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  1. hevans1944

    Electromagnet with strength controlled by photoresistor

    Your N-channel MOSFETs need a positive voltage on their drains. Reverse the polarity on the 24 V DC supply and reverse the diodes across the coils. Ground the negative terminal of the 24 V DC supply. Don't power the 3-terminal 5 V regulator from the 24 V DC power supply. It will drop 19 V...
  2. hevans1944

    Electromagnet with strength controlled by photoresistor

    No, it wasn't wrong. Coils wired in parallel to a constant-voltage source will each draw their own particular current depending on the coil resistance. These currents are all independent of each other. Add or subtract coils and the total current varies, but not the current through each coil...
  3. hevans1944

    Mosfet / Gate drive problems

    That toroid power transformer is really nice. Price seems reasonable, too, if you need 1000 VA capacity. You could use the two 64 V windings to power your MOSFETs and have two lower-voltage windings left over for +5, +12, or whatever power supplies you need for supporting electronics. I think...
  4. hevans1944

    Chosing the Right Tweeter

    I just used the on-line calculator at this web site. Plugged in 0 for R, 4.7 μF for C, and 1 kHz for frequency. Result was 33.86 Ω for Xc. After reading your post, I used my Windows calculator to compute Xc = 1/(2πfC) using f = 1000, C = 4.7 x 10^(-6). Same answer. I must admit I did make a few...
  5. hevans1944

    Chosing the Right Tweeter

    So did you do the test with the 9V battery to see if the horn-tweeters are actually damaged?
  6. hevans1944

    Electromagnet with strength controlled by photoresistor

    I wouldn't do that. You might have noticed that some of my posts are longish. It is better, IMHO, to provide too much information rather than to leave something out because you don't think it is important. If folks don't want to read a long post, well, they won't. Perhaps a few zillion electrons...
  7. hevans1944

    Chosing the Right Tweeter

    Your drawing shows two horn tweeters wired in series and also connected in series with a 12 Ω, 10 W, resistor and a 4.7 μF, 100 V, capacitor. Is this correct? At 1000 Hz (the typical minimum frequency for a "tweeter") the RC network presents an impedance of about 36 Ω. At 20,000 Hz the network...
  8. hevans1944

    Electromagnet with strength controlled by photoresistor

    @purj I notice that @duke37 has been giving you some pretty good advice. You need to be aware that rheostats have both a current limit as well as a power limit, as @duke37 alluded to in his post #18 and clarified further in his post #21. The 100 Ω, 100 W, rheostat that you cited with your link...
  9. hevans1944

    Mosfet / Gate drive problems

    Isolation transformers make some measurements possible, but not necessarily safe. And, yes, working with electricity can be dangerous. You have to know the consequences of "floating" a circuit if, by mischance, you make a connection that defeats the isolation. Really high-quality isolation...
  10. hevans1944

    Mosfet / Gate drive problems

    Note the ringing on the waveform, which occurs during the transition period when both MOSFETs are off. I would have expected this ringing to be damped by the body diode in the low-side MOSFET, but maybe you need an external diode across the inductor and perhaps one across the drain-to-source of...
  11. hevans1944

    Mosfet / Gate drive problems

    There should not be +32 V on ANY of the IC pins. The only place +32 V is applied is to the drain of the high-side MOSFET. Pin 1 (Vcc)connects to the junction of Rvcc=120 Ω and the 22 μF capacitor, pin 1 (Vcc) being powered with +16 V from the LM317 through current-limiting resistor Rvcc. Pin 4...
  12. hevans1944

    OpAmp Circuit assistance - :(

    I am all for using micros and DACs, but I think the @AnalogKid has the least troublesome solution. Basically you use your original circuit but place a resistor between the 0 to 5V source and the non-inverting input to the op-amp. Call this resistor Rin. Then you connect another, much larger...
  13. hevans1944

    Mosfet / Gate drive problems

    Let's back up to the beginning and your original circuit. As I suspected, all of your power rails share a common "ground" connection, i.e., the center-tap of the power transformer. This will not work for reasons already discussed! The original problem you discovered with this circuit was the...
  14. hevans1944

    Chosing the Right Tweeter

    I would take a closer look at the "10W12ΩJ ceramic cement resistor" to make sure (1) it really is a twelve ohm resistor and (2) that it hasn't been burned out and become an open circuit, especially if it is in series with the tweeter. Disconnect the speaker from the amp and make two...
  15. hevans1944

    Mosfet / Gate drive problems

    So what is the common rail of the +16 V power supply connected to? As I mentioned in an earlier post, this power supply must be "floated" on the -32 V rail, meaning the +16 v power supply common must be connected to the -32 V rail. Clearly this cannot be done if the +16 V power supply shares a...
  16. hevans1944

    Help with Voltage Transients

    This works, but at the expense of extra power dissipation in the resistor while the relay coil is energized. See @duke37's post #2.
  17. hevans1944

    linear actuator lift a truck rack

    Clearly you have never tried to synchronize the motion of "linear actuators" which is what this project requires. AFAIK there are two ways: use just one actuator to operate a scissors lift, or add a linear displacement transducer to each actuator and implement a negative feedback control system...
  18. hevans1944

    Mosfet / Gate drive problems

    What you need to do is connect the source of the low-side MOSFET to pin 4 (COM) instead of to a negative voltage referenced to that same pin 4 (COM). No. The "ground" goes away and is replaced by the -32 V power supply rail. That will "float" the IRS2153D on the -32 v rail, and it should work...
  19. hevans1944

    Mosfet / Gate drive problems

    The gate drive signal for the low-side MOSFET is a positive-going, square-wave pulse from pin 5 (LO) to pin 4 (COM). It is intended that this pulse be applied between the gate and the source terminals of an N-channel MOSFET to turn the MOSFET on when the pulse is positive, and to turn the MOSFET...
  20. hevans1944

    Mosfet / Gate drive problems

    According to the IR Application Note, the line you are supplying with -32 V should be at common potential. This is likely causing the low-side MOSFET to be driven into conduction regardless of whether LO on pin 5 is high or low.
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