Halp me /diy/, you're my only hope.
Can anyone explain why pic related is frying my 555 timer? I'm using the CMOS TLC555CP. It works fine at 6 volts but 9 fries it immediately. The highlighted 10 ohm resistor is actually a DC motor. The diode in parallel with it should be protecting the rest of the circuit from the voltage spike caused by the inductor. It's a 4148 diode rated at well over the frequency at which the circus operating. Any ideas?
Is this what you had in mind?
I'm getting less than 1 milliamp through that diode in the simulation. I don't have any equipment to measure the real circuit with but it seems impractical that this would cause a problem.
could be a problem with the 555 chips you have (you might have a bad batch). try running the 555 while drving a led. i've come across 555 chips that were labeled cmos but wouldn't work/overheat at vcc over 5v.
no. the 555 with an LED (also add a resistor to limit current) instead of the motor, that would eliminate any back emf. If it still goes, you've either looked at the wrong datasheet, have a bad batch, ESD'd the fuck out of them, or have an obvious issue with the breadboard circuit.
Post a picture.
That's what I meant. I should have chosen my words better. I'm away from home right now so I can't immediately post a pic. I'll give your suggestion a shot later and post results. Thanks.
ya i distinctly remember running 555s with a 10ohm in series with the power supply just fine. Having a filter right after the resistor should do the trick, but would probably just make the timing more accurate.
seriously just take the 10k resistor out of series with the flyback diode. it's neutering it. unless there's a bad batch or a very obscure problem, the motor's inductive voltage spike is what's killing your circuit. if there was an overcurrent problem you'd be able to feel your 555 heating up for a few seconds before it died.
Think about it this way. Eliminate everything on the output side or your circuit. Pin 3 goes to ground via a 1k resistor. Even if your power rails are a stable 9v source coming in the 555 will destabilize it during the charge cycle while it fills up the timing cap and every time the trigger fires you'll have a relatively high current draw. The power supply can not instantaneously compensate for these draws since it is far away but it will try by increasing current. If that current arrives in the middle of the charging phase it will have no where to go and spike the rail. Because this is happening regularly it will cause the voltage on the rail to oscillate. Add back in your npn transistor and motor drawing relatively massive amounts of current and think what the power rail will look like without a cap to handle those surges. Make sense?
cap and tvs diode to ground from that motor supply. If you are using that bjt to cut the motor off, the motor windings will push the voltage to whatever value it needs to be to push the current stored.
This is my first time hearing of TVS diodes. I'm reading about them now.
The only thing I can add about the transistor is that it works properly at 6 volts. I've tried the circuit with two different 9 volt supplies. The first is a cheap one that isn't a very smooth dc. The second is a switch mode power supply. The cheap one fries the chip in around a 10th of a second. The switch mode ran the circuit for about 5 seconds before the chip died.
then I'd guess you have damaged components. There is no need for a suppression, low pass filter, or any other crap that is being spouted. Try with a purely resistive load. See how the timers react.
It may also be possible that it's not the timer that's dead, it could your bjt. Check that you haven't damaged that. What criteria are you using to determine the timer as dead?
the 1N4148 is a low-current signal diode. it should never be used like this, to kill back EMF. not fucking ever! you want a 1N4001 or better. it's entirely possible the 1N4148 died so it's not doing anything anyway.
You don't know the size of the motor he's driving. A 4148 maybe more than enough to handle it.
Also OP, be wary of anyone in this thread calling the reverse current 'EMF'. EET's would never call it that. The correct term is inductive kickback.
not him. You're retarded. Learn to scroll up before you post a question that has already been asked.
not the guy warning about terminology other use, but he's kind of right. Inductive kickback is just a bit more specific than back emf, it helps with communication. It's still a stupid characteristic to dismiss other's input in my opinion. Also, no one's pointed out that it appears to fail during operation and already has a diode. Powersupply is sufficient, and replacing the load has not yet been done. Make sure the IC can handle the 9 volts (it should, most cmos can handle at the very least 12V). testing with an led/resistive load at the output instead of the motor should give some info without needing an oscilloscope.
Okay all dumb asses, heres the easy way to deal with op's voltage problem, seperate source for the motor, no emf on the 555, and an opto-isolator.
The IC can handle 18 volts according to the spec sheet. I can't remember the max current but it doesn't surpass that in the simulation. Not with the resistive load at least. The simulator is giving me incoherent results for an inductive load. A 9 volt to 9 volt spike. Pic related.
1 nH is the default value of inductors in this app. No idea what the true value is. I set up a voltage divider circuit and calculated a resistance of 10 ohms if that means anything.
Inductive kickback is a current, not a voltage.
I never said to dismiss others input, just be wary of it.
The confusion here seems to be that EMF in electronics stands for electromotive force not electromagnetic field. Electromotive force is synonymous for voltage. So people saying you have to deal with back EMF are actually just saying you have to deal with back voltage when they actually mean back current as the collapsing magnetic field is in fact a current source. Does that explain the terminology difference better?
hate to enter pointless terminology wars, but it seems to me that 'inductive kickback' might be appropriate for pure inductors, like a solenoid, whereas 'back EMF' is appropriate for motors, referring to voltage generated when a motor acts like generator. when you cut off power to a motor, it continues spinning, so it generates back EMF, and probably also has an inductive collapse as well, so presumably both phenomena are present at the same time, and add up.
so you keep doing the same thing over and over again. That's madness.
Try testing the 'fried' chips at lower voltages with other components to tell if they are truly fried. Depending on the motor you are using, the bjt may not be able to switch the current. The diode may not be able to handle the [back emf][kickback][motorshuttingoffdigliddy]. Start probing. Start testing individual components(bjt, diode, 555, power supply, motor, etc.)
quite the opposite. Inductive kickback lumps those two issues together and refers to both motors and inductors. It's simply a more specific form of back emf. Think "fruit" and "tomato."
The only thing I'm doing over and over again is trying the suggestions I keep getting. Every attempt I've made so far has been with a different setup backed by a reasonable prediction that it would solve the problem. I wish I had better test equipment but I don't and unfortunately it's not practical to take this circuit into a lab. I can say with reasonable certainty that the rest of the components are still good because they still function with a fresh chip at 6 volts. The one exception to that statement is the flyback diode, but it's been established that the diode is likely insufficient to protect the circuit for whatever reason. I will hopefully have an opportunity to test the circuit with LED's later.
It was suggested to me by someone else that a 15 volt zener diode from VCC to ground would probably protect the circuit from the voltage spike. Assuming of course that the diode responds fast enough.
Right. So now instead of having 1 inductor kickback I now have two inductors kicking back. I can't picture a scenario where this doesn't make the problem worse but I'm open to further explanation.
I'm going to amend my previous statement. If I put the inductor on VCC they should theoretically kick against each other. It seems like this would create an oscillating effect and cause the motor to behave erratically. I'm tempted to give this a shot just out of curiosity.
The proper term is inductive kickback. If anybody else mentions the term back EMF they will live to regret it. No More Mister Nice Guy! This is your final warning! I mean it! You will use the proper terminology or your board will disappear from the Internet.
I ran the timer with LED's at 9 volts for over 2 minutes with no failure. The LED's got nice and toasty but the 555 and the bjt had no heat change discernable by touch. Other than an act of Jebus punishing me for my wickedness, this narrows it down to inductive kickback. I guess I'll see if radio shack has the diodes I need.
So between adding a 15V zener from pin 8 to ground, replacing the flyback diode with a 4001, adding the cap to the supply rails, and adding some decoupling caps to vcc and ground of the chip, I have a working circuit. I probably gave it more protection than it needs but I'm just glad to have it working.
On a side note this is only part of a larger circuit I'm building. The final circuit will have 3 motors each driven by a 555. I tried one of the other motors on the protected circuit just to see if it would work. The newer motor actually activated the zener where the first one didn't. I know this because I put an LED in series with the zener. It also caused the tip32 bjt to get so hot it died. I burned my finger on it trying to make sure it was still seated in the breadboard. Aside from buying a new bjt that can handle more current, should I put a resistor in series with the zener to protect against the possibility of it overheating?
most all dc brush motors circuits i've seen uses caps across the terminals.
You keep saying that but I'm not sure what you're talking about. A resistor should just limit the current through that loop and keep the associated components from overheating. What am I missing here?
I mentioned earlier I had 3 motors I need to drive. One of the motors originally operated on 4.5 but when I put it on the 9 volt PWM circuit it runs slower even with the potentiometer maxed out. I can't actually see the motor or any other components that might be connected to it, only the power leads. Any ideas what could be causing this?
if you have a 15V zener and you hit with a 20V spike, the zener will eat the spike current, and the voltage across will not go over 15V.
if you put a 1K resistor in series with it, the resistor will limit the amount of current the zener can eat to 5mA, and so your circuit gets the full 20V. so, you're protecting the zener, but not allowing it to protect your circuit.
I thought over this for a while and I suspect what is happening is that there is a capacitor soldered across the leads of the motor in parallel forming a low pass filter. The best solution I can think of is to change the capacitor in the 555 circuit to lower the frequency enough that it's outside the range of the filter.
Does this make sense to anyone else?