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  1. audioguru2

    0-30V Stabilized Power Supply

    The latest revision (schematic Rev2 and parts list Rev3) is reliable, inexpensive and works well.
  2. audioguru2

    Help for a school Physic Projet ''Bulding a FM transmitter ''

    Please explain what is the problem with the quality. Does it have hiss? Does it have hum? Is it distorted? Is it too loud? Is it too soft? Does it sound muffled with no high audio frequencies? Does the radio signal appear at many spots on the dial of the radio?
  3. audioguru2

    0-30V Stabilized Power Supply

    C1 must be a huge value to reduce ripple on the output. Therefore with a small load current it takes a long time to discharge. But the negative supply discharges quickly then U3 loses its negative supply and cannot hold the output voltage down through D9 when the power is turned off. R13 andf...
  4. audioguru2

    Op - Amp Application in a Device ..

    An opamp is very inexpensive. They are used in millions of products. Look in Google for Op-amp Applications.
  5. audioguru2

    0-30V Stabilized Power Supply

    The problem of the output regulated current increasing when the power is turned off is caused by the -1.3V supply dropping too fast. In addition to increasing the value of C3 maybe the value of C2 should also be increased and the power rating of R2 should be increased. You can add Q1 to short...
  6. audioguru2

    Help for a school Physic Projet ''Bulding a FM transmitter ''

    3mm is the inside diameter of the coil. Wrap enamelled wire around a 3mm drill bit, slide the coil off  then scrape off the enamel at each end so you can solder to the wire. I use thick wire that has 1mm diameter so it is strong enough not to get bent out of shape that changes its inductance...
  7. audioguru2

    HELP! how can i increase a piezo electric current?

    It was one or two years ago and i don't remember which website. . Look at Energy Harvesting in Google. There are millions of links.
  8. audioguru2

    HELP! how can i increase a piezo electric current?

    We talked on one of these forums about harnassing energy from a piezo transducer in a shoe. It drives an IC made for the very low voltage and very low current. Then the IC charges a capacitor or battery. When enough energy is stored then another IC can blink an LED. 
  9. audioguru2

    0-30V Stabilized Power Supply

    It looks like you have the output set for current regulation and the output voltage of your project increases when the power supply is turned off. Then the output current also increases. I think it is because the negative supply becomes zero volts quickly so D9 cannot keep holding the output...
  10. audioguru2

    0-30V Stabilized Power Supply

    Hi fly3rman, The original circuit used TL081 opamps that have a problem of "phase inversion" when an input voltage got within 3V of the negative supply. So when the power was turned off the negative supply voltage dropped and the output went as high as it could go. So transistor Q1 was added to...
  11. audioguru2

    0-30V Stabilized Power Supply

    Hi fly3rman, With the output set to a low voltage or is shorted and the current is set to 3.0A then each output transistor has 40.6V and 1.5A which is heating of 60.9W. Your little heatsinks are rated for only about 10W each. The 2N3055 is rated for a chip to case max thermal resistance of 1.5...
  12. audioguru2

    0-30V Stabilized Power Supply

    Hi fly3rman, You used Redwire's pcb but my parts list. They have different resistor values but  they should work properly even if the parts are mixed up. Your output amplifier has a gain of only slightly more than 1 so maybe R11, R12 or RV2 are broken or wrong values. Maybe C6 is shorted. Here...
  13. audioguru2

    0-30V Stabilized Power Supply

    Hi fly3rman, When the 2N3055 transistors are connected with their base and emitters backwards, then the driver transistor Q2 takes almost the entire output load and probably burns out if the project has a load. The positive supply pin 7 of U3 has a 10V zener diode in series so its voltage...
  14. audioguru2

    Discharging Li-Ion batteries

    The load on a rechargeable lithium battery cell must be disconnected when the voltage drops to 3.0V. The battery cell will be damaged and might catch on fire when charged if its voltage is below 3.0V. The battery cell will last longer if the low voltage limit is higher, maybe 3.2V. Discharge...
  15. audioguru2

    Help for a school Physic Projet ''Bulding a FM transmitter ''

    The radio frequency of the FM transmitter is determined by the LC tuned circuit. But the text of this project is wrong, the coil is about 0.1uH, not 1uH. The text does not say how to make the coil. It is about 6 to 8 turns of enamelled wire with an inside dimension of 3mm. I attach a photo of a...
  16. audioguru2

    LM358 - Dual Low Power Operational Amplifier

    Its slew rate is 1/10th as high as half-decent opamps because it is low power. The low power produces horrible crossover distortion. Its datasheet has a graph "Large Signal Frequency Response" that shows it produces an output of only 12.5V p-p at only 5kHz. At full output level of 30V p-p it...
  17. audioguru2

    Need help with inverter circuit

    The 2SC1061 transistors are driver transistors for the 2N3055 transistors. They amplify The 20mA from the output of the opamps to about 200mA. The maximum power output from the inverter will be very low without them. Maybe you had their pins connected backwards. Thje "corrected" circuit is...
  18. audioguru2

    Modify existing project

    I am the designer of the 3V and 6V chaser projects. They are designed to use low battery voltage and operate with extremely low average current so that a little battery lasts for a long time. Many extra parts are used to reduce the average current but still allow bright flashes. A much simpler...
  19. audioguru2

    Modify existing project

    We don't know which chaser project you are talking about. Please post a link to it. Using a chaser of LEDs on the back of a motor vehicle might be illegal.
  20. audioguru2

    LM338 Power Suply Current Regulator

    The schematic is attached as a thumbnail in the first post. Click on the thumbnail to enlarge it. The schematic is copied from the datasheet of the LM338 IC.
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