Ground triggered Latching Circuit using transistors

Thread Starter

stillgrowingup

Joined Jul 15, 2015
210
Simulation shows it won't toggle. It would be better to base your circuit on the tim17 bistable you linked to in post #22. That bistable will toggle ok with a ground-going pulse, provided the pulse source has a pull-up to >1V (e.g. to V+).
I modified it for my application. See attached.
I have to agree it doesn't toggle. And for LED D2 instead of 330 ohms, maybe 1K.
I've used a 1k resistor in another circuit. LED did not illuminate. I kept change resistor out til LED came on with 330.

I have no suggestion for making it toggle without a lot more circuitry.
What MrAI stated, definitely seems to be "lot more circuitry".

Hi,

I believe what you need would be equivalent to a JK master/slave flip flop.
Check into that and see if you can use that.
That is VERY detailed. But, I do not even know where to begin on that drawing. Is there an "Over my Head" emoji for your response. :)

That one should work. You have wide latitude in resistor values and probably don't need the resistors across the B-E junctions.
I didn't included those resistors in my newer drawing.

------

Thank you for all your responses. You guys are great help. I did create a newer drawing based in the TIM17 drawing from post #22.

I need it to be GND trigger pulse Push ON/Push OFF. Have GND Out to illuminate 12v Bulb. Drive a LED when circuit is Active. Latch a 12v relay.


TONY
 

Attachments

cmartinez

Joined Jan 17, 2007
7,879
I modified it for my application. See attached.


I've used a 1k resistor in another circuit. LED did not illuminate. I kept change resistor out til LED came on with 330.



What MrAI stated, definitely seems to be "lot more circuitry".



That is VERY detailed. But, I do not even know where to begin on that drawing. Is there an "Over my Head" emoji for your response. :)



I didn't included those resistors in my newer drawing.

------

Thank you for all your responses. You guys are great help. I did create a newer drawing based in the TIM17 drawing from post #22.

I need it to be GND trigger pulse Push ON/Push OFF. Have GND Out to illuminate 12v Bulb. Drive a LED when circuit is Active. Latch a 12v relay.


TONY
Q1 is backwards. Its emitter should point to ground. Otherwise your circuit won't work.

Here's an example:

transwitcho.jpg
 

dl324

Joined Mar 30, 2015
15,453
I did create a newer drawing based in the TIM17 drawing from post #22.
Could you draw your schematics in the conventional way (e.g. ground pointing down)? In general, flow should be left-to-right and top-to-bottom. If you use the connection dots method, you don't need the crossover "humps".

There won't be much current in the LED the way you have it connected.
 

Thread Starter

stillgrowingup

Joined Jul 15, 2015
210
Could you draw your schematics in the conventional way (e.g. ground pointing down)? In general, flow should be left-to-right and top-to-bottom. If you use the connection dots method, you don't need the crossover "humps".

WIll do.

Thanks

TONY

Update Edit: I did change things to match what dl324 recommended.
 

Attachments

Last edited:

hp1729

Joined Nov 23, 2015
2,304
I modified it for my application. See attached.


I've used a 1k resistor in another circuit. LED did not illuminate. I kept change resistor out til LED came on with 330.



What MrAI stated, definitely seems to be "lot more circuitry".



That is VERY detailed. But, I do not even know where to begin on that drawing. Is there an "Over my Head" emoji for your response. :)



I didn't included those resistors in my newer drawing.

------

Thank you for all your responses. You guys are great help. I did create a newer drawing based in the TIM17 drawing from post #22.

I need it to be GND trigger pulse Push ON/Push OFF. Have GND Out to illuminate 12v Bulb. Drive a LED when circuit is Active. Latch a 12v relay.


TONY
Rough draft of a J-K flip flop ...I haven't got it to work as desired yet. Basically two flip flops. The lower one follows the switch. The upper one follows the lower one and retains the state after the switch is released.
 

Attachments

Thread Starter

stillgrowingup

Joined Jul 15, 2015
210
Rough draft of a J-K flip flop ...I haven't got it to work as desired yet. Basically two flip flops. The lower one follows the switch. The upper one follows the lower one and retains the state after the switch is released.
Thank you. Will the 2 onboard LEDs be necessary? I only need LED to be on when Latch circuit is active.


Where would the Relay go? I do not see an output on the drawing? Same spot as LEDs?

TONY
 

Thread Starter

stillgrowingup

Joined Jul 15, 2015
210
The last schematic you drew was for a toggle flip flop; you don't need a JKFF (it has twice the components you need).
My gut told me the same. But I'm so green on this, that I was not sure.

Does my Last drawing same valid? ... Please look at post #42 and #44


TONY
 

Thread Starter

stillgrowingup

Joined Jul 15, 2015
210
Q1 is still connected wrong and the LED current is limited by R1+R3 so you're only going to get a few mA (and personally, I wouldn't load the output of the flip flop that way).
I changed the Q1 and put more stress on the BD140 output, not the flip flop.

I'm looking at the output of the Flip flop to deliver 12vdc out ... Not Ground. Correct?

TONY
 

Attachments

dl324

Joined Mar 30, 2015
15,453
I changed the Q1 and put more stress on the BD140 output, not the flip flop.
Do you mean BD139? The rule of thumb is base drive needs to be 0.1X collector current in a switch. What is the coil resistance?
I'm looking at the output of the Flip flop to deliver 12vdc out ... Not Ground. Correct?
Yes. LED, lamp, and relay will be on when Q3 is off.
 

Thread Starter

stillgrowingup

Joined Jul 15, 2015
210
Do you mean BD139? The rule of thumb is base drive needs to be 0.1X collector current in a switch. What is the coil resistance?
Yes. LED, lamp, and relay will be on when Q3 is off.
Yes, BD139. Oops! .... Coil Resistance is 320 ohms.

I wasn't sure. How all the ground and power flows through all the components. So I wasn't sure if the Out was 12v or GND. .. Like I said before. I'm green on this. ... But Learning, :)

TONY
 

dl324

Joined Mar 30, 2015
15,453
Yes, BD139. Oops! .... Coil Resistance is 320 ohms.

I wasn't sure. How all the ground and power flows through all the components. So I wasn't sure if the Out was 12v or GND. .. Like I said before. I'm green on this. ... But Learning, :)
Total current in the power transistor is about 300mA so loading on the flip flop is too high.

I suggest you add a PNP transistor to drive the BD139 and use a LOW output from the flip flop to turn everything on.

I'd also reduce the current in the LED. It's just an indicator, so 5-10mA is probably sufficient.

upload_2016-2-11_9-33-34.png
 

cmartinez

Joined Jan 17, 2007
7,879
Total current in the power transistor is about 300mA so loading on the flip flop is too high.

I suggest you add a PNP transistor to drive the BD139 and use a LOW output from the flip flop to turn everything on.

I'd also reduce the current in the LED. It's just an indicator, so 5-10mA is probably sufficient.

View attachment 100487
Shouldn't you bias Q1's base to ground with, say, a 10k resistor?
 
Last edited:

hp1729

Joined Nov 23, 2015
2,304
Thank you. Will the 2 onboard LEDs be necessary? I only need LED to be on when Latch circuit is active.


Where would the Relay go? I do not see an output on the drawing? Same spot as LEDs?

TONY
The LEDs are just for monitoring the operation. Once we get something that works we can add relay and stuff.
 

Thread Starter

stillgrowingup

Joined Jul 15, 2015
210
Total current in the power transistor is about 300mA so loading on the flip flop is too high.

I suggest you add a PNP transistor to drive the BD139 and use a LOW output from the flip flop to turn everything on.

I'd also reduce the current in the LED. It's just an indicator, so 5-10mA is probably sufficient.

View attachment 100487
Thank you for the drawing. How would you trigger the circuit?

I couldn't get this one to toggle. (Used 2N3904 instead of 2N3906.)
Are you saying my least Drawing in post #51 doesn't work? But swapping the 2n3904 to 2N3906 will make it work?

TONY
 
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