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  1. Audioguru

    Transistor Help

    Yes you are missing information shown on the datasheet of almost every transistor: 1) hFE (current gain) is used when there is plenty of collector to emitter voltage so that the transistor is a linear amplifier, not a switch. 2) The base current should be 1/10th the collector current when the...
  2. Audioguru

    Transistor Help

    The datasheet of almost every transistor shows that they conduct very well when the base current is 1/10th the collector current. But I guess your Arduino cannot provide 5V at 40mA, it provides much less then the transistor is starved of enough base current and does not fully turn on producing...
  3. Audioguru

    Audio speakers

    Computer speakers are cheap little things and are not capable of providing clean sound at high volume. Of course the LM386 powered from only 6V produces distorted awful sounds when you turn the volume higher than only 0.25W which is as loud as a whisper.
  4. Audioguru

    Op-amp buffer

    The opamp has a high impedance input so that it does not overload the filtered input signal and it has a powerful output that can drive a low impedance output circuit that is not shown. How can the opamp drive a circuit not shown that has 45V? Maybe the output of the opamp clamps the 45V to its...
  5. Audioguru

    Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

    This is an NPN transistor and in this circuit the emitter must NEVER higher than the base voltage. Since your circuit does not have a load then maybe the BD139 leaks a little current from its 41V collector that is causing the emitter voltage to rise too high. I do not understand how you measured...
  6. Audioguru

    Transistor Help

    You used the NPN transistor as an "emitter-follower" instead of as a switch. Then when the Arduino output went to +5V the base went to about +4.8V. But the emitter is about 0.7V less than the base so the solenoid got only about 4.1V instead of 12V. I mentioned this problem in my post #4.
  7. Audioguru

    Transistor Help

    If the transistor does not need to turn on completely and can have a voltage of about 1V between collector and emitter then the hFE of the transistor is used in the calculation for the base current. If you want the transistor to turn on very well then its saturation voltage loss is used where it...
  8. Audioguru

    Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

    Something wrong is causing the emitter voltage of the BD139 to be too high. First I wanted to see if U2 works properly by disconnecting the BD139 and connecting the negative feedback from R12 and C6 to U2 pin 6 without the output transistors. You measured not enough voltage swing at the input...
  9. Audioguru

    Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

    no, its voltage is 10V less than the +40V positive so the 10V zener diode is doing its job. I will look at them later. That is wrong. The output of U1 is +11/2V and feeds pin 3 of U2 though R8 and R9 which total only 29.2k so pin 3 of U2 should go from 0V to +11.2V. Maybe your voltmeter is an...
  10. Audioguru

    (Please help) Portable solar powered powerbank

    I was saying what we say to most students, "We will not do your homework for you". These students missed many classes and do not have a clue about their project. I think the students are shamed to ask their professor for some help. You selected a powerbank but your very simple block diagram is...
  11. Audioguru

    (Please help) Portable solar powered powerbank

    You selected this project so you do its calculations and you select its parts. That is what you are expected to do for your degrees final year project. Your project might not be accepted if the professor learned that you asked about how to do it on an online forum.
  12. Audioguru

    Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

    D7 is two forward biased diodes, not a reverse biased zener diode. Here is how -1.3V is made:
  13. Audioguru

    lm 317 tip 3055 constant current

    The 40VAC transformer might produce 42V with not much load current. Then its peak is 59.4V and is reduced to 58V by the bridge rectifier. Then the LM317 and the TIP3055 might be destroyed by too much voltage if anything shorts the output. I agree that the circuit will provide poor voltage...
  14. Audioguru

    How to change input voltage on DC-DC booster

    A small 9V battery quickly drops to less than 8V then the booster will not work. If the current is fairly high then a brand new small 9V battery also will not work. Energizer battery company shows in their datasheet of their 9V alkaline battery the voltage dropping to 4.8V. But the current is...
  15. Audioguru

    Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

    If the light in series flickers then something is wrong. I do not know which of your many problems is causing it. If a multimeter has more than about 5V in the continuity test and its red lead is on the emitter and its black lead is on the collector then the emitter-base junction is reverse...
  16. Audioguru

    Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

    A transistor does not have a "common", it has a base-collector diode and a base-emitter diode. It should not conduct collector to emitter when its base is not connected. When the base-emitter diode is reverse-biased with about 6V or more it conducts like a zener diode which damages the junction...
  17. Audioguru

    Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

    A blown transistor is either shorted or it has its parts disconnected (blown out). But your transistors have the emitter voltage higher than the base voltage which is impossible unless they are leaking current very badly collector to emitter or have their pins mixed up. The power supply output...
  18. Audioguru

    Need some help on this Project

    Sorry, I have never looked at sites with simple school projects until you posted that wrong and useless circuit. Look at www.555-timer-circuits.com where there are many simple circuits but most are missing an important supply bypass capacitor that is mentioned on the LM555 datasheet.
  19. Audioguru

    Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

    U3 does not work properly because its negative power supply voltage of -1.3V on pin 4 is wrong and the -1.3V should not change when U3 is installed. Check or replace R2, R3, C2, C3, D5, D6 and both diodes making D7. U2 has its pin 2 wrong at 0V when it should be the same voltage as pin 3. You...
  20. Audioguru

    Need some help on this Project

    The capacitor might prevent a nearby radio station transmitter from activating the relay when the wire loop is cut. The 1k resistor causes the input of the useless logic circuit to be high when the wire loop is cut and prevents the wire loop from shorting the 5v power supply when the wire loop...
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