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  1. KrisBlueNZ

    Op-Amp Problems, constant output voltage

    OK, you need to modify that circuit to work from a single supply. You need to create a "virtual" or "derived" ground rail at around half the supply voltage. Then you need to return R2 and R3 to this rail instead of the 0V rail. A derived ground rail is typically created using two equal...
  2. KrisBlueNZ

    Comparator inputs

    A comparator just compares two voltages. There's no requirement that one of those voltages is a fixed reference voltage. You just need to ensure that the two inputs are always within the operating range of the comparator. A comparator compares instantaneous voltages. Your current transformers...
  3. KrisBlueNZ

    Op-Amp Problems, constant output voltage

    That circuit is designed to use split supply rails. The positive supply pin on the LM324 should be positive relative to the 0V "common" rail (the earth symbol in the schematic) and the negative supply pin should be negative relative to the 0V rail. The LM324 is a "single supply op-amp" but that...
  4. KrisBlueNZ

    1 Mhz oscillator needed

    http://www.digikey.com/product-detail/en/FXO-HC735-1/631-1122-1-ND/1868762 (3.3V supply, SMT) http://www.digikey.com/product-detail/en/MXO45HS-3C-1M0000/CTX745-ND/1801860 (5V, THT)
  5. KrisBlueNZ

    SMPS boost regulator using a schmitt trigger oscillator

    I guess that's because the transistor in the feedback loop will respond to a pretty low base current. I was thinking that you might want to add a base-emitter resistor there, to make it more immune to the zener's leakage current. Do zeners become more leaky with age? I guess they'll be more...
  6. KrisBlueNZ

    SMPS boost regulator using a schmitt trigger oscillator

    Cool Steve :-) This is quite interesting.
  7. KrisBlueNZ

    SMPS boost regulator using a schmitt trigger oscillator

    Cool Steve, thanks for the update. I'd be interested to see its performance at a higher output voltage - maybe twice the input voltage. But it's just curiosity; don't feel obliged to do any testing you don't want to do! I just noticed in post #17 in this thread, there's a resistor, R2, between...
  8. KrisBlueNZ

    Please help me with a project!

    wingnut, I've found the thread on the LTSpice yahoo group. It seems that that distribution is a mixture of files from various sources. Helmut, the moderator, doesn't recommend it. See http://tech.groups.yahoo.com/group/LTspice/message/33517 In any case it's no longer available from 4shared.com...
  9. KrisBlueNZ

    Please help me with a project!

    wingnut, is that the TIP121, 122 and 127 set from the library? I joined the yahoo group too, and downloaded the 2012-08 library, but those are the only Darlingtons I can find in it. Re your version of LTSpice with "much more", was this a single installation that contained a lot more library...
  10. KrisBlueNZ

    Please help me with a project!

    Don't worry, I've got that sorted! It's been working so far :-)
  11. KrisBlueNZ

    Please help me with a project!

    Thanks guys :-)
  12. KrisBlueNZ

    Please help me with a project!

    No, but I may have previously used the trick of coupling positive and negative pulses onto the base and emitter of one transistor to combine them together. Thanks Chris :-) Oh dear, that sounds serious... Thank you for the kind words :-)
  13. KrisBlueNZ

    Please help me with a project!

    Heartbeat throb on LEDs This may not be useful to the OP but I liked the idea of making LEDs "throb" like a heartbeat, so I designed this circuit. It's not suitable for a beginner but might be useful to others in future, so I'm posting it here. Here's the design along with a simulation...
  14. KrisBlueNZ

    Does this Circuit make sense?

    If your maximum load is 560 mA I would think a 1A switching supply would be a good choice. With incandescent bulbs you need to ensure that the power supply will start up when the bulbs are all cold. They draw significantly more current when they're cold than when they're hot, but I don't know...
  15. KrisBlueNZ

    Problems substituting a relay

    I get about 220 mA peak (about 155 mA RMS assuming it was a proper sinewave) with my simulation. Is that 116 mA RMS? It's quite a lot lower than my simulation shows. I wonder why. Those figures all sound fine. I wasn't questioning them. How did you measure the zener current with your...
  16. KrisBlueNZ

    Problems substituting a relay

    The 100 ohm resistor doesn't limit the current flowing in the circuit - it's limited by the reactance of the 2.2 uF capacitor. These values you've given, are they measured on the actual unit or are they from a simulation? I've re-run the simulation. Please check that my schematic matches...
  17. KrisBlueNZ

    Does this Circuit make sense?

    Yes, you're exactly right so far. Yes, 0.1 amps is one hundred milliamps. Others have already covered this. No, that's not the best way, because that measures the COLD resistance. When the filament is glowing, its resistance is higher. Connect the bulb to the power supply, and insert the...
  18. KrisBlueNZ

    Does this Circuit make sense?

    The first drawing is right. Each chain should have one 270 ohm resistor. BTW your comment "LED = FW Current 3.2 v" should say "LED forward voltage = 3.2V". If the incandescent bulbs are rated at 12V and you have a 12V power supply, they should all be connected across the power supply, i.e. in...
  19. KrisBlueNZ

    A light-sensitive motor

    Thanks Bob :-) I was just aiming to minimise the component count.
  20. KrisBlueNZ

    A light-sensitive motor

    OK, here's my suggested circuit. Q1 responds to the voltage between its base and emitter, which is the product of the current flowing through the LDR and the VR1 resistance. As the light on LDR1 increases, this current increases, until the voltage across VR1 reaches about 0.7V, and Q1 starts...
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