WOBBLkicad-board.kicad_sch

Will anything on this board overheat with a 2 A LED strip on J2?

Circuit report
2026-10-15 19:19
OK

Works and nothing is stressed: the hardest working part is C1 (capacitor) at 53% of its voltage rating.

hardest part
C1 at 53%
supply power
24.1 W
hottest part
Q1 at 32.7 C
analysis
transient

Confidence high

  • passed KCL, power balance, time step convergence, hand calculation, model provenance

Simulation

Bench setup drawn from this run, with 11 parts on a breadboard, 1 instrument and the measured current on every wire. DC POWER SUPPLY 12.00 V 0.248 A CV a a b b c c d d e e f f g g h h i i j j 1 5 10 15 20 25 30 35 40 45 50 55 60 65 70 104 104 RLOAD_J2 XU1 ATtiny8 MQ1 C1 VOLTAGE 13.2 V OK with J1 at 13.2 V
Bench setup, drawn from this run
Parts and nets of KiCad schematic kicad-board.kicad_sch, listed from the netlist. SCHEMATIC KiCad schematic kicad-board.kicad_sch Drawn as a list, since this circuit is not a simple ladder. PARTS NETS VJ1 p12v 0 12 XU1 p12v 0 p5v U_L7805 C1 p12v 0 100u C2 p5v 0 100n XU2 n_u2_1 n_u2_2 n_ ATtiny85-20PU C3 p5v 0 100n R1 led led_k 330 D1 led_k 0 LED_green_20 R2 gate_drv gate 100 R3 gate 0 10k MQ1 stripm gate 0 m_ MOSFET RLOAD_J2 p12v stripm 6 ground VJ1, XU1, C1, C2, XU2, gate R2, R3, MQ1 gate_drv XU2, R2 led XU2, R1 led_k R1, D1 m_irlz44n MQ1 n_u2_1 XU2 n_u2_2 XU2 n_u2_3 XU2 n_u2_7 XU2 p12v VJ1, XU1, C1, RLOAD_J2 p5v XU1, C2, XU2, C3 stripm MQ1, RLOAD_J2
Schematic, drawn from the netlist

Checks

statuscheckresult
passKCLcurrents into every node sum to zero within 2.40e-09 A (largest at STRIP-, against 18.7 A flowing)
passpower balanceover the run the supplies gave 0.0585 J, the parts dissipated 0.0511 J and the capacitors and inductors stored 0.0072 J (1/2 C V^2 and 1/2 L I^2), 0.33% apart
passtime step convergenceevery part's power and current agree to 0.26% with half the time step; the most moved is C2 current: 6.71e-07 and 5.88e-06
passhand calculationdivider R2/R3: 4.98 V x 10000 / (100 + 10000) = 4.93 V by hand, ngspice 4.93 V (4e-06% apart)
passhand calculationR1 into D1: the diode equation solved by hand gives 5.43 mA, ngspice 5.43 mA (4.4e-05% apart)
passhand calculationU1 dissipates (Vin - Vout) Iout + its own current: 0.136 W by hand, 0.136 W from its pins (2.7e-11% apart)
passhand calculationQ1 conduction loss I_rms^2 R_ds(on) = 1.99^2 x 30 mohm = 0.119 W by hand, ngspice 0.119 W (0.25% apart)
passmodel provenancemodels: 11 from the parts library
infosupply rangesolved at both ends of the supply (J1 10.8 to 13.2 V (10% either way, a guess)); the hardest parts there: C1 at 53%, C3 at 34%, Q1 at 34%

Assumptions

  1. Wobbl guessed: air temperature around the board not given, so Wobbl assumed 25 C.
  2. Wobbl guessed: J2 (LED strip) drives 2A, as set.
  3. U1: L7805 datasheet: 5 V, 2 V dropout at 1.5 A, 2.2 A limit, 35 V most in, TO-220.
  4. C1: 25 V rating as marked, aluminum.
  5. U2: ATTINY85 datasheet: 2.7 to 5.5 V (6 V absolute), about 5 mA running, pins drive through about 40 ohm and take 40 mA most.
  6. D1: green 0805 indicator LED: 3.1 V at 20 mA, 30 mA most.
  7. Q1: VDMOS fitted to the IRLZ44N datasheet: 22 mohm at 10 V, 25 mohm at 5 V, 35 mohm at 4 V, threshold 1.5 V, 55 V 47 A TO-220.
  8. J2 load: what J2 drives, 2A.
  9. Ambient 25 C; temperatures are ambient plus average power times each part's thermal resistance.
  10. Transient: run for 0.0036 s, six of the longest time constant (0.0006 s).
  11. Transient: outputs switch on at power up and off at 60% of the run, so both states and the switch off are seen.