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Tornado S Missile IMU Teardown: Power Supply and ADC Boards
0:00:04 IMU Components Overview: The Inertial Measurement Unit (IMU) contains three accelerometers, each with a dedicated Analog-to-Digital Converter (ADC) board and a shared power supply board.
0:00:21 Power Supply Board Details: The power supply board features multiple bridge rectifiers, filtering capacitors (including tantalum capacitors), and a transformer with several secondary windings.
0:00:39 Triple Power Supplies: Each accelerometer is powered by three separate power supplies derived from the board, explaining the multiple rectifiers and capacitors.
0:00:45 Step-Down Converter: A step-down (buck) converter reduces the battery voltage (25-30V) to 20V using a coil, diode, PNP switching transistor, and a MOSFET for feedback.
0:01:15 PCB Bodges: Visible modifications ("bodges") are present on the power supply board.
0:01:21 Auto-Oscillant Converter: A secondary, auto-resonant DC-to-DC converter is present, utilizing a dual transistor and transformer, without any dedicated ICs.
0:02:27 Auto-Resonant Converter Details: This converter has multiple identical secondary circuits, a feedback winding, and a current-limiting circuit with an NPN transistor operating in reverse mode.
0:03:30 Secondary Side Voltages: The auto-resonant converter provides multiple output voltages: bipolar (around +/- 12.5V or +/-15V), a voltage for the digital circuits, and a voltage for the accelerometer itself.
0:03:53 ADC Board Overview: The ADC board has distinct analog and digital sections.
0:04:02 Key Components: Notable components include a high-performance capacitor (likely for low dielectric absorption), an operational amplifier (op-amp), two comparators, an analog switch, and a reference voltage diode.
0:04:25 Multi-Slope ADC: The circuit is identified as a multi-slope ADC, relying on a custom ASIC (Application-Specific Integrated Circuit) called a "Matrix Crystal" (H1537XM1).
0:04:50 Other Digital Components: The board also contains resistor arrays, a pulse transformer, an hex inverter, and a transistor array.
0:05:12 Servo Accelerometer: The design uses a servo accelerometer, that has a zero detector that uses an LED.
0:05:32 LED Bodge: A bodge involving a transistor in reverse mode and a Zener diode is present on a 2024 board, but not on a 2022 version. This circuit likely activates the accelerometer's LEDs above a certain voltage threshold.
0:06:05 Accelerometer Output: The accelerometer outputs a current (positive or negative) that is converted to a voltage by resistors.
0:06:23 Integrator: An integrator circuit sums the measurement current and a reference current (which can be positive, negative, or zero) controlled by analog switches.
0:06:38 Dual Reference Currents: The are two reference currents (+6.4 and -6.4 Volts)
0:07:25 Multi-Slope Operation: The integrator output produces ramps (up and down) that are compared against two thresholds (+0.5V and -0.5V). The comparator outputs control the switches, changing the ramp direction and extending integration time.
0:07:53 Digital Section: The Matrix Crystal ASIC handles the digital logic, receiving comparator outputs and controlling the analog switches.
0:08:04 No Clock Generator: The board lacks an on-board clock generator; the clock signal is supplied externally through the pulse transformer.
0:08:32 Output Circuit: The ADC output is not complete. It uses small pulse transformers to generate short pulses, indicating the start of positive and negative-going ramps.
0:08:54 Ramp Timing: Each ramp has a duration of 8 clock cycles, with a 1-clock-cycle dead time between ramps.
0:09:33 End-of-Measurement Detection: The end of the measurement is indicated by two pulses on the output signal.
0:10:34 Test Setup: A current source simulates the accelerometer output for testing.
0:11:26 Clock Frequency: The clock frequency used during testing is 10 kHz.
0:11:55 Future Plans: The presenter plans to examine the accelerometers in more detail in a future video.