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By combining the three DC power supplies on the PB-503A, the user may work with virtually
any type of integrated circuit or discrete component. The fixed 5 V / 1A supply has become
an industry standard for powering digital IC’s. Integrated circuits which r5 V, +12 V,
and -5 V are easily accommodated by the PB-503A. The variable supply output voltages may
be changed by adjusting the knobs at the top on the front panel. The positive and negative
outputs are variable from +1.3 at 150 mA to +15 V 500 mA and -1.3 at 150 mA to -15 V at 500
mA. Both variable supply outputs are referenced to circuit common. This creates a split supply
which is often used with differential and operational amplifiers (op amps).
Components and Features
Sixteen LEDs, eight red and eight green, make up eight Logic Indicators that will display logic
high and low conditions based on either TTL or CMOS thresholds, selectable by the user.
Operating voltage can also be selected by the user to be either at +5 V, or +1.3 V to 15 V
at the setting of the +V supply. This selection should be the same as the operating circuitry
that is to be monitored. The red LEDs will light when the voltages at the inputs are 2.2 V or
higher when in the TTL position, or 70% of the operating voltage or higher when in the CMOS
position. The green LEDs will light when the voltages at the inputs are 0.8 V or less when
in the TTL position, or 30% of the operating voltage or less when in the CMOS position. An
unconnected input, or an input not at a valid logic level, will cause both LEDs to be off. Note
that the thresholds determined by the TTL positions are only accurate when the +5 volt range
is selected. The 100 kΩ input impedance ensures minimal loading effects of the circuit under
test.
Power Supplies
Digital Function Generator
Logic Indicators
The multi-waveform digital function generator provides continuously variable frequency
signals from 0.1 Hz (for extra-low frequency work) to radio frequency signals of 100 kHz. The
frequency is selected in two ranges, with a LED screen to easily view the current settings. The
generator can be set in increments of 0.1 Hz or 0.1 kHz in their respective ranges as desired.
The sine wave output is factory adjusted for minimum distortion. The triangle waveform is
adjusted for best linearity. The standard square wave and TTL level outputs are both set at a
50% duty cycle. The low output impedance of the sine, square, and triangle waveforms (600
Ω) assures maximum coupling of the output signal to the device being driven. All outputs can
withstand a continuous short circuit to ground. The signal amplitude can be adjusted from 0 to
20 Vpp with an open circuit and 0 to 10 Vpp with a 600 Ω load.
