need help for my circuit

Mar 15, 2022
28
Hi everyone, i all my life have a passion for electronics, but i never study it, and recently i started to do some research about its basics and fortunately i understand a little bit, i maked some simple circuits and worked fine,
and now i maked a simple circuit i dont know what its can named or its type, this circuit is like the leds flashes ciruits it has two signal output, let say the 1 output and the 2 output, when the 1 is on, the 2 is off and then the 1 turn off and the 2 turn on and the cycle continues,
and the time between this circle is around 1 second but i want to make it very, very fast, so to do that from my understanding is to lower the capacitors value and maybe lower the resistors value without changing the circuit "circuit structure",
so i would like to know if i am correct or wrong, will the circuit work? or to do that the whole circuit must be changed,

the picture of the circuit below, and THANK YOU.

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,100
The structure of your circuit is similar to an astable multivibrator but imho too complex. Look up astable multivibrators, how they operate and how to select components for a specific frequency.

Mar 15, 2022
28
i appreciate your reply, and i will Look up to astable multivibrators, but do you have an idea if i reduce capacitors value like pf or nf capacitors to make the circle faster, does the circle will work?, because i dont have the tool to test that much of speed,
also i want to use this circuit for DC to AC, i will add to it another circuit contain MOSFTs, so i dont know if i am thinking crazy, thanks

AnalogKid

Jun 10, 2015
2,701
You are correct about reducing component values to make the circuit oscillate faster. But not yet.

The circuit has several problems. Please add a reference designator to each component and re-post so we can discuss how they work. A reference designator is a unique label for each part. For example, label the transistors Q1, Q2, etc. R for resistors, C for capacitors. Label the outputs OUT1 and OUT2. also, add a GND connection to the right side of the battery.

This might sound picky, but it is important. Discussing a circuit without reference designators is very difficult, and causes many mistakes. A good, clear schematic is essential to learning electronics.

Also, ***all*** ground symbols point down.

ak

Last edited:

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,100
My apologies if I sound rude, but your circuit makes no sense to me. I rearranged the components and connections a bit to make it conform better to standard circuit diagram layout:

Note that I also labeled the two outputs with different names out1 and out2 to make it easy to distinguish between them. Unless you wanted the two to be connected, that is, which also makes no sense to me.

Since Q4 is always biased in the ON state, Q3 will always be OFF and the circuit is equivalent to this simpler one:

This circuit doesn't oscillate in my simulations. Out2 is at 12 V fixed, depending on the initial conditions (.ic command at the bottom of the screenshot) either immediately or after some time.

Audioguru

Sep 24, 2016
3,653
Your circuit will not work. Here is a common circuit that works, and a warning about damage if the supply voltage is higher than about 6V without using protection diodes.

Attachments

• multivibrator circuit.png
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• multivibrator voltage problem.png
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Mar 15, 2022
28
thank you guys for your help,
i understand that i didn't add references in the circuit, its because the app that i am using for design, it does not allowed to write references,
also i builded this circuit with two LEDs and it work fine, but the time between them (flashes) is around one second,
i designed the circiut now on a pap er with references, also i have a video i filmed it when i tested this circiut, but i am not sure if this website allowed posting videos.

Mar 15, 2022
28

Audioguru

Sep 24, 2016
3,653
Your Q3 is always turned on which always turns Q1 off, then they both are not needed.
I do not see how your circuit works since it is completely different to the normal circuit.

Attachments

• multivibrator project.png
290 KB · Views: 5

AnalogKid

Jun 10, 2015
2,701
Rather than have us guess, why don't you tell us: What is the purpose of Q1 and Q3 in your circuit?

ak

Mar 15, 2022
28
Rather than have us guess, why don't you tell us: What is the purpose of Q1 and Q3 in your circuit?

ak

maybe i am wrong about something, i thought that if i made this circuit without Q1 and Q3 the circuit wont work, because i wanted that the line that feed C1 then to Q2 and the line that feed C2 to Q4 have the same value for perfect timing,
meaning : the resistors of line C1 to Q2 have the same value as the resistors of line C2 to Q4, so i thought in this way the Q2 and Q4 will work togather at the same time, meaning the circuit wont work, so i thought to make Q1 with lower value resistor to work first to cut current of C2 and Q4 to allowed current pass to C1 and Q2 first, in the same time current will pass to Q3 to cut current of Q1 to allowed current pass to C2 but current wont pass until C1 get fully charged.

Audioguru

Sep 24, 2016
3,653
I am showing your wrong circuit again and explaining its errors. I show the correct circuit again.
If the resistor and capacitor values are exactly the same, and the transistors have identical specs then the outputs will be perfect squarewaves with on times identical to off times.
A CD4047 IC has an oscillator built in and has a digital "divide by two" circuit to make two "perfect" squarewave outputs.

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• multivibrator project again.png
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• CD4047.png
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Mar 15, 2022
28
I am showing your wrong circuit again and explaining its errors. I show the correct circuit again.
If the resistor and capacitor values are exactly the same, and the transistors have identical specs then the outputs will be perfect squarewaves with on times identical to off times.
A CD4047 IC has an oscillator built in and has a digital "divide by two" circuit to make two "perfect" squarewave outputs.
like i told you before it work fine, i build it and tested it with my hand, and i didn't do it for oscillator purpose, all i want is just a circuit that give a controlled alternating two signals to use it with another circuit that i will build to converting DC to AC,

i uploaded right now the video showing the operation of the circuit.

kellys_eye

Jun 25, 2010
5,512
i build it and tested it with my hand,
Build it without Q1 and Q3 and save yourself some components. They aren't necessary and do nothing.
i didn't do it for oscillator purpose
What? You state, in the next sentence, that you :
want is just a circuit that give a controlled alternating two signals
which is an OSCILLATOR!

Audioguru

Sep 24, 2016
3,653
Since your supply voltage is 12V which is much higher than the 5V maximum allowed Veb breakdown voltage of the transistors as I showed earlier, then maybe the transistors are breaking down and dimly lighting the LEDs. Then the transistors are slowly being destroyed.

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• transistor oscillator.png
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Mar 15, 2022
28
Since your supply voltage is 12V which is much higher than the 5V maximum allowed Veb breakdown voltage of the transistors as I showed earlier, then maybe the transistors are breaking down and dimly lighting the LEDs. Then the transistors are slowly being destroyed.
even if the power supply is 12v there is resistors to control power, is not?,
i am not educated about electricity, electronics, i never study it.

Mar 15, 2022
28
Build it without Q1 and Q3 and save yourself some components. They aren't necessary and do nothing.

What? You state, in the next sentence, that you :

which is an OSCILLATOR!
i will remove Q1 and Q3 and test it

Mar 15, 2022
28
thank you guys

Audioguru

Sep 24, 2016
3,653
even if the power supply is 12v there is resistors to control power, is not?,
i am not educated about electricity, electronics, i never study it.

The datasheet for every transistor shows Absolute Maximum allowed voltages and currents.
The reverse-biased emitter-base of a transistor is always rated at a maximum allowed voltage of 5V or 6V.
A series resistor limits the current, not the voltage.

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