PWM RGB sequencing circuit design - Page 1
Forum section: electronics / beginners

author: CRCLARKE
author_rank: Contributor
timestamp: January 09, 2020, 02:28:08 am
content: I retract my inquiry, my apologies for not approaching this topic in a sufficiently planned way

author: aheid
author_rank: Regular Contributor
timestamp: January 09, 2020, 04:52:25 pm
content: If you don't know what you're doing, IMO you shouldn't be messing with mains voltages. Mains voltages can kill or start fires.Start with low voltage, 12V or 24V, get a solid understanding first.

author: Yansi
author_rank: Super Contributor
timestamp: January 09, 2020, 07:03:44 pm
content: If you are that experienced electrician, at least learn what components have what schematic symbol and do not use a rectangles. I am lately becoming quite allergic on these rectangles.Not to mention the circuit does not seem to be even remotely functional.

author: Yansi
author_rank: Super Contributor
timestamp: January 09, 2020, 07:59:45 pm
content: Problem is, your circuit does not even seem to be correctly hooked up, even looking at the "IGBT rectangles" did not look like a correct pinout an average IGBT has.High voltages of course can be switched with IGBTs, but whats the point of using especially IGBT? Why not other switching components?It seems your question is very poorly built, and seems to be a typical X-Y problem. So, what problem in the first place are you trying to solve with all this?The diagram is horrid sure, an electrician by trade should know at least what schematic symbol a switch has. Took me a good couple minutes staring at that nonsense to even get a basic idea what it should do. Please state the original problem you are trying to solve, then a relevant help can be offered. But not much can be done with a diagram, that is obviously beyond wrong. Hence why other like aheid may want to discourage you from continuing with all this.

author: Yansi
author_rank: Super Contributor
timestamp: January 09, 2020, 09:23:17 pm
content: Quote from: CRCLARKE on January 09, 2020, 08:26:49 pmChildish drawings do unfortunately the exact opposite. Only *duino folks, that can't do any better, need them.Quote from: CRCLARKE on January 09, 2020, 08:26:49 pmYes, exactly this. If you are an electrician, you know how to draw a proper schematic for an engineering forum.But regarding your goal:First, what frequency of PWM does the RGB sequencer output? Only then can one decide of the appropriate power switching device and signal conditioning. (for example, passing a higher frequency PWM through conventional optocouplers is not possible, they are quite slow. Motor inverter IGBTs are also usually switches on the slow side, etc...)Second, why a 240V LED string? That sounds odd. Have you made one yourself? Or have you just soldered a bunch of 12V ones in series? Who will be the end user of that contraption? If just you, then likely fine, you electrocute yourself. But mind you, as an electrician, you shall know about safety a lot. So how are you going to insulate the LED string from a dangerous contact with the end user or even a random lab visitor? Conventional 12V strips are nowhere near safe to be used beyond what is ELV voltage. Removable plastic LED strip cover ain't gonna do it, because removable and the led strip substrate does not have the required dielectric strength against the mounting substrate, which for LED strips may as well be aluminium - unacceptable. Think about this.Also, what for? Even a 5m long string can be fed from just 12V (depending on their power rating of course, some may need shorter sections reinforced with external higher capacity wiring). 240V seems very very excessive.Where are you going to get 240V DC? Just by rectifying mains directly? How about the resulting 100Hz flicker? Adding any filtering capacitance will increase the output voltage, up to sqrt(2) times your input (340V) and also decrease power factor, which, at least in Europe would be problem if the device would need certification.

author: CRCLARKE
author_rank: Contributor
timestamp: January 09, 2020, 09:36:39 pm
content: Quote from: CRCLARKE on January 09, 2020, 02:28:08 am

author: aheid
author_rank: Regular Contributor
timestamp: January 10, 2020, 12:54:02 am
content: I second the suggestion to give more information about what you're trying to do. More details pleaseThe reason I got safety triggered was due to the schematic looking downright dangerous, with high voltage at the wrong places.