Pulse circuit issue

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sabu31

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Hi all,

I have schematic as attached. I want the GN LED and RT1 led to blink alternatively. And when a 12 V is applied to R29 resistance the RT1 LED should blink and other LEDs should turn off. Presently its working in opposite manner. Can somebody give help in analysing the function/give reference for this circuit. I am attaching schematic.

Thanking you

 

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maybe its just me
the bottom of your schematic, below the values of R20 and R21 is black.
please resend schematic
 

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wwfeldman said:
maybe its just me
the bottom of your schematic, below the values of R20 and R21 is black.
please resend schematic
Click to expand...
I am attaching the PDF of the schematic. Please let me know how to obtain the desired operation as mentioned in post 1. Also how do we attach LTSPICE simulation?
 

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  • Transistor_LED_Circuit.pdf
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RT1 current is blocked by a capacitor, the red LED is permanently off. Post #1 is asking about R29 control input, but unconnected in the final schematic. "Desired operation" can't ever happen.

Please correct the schematic or update the specification.

LTspice .asc file should be zipped.
 

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Thanks FvM for the reply. The capacitor is connected to opto triac. I have updated the schematic and attached the LTSPICE File. The opto triac output presently I have put a resistive load for simplicity.


The R29 should be connected to 12 V for the system to give pulses and operate. The LED GN and RTI should be complementary .

When no input is given to R29, the RT should be on and other two LEDs should be off.

Please let me know if circuit is designed for such operation or if any changes are required.
Also why is the PNP- PNP base connection transistor connection which is then connected to NPN required for such operation? Are there any other simpler methods for obtaining the same function
 

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  • Transistor_LED_SECTION_2.rar
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Hi All,

In order to study the alternate switching of the LEDs , can the above circuit be simplified to as attached. However, while simulating, the LED in path with opto is always off. What factors affect the switching of the LED in opto path.

Thanks
 

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  • Simplified.zip
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Nothing limits the current in D3 and the LED in the opto so they will burn out immediately.
Nothing also limits the current in Q2 and D2 so they will burn out next.
 

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Your simplified schematic will never work.

You may consider a low side NPN switch to opto U1 but must add a current limiting R to collector.
Instead, I used low side NPN Darlington normally drive XP-E2 OFF with open input or 0V and LEDs may be dim but enough to enable Optocoupler. at 10 mA

Here any logic signal may be DC trigger the Opto OFF and 1W LED ON with a power Darlington driver.
Red LED in series affects current limit series R.

my simulation




The XP-E2 will get very hot with 2nd NPN for any large V*I product, so you MUST choose a heatsink or safe current. 2nd NPN must be a TO-220 or equiv. With 12V and only one XP LED will be very inefficient. You could have 3 LEDs.
 
Last edited:

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Thankyou Tony and Audioguru for the reply. I think my simplified circuit post caused a diversion from actual question. The following is requirement.

a) I need to make the circuit in post #5 work with LED Green and LED RT1 to work complementary against input pulse to T6. If no pulse is there Green should be 'ON' continuously. This circuit should work when R29 end is connected to 12V.

b) If R29 is kept open. The led RT should become 'ON' and other two LEDs should be off (thereby indicating no pulses is being send to input of opto)

Please let me understand how this circuit works with similar/alternate references. Also please suggest if there are any minor changes to circuit in post #5 to obtain the required objective .
 

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Thanks FvM for the reply. Can you let me know the circuit's functionality, you may substituting the missing element with alternate.
--- Updated ---

sabu31 said:
Thanks FvM for the reply. Can you let me know the circuit's functionality, you may substituting the missing element with alternate.
Click to expand...
I have updated the circuit by removing the non-standard parts. Kindly let me know how complementary turn is achieved in Green and RT1 LED
 

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  • Transistor_LED_SECTION_2.rar
    1.1 KB · Views: 179
Last edited:

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Audioguru said:
My pc cannot open a RAR file that has not been seen for many years.
Can somebody please open and convert it to a normal schematic (PNG)?
Click to expand...
Here is a RAR utility, attached.


Regards, Dana.
 

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  • winrar-x64-540.zip
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Thank-you for the WinRAR installation trial.
The LTspice simulation says that many parts are rare and have "no definition".
Therefore, I give up with this thread.
 

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Audioguru said:
My pc cannot open a RAR file that has not been seen for many years.
Can somebody please open and convert it to a normal schematic (PNG)?
Click to expand...
RAR and any other compressed file is easily opened with free https://www.7-zip.org/

Then with PTspice installed I opened the .asc file and ^prtsrcn pasted here ^V

I see a ground Opto base as a problem.... open that then use 10k pull up to +v instead so that it uses less current than diode. Beta = 0.25 to 0.5

AG you owe me a coffee
--- Updated ---

Your design requires too many fixes and is overly complicated.

Did you not understand my simple solution is complementary?

If this does not do what you need, define all input outputs explicitly with tolerances and a timing diagram.
 
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    sabu31

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Thanks Tony for the reply,

I cannot change the original circuit as I have to rectify the issue in the existing configuration (using PNP Transistors) (as far as possible)

The secondary of opto is not the issue . I have used opto here (in actual circuit , its opto triac).For simplifying I have used the available model in LTPSICE.You may modify the secondary connection of opto to make it functional( so that it does not affect the primary).

By changing the value of R10 resistor, I have been able to get the delay in the switching of GN LED and RT1 LED (at 100k switching of LEDs are instantaneous, by increasing to 560 K and higher the delay is observed). Now only one issue remains to be resolved, ie. when there is no pulse GN LED should glow continuously and RT1 should be off.

Does capacitor C4 or C1 have any role to play in the LED switching sequence/delay.
--- Updated ---

Audioguru said:
My very old pc opened RAR files in Windows 3.1 (remember dial-up?).
Click to expand...
What is the contribution of the post to resolving the issue.
 

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Hi sabu31,

It took me a while to reply as I wasn't sure of what the LEDs had to do, now I think I understand. Only PNPs was a terrible experience, It just made getting Always A on except when B is on and neither A nor B when C is on convoluted and problematic, adding a couple of NPNs makes the circuit much easier to make work as intended, so my version is three PNPs and three NPNs. It's not great, only a simulation, only tested at 27ºC, component values are rule-of-thumb, but maybe you can adapt the attached schematic to the circuit you have for: LED1 is on all the time, unless LED2 turns on (then LED1 turns off) and if LED3 turns on then LED 1 and LED2 must be off. I understand the third LED has the NPN with it that turns LED1 and LED2 off if input signal 2 is high, or actually the purpose is that the NPN is used as feedback to modulate a real sine wave input at its base and control how much current flows through LED1 and/or LED2 and therefore through the optotriac LED and control the current to a load represented by that resistor shorting the opto output device in the schematic Tony posted? I tested VG1 as a sine wave and then VG2 as a sine wave and the LED1 and LED2 still operate the same and are subserviant to/controlled by LED3 (input signal 2). It's a rough idea and not exhaustively tested.




If all you need is a digital/logic circuit that prioritizes input signals, this is a nice, simple circuit and you can extend it theoretically forever as each stage is only controlled by the preceding parallel stage (and the sum of signals that were fed into that) its own signal and an enable signal, not by a series stage that might lead to fan-out style-limitations:

 

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    sabu31

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Hi sabu31,

Changed the function of LED1 and LED2 (as you seem to have requested in a recent post where you said LED3 function works) for what I think is the circuit in post #15. At power-up, LED1 is off and LED2 (and opto LED) are on and stay on, unless VG1 goes high and then LED1 turns on and LED2 and opto LED turn off, if LED3 turns on then LED1 and LED2 turn off. As the input sine wave signal is not fully visible, I guessed it as 14V at 50 Hz, and chose VG1 arbitrarily.

 

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  • eda led alternate pnps LED1 LED2.JPG
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Thanks d123 for the reply. Your simulation have give new insights to the issue.
 

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