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  1. Audioguru

    Need help testing this circuit

    Why did you connect the indicator LED to the very low current phototransistor? Then the 2N2222 transistor does nothing. Do it like this:
  2. Audioguru

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

    The LED that indicates current regulation is turned on and off by Q3 that is controlled by U3 that is activated by its comparison of the voltage from the current sensing resistor R7 with the voltage set by the current setting pot P2. With no output current then pin 2 input of U3 is 0V and if P2...
  3. Audioguru

    Solar powered fan

    I think he want to control the temperature by having the solar powered fan to blow away the sun. Then when it gets too cool the sun comes back. Oh, instead blow away the clouds?
  4. Audioguru

    Need help testing this circuit

    In a conversation, Mark said that he wants blocking and unblocking the light from the phototransistor to turn the load LED on and off and if replacing the SCR with a transistor will do it (like I explained in my last post here) and I said yes, but I also explained all the missing details that...
  5. Audioguru

    Need help testing this circuit

    Maybe you do not know how an SCR works. After it is triggered then it stays turned on until its power supply is turned off. If you want the test LED to turn on and off when the light is blocked and not blocked then you need a transistor or Mosfet to drive the test LED, not an SCR. It was...
  6. Audioguru

    Solar powered fan

    The datasheet for the LM555 shows a graph with a monostable delay of 100 seconds maximum but you might get 3 or 4 minutes with a larger capacitor than the 100uF shown. A digital timer circuit would have much longer more reliable times.
  7. Audioguru

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

    Since your -1.5V supply is missing then something is broken or disconnected. Before I listed its 8 parts to be checked. Your supply is 42V so the 2.2k for R1 dissipates (42V squared)/2200 ohms= 0.8W. My parts list says it should be a 2W resistor (and it should not be near R7). What size is yours?
  8. Audioguru

    Need help testing this circuit

    The Mcr 22-6 SCR is rated for 400V and 1.5A but it has a sensitive gate and low holding current so it should be fine.
  9. Audioguru

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

    Of course, I forgot that R20 will lift the pin 6 pad to +32V when the U3 is removed and is not holding it down. Before, pin 6 voltage was higher than it should have been but it was later found to be caused by the missing negative voltage on pin 4. Your U3 pin 2 voltage problem was fixed somehow...
  10. Audioguru

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

    With U3 removed then isn't its pin 4 pad at -1.5V? Your voltage on pin 7 is normal. Your voltage on pin 6 makes the IC hot and might destroy it. U3 is destroyed anyway because its pin 2 input had a voltage that is gone when the IC is removed. How can the 10V zener diode D3 survive if U3 was...
  11. Audioguru

    Need help testing this circuit

    On the other website you showed a photo of your photo-receiver that is not a phototransistor and I think you had its pins mixed up. It rejects continuous light. It needs bursts of 38kHz modulated IR radiation. Maybe your LED produces visible light but not IR radiation? And your LED does not...
  12. Audioguru

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

    Simply remove U3 and post the voltages of its pin pads. If pin 2 drops to 0V and its pin 4 is at -1.5V then its replacement might survive. Maybe it was mounted backwards so that its pin 6 was on the pin 2 pad?
  13. Audioguru

    Need help testing this circuit

    It is a very powerful SCR that needs a lot of gate and holding current: 1) Max gate current needed= 15mA then ... the circuit should be re-designed. 2) Max latching current needed= 40mA that is higher than the max allowed current of an ordinary LED. Why not use a little 2N5061 SCR? Its max...
  14. Audioguru

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

    The U3 output pin 6 will be 1.7V when its (-) input pin 2 is higher than its (+) input pin 3. But pin 2 connects to 0V though 0.47 ohms R7 so it is 0V when the project has no load and pin 3 has a voltage usually positive for the current regulation setting. How can its pin 2 be +3.2V? Then the...
  15. Audioguru

    Need help testing this circuit

    Your SCR has no part number so we don't know if the 10k resistor will feed its gate with enough current and we don't know if the LED will draw enough current for it to stay turned on. The LED and/or SCR will make a spectacular explosion if you do not limit its current with a series resistor.
  16. Audioguru

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

    Yes, because they limit the negative voltage to two series forward voltage drops. When I replaced a 5.6V zener diode that was in the original circuit with the diodes then I did not know their current so I guessed a few mA but since you have 0.75V each then their current is about 15mA which is...
  17. Audioguru

    Need help testing this circuit

    If you want the SCR to be triggered when the light is blocked then what you were told is wrong because the person wrongly thought you wanted the SCR to be triggered when the phototransistor has light. When the phototransistor is lighted then it conducts and turns off the 2N2222 transistor. When...
  18. Audioguru

    Need help testing this circuit

    The output level from a photodiode is too small to turn off the 2N2222 transistor. A phototransistor amplifies the tiny voltage or tiny current at its base when light shines on it. Usually an opamp with high gain is used with a photodiode.
  19. Audioguru

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

    Yes your D7 diodes are backwards. See the symbol on the pcb where one end of the diode box has a white bar? The diodes also have a bar (but it is black) on the cathode end. The straight line in the schematic symbol of a diode is its cathode.
  20. Audioguru

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

    No. The datasheet for the 1N4148 diode shows 0.65V when its current is 1.8mA. It is never as high as almost 2V even when its current is massive at 800mA. I think your D7 diodes are connected backwards. D5 and D6 have a correct forward voltage. As a test remove U3 and replace the D7 diodes. They...
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