Global Specialties PB-203A - Manual - Manual (Page 10)

10
USING THE PB-203A
The PB-203A is ideally suited for virtually any type of bread-boarding circuitry, from
TTL, CMOS and ECL, to op-amps, audio, comparators, video amps, microprocessor
components, phase locks and more. In order to get the most out of your breadboarding
experience, the following guidelines and tips should be observed.
Ground Loops: A ground loop is a Voltage drop on a ground bus, caused by a power
stage output ground, when entering the ground bus some distance away from the power
supply ground binding post. Although this Voltage drop may only be in the millivolts or
microvolts, it’s part of the output load. If a preamplifier input or circuit ground is
connected to a portion of this ground bus, feedback and oscillation can occur. This
issue can be resolved by positioning all output stages closest to the ground terminal,
with pre-amps further away.
By observing this simple rule, you will save hours of troubleshooting. Many audio ICs
have separate input and output grounds to prevent ground loops.
By-Pass Capacitors: Even though the PB-203A's power supplies are tightly regulated,
even a short length of power bus can cause a linear IC to break into oscillation at high
frequencies due to increased inductance. This increased inductance can be offset by
adding simple by-pass capacitors. By-pass capacitors (0.1pF ceramic disk type will be
sufficient) should by-pass the power buses as close to the ICs power supply pins as
possible. Utilize this technique for each IC.
Do not use electrolytic or paper capacitors as power bus by-pass capacitors. They have
high inductances, and become unreliable as by-passes above 1MHz.
Good by-passing should also be used with digital ICs to prevent the inability to reset or
clear, and false triggering.
COMBINING POWER SUPPLIES
The PB-203A can be configured in 2 additional voltage configurations beyond the 3
available fixed supply voltages. (See figure 3 below)
1. 30V Supply. By adding the 15 Volt supplies we can produce a 30 Volt supply at
0.25 Amps. This configuration requires that the load be placed across the +15
Volt terminal and the -15 Volt terminal.
2. 20V Supply. The +5 V supply can be added to the -15 V supply to make a 20 V
supply. This configuration will require that the load be placed across the -15 Volt
terminal and the +5 V terminal.