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[Help] 555 IC Keeps Blowing Up

Discussion in 'General Electronics Chat' started by Vimal Raj, May 20, 2017.

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  1. chemelec

    chemelec Well-Known Member

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    Sorry I ment to say Drain to Source.
    And Yes the Load Must be: Supply to Drain.
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A DRL is a Daytime Running Light that is supposed to be dimmed low beam headlights or maybe dimmed turn signals lights. Some stupid car companies (Fiat Chrysler, Kia and VW) use high beams at full brightness to blind everybody.
    Why are you using a 555 oscillator at a low frequency to flicker the lights?
     
  3. ci139

    ci139 Active Member

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    555-v-13005.png
    ~chk~chk: /!\ PS /!\ -- all values blow are !! approximate/speculative
    • 12V sys , hfe.13005A=√(15·32)=22 , finding !! I.B values
      • (12.8-1-3·3.2)·1V/(40Ω/5)=280mA , /22=13mA , /9.4=30mA
      • (14.7-1-3·3.2)·1V/(40Ω/5)=510mA , /22=23mA , /9.4=54mA

    • 24V sys
      • (25.6-1-3·3.2)·1V/(40Ω/5)=1.8A , /22=80mA , /9.4=190mA
      • (29.4-1-3·3.2)·1V/(40Ω/5)=2.1A , /22=96mA , /9.4=220mA ***
    . . . there might be higher I.B actual values as (using a speculative hfe normalization hfe.norm=2·√(22)=9.4 ***)
    . . . above hoax is also not strictly following
    555-v-13005-hfe~dr.png
    __________
    fast lab for MJE13005 with 4 in² heat sink mounted : R.CE.ON.min < 1Ω , hfe - depends on many along having a positive temperature coefficient (as junction getting hot passes ever more current)
    555-v-13005-xp.png
     

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    Last edited: May 22, 2017
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  4. dave

    Dave New Member

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  5. Vimal Raj

    Vimal Raj New Member

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    I soldered the things and fitted, works well so far. Yes, MOSFET should have been my first choice(at least for automotive stuffs), will do that next time.
     
  6. Vimal Raj

    Vimal Raj New Member

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    Yes, having on off ratio of 3:1 and cycle of around 10 times per second, you could barely see flicker from sideways but can notice little upfront.
     
  7. Colin

    Colin Member

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    The output of the 555 is about 1v lower than the supply and the base emitter voltage is 0.7v, so you are losing 1.7v with an emitter-follower configuration.
     
  8. Vimal Raj

    Vimal Raj New Member

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    I had to stick with emitter follower since wire from emitter alone is enough to power up led as I can use any near by metal parts as a ground whereas in collector follower I need to have a wire from battery positive to leds and its negative to collector. I don't want to see the wires going all across under the hood.
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    You used an NPN transistor as an emitter-follower when you should have used a PNP transistor or a P-channel Mosfet as a switch to feed the positive supply through resistors to the grounded LEDs.
     
  10. Vimal Raj

    Vimal Raj New Member

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    I want to have 3:1 on-off ratio, using pnp rather than npn will change my on-off ration to 1:3, and I read somewhere that you cannot achieve duty cycle lower than 50% that is more off time than on. So I doubt that I'll get same output by using pnp.
     
  11. chemelec

    chemelec Well-Known Member

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    Actually you can, using a circuit that has 2 Diodes in it.
     
  12. ci139

    ci139 Active Member

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    Last edited: May 22, 2017
  13. Vimal Raj

    Vimal Raj New Member

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    Yes, it will work as inverter I presume. Actually I want to do that in my circuit, since my drl is just below indicator lamp, incoming vehicles could not able see the turn signal clearly. So I should make drl go off when indicator is on, hope using inverter will solve this(don't wanna use relay). I can see variety of inverter solution(i.e RTL, TTL, CMOS) any suggestion that will work best for me.
     
  14. alec_t

    alec_t Well-Known Member Most Helpful Member

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    No. The 555 still behaves as an oscillator, but the On and Off times can be independently adjusted to give a PWM output with a duty cycle variable from typically 5% to 95%.
     
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  15. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Here's the circuit configuration that Alec is referring to:
    Pot P1 allows adjustment of the output duty-cycle over a wide range.

    upload_2017-5-22_13-8-30.png
     

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  16. ci139

    ci139 Active Member

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    nothing 2c here , move on
    [​IMG]
     
    Last edited: May 22, 2017
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  17. Vimal Raj

    Vimal Raj New Member

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    Will try this circuit, seeing many different ways to do the things. Good to have potentiometer to adjust speed as I saw duty cycle changes to different voltages(9 t0 12).
     
  18. ci139

    ci139 Active Member

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    found 13005 model ,
    .model MJE13005 NPN(IS=2.58674e-10 BF=34.4393 NF=0.85 VAF=23.8713 IKF=4.47595 ISE=3.99999e-12 NE=3.5 BR=2.23806 NR=0.75 VAR=2.31727 IKR=9.69329 ISC=5.5e-13 NC=3.9375 RB=2.24801 IRB=0.1 RBM=0.1 RE=0.000429335 RC=0.105551 XTB=0.150853 XTI=1 EG=1.05 CJE=1.38055e-09 VJE=0.4 MJE=0.354762 TF=1e-08 XTF=0.05 VTF=0.1 ITF=142.836 CJC=1.68882e-10 VJC=0.4 MJC=0.347144 XCJC=0.1 FC=0.8 CJS=0 VJS=0.75 MJS=0.5 TR=1.91316e-06 PTF=0 KF=0 AF=1 Vceo=400 Icrating=8 mfg=On_Semiconductor)
    , did some tests 555-v-13005-Rxp.png 555-v-13005-Rxp-b.png i can't see anything critical unless
    • the resistors are way lower than 40Ω
    • the led-s have a dropout below 3V
    • the switching speed or too slow transitions causes timer chip to overheat
    • or using the 13005 without appropriate heat sink ? significantly increases it's base current ?
    • in common emitter configuration the 13005 requires near-greater-equal but not less than 150Ω shunt from B to E
      -- see update @ #31
      -- i haven't used this particular bjt model in common collector - so i can't make guesses about
     
    Last edited: May 23, 2017
  19. Vimal Raj

    Vimal Raj New Member

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    Thanks for these statistics, may be I should do this for all my projects beforehand.

    Being a web developer, I thought I'd never have to use math, I was wrong.
     
  20. ci139

    ci139 Active Member

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    you can't trust the spice but 10% !!!
    coz the models are simplified mathematical (theory -- what we "know"/guess/hope will happen)
    and they are not quantum-mech. - thermodynamic (practise -- much more processor exhausting -- what there most likely will happen)

    the general rule is if something has worked so far -- don't change/loose it
    while you may test the different approach don't switch to it until it has proven justified
     
  21. ci139

    ci139 Active Member

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    i attempted to set up the 13005 based dimmer when i realized that the common collector e.g. an emitter follower setup is not good for current limiting/regulation
    • you can always make sure your led-s not over loaded by choosing the proper resistors **for max Vcc
    • but it's likely more reasonable to build your thing up from 2 modules
      1. a dimmer (generating proper waveform for ↓2.↓)
      2. a led switch (controlling the LED-s current) -- would also ensure enough brightness running from battery only**
    as your next concern may turn out the LED-s not holding up
     

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