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  1. KrisBlueNZ

    Attempting to get volt/octave response in Tube VCO

    In a normal VCO, the control voltage determines the charge (and/or discharge) current fed into the timing capacitor(s). This current is directly proportional to the control voltage. There may also be an offset, but I'll ignore offsets for simplicity. Take a conventional simple...
  2. KrisBlueNZ

    SMPS's with cascoded opto feedback

    No, if that's true, then it can't. But if you're running the phototransistor side from a 9V battery (which is fine and a good idea), it's easy to repeat Steve's test. Just connect the scope across the load resistor in each case. Here are the node lists for each configuration. Collector output...
  3. KrisBlueNZ

    SMPS's with cascoded opto feedback

    It looks like you're comparing the turn-on time with the turn-off time. In the second picture you have the scope connected with reversed polarity across the load resistor. This means that the first part of the scope trace, from which the edge rises upwards, corresponds to the phototransistor...
  4. KrisBlueNZ

    auto on and of to over-ride a manual switch

    OK Oliver, here's the design I've come up with. It uses quite a few more components than I had hoped, but I can't see any way to simplify it, and it does seem to work pretty well (in simulation, at least). The circuit requires a 24V DC power supply that is powered via your timer. When the...
  5. KrisBlueNZ

    SMPS's with cascoded opto feedback

    Thanks for the link to the LT4430 data sheet. As usual for Linear Technology, the applications section is full of interesting and useful information. The last paragraph on page 17 says "The common-collector configuration eliminates the Miller effect of the output transistor's collector-to-base...
  6. KrisBlueNZ

    SMPS's with cascoded opto feedback

    I wasn't quite right about the reason for the overshoot in post #40. I think the right explanation is: At startup, there is no conduction in the optocoupler until the output rail reaches its target voltage. With the emitter output configuration, with the error amp in circuit, the capacitor from...
  7. KrisBlueNZ

    SMPS's with cascoded opto feedback

    I think you're probably wrong about that. The emitter output and collector output configurations are fundamentally different in how the feedback is applied to the control IC, and I believe this is the reason for the different feedback loop response (i.e. the overshoot). Have a look at the...
  8. KrisBlueNZ

    auto on and of to over-ride a manual switch

    Sorry for the delay. I'm still trying to figure out a good way to design this circuit. I'm with my partner for the next three days so I can't spend much time on it, but I'll get there, don't worry!
  9. KrisBlueNZ

    SMPS's with cascoded opto feedback

    No, I'm not upset. Likewise. This thread has gotten a bit out of hand. I'm looking forward to the report from Steve's testing!
  10. KrisBlueNZ

    Sony Bravia KDL-46XBR4 Problem

    It looks fine to me. I don't know what the purple colouring is, but I doubt it's a problem. The component looks undamaged and properly soldered. Are you sure that marking relates to the component beside it? It looks like a glass component. Maybe that's just the photograph. If it's made of...
  11. KrisBlueNZ

    auto on and of to over-ride a manual switch

    OK, I'll stick with the design I've been working on. It uses a 24V DC power supply that's plugged into the timer. I'm still in the process of drawing it up, then I will simulate it because it's a bit of an unusual design. Then I'll post it. It should be up within 24 hours.
  12. KrisBlueNZ

    SMPS's with cascoded opto feedback

    In my experience, the optocouplers that I've used have all had the base connection brought out. Do you mean to imply that Steve or I "struggle with this"? That's right, and that base current comes from the collector. From http://www.johnloomis.org/ece445/topics/egginc/pt_char.html...
  13. KrisBlueNZ

    auto on and of to over-ride a manual switch

    Have you bought that timer? If not, can you find one that has a contact closure output instead of a switched mains socket on the back? You can use that one, but you'll need some way to convert the switched mains voltage on the socket into a signal that can be used by the switching circuit...
  14. KrisBlueNZ

    Op Amps

    The "DAC3" connections into U13D and U17A feed into their inputs, on pins 13 and 2 respectively. Likewise, the DAC4 connection into U17C feeds into its input on pin 9. The way these circuits are arranged, my guess would be that the DAC outputs are being used to provide an adjustable DC offset...
  15. KrisBlueNZ

    auto on and of to over-ride a manual switch

    Hi Oliver and welcome to Electronics Point :-) That's a good description of the problem. It's possible to make a circuit that will take the output from your timer and pulse one relay when the output goes ON, and another relay when the output goes OFF. The contacts of those relays can then be...
  16. KrisBlueNZ

    Op Amps

    The device at the right side of the diagram is not a DAC. It's a DG4051A, Vishay Siliconix's enhanced version of the CD4051 eight-to-one analogue multiplexer IC. Its output, on pin 3, is not shown. There is no DAC in that diagram. And without seeing the rest of the design, it's impossible to...
  17. KrisBlueNZ

    Dissolved O2 Switch

    Can you provide a link to the dissolved oxygen sensor you're using (or considering)? Generally this kind of switch circuit is most cleanly implemented using a device called a voltage comparator, or just comparator. It compares the voltage from the sensor with an adjustable threshold voltage and...
  18. KrisBlueNZ

    SMPS's with cascoded opto feedback

    1. A transistor audio amplifier with a capacitor connected to the base does have something connected to the base. You said it has no DIRECT connection to the base. If you had said that it has no DC connection to the base, I would agree, but it's irrelevant because I didn't say "how can a...
  19. KrisBlueNZ

    Building a Frequency/Sound Generator

    I'm no expert but here's a brain dump that may be helpful. I agree with Harald that frequency shifting isn't going to be of much use. If you want to record and reproduce a frequency of n Hz, you need to sample at at least 2n samples per second, according to the Nyquist theory. This is an...
  20. KrisBlueNZ

    Adjustable Pulsing Ground

    You may not get any more help with this project here, because it's clear that it's an automotive modification. Some sites, and some users, avoid these projects because of the inherent dangers. If something were to go wrong, and someone was injured or killed, even if no one tried to blame it on...
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