LED Drive-PCB Assembly Description

Charge LED Drive

The Charge LED Drive signal from the System microprocessor controls Q 14 when the energy storage capacitor is charging. Transistor Q14 drives the front panel CHARGE LED and the paddle CHARGE LED. Resistor R128 on the drain of Q14 limits the current to the Paddle LED. The gate of Q13 is connected to the Charge Valid signal. When the voltage for the selected energy level has been reached, Q13 conducts. Transistor Q14 then clamps the charge LEDs on continuously.

Interconnect PCB Assembly (803761)

The Interconnect PCB provides electrical connection between the Main PCB and the Power Conversion PCB. It also drives the front panel LEDs and generates the audible tones. The LED drive circuitry consists of Q4, Q5, Q13, R 14, R15, and R 11. Static protection is provided by R9, R21, R22, C6 through C8, and CR1 through CR11. The Main PCB System microprocessor selects 1 of 8 volume levels by writing the appropriate binary number (000 for the loudest and 111 for the softest) on line VOL1, VOL2, and VOI,3. These lines are routed to 3-to-8 decoder U l on the Interconnect PCB. Static protection is provided by R I through R4, CI through C3, and C5.

The decoder U 1 sets the voltage required for the volume level selected by the System microprocessor. The decoder output turns on one of the transistors (Ql through Q3 or Q7 through Q10) which puts the corresponding resistor in series with R8. The center tap of the resistor divider is routed to the input of either U2A or U2B as determined by Q11, Q 12, and Q6. The output of U2A or U2B applies the voltage to the piezoelectric transducer, X 1.

The free-running oscillator in the System microprocessor generates the desired tone frequency. The oscillator generates a square wave, Audio Drive, which is routed to the gate of Q 11. If the voltage at the gate of Q11 is low, Q12 conducts, grounding U2A pin 3. Transistor Q6 then shuts off, applying the selected voltage to U2B pin 5. If the voltage at the gate of Q l I is high, Qll switches on and Q12 switches off, applying the selected voltage to U2A pin 3. Transistor Q6 then turns on, grounding U2B pin 5. Therefore, the frequency of the oscillator controls transistors Q11, Q12, and Q6, which drive the transducer. Op amps U2A and U2B provide buffering and high current drive to X1.

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