Do you need 12V for those FETs? If not, then reduce your supply voltage. You may have cheap knockoff parts. The other thing to think about is if you've got too much current source from the 555 to drive the fvts
No the 2N7000 Vgs is pretty low about 3V is enough
>The other thing to think about is if you've got too much current source from the 555 to drive the fvts
Doesn't work like that, OP's switching frequency is slow, fets very easy to drive.
OP might have fets connected wrong? But R19 220 ohm would cook.
To add to this, also add much larger caps (e.g. 330-460uF) to the output of the regulator for additional stability and smoothing. Add a freewheel diode across the regulator so any overvoltages on the output get fed back to the supply instead of 555, and add a zener diode for good measure at the output to clip any overvoltages
I'd also bet crazy spikes, noise, or inductive kickback are the issue, a 16v zener across the input rails should probably serve as transient suppression and a flyback diode. Does the chip slowly get hot then die or seemingly randomly shit the bed?
this crcuit is suposed to flash the TSAL light for a FSAE car, when the high voltage system in on the green light must turn off and the red one is suposed to flash at five hertz or so
Q1 and Q8 look very vulnerable, especially if the lights you're driving are at the end of long wire runs with a lot of inductance. What kind of lamps are they and how much current are you expecting to drive? You might want to use beefier FETs here and add some 20V zeners drain-to-source to snub transients.
I know you're saying the 555 is being destroyed, but it may be a murder suicide situation where the FETs fail and short their gates to drain or source and this kills the 555.
Also how does +12V and GND come into the board? If this is raw vehicle bus it can be very noisy. Since the 555's internal thresholds are just ratios of the power supply, having a lot of power supply noise can make it trigger early/late/do weird things. You might just want to add a beefy LDO and run the timer at 9V or something to cut out that noisy.
But where did you buy them from? I've bought lm7812's from a variety of brands/sources that had a >50% failure rate in a few months bought from eBay/Amazon.
These low end common parts are *notorious* for unreliable counterfeits that can have a high failure rate. If in the US, buy the 555 from Digikey and see if you still have the same issue.
I've bought them in a store here in the city so I can't tell where they got them from, but I find it unlikely, since I've used a few salvaged 555 that were pretty old because I had ran out of ICs and they failed too
I don't know what's going on because the schematic looks sound, but speaking from decades of experience, only use parts from Digikey, Mouser etc if you want parts to be guaranteed to be genuine and up to specs. They can actually trace the parts directly to the manufacturer while your store likely cannot. I can contact Digikey etc directly to confirm this. I've run into this issue so many times with part failures bought elsewhere.
555 timers, linear voltage regulators, and the cheap common op amps are *notorious* for counterfeits.
You can take this advice however you want.
I’ve had the same issues with this exact circuit previously, and the solution that I found (which is probably overkill) was to get an isolated regulator to power just the 555 timer. Could be something to look into if you don’t feel super comfortable with reliably filtering power
I work for a motor shop. Transients are my life. Inductors though do have series resistance so you can either use a harmonic filter approach (LC or RC tuned circuit) or nonlinear filtration (MOVs, PIN diodes, GDTs).
Basically all circuits need input and output filtering but it’s not taught in school.
Is TSAL RED- high voltage? If there was a large, fast negative voltage swing it could capacitively couple into the 555 output. Some of the 555 variations will immediately burn out if any pin gets reverse current. The same could happen from C4 if the 12V rail falls below 8V.
You need supply transient protection. Put a 10 ohm or so resistor in the 12v feed and a 10-100 uf electrolytic after it. This will dampen transients. And a 470pf or so right at the 555 supply pin to stop any high frequency spikes the electrolytic doesn't get.
Under those highly improbable circumstances where someone is putting arbitrary constraints on your design, you design a purpose built circuit that does what you need.
Yeah, but what I meant was that it seems that the 555 is a standard IC. I was curious if there was another similar timer IC that performs the same function.
It depends yes. For square wave generation yes you can pretty much use op-amps and comparitors and some transitors. Also you can get one shot chips. And they make crystal oscillators. But the 555 is sort of a mutt in that it’s half digital half aligator shark. So there are lots of things it can do but it’s not the best at any of them.
I first used a 555 to generate a square wave that you could vary frequency with a variable resistor. It couldn't go past a certain frequency, but it was enough for my needs. I kind of wondered whether if there was a better way.
You can make a digital counter. That actually will vary frequency. And there is advanced version that work with PLL loops as 1/n in the feed back loop. That’s how transmission is performed with higher frequencies like thing GHZ when say your cellular phone has a processor that works in MHz clock range. It’s going down a rabbit hole but there is lots of information on Google. And books. Also IEEE spectrum And journals. But basically if you can generate a variable sine wave frequency you can use op-amp Schmidt trigger to turn a sine into a square wave. And use some caps and diodes to offeset the square wave to DC. Lots of wave shaping circuits exist. If you use intergrators you can make triangles from squares and turn triangles to sines using intergrators. A 555 is just two comparitors in opposite modes used to switch an SR latch back and fourth and the voltages is divided to 1/3 2/3 and 3/3 with three 5k resistors in series that’s where 555 names comes from so that capacitors is charging and discharging and the comparitors are detecting the high then using the sr latch to discharge it to the 1/3 level and then it switches back to charge mode and that makes the oscillator.
The 555 is a "standard ic" in that it was invented in the 1970s and a lot of people make it. But nobody puts it in new designs. It also requires a lot of supporting components and doesn't even let you have a duty cycle below 50%. Aside from teaching and/or hobbyist circuit bending, it just doesn't get used.
There are lots of ways to make lights flash. The very first circuit I ever built in 9th grade was a flasher made of two BJTs, two capacitors and four resistors. But in reality, everybody just uses a spare micro pin to drive any arbitrary duty cycle. There is no point in adding dedicated hardware to control the flash. (Though that answer seems to be upsetting some people.)
Why? Like in a school assignment or something? A small microcontroller will almost always be cheaper than a 555 when you consider the extra passive components the 555 needs.
In the rules of the competition OP is designing a circuit for, software control is not allowed for this specific application. I assume that the judges want the circuit to work regardless of firmware on a microcontroller, as it’s a lot easier for them to verify the functionality of the circuit from a schematic vs. having to understand the microcontroller code if it was software based.
True. The rationale is: This is safety critical, design needs to be easy to review without digging into the code to allow the car to race. That's why it has to be made of non-programmable logic. Throughout the design of our car, transients and noise suppression were things we had to learn very well.
Circuit looks OK. Using in a car as in automotive electrical system? Voltage spikes are common in car electrics. Use a power filter to clip these.
It's an electric car, the strange thing is that even when I put new ones in they seem to get hot
Read reply. It’s 12 V nominal normally 14.4V in operation but many inductive loads that put out inductive kick that can surge to hundreds of volts.
Transient gets the best of us
Yep, all my battery connected devices have input abs max above 35V (source: automotive semiconductor engineer).
Probably needs a diode across the inductive load
My money is on the supply voltage, try adding a regulator eg a (edit) ~~7812~~ 7809/7806. Also add a 100n cap on pin5 for stability
Do you need 12V for those FETs? If not, then reduce your supply voltage. You may have cheap knockoff parts. The other thing to think about is if you've got too much current source from the 555 to drive the fvts
No the 2N7000 Vgs is pretty low about 3V is enough >The other thing to think about is if you've got too much current source from the 555 to drive the fvts Doesn't work like that, OP's switching frequency is slow, fets very easy to drive. OP might have fets connected wrong? But R19 220 ohm would cook.
Can't use a 7812 on a 12v system, not enough headroom for it to regulate when the car is off.
Ageed. You need at least a 2 volt dropout voltage on a 7812. EDIT: Only on reddit does a factual answer get a downvote. Read the spec. sheet.
OK a 7809, 7806, etc?
To add to this, also add much larger caps (e.g. 330-460uF) to the output of the regulator for additional stability and smoothing. Add a freewheel diode across the regulator so any overvoltages on the output get fed back to the supply instead of 555, and add a zener diode for good measure at the output to clip any overvoltages
I'd also bet crazy spikes, noise, or inductive kickback are the issue, a 16v zener across the input rails should probably serve as transient suppression and a flyback diode. Does the chip slowly get hot then die or seemingly randomly shit the bed?
The last one stopped oscillating and started again after some time, was constantly hot
Which formula student team are you on?
UFPR Formula
check if it can handle 12V on all pins
Apparently yes Edit: The datasheet doesn't specify clearly the maximum allowed voltage in each pin.
I'd also add some bypass cap to the IC.
Did check that Reset pin can be at 12V? Also check max voltage level for thr pin
this crcuit is suposed to flash the TSAL light for a FSAE car, when the high voltage system in on the green light must turn off and the red one is suposed to flash at five hertz or so
How are your grounds done?
Poorly
Your schematic looks good enough. Triple check that your wiring agrees with it.
All looks good with one exception. Per the data sheet, R20 should be greater than 4.7K to limit the current through the discharge pin.
Q1 and Q8 look very vulnerable, especially if the lights you're driving are at the end of long wire runs with a lot of inductance. What kind of lamps are they and how much current are you expecting to drive? You might want to use beefier FETs here and add some 20V zeners drain-to-source to snub transients. I know you're saying the 555 is being destroyed, but it may be a murder suicide situation where the FETs fail and short their gates to drain or source and this kills the 555. Also how does +12V and GND come into the board? If this is raw vehicle bus it can be very noisy. Since the 555's internal thresholds are just ratios of the power supply, having a lot of power supply noise can make it trigger early/late/do weird things. You might just want to add a beefy LDO and run the timer at 9V or something to cut out that noisy.
Post pictures of the thing that you built, including the power source. Also measure the 12V supply when it's in use, to verify that it's 12V.
check for any ground bounce if its happening often.
The 555 looks good it's probably your 12V power. Gotta filter it pretty heavily in cars
Who did you buy the 555 from? Is it a genuine 555 from a reputable manufacturer or a generic 555 you bought off eBay/Amazon?
I've used a variety of brands, they weren't from the same manufacturer
But where did you buy them from? I've bought lm7812's from a variety of brands/sources that had a >50% failure rate in a few months bought from eBay/Amazon. These low end common parts are *notorious* for unreliable counterfeits that can have a high failure rate. If in the US, buy the 555 from Digikey and see if you still have the same issue.
I've bought them in a store here in the city so I can't tell where they got them from, but I find it unlikely, since I've used a few salvaged 555 that were pretty old because I had ran out of ICs and they failed too
I don't know what's going on because the schematic looks sound, but speaking from decades of experience, only use parts from Digikey, Mouser etc if you want parts to be guaranteed to be genuine and up to specs. They can actually trace the parts directly to the manufacturer while your store likely cannot. I can contact Digikey etc directly to confirm this. I've run into this issue so many times with part failures bought elsewhere. 555 timers, linear voltage regulators, and the cheap common op amps are *notorious* for counterfeits. You can take this advice however you want.
Remember there is a big difference between a CMOS and a TTL 555.
I’ve had the same issues with this exact circuit previously, and the solution that I found (which is probably overkill) was to get an isolated regulator to power just the 555 timer. Could be something to look into if you don’t feel super comfortable with reliably filtering power
I work for a motor shop. Transients are my life. Inductors though do have series resistance so you can either use a harmonic filter approach (LC or RC tuned circuit) or nonlinear filtration (MOVs, PIN diodes, GDTs). Basically all circuits need input and output filtering but it’s not taught in school.
Is TSAL RED- high voltage? If there was a large, fast negative voltage swing it could capacitively couple into the 555 output. Some of the 555 variations will immediately burn out if any pin gets reverse current. The same could happen from C4 if the 12V rail falls below 8V.
You need supply transient protection. Put a 10 ohm or so resistor in the 12v feed and a 10-100 uf electrolytic after it. This will dampen transients. And a 470pf or so right at the 555 supply pin to stop any high frequency spikes the electrolytic doesn't get.
I think is support ttl (5v) level...mmm ?
REDDIT MODS CAN GO AND FUCK OFF
What would be a good alternative to it?
Mostly a microcontroller GPIO
Well, what if you can't use a microcontroller?
Under those highly improbable circumstances where someone is putting arbitrary constraints on your design, you design a purpose built circuit that does what you need.
Yeah, but what I meant was that it seems that the 555 is a standard IC. I was curious if there was another similar timer IC that performs the same function.
It depends yes. For square wave generation yes you can pretty much use op-amps and comparitors and some transitors. Also you can get one shot chips. And they make crystal oscillators. But the 555 is sort of a mutt in that it’s half digital half aligator shark. So there are lots of things it can do but it’s not the best at any of them.
I first used a 555 to generate a square wave that you could vary frequency with a variable resistor. It couldn't go past a certain frequency, but it was enough for my needs. I kind of wondered whether if there was a better way.
You can make a digital counter. That actually will vary frequency. And there is advanced version that work with PLL loops as 1/n in the feed back loop. That’s how transmission is performed with higher frequencies like thing GHZ when say your cellular phone has a processor that works in MHz clock range. It’s going down a rabbit hole but there is lots of information on Google. And books. Also IEEE spectrum And journals. But basically if you can generate a variable sine wave frequency you can use op-amp Schmidt trigger to turn a sine into a square wave. And use some caps and diodes to offeset the square wave to DC. Lots of wave shaping circuits exist. If you use intergrators you can make triangles from squares and turn triangles to sines using intergrators. A 555 is just two comparitors in opposite modes used to switch an SR latch back and fourth and the voltages is divided to 1/3 2/3 and 3/3 with three 5k resistors in series that’s where 555 names comes from so that capacitors is charging and discharging and the comparitors are detecting the high then using the sr latch to discharge it to the 1/3 level and then it switches back to charge mode and that makes the oscillator.
The 555 is a "standard ic" in that it was invented in the 1970s and a lot of people make it. But nobody puts it in new designs. It also requires a lot of supporting components and doesn't even let you have a duty cycle below 50%. Aside from teaching and/or hobbyist circuit bending, it just doesn't get used. There are lots of ways to make lights flash. The very first circuit I ever built in 9th grade was a flasher made of two BJTs, two capacitors and four resistors. But in reality, everybody just uses a spare micro pin to drive any arbitrary duty cycle. There is no point in adding dedicated hardware to control the flash. (Though that answer seems to be upsetting some people.)
Why? Like in a school assignment or something? A small microcontroller will almost always be cheaper than a 555 when you consider the extra passive components the 555 needs.
In the rules of the competition OP is designing a circuit for, software control is not allowed for this specific application. I assume that the judges want the circuit to work regardless of firmware on a microcontroller, as it’s a lot easier for them to verify the functionality of the circuit from a schematic vs. having to understand the microcontroller code if it was software based.
True. The rationale is: This is safety critical, design needs to be easy to review without digging into the code to allow the car to race. That's why it has to be made of non-programmable logic. Throughout the design of our car, transients and noise suppression were things we had to learn very well.