Ground triggered Latching Circuit using transistors

Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
Hi guys,

I am at a complete loss. I have googled Latching transistor circuits and have only found diagrams using 12v Positive triggers, not a ground trigger. I am looking to build a latching circuit using NPN PNP transistors when pulsed by a N.O. switch to Ground.

Requirements:
Has to work with 12v DC to be used in my car.
Circuit Latches when pulse to ground by N.O. switch. Unlatched when SAME N.O. switch is pressed to ground.
Output from transistors need to offer Full Ground when active. Output will activate an 'On Board' 12v SPST Relay And send a Ground signal to illuminate a 12v Lamp 'OFF board'.
No reset switch needed or will be used.
Would like to have LED on board to light when circuit when circuit is active/Latched.

I'm not looking for someone to the work for me. Hoping Someone here can point me in the right direction for answers or send a link that have answers. Doesn't even have use NPN PNP transistors. That just what I am thinking need to be used.

Any feedback will be great and appreciated.

TONY
 

dl324

Joined Mar 30, 2015
9,620
Post a schematic for one of the positive trigger latches you found. Might be as simple as adding an inverter before the trigger input.
 

#12

Joined Nov 30, 2010
18,182
Das ist nicht ein latch. Das ist ein flippen-floppen. You've been looking for a one state circuit and you need a two state circuit. It might be called a bi-stable latch.

This is the wrong one, but it's a start. It shows you need at least 2 transistors to achieve 2 stable states.
 

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Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
Post a schematic for one of the positive trigger latches you found. Might be as simple as adding an inverter before the trigger input.
In all my Google searches .... This was always the first one listed in search results. Its missing the LED and Ground output to External/Off-board 12v Lamp.

Here's the parts list for the schematic.

R1, R2, R4 = 10K,
R3 = 100K,
T1 = BC547,
T2 = BC557
C1 = 1uF/25V
D1 = 1N4007,
Relay = As preferred.


TONY
 

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Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
Relay only flip flop?
Single P.B.
Max.
Yes single Push button, N.O. sends ground to this circuit. The way I imagine this working is .....

Ground pulse in. Activates transistors. Out from main controlling transistor will energize 12v Relay coil AND activates on board LED. I believe a third transistor will be needed to send Ground output to OFF-Board external 12v Lamp. This Third transistor will also be activated by Main controlling transistor.

Am I making sense? ... I have an idea of where I want to go, but have no map to take me there. :(

TONY
 

Alec_t

Joined Sep 17, 2013
10,739
I don't think that linked circuit in post #9 will work for you. Simulation shows it doesn't toggle. Even if the circuit could toggle, the LED would draw>40mA. It's what you might call a flop circuit ;).
 

hp1729

Joined Nov 23, 2015
2,304
Hi guys,

I am at a complete loss. I have googled Latching transistor circuits and have only found diagrams using 12v Positive triggers, not a ground trigger. I am looking to build a latching circuit using NPN PNP transistors when pulsed by a N.O. switch to Ground.

Requirements:
Has to work with 12v DC to be used in my car.
Circuit Latches when pulse to ground by N.O. switch. Unlatched when SAME N.O. switch is pressed to ground.
Output from transistors need to offer Full Ground when active. Output will activate an 'On Board' 12v SPST Relay And send a Ground signal to illuminate a 12v Lamp 'OFF board'.
No reset switch needed or will be used.
Would like to have LED on board to light when circuit when circuit is active/Latched.

I'm not looking for someone to the work for me. Hoping Someone here can point me in the right direction for answers or send a link that have answers. Doesn't even have use NPN PNP transistors. That just what I am thinking need to be used.

Any feedback will be great and appreciated.

TONY
Low in turns something on is no problem. What kind of "latching do you need? Transistor? Relay? How mucg current?
 

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Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
So the relay version won't work?
You mention relay output.
Max.
This circuit I need is for energizing a relay. This relay is for controlling power to other devices in my car and will not exceed 10A. Exampl of items I may want to control are .... Head lamps, Parking Lights, Radio, heat seats, etc....


I don't think that linked circuit in post #9 will work for you. Simulation shows it doesn't toggle. Even if the circuit could toggle, the LED would draw>40mA. It's what you might call a flop circuit ;).
Figures, my life would be too easy if it did. LOL


The last circuit in my write-up may work for you, which uses the same wire for the push-button and the indicator.
The indicators are LEDs if that's okay.
Hi Crutschow, thanks for your help in my previous post. That circuit is up and running fine. :)

The switches I will be using have 12v incandescent light bulbs. I definitely need separate input ground trigger and with separate Ground output to illuminate the 12v incandescent light bulb.

TONY
 

hp1729

Joined Nov 23, 2015
2,304
Hi guys,

I am at a complete loss. I have googled Latching transistor circuits and have only found diagrams using 12v Positive triggers, not a ground trigger. I am looking to build a latching circuit using NPN PNP transistors when pulsed by a N.O. switch to Ground.

Requirements:
Has to work with 12v DC to be used in my car.
Circuit Latches when pulse to ground by N.O. switch. Unlatched when SAME N.O. switch is pressed to ground.
Output from transistors need to offer Full Ground when active. Output will activate an 'On Board' 12v SPST Relay And send a Ground signal to illuminate a 12v Lamp 'OFF board'.
No reset switch needed or will be used.
Would like to have LED on board to light when circuit when circuit is active/Latched.

I'm not looking for someone to the work for me. Hoping Someone here can point me in the right direction for answers or send a link that have answers. Doesn't even have use NPN PNP transistors. That just what I am thinking need to be used.

Any feedback will be great and appreciated.

TONY
Latching version.
Easily adapted to a relay if you want. It just turns on LEDs at this point. It defaults to "Reset" state on power on. You wanted transistors only? Only two PNP transistors required. Untested so far. But in theory it should work.
 

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Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
Latching version.
Easily adapted to a relay if you want. It just turns on LEDs at this point. It defaults to "Reset" state on power on. You wanted transistors only? Only two PNP transistors required. Untested so far. But in theory it should work.
I see 2 switches. How about just a single push on / push off. No reset.

Thanks for ideas guys. This is great. Keep em coming :)
 
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