The 2N3906 has an Ic of 200mA, so I would make the base resistor 4.7K. Add a 10K pull-up because the 555 won't necessarily source the full +9V and turn off the xstr.

Check that the transistor is actually a 2N3906 and not something else (such as 2N3904).

Check that the transistor is wired correctly, the Emitter should be connected to +9V, and the Collector to the buzzer/LED. See attached:

 

Since the output of the 555 was overloaded by the transistor without a series base current-limiting resistor and the transistor was over-driven by the 555 then they are probably both destroyed and both should be replaced.

The circuit is missing the two supply bypass capacitors that are recommended on the datasheet for the LM555. The 555 might be oscillating at a high frequency without them and then it will be very hot.
The heat might have destroyed it.

 

Solved the problem. I had an LED and 470 ohm resistor attached to pin 3. for whatever reason when that was removed both the sinking function and the pnp operating function works. thanks for the help. And neither transistor or 555 was burned out.

 

Solved the problem. I had an LED and 470 ohm resistor attached to pin 3. for whatever reason when that was removed both the sinking function and the pnp operating function works. thanks for the help. And neither transistor or 555 was burned out.

That's probably also the reason the buzzer didn't shut off when you connected it from the 555 output to +9V. I don't think you need the PNP. If you have a PNP fetish, it obviously won't hurt anything.

 

haha not a fetish, I'm using the pnp bacause the pnp will be connected to an astable 555 for a beep beep beep

 

Do you have the buzzer connected to the collector ?

 

If you are asking if I have the wires connected to the right leg, yes I do, it works fine now.

 

Let me make it easier ... you have the buzzer connected between ___ and ____.

It's either between the emitter and the 9V supply or the collector and ground.

 

Ron,

If the output of the 555 is a diode drop from the 9 volt supply, that would make the e-b junction of the PNP one diode drop ... or ... forward biased. That could make the buzzer produce softer sounds.

That is the only reason I can think of for the "supposedly off" PNP to be "on". Moving the load to between the power supply and the emitter certainly solves that type of problem, as it decreases the "forward bias".

 

Solved the problem. I had an LED and 470 ohm resistor attached to pin 3. for whatever reason when that was removed both the sinking function and the pnp operating function works. thanks for the help. And neither transistor or 555 was burned out.

Can you tell us what form the final hookup took by attaching an updated schematic?

hgmjr

 

Ron,

If the output of the 555 is a diode drop from the 9 volt supply, that would make the e-b junction of the PNP one diode drop ... or ... forward biased. That could make the buzzer produce softer sounds.

That is the only reason I can think of for the "supposedly off" PNP to be "on". Moving the load to between the power supply and the emitter certainly solves that type of problem, as it decreases the "forward bias".

Joe, I was addressing the OP's statement to the effect that his buzzer still buzzed when the output was high. At that time, he had not indicated that he also had a resistor/LED connected to ground.

If the schematic of the LM555 below (from the National datasheet) is accurate, there is no way the output can sink current when it is high. If there is a pullup resistor to +V, the output should go to +V, cutting off the pullup transistor. However, if there is still a path to ground when the output is high, the output will limit at a couple of diode drops below +V, indeed leaving a PNP on, or a path for a little buzzer current, if he has it connected directly from the output to +V.

 

Yup, Im going to post a final shecmatic of the entire 1-5 minute timer incase any one else here plays hockey and wants a line change timer. but basically I have a standard pnp setup and pin 3 on the 555 goes to a 470 ohm resistor then into the base. I used the 470 cause its was on the bench at the time and if I sub it with a 20k one it wont work... dunno why. and it wont work without one.... anyways it doesnt heat up a bit now, and the occisliscope says everythings fine so im happy

 

Yup, Im going to post a final shecmatic of the entire 1-5 minute timer incase any one else here plays hockey and wants a line change timer. but basically I have a standard pnp setup and pin 3 on the 555 goes to a 470 ohm resistor then into the base. I used the 470 cause its was on the bench at the time and if I sub it with a 20k one it wont work... dunno why. and it wont work without one.... anyways it doesnt heat up a bit now, and the occisliscope says everythings fine so im happy

I just ballparked the suggested value. It is apparent that the beta of the transistor together with the load being driven dictated a smaller value of resistance. 470 sounds a bit on the small side but if it works then who am I to argue.

Once we have a schematic all will become clear.

hgmjr

 

Kevin, as I said once before, we really need to know how much current the buzzer requires before we can recommend a drive circuit for it. Do you have a multimeter? If so, just connect it in series with the buzzer and the 9V supply and measure the current