transistor circuit with less batteries

[wildebeest87]

transistor circuit with less batteries- Help please

First of all, I'm working with a very limited selection of components, not all of which I've completely identified.
I'm trying to set up a buzzer circuit using a latching transistor to trigger it and leave it on. The problem I've run into is that apparently the transistor can't handle that much load and it doesn't latch. I've solved that by adding another transistor(I think, that's the part I'm not sure about, it works like a transistor, but the legs are setup differently.). With the other transistor in the circuit, the first transistor latches fine, but I have to add another battery to the circuit to function all of that. I've tried a couple different ways to setup the circuit with just two batteries but can't get it to work. I don't see why I can't set up one of the batteries to activate the transistor and to sound the buzzer after it trips. Is it possible? Any help would be appreciated.

 

[Nigel Goodwin]

As you haven't posted a circuit we've no way of knowing - but you need two transistors to make a latch.

 

[wildebeest87]

Sorry, I'm new to the site and pretty new to electronics, I tried my best on the schematic, hopefully it gets the point across. I would like to remove one of the 1.5V batteries and just have the 1.5V and the 9V. But I haven't been able to get it to work. Any help would be great, thanks.

 

[unijabnx2000]

Would this work?

 

[audioguru]

The first circuit has a 1.5V battery burning out the base-emitter of the first transistor and the remainder of the circuit makes no sense. It does not latch.

The second circuit also does not latch so the switch and battery can turn the buzzer on and off without the transistors.

 

[wildebeest87]

i'll try that when i get a chance, but it can't just be one power supply, the first transistor needs to be tripped by another battery. I was going to use an electronic kitchen timer to sound the buzzer, and i want the buzzer to stay on instead of blipping like the timer speaker does.
Thanks for the idea though, i'll definitely be trying that one too

 

[unijabnx2000]

The first circuit has a 1.5V battery burning out the base-emitter of the first transistor and the remainder of the circuit makes no sense. It does not latch.

The second circuit also does not latch so the switch and battery can turn the buzzer on and off without the transistors.

Would my circuit work?

 

[wildebeest87]

The first circuit has a 1.5V battery burning out the base-emitter of the first transistor and the remainder of the circuit makes no sense. It does not latch.

The second circuit also does not latch so the switch and battery can turn the buzzer on and off without the transistors.

Maybe I drew the circuit wrong, I've set the circuit up with all three batteries and the buzzer stayed on just fine. I'm trying to cut it down to just two batteries. There's not actually going to be a switch, the first battery will be from an electronic kitchen timer that i want to sound the buzzer. I want the buzzer to keep sounding, even though the timer beeps.

 

[audioguru]

Would my circuit work?

When the battery is exactly 9.0V then your circuit feeds only about 4V into a 100 ohm buzzer.

Your circuit has a high voltage loss because its transistors are a follower with a loss of 1.8V and the base resistor value is much too high and will also have a voltage loss.
If your transistors are common emitter (the emitter of the second transistor connected to ground and the buzzer connected to tne collectors and to the positive supply) then the buzzer will get a voltage that depends on having enough base current.

 

[wildebeest87]

what about this circuit?

 

[audioguru]

what about this circuit?

The base-emitter of the first transistor will blow up since its base current-limiting resistor is missing.
The circuit still will not latch on.

 

[wildebeest87]

any ideas how to make this circuit work then?

 

[audioguru]

any ideas how to make this circuit work then?

Yes.
Instead of using transistors, use an SCR that has its gate current limited with a series resistor. It will latch on when triggered by the timer.

 

[wildebeest87]

Yes.
Instead of using transistors, use an SCR that has its gate current limited with a series resistor. It will latch on when triggered by the timer.

Does an SCR need another transistor to latch?

 

[wildebeest87]

like i said, i've made the first circuit latch, i just want to try to do that with two batteries instead of three. i'm not sure exactly what kinds of transistors i have, and like i said, my choices are limited. i only have the two kinds that i've used.

 

[unijabnx2000]

Yes.
Instead of using transistors, use an SCR that has its gate current limited with a series resistor. It will latch on when triggered by the timer.

Not exactly knowing the diagram for the SCR the first "transistor" in the drawing is supposed to be a SCR.
I did some research and found that to make a latching transistor without having an SCR on hand, you need a PNP and NPN linked together.

 

[unijabnx2000]

How about this?

 

[unijabnx2000]

Does an SCR need another transistor to latch?

No - remember it latched with just the LED during testing

 

[audioguru]

An SCR is made to latch when it has a small trigger current in its gate pin. Look at it in Google.

Wildebeest,
Your first transistor is missing a base current-limiting resistor so its base-emitter diode is probably burnt out.
There is no positive feedback in your circuit to make anything latch.

 

[unijabnx2000]

Can you draw a circuit to teach us?