converting power supply signal into pulse signal

Recall the schematic you posted early in the discussion (in another thread). I recognized the structure of an SR flip-flop made from two cross-biased transistors. The crucial turn-On trigger appeared to be the detection of the negative supply rail. (This had to occur after the positive rail was already present.)

Soon after that moment the flip-flop turned on the PNP. The PNP conveyed power to the rest of the circuit.

search for “reset ic”.

Hello Brad , I looked at every discussion in the last 3 pages.
Could you say Where is this circuit so i could try and recreate it?
I cant see ant back to back BJT structure.
Thanks.

From several weeks ago:

edaboard.com/threads/voltage-delay-mechanism-question.412199/

I circled the two cross-coupled transistors. Each draws its bias from the other's collector leg (like an SR flip-flop). As far as I can tell the resistors are adjusted so you need to apply the positive supply first and then the negative polarity. This pulls the PNP bias low to turn it on.

Hello Brad, I have tried to implement this circuit as shown below but i cant see it converts my power supply into straight +12V -12V lines on the output.
What did i miss?
Thanks.

First of all, the PNP is vital. It turns On as a result of bias being pulled negative. When the PNP turns On it carries positive polarity supply to the rest of your amplifier.

Secondly, by arranging the two NPN as an SR flip-flop, it stays idle until both positive and negative supplies are present and healthy and stable... Only then it applies 'snap-action' switch-On effect for the PNP.

It's not obvious inside the orange circle although the two cross-biased transistors form the classic SR flip-flop. Someone added the resistor network designed so that -12V at one leg causes a change of state.

Classic SR flip-flop. It requires experimentation to discover what causes a change of state and what doesn't cause a change of state. Different topologies abound such as pulling a bias wire high, or using PNP type, or making it into an astable multivibrator, or monostable, etc.

Hello Brad , Is there some theory manual video manual i could see how BJT can be used for SR LATCH?
I googled it and there is only general plug and play .No rigurous analog theory explanation regarding How exactly its working?
Thanks.

barry said:

search for “reset ic”.

Click to expand...

UPDATE:

Hello, I see reset ic definition ,How can i use it to create a pulse of 12V and -12V from my power supply input?
Thanks.

A reset IC is used mainly for monitoring the power supply voltage of electronic devices to monitor and detect whether the voltage drops below a threshold or exceeds a certain level.

Introduction – What is a Reset IC? – ABLIC Inc.

What is a Reset IC? A Reset IC can Ensure the safe startup of a microcontroller Extend battery life Add redundancy to the MCU Monitor for voltage rises (=

www.ablic.com

yefj said:

Hello Brad , Is there some theory manual video manual i could see how BJT can be used for SR LATCH?
I googled it and there is only general plug and play .No rigurous analog theory explanation regarding How exactly its working?

Click to expand...

You may spot more tutorials about building logic gates (and latches) from NAND gates. Flip-flops are easily built from logic gate IC's, and their operation is more easily grasped.

The reason to include transistors in your power supply is because the rails contain positive polarity and negative polarity, which both must be recognized by your timed logic function, and which both must be turned Off and On with greater current than little op amps or logic gates can handle.

Hello Brad, Is there a way to use a reset IC to make this idea work?
Thanks.

yefj said:

Hello Brad, Is there a way to use a reset IC to make this idea work?
Thanks.

Click to expand...

Sorry, I lack experience with reset IC's.

Remember any method you use needs to work with positive and negative polarity both.

yefj said:

Hello Brad, Is there a way to use a reset IC to make this idea work?
Thanks.

Click to expand...

You said you wanted to "make a pulse", but it looks like you want enable the power supplies, is that right?I'm just not clear what you're trying to do.