Table of Contents
Advertisement
Technical Supplement
Constant power (VPRN) and a power control line (PWR_ON) are provided by the auxiliary PCB. Q1
is used as a power control FET. Both halves are used in parallel to reduce the on resistance. When
PWR_ON is high, the sources (S1, S2) short to the drains (D1, D2), connecting ground to U1 and C3.
PWR_ON also controls the regulated power supplies; thus, Q1 and the power supplies are both
enabled and disabled at the same time.
The large bulk capacitor C3 is required due to the large current spikes that are required by the printer
and the large internal series resistance of disposable batteries. Bulk capacitance is required to lessen
the drop in battery voltage caused by the current spikes.
The N-20P has three additional user-control buttons. L8, L9, L10, C120, C121, and C122 provide
ESD protection. R103, R104, and R105 provide pull-ups when the user buttons are open. These
pull-up resistors are in the printer interface circuit to ensure that the buttons (ON, ADV, and D/D) are
never left floating, regardless of whether an optional printer flex circuit is installed or not.
The optional user controls consist of three momentary push-button elastomeric contact switches.
Pull-up resistors are provided by the printer interface circuitry. R1, R2, and R3 help protect the input
port by providing some current-limiting capability. C4, C5, and C6 debounce the switch contacts.
9.11
Support Illustrations
These illustrations, at the end of this section, support the descriptions within this manual.
9-30
Figure 9-8: LED Drive Circuit
Figure 9-9: Differential Synchronous Demodulation Circuit
Figure 9-10 N-20 HSO Timing Diagram
Figure 9-13: AC Variable Gain Control Circuits
Figure 9-19: Output Port Circuit
Figure 9-22: Display Control Circuit
Figure 9-24: Power Supply Circuit
Figure 9-25: Power Control Circuit
Figure 9-31: Printer Interface Circuit
Figure 9-33: N-20 SpO
Figure 9-34: CPU Circuit
Figure 9-35: N-20 Main PCB Schematic Diagram
Figure 9-36: N-20 Auxiliary PCB Schematic Diagram
Figure 9-37: N-20 Flex Circuit Schematic Diagram
Analog Block Diagram
2
Advertisement
Table of Contents
