Gas station without pumps

2015 November 5

Book draft 2015 Nov 5

Filed under: Circuits course — gasstationwithoutpumps @ 22:39
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I released an updated version of the Applied Electronics for Bioengineers text today.  This draft involved several changes:

  • Added modifier for “resistor” at end of Section 5.1
  • Changed “load resistor” to “bias resistor” in microphone chapter and lab.
  • Fixed microphone schematics to use polarized microphones.
  • Figure 11.2 changed to use only one differential channel on PteroDAQ.
  • Brief explanation of RMS added to Section 3.2
  • Small fixes to Chapters 9–16 and indexing terms added.
  • Index cleaned up.
  • 60Hz FM figure added to Chapter 14
  • Updated power discussion in Sections 0.5, 12.3, 23.1
  • Updated to include Teensy 3.2
  • Major rewrite of Chapter 23 (Class D power amp)

I’m still not finished with the Class D chapter, but I managed to test today an H-bridge circuit using a 9V power supply, which could provide ±9v signals to a loudspeaker (the full 10W that the loudspeaker can take).  I did not actually drive the loudspeaker that far, but I confirmed that the H-bridge was providing the full voltage range for PWM and that I was getting clean signals at the loudspeaker for loudness I was willing to tolerate listening to.

I’m now convinced that an H-bridge design is a simpler approach to teach the students, as well as being more useful for students who go on into the “assistive technology: motor” concentration.  Modifying the H-bridge to use logic-level signals from the comparator but high voltages for the power FETs turned out to be quite simple.  I just added a small nFET and a couple of resistors to make an inverter with a small voltage swing on the output:

Q1 and the resistors R1 and R2 form an inverter for driving the pFET.  Sizing R1 and R2 determines the voltage swing on the pFET gate  (Q2) and how fast the turn on and turn off are.  Of course, when Q3 is on, there is a current through it that is wasted (not delivered to the load), but I was able to keep that down to about 15mA.

Q1 and the resistors R1 and R2 form an inverter for driving the pFET. Sizing R1 and R2 determines the voltage swing on the pFET gate (Q2) and how fast the turn on and turn off are. Of course, when Q3 is on, there is a current through it that is wasted (not delivered to the load), but I was able to keep that down to about 15mA.

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