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I am trying to simulate TLC555. Simulation results don't show any issue except that the out is almost negligible.


1 Answer 1


In SPICE, "10M" means "ten milli-ohms". To get ten megaohms you need to say "10MEG".

So you have connected a 10m\$\Omega\$ resistor between the output and ground, which means that the low output is expected.

Change the value of R3 to 10000K or 10 MEG.

SPICE hails from the 1970s, an era when accommodating both upper and lower case characters was considered a bit of a luxury for serious computations.

  • \$\begingroup\$ Which simulator does OP use? Some know the difference between the ‘m’ (milli) and ‘M’ (mega) suffix. \$\endgroup\$ Commented Apr 10, 2022 at 21:37
  • \$\begingroup\$ @hacktastical obviously one that doesn’t , with ~200mA flowing into a “10M” resistor. Looks like the Orcad interface, so likely PSPICE. \$\endgroup\$ Commented Apr 10, 2022 at 21:41
  • \$\begingroup\$ Wow, that’s pretty lame on Cadence’s part that they don’t get that right. \$\endgroup\$ Commented Apr 11, 2022 at 0:26
  • \$\begingroup\$ @hacktastical well, it's backward-compatible so it doesn't break MH inductors or whatever. Always with the trade-offs y'know. \$\endgroup\$ Commented Apr 11, 2022 at 0:27
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    \$\begingroup\$ Quick check: LTSpice forcibly translates 'M' to 'm' (milli). You have to explicitly enter 'meg' to get 10e6. You can also enter '10e6'. As good as LTSpice is, I think this is broken. As for the other sims, here we have a user who got tripped up by it in Pspice. So, also broken. On the other hand Falstad gets it right, SI-unit wise: 'M' is correctly interpreted as 'mega' (10e6.) \$\endgroup\$ Commented Apr 12, 2022 at 0:20

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