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  1. audioguru2

    Half bridge driver

    Hi Mr. Heckles, It seems to be a tremendous waste of power to accellerate the motor with the high side then brake it with the low side on each and every cycle! But hey, if you want to keep the motor, Mosfets and power supply nice and warm ... Didn't you do it like this?
  2. audioguru2

    Half bridge driver

    Hi Mr. Heckles, Your boost voltage pin VB is missing a diode.
  3. audioguru2

    collector dynamic ro (2N2222)

    Hi Meee, The beta is shown on all transistor's datasheets and is called "hFE". The dynamic resistance is called "impedance" and is shown on only a few transistor's datasheets. The impedances are affected by temperature, voltage, current and frequency. Fairchild's 2N3904 datasheet shows a graph...
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    Ask your Farnell distributor to order it from themselves online. Then they'll have it for you the next day.
  5. audioguru2

    Electronic Stethoscope

    I didn't add the lowpass filter in this project. I just corrected the original circuit's filter that was missing a solder joint on its schematic. The author states in the text that his lowpass filter is used to remove background sounds picked-up by the microphone. Not true. The noise from opamps...
  6. audioguru2

    Amplified Ear help!!!!

    Yes. Why? The project is designed for 1.5V. With 3V some of its biasing resistors need to be changed. The earphones and Q4 might be damaged.
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Gruber, See if www.farnell.com has parts distribution in your country, click on your flag. Quote: The OPA445AP (Texas Instruments, Burr-Brown division) has a 90V rating, a 741A opamp, an MC34071CP (used to be Motorola, then ON Semi and now maybe another name), a TLE2141CP (Texas Instruments)...
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Pigster, Nice going, you fixed it. ;D How well does it perform? If you can find a very big 10 ohms resistor or ten smaller 100 ohms resistors in parallel, use them to provide a 30V/3A load: 1) can it provide a 30V/3A output? 2) How much or how little is the AC ripple voltage at the output...
  9. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, It looks good. An NE-2 neon light bulb begins to light with 70V to 90V across it. An NE-2H is a little brighter and needs 90V to 110V. Perhaps you should add an 80V zener diode in series with it so that you will have a more accurate indication that a capacitor is nearly fully charged. ;D
  10. audioguru2

    time beeper

    Hi Prateek, The piezo oscillating beepers I have produce a low sound level with a 3V supply, much louder with 6V and are very loud with 9V. I didn't want to deafen myself so I didn't try even higher supply voltages. Digikey have Panasonic oscillating beepers similar to mine. They are rated for...
  11. audioguru2

    Electronic Stethoscope

    The lowpass filter would reduce any hiss, so I think noise from an opamp would sound like a rumble.
  12. audioguru2

    Power Supply - looking for 200pf capacitor

    Hi Poschi, We have a thread where we dicuss that project about how to fix its problems here: http://www.electronics-lab.com/forum/index.php?topic=128.0 I have a revised parts list:
  13. audioguru2

    Electronic Stethoscope

    Real doctors are using this project. A doc used to using a mechanical stethoscope with no noise whatsoever, is in for a big surprise if he hears noise from a noisy old opamp. I don't think docs use a stethoscope to hear if the patient's heart is beating, that is obvious. He is listening to the...
  14. audioguru2

    time beeper

    Our Timed Beeper project uses ordinary Cmos ICs that are guaranteed to work only when their supply voltage is 3V or more. But the project uses a 3V battery that drops to 2V over its life. I would use 74HCxx ICs that are guaranteed to work when their supply voltage is 2V or more, or you could use...
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Pigster, I am sorry I made a mistake that I corrected in a later post. The emitter of Q1 should be connected at its original position at the negative terminal of C1. Check the pins on Q1:
  16. audioguru2

    Low drop out voltage regulator with TL431 Problem!

    Typo? The threshold voltage of a TL431 at its adj terminal is 2.5V, not 2.1V. I haven't tried it but the datasheet shows that it makes a pretty good low power class-A audio amp, much better than a single transistor. It has only about 11 transistors inside. ;D
  17. audioguru2

    Low drop out voltage regulator with TL431 Problem!

    Hi Shahriar, Great, you fixed it! ;D It won't be low dropout until you reduce the value of the 2.2k resistor low enough that it can supply base current to the NPN transistor when the circuit is fully loaded plus at least 1mA to the cathode (its power supply) of the TL431 at 2.5V or more.
  18. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    I don't know Rl. Ohm's Law. C5 is the circuit's high frequency bypass cap for stability from oscillating. C1 is big and has inductance which reduces its effectiveness at high frequencies. No. Q4 gets hot which causes it to leak current. R16 bypasses its leakage current. The current gain of...
  19. audioguru2

    Comparator help

    The datasheet shows that there are voltage spikes across the sense resistor. It needs a filter like this, but it will cause a small delay.
  20. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Pigster, Quote: "I said it before. "Q1 is supposed to conduct when the project is turned off and then it will immediately drop the output voltage to zero. The negative supply has low-value capacitors that discharge much quicker than C1, therefore Q1 becomes biased on." Did you use a TIP31A...
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