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  1. Arouse1973

    Voltage controlled thru opamp playing up?

    Ah ha. Increasing the frequency will cause your output filter to antenuate any noise from the output even further improving matters. Still could be the opamp. Just a thought. Adam
  2. Arouse1973

    Voltage controlled thru opamp playing up?

    Hey Kris you'll find this interesting. I simulated it and to be honest didn't expect to see anything. The simulations show the effect on power up of having to high a resistance on the input versus the feedback. The second graph I replaced the input resistance with a 10R. The graphs are of the...
  3. Arouse1973

    Voltage controlled thru opamp playing up?

    Hi Kris Having a high source impedance reacts with the input capacitance causing a zero on the input. The noise gain of the amp increases at 6dB/octave but the gain reduces by 6dB/octave. This results in a 12dB point where they meet, this is an unstable condition. Standard buffers can be used...
  4. Arouse1973

    Half Bridge Converter Question

    Agree. I love stuff like this, It's the reason I stay up all night :)
  5. Arouse1973

    Voltage controlled thru opamp playing up?

    Having a look at the data sheet the capacitance graph only goes to 10nF and needs a resistor over 100R. I would get rid of it. But I have just noticed an even bigger problem which might explain the strange behaviour of the op-amp. The common op-amp buffer circuit that everyone uses, short...
  6. Arouse1973

    Current Mirrors

    The diode connected transistor is often used when better temperature response is needed and the voltage drop doesn't rise as much versus current. @Steve At last I have found someone that agrees with me, transistors being voltage controlled devices. Adam
  7. Arouse1973

    Half Bridge Converter Question

    KTP is a knowledge transfer scheme for student at university. NPC is a modern way to drive high voltage motors or inductive loads, it stands for Neutral Point Clamping Adam
  8. Arouse1973

    Voltage controlled thru opamp playing up?

    The 100nF on the output. I have seen this sort of thing cause issues even with buffers. It might be ok because of the 47R but it's worth considering. Thanks Adam
  9. Arouse1973

    oscillator doesn't oscillator as I expect

    Yes correct I only used the pickup coil as to not load the circuit with my scope. Any old coil will probably do. Even connecting the scope clip to the tip and drape the wire over the coil should pick up something. Adam
  10. Arouse1973

    Half Bridge Converter Question

    Thanks Kris. It's so nice to have a good technical discussion with you. To be honest I just through in some values for the caps to keep ESR low which is what is needed. The actual value from memory is about 1uF per Watt. They normally are electrolytics. Your right about the voltages I was...
  11. Arouse1973

    LED - Light Intensity vs. Current Relationship

    The light output from an LED is reasonably linear with current. But the human eye does not see it that way but a sensor will. You need to choose the correct current for each LED for the purpose of which they are being used. You could drive the red LED at the same current as the IR LED but this...
  12. Arouse1973

    laser ablation of PCB resist

    Looking pretty good Steve :)
  13. Arouse1973

    Voltage controlled thru opamp playing up?

    Try removing the 100nF capacitor on the output. Sound like it's oscillating, you have basically formed an RC time constant between the internal resistance of the op-amp and the capacitor. This might cause you problems. Adam
  14. Arouse1973

    Electric motor

    I have in the passed used an old RC servo. Take out the control circuitry and cut the tab off of the spindle cog which limits it's travel. Solder the red and black wires to the motor and connect 4.8-6V across the red and black wire and you will have a slow motor that uses the gears inside to...
  15. Arouse1973

    oscillator doesn't oscillator as I expect

    Hey Long don't panic. I tried your circuit and got the same results as you. It was oscillating at high frequency. This circuit as I mentioned earlier is used for small FM transmitters. I remember years ago trying to get one of those to work and I did but with only a few turns of wire an a...
  16. Arouse1973

    Half Bridge Converter Question

    I have done a bit of digging and I have changed my circuit to match the microchip drawing from the app note AN1114 I found that explains what I am trying to explain but I probably explained it all wrong. Please feel free to comment and agree or disagree. If the circuit works differently to how...
  17. Arouse1973

    Half Bridge Converter Question

    I think we will have to beg to differ on this for a momemt. :) I am talking about the first circuit posted and yes the primary of the transformer. I will dig out some of my books and have a look. Cheers Adam
  18. Arouse1973

    oscillator doesn't oscillator as I expect

    I don't really know what this issue is but I think you might need a lower base resistor for extra drive. Here is one I just designed at it oscillates at about 956KHz. Adam
  19. Arouse1973

    Some help on bypass and filtering needed.

    Ok lets give an example. If you have an IC that dissipates 1W and you have only a decoupling capacitor of 1nF with a supply voltage of 3.3V and you can only tolerate a 5% droop of the supply then this will only decouple for 0.5ns = C*0.05*V/P. That's not very long. We want something like 5us to...
  20. Arouse1973

    Half Bridge Converter Question

    Flux walking as you know happens if the coils core hysteresis loop is not reset to its original value i.e the exact same change of voltage over time for both transistors must occur. This very rarely happens and the simple fix is to put a series capacitor on the coil. The two capacitors don’t do...
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