# I just fried a 555 timer IC and I'm trying to figure out how

I'm very new and just fried my first ic, trying to learn a lesson from it.

Here's what I was building:
(also here)

I'm pretty sure I had all the components connected properly but the IC started to smoke and my speaker just clicked. Is 7.5v enough to fry a 555?

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What was the exact part number of the 555 that you used? Intersil ICM7555 for example is rated for 15V operation. Texas Instruments NE555 is rated for 16V supply voltage. But the supply voltage rating depends on the manufacturer's process, so we need the actual manufacturer and part number to answer this question. – MarkU Sep 1 '14 at 5:12
Incidentally, each AA battery is approximately 1.5V, so you only need 4 AA batteries to get 6V. – MarkU Sep 1 '14 at 5:12
Did you build this on a white solderless breadboard? Could you include a photo of what you built? Perhaps there's a wiring error. – MarkU Sep 1 '14 at 5:15
it's actually an NTE955M. It's rated for 18V and the docs say it's a direct replacement for the 555. – user1131308 Sep 1 '14 at 5:21
Yeah, let's see exactly how it's connected up. Photo time... 8) – TDHofstetter Sep 1 '14 at 5:25

No, not generally, not if it's connected correctly. 555s generally can handle a lot more voltage than that. Which specific 555 did you use?

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The 555 - in all its incarnations - is a pretty robust little guy, so if you let the magic smoke out I'd guess that you did something like hook it up to the supply backwards. Especially since six AAs is 9 volts, and if you got 7.5 out when it was connected to the 555, that's some serious current dragging it down.

It's also possible that if your speaker impedance is very low you could be dissipating a lot of power in the 555's output stage, killing it.

I've taken the liberty of redrawing your schematic with LTspice, below, and I've included the circuit list, so if you want to run the simulation all you'll have to do is go here, download the program for free, install it, and run the circuit list.

To do that, copy the circuit list and save it to a file, with a .asc extension, and then left click on the filename. LTspice should find it and present you with a schematic that you can edit, and if you want to run it, right click anywhere on the grey background and then left click on RUN when the menu pops up.

Just as an aside, R4 isn't doing anything much, so it can be removed.

Version 4
SHEET 1 960 936
WIRE -352 96 -480 96
WIRE -288 96 -352 96
WIRE 64 96 -288 96
WIRE -352 128 -352 96
WIRE -288 192 -288 96
WIRE -240 192 -288 192
WIRE 112 192 -16 192
WIRE -352 256 -352 208
WIRE -240 256 -352 256
WIRE 16 256 -16 256
WIRE -352 304 -352 256
WIRE -240 320 -288 320
WIRE 176 320 -16 320
WIRE 176 352 176 320
WIRE 64 384 64 96
WIRE 64 384 -16 384
WIRE -352 448 -352 384
WIRE -288 448 -288 320
WIRE -288 448 -352 448
WIRE 16 448 16 256
WIRE 16 448 -288 448
WIRE -480 464 -480 96
WIRE -352 480 -352 448
WIRE 16 480 16 448
WIRE 176 480 176 416
WIRE -480 592 -480 544
WIRE -352 592 -352 544
WIRE -352 592 -480 592
WIRE 16 592 16 560
WIRE 16 592 -352 592
WIRE 112 592 112 192
WIRE 112 592 16 592
WIRE 176 592 176 560
WIRE 176 592 112 592
WIRE -480 640 -480 592
FLAG -480 640 0
SYMBOL Misc\\NE555 -128 288 M0
SYMATTR InstName U1
SYMBOL res -336 112 M0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -336 288 M0
WINDOW 0 36 43 Left 2
WINDOW 3 49 74 Left 2
SYMATTR InstName LDR1
SYMATTR Value 10k
SYMBOL cap -336 480 M0
WINDOW 0 -23 6 Left 2
WINDOW 3 -41 58 Left 2
SYMATTR InstName C2
SYMATTR Value .44µ
SYMBOL cap 160 352 R0
SYMATTR InstName C1
SYMATTR Value 100µ
SYMBOL res 160 464 R0
WINDOW 0 34 42 Left 2
WINDOW 3 47 72 Left 2
SYMATTR InstName LS1
SYMATTR Value 8
SYMBOL res 0 464 R0
WINDOW 0 -54 37 Left 2
WINDOW 3 -81 67 Left 2
SYMATTR InstName R4
SYMATTR Value 1meg
SYMBOL Misc\\battery -480 448 R0
WINDOW 0 12 95 Left 2
WINDOW 3 17 9 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 9
TEXT -360 616 Right 2 !.tran 1 uic
TEXT -8 176 Left 2 ;1
TEXT -8 240 Left 2 ;2
TEXT -8 304 Left 2 ;3
TEXT -8 360 Left 2 ;4
TEXT -264 368 Left 2 ;5
TEXT -264 304 Left 2 ;6
TEXT -264 240 Left 2 ;7
TEXT -264 176 Left 2 ;8

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Besides that for extra points the battery could use some series resistance (1-2Ω for 6AAs) to show the voltage drop there this is the right answer. The speaker would need to have an impedance of around over 20Ω-30Ω at the ~100-300HZ (depending on the light conditions) this is running at. Not something you would expect from the casual speaker lying around. – PlasmaHH Feb 18 '15 at 12:36

NE555 can output up to 250mA at its output. What is the resistance of your speaker. Perhaps you are trying to get too much from it. If your power supply is about 7.5V and you connect a speaker of 8 ohms, the current will easily peak almost 1A.

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Simply put yes.

The way the circuit is now it does not have a voltage divider between the positive and the chips #8 pin. Most 555 timer chips I have seen can only go up to 5v5 for their max voltage.

That means that the 6v already displayed is to much for them. 7v5 will be 2v more than what should be supplied to the 555.

To fix this you need to calculate the resistors you need when using the 7v5 source or the 6v source.

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you cant really drop voltage like that, with series resistor into an unknown load. Doesn't work like that. Either regulate the voltage properly, or do some other voltage dropping magic. Series resistor into the 555 load will only really act as a current limit and damper of transient response to the 555 current sourcing – KyranF Sep 1 '14 at 5:25
Sorry I meant to say use resistors to make a voltage divider. Not sure why I said to just put in resistors. I will fix that thanks. – deathismyfriend Sep 1 '14 at 5:27
You can't realistically drop the supply with a voltage divider because if the 555 is sourcing current into a low-side load the load will appear in parallel with the grounded divider resistor, and if the 555 is sinking current from a high-side load the load will appear in parallel with the Vcc connected end of the divider, causing both Vcc and the voltage across the load to be either higher or lower than expected. – EM Fields Sep 1 '14 at 8:01
for low power (like, 10mW or something) you can use a shunt regulator diode with a resistor to act as a "voltage divider" that responds to current loads and changes of input voltage. Anyway this entire topic is irrelevant because the input voltage to the 555 timer IC was NOT the issue, as stated by the OP identification of the IC used, where the input voltage rating far exceeds that used in the circuit, therefore it was some OTHER issue. – KyranF Sep 1 '14 at 8:43