problem with 555

[Thunderchild]

so I made the atached circuit with the adition of a mosfet conected to the output, gate to 555 output source to nneggative drain to motor to be controlled and of course the motor between the + and drain, the 555 I think burnt out it got very hot and considering there is not much load and it can handle 500 mA output cant figure what went wrong.

 

[Hayato]

so I made the atached circuit with the adition of a mosfet conected to the output, gate to 555 output source to nneggative drain to motor to be controlled and of course the motor between the + and drain, the 555 I think burnt out it got very hot and considering there is not much load and it can handle 500 mA output cant figure what went wrong.

Did you put any current limiting resistor between the 555 Output and the MOSFET Gate?
We have to remember that the GATE and the SOURCE or the BASE and the EMITTER forms a diode-like connection, so they are practically shorted. We need current limiting resistors.

Another thing, the 555 maximun current output is about 200mA, not 500mA. And, I have noticed that 555 does not like the voltage supply above 9V, it gets very hot with voltages above 9V.

Thanks.

 

[Thunderchild]

well no i had no resistor and it is 12 car battery for car fan
not in car thought

 

[mramos1]

Thunderchild:

Just wondering, what are you tring to do with the fan in the car?

I live in Florida USA, very hot here most of the time (90's today and humid). I was just in the (very hot) garage and thinking about a thermistor and 12F509 PIC to flip on a fan in the car, I have not figured where I am going to vent the hot to yet.

On the 555 issue, what size resistor did you have to the gate? If all the wiring is good, the 555 can handle a car battery easy. If you plan to use it on the car running, think about the alternator noise and extra volts, though it is still in the specs.

 

[Thunderchild]

everything is off the car it is the remants of my dead car
I have yyet to put a resistor on the gate, is the 555 unprotected from shorts ? I tried measuring the ohms on the most and it was off the scaled I thought the impedence of a moss was megaohms or at lest 100's of K

 

[Thunderchild]

could I have blloown the most as well ? it is and irf 540

 

[Hayato]

Hmm.

But what was the resistor value?

The 555 is unprotected.

Yes, MOS have high impedance, but that does not apply to DC-like applications.

I don't know if it has blown up, but it's a possibility.

Like MRamos said, if you are going to use the 555 in your car, remember to stabilize the 555 supply, with 12V zeners + transistor regulators to get 12V, or a 7805 to get 5V.

Imho, I prefer to supply the 555 with 5V, because it does not get hot.

 

[Thunderchild]

used a resistor some breif spurts and the 555 overheatd, there was no pproblem while the 555 was not conect to the mos it produced a variable voltage based on the potentiometer position, shout I use a reveresed Diode on the motor for spikes ?

 

[mramos1]

Hayato: Same here, let the regulator take the heat and the caps filter the noise. I basically make a simple 5VDC power (LM7805) supply for the car..

Not that this will fix his 555 driving the FET. But the voltage is low and stable.

I do use the 12volts to power relays though, 12V relays seem to be easy to get and cheap.. Again, with current limiting on the transistors driving them.

 

[Hayato]

Thanks MRamos.

used a resistor some breif spurts and the 555 overheatd, there was no pproblem while the 555 was not conect to the mos it produced a variable voltage based on the potentiometer position, shout I use a reveresed Diode on the motor for spikes ?

I know you used a resistor, but what was it value!?

Yes, you should use a reversed diode to protect the mosfet from spikes.

 

[mramos1]

Yes protect the FET from inductive spike.

 

[Thunderchild]

here is the current diagram unless a reverse spiike can backfire thru the gate to the output of the 555 I can't see how it was damaged

 

[Hayato]

here is the current diagram unless a reverse spiike can backfire thru the gate to the output of the 555 I can't see how it was damaged

Well, I don't think a spike generated from a 12V dc motor is capable to do such a damage, but it's always possible. So use a diode protection on the motor.

I think that the main problem there was the 555 supply and something else (I don't know, but something is telling me that it was not 1k).

Try to supply the 555 with 5V to see what happens.

 

[Thunderchild]

is 5 volts still enough for the driving of the mos ? this this is supposed o run on 18 volts and this is a standalone car battery so no mains hum or spikes and works fine til i put the mos and motor on it, I use my meter and turned the pot and got a variable voltage.

 

[mramos1]

Move the motor line from VCC to 12VDC of the car battery.

 

[AllVol]

Whoops!

According to your attached schematic, you have the 555 wired wrong, omitting the timing resistor(s) on pin 7. Check out my attached from 555Timer.Pro.

AllVol

 

[Hayato]

Whoops!

According to your attached schematic, you have the 555 wired wrong, omitting the timing resistor(s) on pin 7. Check out my attached from 555Timer.Pro.

AllVol

It's not wrong, AllVol, it's just another configuration for the astable operation.

Thunderchild,
I suggest to take those diodes out, I don't know why they are there.
When 555 is wired in 5V, maybe it wont drive the MOSFET, but just assemble a simple "voltage amplifier".

 

[audioguru]

I suggest to take those diodes out, I don't know why they are there.

The diodes cause the setting of the pot to create Pulse-Width-Modulation to control the speed of the motor.
Your circuit is a variable frequency oscillator with a fixed pulse duty-cycle so the motor's speed remains the same.

 

[Thunderchild]

whos circuit audio guru ?
mine on it's own with a meter on the out put and turning the pot shows a variable voltage so I presume that it is ok problems are when the mos and motor are put on am I controlling the mosfet correctly. it has been suggested that I use a capacitor on the mos gate and I though of a diose as well perhaps ? to stop reverse pulses, I also thought about putting a diode in series with the 555 to help protect it from reverse spikes as i suppose the motor could act as as a reversed power supply to the 555 so that is perhasp the wisdom in powering it by a 5 v regullator to protect it but a diose should do this ?
is a diode on the motor recomended ?

 

[Hayato]

The diodes cause the setting of the pot to create Pulse-Width-Modulation to control the speed of the motor.
Your circuit is a variable frequency oscillator with a fixed pulse duty-cycle so the motor's speed remains the same.

Thanks, Audioguru.

Thunderchild
Yes, you need to use a reverse diode on the motor coil.