Predict this Toggle Circuits behavior

imix500 · 18th July 2006, 05:32 AM

Hello all, so I needed a simple transistor based toggle/flip flop circuit to turn a momentary spst switch into a latching type. This circuit looks ok, but my question is will this circuit power up in the same state every time? If not, is there a way to modify it to do so? Thanks!

janneman · 18th July 2006, 05:50 AM

Hi,

I don't see how this can toggle? Toggling normally involves saturating one half by for insyance pulsing its base so that the other side comes out of conduction, and vice versa. What you do here is momentary increasing the current in both halves. Tghe pushbutton should be between supply and one of the bases (with a series R of course).

The defined switch-on is normally done with something like a cap from supply to one base to delay that half so the other half switches on first.

Jan Didden

sivan_and · 18th July 2006, 06:28 AM

imix500 wrote:

Quote:

circuit to turn a momentary spst switch into a latching type

Is this what ur looking for ?

gmphadte · 18th July 2006, 07:25 AM

u need this.

Gajanan Phadte

cpemma · 18th July 2006, 12:35 PM

Or with mosfet & PNP (starts with PNP off)

imix500 · 18th July 2006, 03:30 PM

Thanks guys. I was wondering about it charging both sides myself. The explanation provided with the circuit said that one capacitor will charge slightly faster than the other and switch first. Not sure if this is right though. Wouldn't be the first time I pulled a bad circuit off the web.
gmphadte, that looks more like what it should be. Any idea if it will power up with one side on every time?
cpemma, neat idea of using a mosfet. Will it toggle on/off?
Thanks!

Duo · 18th July 2006, 03:51 PM

The first curcuit posted will function quite well as a T-Latch (Toggle Latch).

I use it in a lot of my work because of its inherent simplicity.

If you get the values too out of place, it will become an astable multivibrator, which you don't want.

Either way, the circuit does work as stated.

If you want to get it to start in one state all the time, you have to add a little imbalance to it so that it will 'lean' over to that state a bit, but not enough to get stuck there.

imix500 · 18th July 2006, 05:10 PM

Hi Duo, that's good news since I already ordered parts to make up a few to try. I figured I would use the values as is with the only difference being that I'm using 2n2222 instead of the 2n3053.
So, how should one side be "biased" to come on first? Just increase one 2.7k to a higher value?

cpemma · 18th July 2006, 05:51 PM

Quote:

Originally posted by imix500
cpemma, neat idea of using a mosfet. Will it toggle on/off?
Thanks!

Works in simulation, I'm waiting for a small mosfet to try it, 2N7000 also should be OK.

The problem with all toggles is catering for switch bounce, your first circuit may be sensitive.

A couple more circuits here.

imix500 · 18th July 2006, 06:24 PM

Hi cpemma, those look like great designs. One constraint is that I will have to build 24 of these to accomadate 24 switches. Simpler is better both in time to build and space needed. However, if debouncing is going to be a problem I will have to go with a more complicated design. I will raid the parts bin and see if i can build your circuit.
Thanks!

18th July 2006, 05:50 AM	#2
janneman diyAudio Member Join Date: May 2002 Location: Where Germany, The Netherlands and Belgium meet Blog Entries: 6	Hi, I don't see how this can toggle? Toggling normally involves saturating one half by for insyance pulsing its base so that the other side comes out of conduction, and vice versa. What you do here is momentary increasing the current in both halves. Tghe pushbutton should be between supply and one of the bases (with a series R of course). The defined switch-on is normally done with something like a cap from supply to one base to delay that half so the other half switches on first. Jan Didden __________________ /Another new issue: Linear Audio Volume 3!

18th July 2006, 03:51 PM	#7
Duo diyAudio Member Join Date: Jun 2002 Location: Victoria, BC, Canada	The first curcuit posted will function quite well as a T-Latch (Toggle Latch). I use it in a lot of my work because of its inherent simplicity. If you get the values too out of place, it will become an astable multivibrator, which you don't want. Either way, the circuit does work as stated. If you want to get it to start in one state all the time, you have to add a little imbalance to it so that it will 'lean' over to that state a bit, but not enough to get stuck there. __________________ -- Duo, W1ngs, VA7MON, and lesser known handles. -- -- http://www.w1ngselectronics.com -- My Work and Projects --

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18th July 2006, 03:30 PM	#6
imix500 Proud Union Member diyAudio Member Join Date: Mar 2004 Location: Nashville, TN	Thanks guys. I was wondering about it charging both sides myself. The explanation provided with the circuit said that one capacitor will charge slightly faster than the other and switch first. Not sure if this is right though. Wouldn't be the first time I pulled a bad circuit off the web. gmphadte, that looks more like what it should be. Any idea if it will power up with one side on every time? cpemma, neat idea of using a mosfet. Will it toggle on/off? Thanks!

18th July 2006, 05:10 PM	#8
imix500 Proud Union Member diyAudio Member Join Date: Mar 2004 Location: Nashville, TN	Hi Duo, that's good news since I already ordered parts to make up a few to try. I figured I would use the values as is with the only difference being that I'm using 2n2222 instead of the 2n3053. So, how should one side be "biased" to come on first? Just increase one 2.7k to a higher value?

18th July 2006, 06:24 PM	#10
imix500 Proud Union Member diyAudio Member Join Date: Mar 2004 Location: Nashville, TN	Hi cpemma, those look like great designs. One constraint is that I will have to build 24 of these to accomadate 24 switches. Simpler is better both in time to build and space needed. However, if debouncing is going to be a problem I will have to go with a more complicated design. I will raid the parts bin and see if i can build your circuit. Thanks!

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