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For a DC to AC transformerless power supply, I am trying to find a specific type of IC that produces PWM that can be filtered into sine wave.

What I can find in most websites is an MCU that has to be programmed to produce such PWM.

I am wondering is there any off-the-shelf IC that available so that I don't have to do the MCU programming. I don't need fancy PWM, just a single purpose IC that produce PWM which can be filter into a sine wave.

To be more precise, the square wave pattern I’d like to generate is shown below:

enter image description here

JRE
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Vincent_CHEN
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  • see timerblox from Linear. they are very good and flexible.... for ex: LT6992. https://www.analog.com/en/products/clock-and-timing/timerblox.html – user19579 Jan 16 '20 at 08:20
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    I mean, what you're kind of trying to do is take an analog waveform, modulate a PWM with it, then filter that, just to get the original analog waveform? Why's that? I think there are plenty of solutions to your problem, I'm just not convinced what you're asking for is what they are. Could you maybe elaborate on **why** you want to low-pass filter a PWM to get a sine wave? For what purpose is that sine wave? – Marcus Müller Jan 16 '20 at 08:46
  • @MarcusMüller I want build a DC to AC converter without involving transformers – Vincent_CHEN Jan 16 '20 at 08:50
  • @MarcusMüller by the way, I just trying to find a IC that takes D.C. input and produces PWM and filter into Sine. – Vincent_CHEN Jan 16 '20 at 08:52
  • (that's a valid use case, and you'd normally achieve that with a cheap microcontroller) Um, stupid question, what do you think your filter will consist of? – Marcus Müller Jan 16 '20 at 08:54
  • by the way, just asking for IC recommendations is explicitly off-topic here, but asking for solutions to problems is not, which is why it's crucial for your question not to be closed that it explains the *problem* you're trying to solve; which is why I added your usage info to the very beginning of it. – Marcus Müller Jan 16 '20 at 08:57
  • @MarcusMüller filter would consist of resistor and capacitor, just a simple low pass filter. Microcontroller is not a perfect solution because it involves programming which is what I am trying to avoid. – Vincent_CHEN Jan 16 '20 at 15:47
  • um, a resistor that burns most of your energy? You're sure you don't want something inductive here? It's usual that you use an LC filter or a transformer-based filter. – Marcus Müller Jan 16 '20 at 22:17
  • @MarcusMüller good point! We may evaluate different scenario – Vincent_CHEN Jan 16 '20 at 22:35
  • _"For a DC to AC transformerless power supply,"_ - so you want to make an [inverter](https://en.wikipedia.org/wiki/Power_inverter)? What AC (rms) voltage and current ratings are you aiming for? – Bruce Abbott Jan 17 '20 at 22:11
  • @BruceAbbott 200V(AC) Vpp is good enough, current is low, 10mA should be good. – Vincent_CHEN Jan 18 '20 at 20:55
  • So you have a >=200V DC supply to modulate? What frequency? – Bruce Abbott Jan 18 '20 at 21:04
  • @BruceAbbott yes. Frequency 10hz-200hz – Vincent_CHEN Jan 19 '20 at 01:04
  • That's an odd frequency range for a **power supply**. Exactly what is the application? – Bruce Abbott Jan 19 '20 at 01:13

3 Answers3

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If you begin with an analogue sine wave (basically an oscillator like a Colpitts or phase shift type), you can adjust it's amplitude to 1 volt peak to peak and feed it into an LTC6992.

  • Pulse Width Modulation (PWM) Controlled by Simple 0V to 1V Analog Input

The LTC®6992 is a silicon oscillator with an easy-to-use analog voltage-controlled pulse width modulation (PWM) capability.

enter image description here

\$R_{SET}\$ adjusts the oscillation frequency of the PWM.

Andy aka
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  • Thanks Andy, I actually want the other way around... generating ac from PWM... – Vincent_CHEN Jan 16 '20 at 08:29
  • Then your question is confusing and muddled. Be totally clear about what you want. – Andy aka Jan 16 '20 at 08:30
  • Edited my question – Vincent_CHEN Jan 16 '20 at 08:40
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    Well, despite your edits, I still offer my answer as a solution to what you have written. – Andy aka Jan 16 '20 at 08:42
  • thanks for your answer, but I don’t have sine input to begin with. I only have d.c. input instead... so I need a IC that takes a D.C. input and output PWM shown in my post. Are you aware any IC that can do this? – Vincent_CHEN Jan 16 '20 at 18:46
  • How will one DC signal define the frequency of the sinewave, its amplitude and the frequency of the PWM cycle whilst simultaneously altering the duty cycle of the PWM waveform. It sounds like you need to do some research on PWM – Andy aka Jan 16 '20 at 18:55
  • then how could MCU which takes one D.C. input and then produces PWM which can be further filtered into sine signal? – Vincent_CHEN Jan 16 '20 at 19:31
  • The MCU has knowledge (in its software) about the PWM frequency, the sinewave frequency, the sinewave amplitude and what duty cycles it needs to run through to produce proper PWM that represents the sinewave of the correct frequency and amplitude. Go and do some research on it. – Andy aka Jan 16 '20 at 20:25
  • i don’t think you know I know these stuff and keep pushing me to do some research (no offense). I’ve done my research and couldn’t find a IC that can produce the PWM(sine wave type) without programming. I actually want a type of preprogrammed IC that contains the software (or actually firmware) already when purchasing them. I don’t need fancy PWMs, just single purpose PWM that do the sine signal job. – Vincent_CHEN Jan 16 '20 at 20:33
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    You won’t find such a chip because there are too many variables involved and how would it compete against an MCU that has PWM outputs under code control AND the MCU can be involved in sinewave amplitude control within a feedback loop AND, it can communicate with a host controller plus monitor current levels via comparators and take corrective action on the PWM signal should it be needed. How can a chip like that you want possibly compete in that market place? – Andy aka Jan 16 '20 at 21:00
  • thanks for your answer which at least saves the time of searching the internet... – Vincent_CHEN Jan 16 '20 at 21:02
  • I added a few more techy reasons to my comment just in case you wanted more information. – Andy aka Jan 16 '20 at 21:05
  • good point and I understand what you’re saying. For some special application, it doesn’t require fancy ‘expensive’ MCU to generate the sine wave PWM :) – Vincent_CHEN Jan 16 '20 at 22:34
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You should use a microcontroller with 'fancy' PWM. This problem is almost purpose built for an inexpensive microcontroller because of the extent to which it needs to be customized (relationship between DC input to AC output frequency and amplitude, output filter configuration, bandwidth...). You can get a microcontroller for less than $1 with an ADC input and PWM output that you can easily program to do exactly what you want.

It seems like you're trying to do amplitude modulation. If you absolutely must avoid programming, you can use the component suggested in Andy aka's answer in conjunction with an amplitude modulation circuit like the one described here: AM Modulator Mixer Circuit. I do not recommend this method, as it will be significantly harder to get working.

Ocanath
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To create the PWM use a comparator with the sine input and a triangular waveform input. The sine input you desire can be generated from an oscillator circuit.

To recover the sine from the PWM, filter the PWM using a low pass filter

OpenCircuit
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