Detailed Circuit Analysis - HP LOGIC PULSER 546A Operating And Service Manual

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BURST CONTROL. Controls the start, stop, and count of a burst.
DISPLAY DRIVE. Controls the LED display to indicate Pulser activity.
Modei546A
ROM. A 256-bit special purpose read-only-memory that controls the operation of the Pulser.
TIME BASE/COUNTER. Used as time base for the ROM to generate the 1, 10, and 100Hz continuous
stream pulses, as a counter for the burst counts and for overall system timing.
CLOCK. Free-running 100Hz RC controlled clock acts as a time base for operation of the Pulser.
OUTPUT. Provides single positive and negative pulses at controlled rates, widths, and levels to the
output drive circuits. Senses the charge delivered to the external load and will automatically terminate
(shutdown), an output that exceeds a predetermined limit.
Detailed Circuit Analysis
As shown in
Figure 16,
transistor Q3 is a series pass element for a voltage regulator in U1 which
generates a 2.7 volt reference voltage. Resistor R4 acts as a series pass helper resistor, diverting
some of the heat normally generated in Q3, especially at high voltage. Capacitors CS and C7 act as
low impedance filter capacitors to the 2.7 volt supply. The LED for DS1 is driven by a switchable
constant current driver on U1 to indicate the output mode. A difference exists between the light
output of the LED and the tip output of the probe. Since the human eye cannot see a 100 Hz,
10 JLS blink, the LED pulses are actually slowed down and stretched, driving the LED at a slower
rate, indicating the particular activity at the tip. Switch 51 is used to program the mode of U1.
Resistor R3 and capacitor C6 are the timing elements that control the accuracy and frequency of
the voltage and temperature compensated 100Hz clock in U1.