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  1. logbook

    Flyback design question

    Keith, >4-way interconnect? The anode end of D5 has a 4 way junction on the circuit. The older drawing convention was to draw little humps to cross over wires. Then they changed it so that you could drive straight across without the humps PROVIDED you never joined 4 wires at point. Joining 4...
  2. logbook

    Flyback design question

    To tell whether this is a flyback converter or a forward converter it is only necessary to look at the phase relationship between the primary drive and the secondary output. This is determined by the dots on the transformer. In this circuit the primary and secondary are in phase. Therefore it is...
  3. logbook

    Coil Field Examiner.

    Detecting an AC field is easy. You just use a small coil of wire. The smaller the coil the less the induced voltage but the better the spatial resolution. You will be using Faraday's Law of Induction. E= N * d(phi)/dt N turns. phi is the total magnetic flux through the coil d(phi)/dt is the...
  4. logbook

    zener diode voltage divider

    We all know that zener diodes are only available down to 2.4V. Below that you either use one or two FORWARD biased silicon diodes (zeners are of course reverse biassed for zener operation). If the load is 300µA then you can't use a shunt regulator diode and a 120K resistor (as suggested by...
  5. logbook

    SMPS with 0.01% ripple

    Well now we have two sorts of ripple. Primary ripple rejection and secondary load rejection. Primary ripple rejection can be made arbitrarily low by filtering the input and using a current mode controller. The resulting increase in cost and reduced efficiency has to be considered. Secondary...
  6. logbook

    SMPS with 0.01% ripple

    A switcher does not need output ripple! now if you use a PWM switcher there will be a finite ripple rejection of the input ripple. However, if you use a current mode switcher the primary ripple rejection will be excellent. Rejection of output load ripple is a whole other matter. First you use a...
  7. logbook

    Voltage drop

    Hang on, the reason why the "must operate" voltage is typically 75% of the nominal is to allow for temperature. Copper has a TC of +0.4%/degC. At 70degC you get significantly less coil current at the nominal operating voltage. Don't use up the margin by operating at 80% of nominal or you will...
  8. logbook

    offset voltage opamp

    dau, yes ordinary protection diodes will leak very badly at elevated temperatures. Because they typically run with several volts reverse bias, you need special "low leakage" types. PAD50/JPAD50 or other members of that family give excellent leakage characteristics. At zero volts input to...
  9. logbook

    electronics hsops

    Use Farnell. They are not as fussy as RS.
  10. logbook

    OpAmp question

    djackman, Your post is quite incomplete. You want an emulator for a magnetic pickup. Ok. A typical simple magnetic sensor does not generate a rectangular waveform. If you have one that gives -15V for no tooth and +15V for a tooth, for example, that is a digital magnetic sensor. It requires one...
  11. logbook

    Charge amplifiers

    I would think this requires an amplifier based on a vacuum tube cascading device, sort of like either a geiger tube or scintillation counter. You are not using an opamp or any other semiconductor device because the noise would be too high. Geiger counters take one disintegration and avalanche it...
  12. logbook

    Video amplifier Test Procedure query.

    Just as a point of drawing "etiquette" / convention, it is usual to have the input on the left and the output on the right. This is much like writing left to right on the page. People get used to it and therefore prefer "standard" drawing practice.
  13. logbook

    Video amplifier Test Procedure query.

    Let's start on the left. There is a rather nasty 22pF capacitor across the inputs of the opamp. I suspect somebody was trying to reduce incoming noise, or something. Then they probably had to add the 6p8 feedback capacitor to make the amplifier stable. (The 22pF is not in a good position!)...
  14. logbook

    Royer Oscillator as a DC-DC converter

    I assume the guts is similar to this: http://www.edn.com/archives/1995/021695/graph/04di1fg1.htm Clearly this is a purely analog circuit, so nobody now knows how to design them! I suspect a common-mode feedback path is causing the problem (in addition to the low transistor gain at low...
  15. logbook

    Low pass filter failing at the lower range

    >Do lowpass filters behave like this? YES! Your circuit is working as designed. You have a low pass filter at 740Hz. It will not filter signals at 500Hz and below. Why does it work for your 120Hz signal? Well, you are reconstructing the 120Hz. This requires higher frequency components such as...
  16. logbook

    Current limiting /diodes or discreets?

    To power a 2V LED from a 9V battery use a series resistor. If you need 10mA then there is 7V across the resistor (9V-2V). 7V/10mA = 700 ohms. Use a 680R. Power is V*V/R = 7*7/680 = 0.07W, so a 1206 surface mount or 1/4W wire ended type will be fine.
  17. logbook

    Need IC for flyback SMPS isolated feedback

    I suppose you want constructive criticism on your "home brew". Phew that's a tough one! If you use an extra winding on the transformer you can use this for the feedback. It is not an exact mirror of the output, but unless your load variations are large, it should be ok. This is much better than...
  18. logbook

    RF Design Consideration

    How large a piece of metal, over what length of the line? The dielectric constant of the pcb/substrate is also relevant, as is the actual width of the 50 ohm track and the gap between the ground plane. A 50 ohm track can be made with an infinite range of track to ground plane gaps. This is...
  19. logbook

    Failed soldering test and wonder why..

    It's too long a letter to send to the agency. If the job is soldering then you needed to correct their setup on the spot. I have never gone below 0603 myself (with an iron) but you certainly get problems when the solder won't wet the iron's tip. recently, even using tip cleaner the solder...
  20. logbook

    Direct me to a hobby site...

    http://www.uoguelph.ca/~antoon/circ/circuits.htm

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