Controlling Large Voltage with Smaller Voltage or Using Transistor/MOSFET as Switch

Discussion in 'General Electronics Chat' started by elec_mech, May 24, 2011.

  1. elec_mech

    Thread Starter Senior Member

    Nov 12, 2008
    1,501
    196
    Hi Audioguru,

    I tested both circuits successfully. The first one toggles the flashing circuit with a 0V signal from the remote circuit, the second one toggles the flashing circuit with a 3V signal from the remote circuit.

    I will have to check if the second circuit is causing an inversion as you point out. I think I confirmed the 5V output, but I didn't record my findings so I will repeat tonight and report the results.

    If the transistor based is pulled down to ground through the 10kΩ resistor, isn't the transistor "open", i.e., not conducting if no signal is being fed from the remote circuit? Shouldn't the output, based strictly on the original circuit I posted at the very top of the same attachment, remain 0V? Again, I'll test and report my findings.

    I'm currently rewiring the rat's nest of beardboards to a single breadboard to eliminate the clutter, verify the circuit diagram matches the circuit and ultimately try powering the entire circuit, sans the remote circuit, with 12VDC to see if I really need the 5V regulator. I also need to see if I need to change something in order to use the CD4093 in place of the CD4050 for the up and down 555 counters.

    Thanks!
     
  2. elec_mech

    Thread Starter Senior Member

    Nov 12, 2008
    1,501
    196
    Okay, the transistor circuit works as expected. When 3V is fed to the base through the 1kΩ resistor, the output of the CD4093 is 5V. When nothing or 0V is fed to the base, the output is 0V.

    I also double-checked the diode circuit and learned that because the 3V signal is less than the 5V maintained at the resistor-capacitor input to the CD4093, the diode still conducts and the output goes high when 3V is applied. In other words, if you apply/pulse 0V to the diode, the output goes to 5V as expected. If you then apply/pulse 3V to the diode, the output goes high for the first pulse. There is probably a simple thing to do to avoid this, but for now I'm sticking with the transistor circuit.

    I rewired the circuit to take out the CD4050 and replaced it with the CD4093, controlling the 555 circuits via the pin 4 reset and everything appears to work just fine. Will post circuit soon under PROJECTS forum.

    Thanks again!
     
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