz/ Vp=5V triangle wave and it gave to 741 to generate PWM signal. out put is Capture1.PNGwhen i going to increase triangle wave frequency to 1KHz it out put is Capture2.PNGi think 1KHz signal is not making required PWM Pulses and need to clarify 500Hz triangle wave ,is it enough to this type of designs.Furthermore, I add a H-Bridge and a transformer (pri 100mH, sec 10mH,) as following Capture4.PNGand its out put is Capture3.PNGi need to Utilize 230V,50Hz ,5A max sine wave inverter, Am I missing some steps to do this?

author: David Hess
author_rank: Super Contributor
timestamp: June 15, 2018, 04:03:04 pm
content: The 741 is too slow to be used as a pulse width modulator. Operational amplifiers are not really suited for this application and a comparator should be used instead.

author: Audioguru
author_rank: Super Contributor
timestamp: June 15, 2018, 04:40:58 pm
content: 50 years ago the designers of the lousy old 741 opamp did not dream that anybody would use it for Pulse-Width-Modulation. Its slew rate is 1/10th the speed of ordinary modern opamps.When a comparator is supposed to be used then don't use an opamp.

author: firewalker
author_rank: Super Contributor
timestamp: June 15, 2018, 05:01:59 pm
content: If you are a beginner it would be easier to use a center tap transformer and drive it with two n-channel low side mosfets.Alexander.

author: NASK
author_rank: Contributor
timestamp: June 19, 2018, 02:57:18 am
content: thanks for support, adding LM111 comparator able to increase triangle wave to 10kHz and made a pwm. Capture2but i need pwm pulses in both positive and negative sides like Capture1in my reference pdf(http://www.ti.com/lit/an/slaa602a/slaa602a.pdf) it did through this circuit Capture3. its non inverting input connected through like "not gate " i think its not possible, then how to make this circuit.

author: NASK
author_rank: Contributor
timestamp: June 20, 2018, 04:24:32 am
content: could you help me to solve this issue.i need to generate 3level pwm signal, therefor i went on following procedures 10kHz/ triangular wave and 50Hz square wave summing amp & generate bipolar triangular with 10kHz : Capture4After that give it to comparator with 50Hz sine wave with 180 phase shift :Capture3but out put wasn't 3 level PWM, it just two level pwm :Capture2could i know the reason for it ?

author: NASK
author_rank: Contributor
timestamp: June 29, 2018, 12:01:12 pm
content: It took me few days to understand the concept and I would like to share with other ad find the attachment.

author: Nitrousoxide
author_rank: Regular Contributor
timestamp: June 29, 2018, 04:18:22 pm
content: If you want to use either a half or full H bridge topology you need to include gate drivers to combat the effects of gate capacitance/charge times. Gate drivers allow for the high side mosfets to switch as you cant reference to the centre of the totem pole. They usually achieve this through the use of optical or magnetic isolation. There are plenty of gate driver chips that achieve these tasks.Alternatively, you can use a push-pull configuration as mentioned before, however, you will need a transformer with two identical primary windings to prevent flux walking. A push-pull configuration doesn't suffer from the issue of ground referencing.Either way, for both topologies you will need to generate sine pwm (SPWM).Also, you will need some form of dead time circuitry to prevent shoot-through (and thus a massive current draw).