Hello All,
Can someone explain to me how this circuit works as shown in the video FET Phaser Light. I know the working of MOSFET, but how it switches on and off with fading effect.
I found some explanation here in the comment section, but not understood completely.




Thanks

 

At start, all Q s off, Cs discharged. Power on; Cs start charging, say Q1 turns on first- red LED on,C2 slowly discharges thru R4., green LED off, C3 continues to charge turning on Q3 which then discharges C1 turning off Q1
allowing C2 to start charging turning Q2 & green LED on. Make any sense??

 

It's basically a Multvibrator oscillator with 3 transistors.

 

Because a FET doesn't have a very sharply defined turn on/off threshold, as the gate voltage rises and falls the LED current doesn't change abruptly, so fading occurs.

 

At start, all Q s off, Cs discharged. Power on; Cs start charging, say Q1 turns on first- red LED on,C2 slowly discharges thru R4., green LED off, C3 continues to charge turning on Q3 which then discharges C1 turning off Q1
allowing C2 to start charging turning Q2 & green LED on. Make any sense??

I understood what you said, but some doubts,

1. Is this the path for capacitor charging?

During this charging process won't LEDs turn ON, since current flows through them or current isn't sufficient to turn these on?

2. The reason Red ights up first is beause of absence of any resistor in its charging path? Since no resistor it charges up quicky compared to other capacitor (C2 & C3)

3. Is this discharging paths for each capacitor. It discharges through respective FETs when they are ON

C2 discharges through Q1


C3 discharges through Q2



C1 discharges through Q3

 

C1 charges through LED3, R3 and R6, slowly increasing current through Q1. The MOSFETs have an ohmic region where the LEDs will will come on and get brighter as it charges and dimmer as they discharge.

 

C1 charges through LED3, R3 and R6, slowly increasing current through Q1. The MOSFETs have an ohmic region where the LEDs will will come on and get brighter as it charges and dimmer as they discharge.

Why that path ?
Isn't this the least resistive path?


Why through LED3, R3 & R6?

What about remaining capacitors charging and discharging path?

 

There is no path as you illustrate.

 

There is no path as you illustrate.

There's no connection at this point? Then Okay

 

There is no connection there.

The schematic shows 2 connection dots but is missing many more, so I can understand the confusion.

 

Agreed - there are two common conventions for schematics to indicate whether apparent intersections connect or not, and either one is fine as long as you're consistent in applying it. Here, they've been pretty random in applying a mix of the systems, so you can't read the schematic accurately without understanding the intent and making educated guesses. Pretty annoying.

Here are some images from this website's education section that illustrate the two systems:

(copied from: https://www.allaboutcircuits.com/textbook/reference/chpt-9/wires-and-connections/ )

 

Hello,

Here I found a page with information on how to read an electronic schematic:

https://learn.sparkfun.com/tutorials/how-to-read-a-schematic/all

That site also uses the newer convention.

Bertus

 

Hello,

Here I found a page with information on how to read an electronic schematic:

https://learn.sparkfun.com/tutorials/how-to-read-a-schematic/all

That site also uses the newer convention.

Bertus

It's a good read, but not much help when the schematic is drawn poorly in the first place!

 

Hello,

If you would use the newer convention (with the dots) the schematic would look like this:



Bertus

 

Hello,

If you would use the newer convention (with the dots) the schematic would look like this:

View attachment 203628

Bertus

Well done! This should make it easier for the thread starter (and anyone else) to read and understand.

 

 

Thanks for all the replies, but one thing still confuses me is, if all capacitors are charging at the same time, and FET, capacitor rating, resistance they are all same, why all FETs are not triggering at the same time? If that happens all leds will dim and light up at the same time, right? Or is there any other tricky part to that?

This sequential effect will happen only if one FET get triggered first.(as explained in the first reply I got)

So whats the reason for triggering only one FET initially? If you check the video comments there are people saying it is due to there wavelengths, but that has no influence on FET triggering.

And it looks like they're all trigering at the same time

But after that they somehow falls in to a sequential order. What causes this?
Also Why leds are not lighting up when capacitors are charging? Is it due to low current?
And which software is this?

And about understanding schematics, you guys figured out actual connection at the first look, so experience matters

 

no reference to ground until mosfets are on.

 

How much current is in a 2V LED when it has a 1M resistor is series and the supply is 6V? 4uA.
If 12mA is fairly bright then how bright is 0.004mA? Maybe producing no light.

 

With a clear lens, a red LED with 4 uA flowing can be seen internally as a small red dot.