PWM Design - Page 1
Forum section: electronics / beginners

author: nick.sek
author_rank: Regular Contributor
timestamp: September 12, 2012, 03:15:37 pm
content: Hey guys I'm looking to develop a basic PWM analog device and I was wondering if anyone has any circuit design that I could use to influence my device - and I don't want to base it on the 555 timer.Ideally op amps - and I has thinking about using a triangle wave generator then using that to drive another op amp with a schmitt tiger in order to adjust the duty cycle then followed by a high gain amplifier then followed by a voltage follower. From there it would feed into a NPN darlington transistor circuit which would be able to drive a DC motor at variable speeds.Anyfeedback would be greatly appreciated.Nick

author: Alana
author_rank: Frequent Contributor
timestamp: September 12, 2012, 04:04:58 pm
content: In this configuration I'd go for triangle or sawtooth waveform generator on first op amp. This signal is passed to a comparator on second op amp on which you set your duty cycle.Most op amps should be able to drive low and medium power darlington NPN or mosfet directly so you may use dual op amp IC like LM358.I think this circut can be made so that duty cycle can be controlled with voltage.BTW why you don't want NE555?

author: poptones
author_rank: Frequent Contributor
timestamp: September 12, 2012, 04:52:29 pm
content: I don't understand the desire to not use a 555. Even the darlington part makes this perfectly suited to a pair of 555s.

author: PSR B1257
author_rank: Frequent Contributor
timestamp: September 12, 2012, 05:02:53 pm
content: http://lmgtfy.com/?q=ne555+pwm

author: madires
author_rank: Super Contributor
timestamp: September 12, 2012, 05:20:50 pm
content: There are a lot of circuits based on the LM339. Just google for "LM339 PWM".

author: Simon
author_rank: Unknown
timestamp: September 12, 2012, 05:30:57 pm
content: use an MCU ?

author: nick.sek
author_rank: Regular Contributor
timestamp: September 12, 2012, 10:53:26 pm
content: There is no real reason as to why I don't want to use the 555 timer - other than there is a lot of material out there and it makes my work less credible. This is a mini project that we must produce in order to develop the process of developing a larger project. What now what I am think of doing in order to obtain a PWM is using the 555 timer to generate a square wave with a variable frequency at a constant duty cycle, then passing it through a integrator in order to develop a triangle wave form - then continuing the same idea to achieve similar PWM. Thanks for the feedback and any unique circuits to obtain a PMW would be appreciated.Nick

author: poptones
author_rank: Frequent Contributor
timestamp: September 13, 2012, 05:30:18 am
content: That's a little silly. It's like rectifying AC to make DC then chopping it to make AC again. Sure there are reasons to do that but I don't see any here.If you really want to make it look leet, then put a 75 cent processor on there with a pot to set the duty cycle and a transistor.

author: Simon
author_rank: Unknown
timestamp: September 13, 2012, 03:14:12 pm
content: PWM is so simple and common that almost any solution you chose will not be unique. You could mdo some fancy things with a MCU if you need more than basic pwm generation.

author: TerminalJack505
author_rank: Super Contributor
timestamp: September 13, 2012, 04:22:54 pm
content: If you have the bookThe Art of Electronics(2nd edition) then check out figure 8.66. They basically use an adjustable current source that charges a cap, two comparators (one for the frequency, the other for the duty cycle) and a couple of digital components. The frequency is adjustable from 60Hz to 30kHz. The duty cycle is adjustable from 1% to 99%.