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Electronics Lab Essentials (2/7): power a circuit with the correct reference

Students learn voltage, polarity, ground/reference, current limiting, and safe power-up habits by measuring two real Hive DC-supply settings.

  • Electronics - Hive
  • 30 min
  • First-year university / introductory vocational electronics / upper-secondary electronics
  • English
  • Electronics
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Electronics - Hive
Electronics - Hive

Learning Outcomes

  • Explain voltage as a difference between two points.

  • Identify positive output, negative output, ground/reference, polarity, and current limit.

  • Predict the sign of a voltage reading when meter leads are reversed.

  • Apply a safe power-up and power-down sequence.

More for this lab

Student activity preview

Activity Content

Preview only. In a class session, students can fill in responses and submit their work to the teacher.

1

1 · A voltage needs two points

6 min

A bench supply can display 5.00 V, but that statement is unfinished until you
know which terminal is 5 V above which reference. The same circuit point can
be +5 V relative to ground, 10 V above a −5 V rail, or 0 V relative to
itself.

In this lesson you will learn output voltage, reference, polarity, and current
limit, then measure two real Hive supply outputs. The physical-supply guidance
is optional theory for future supervised work; this lesson requires no physical
equipment and no earlier lesson.

A laboratory DC power supply

Front panel of the Hive triple DC power supply with voltage and current displays, output controls, and colored terminals.

Physical supplies vary in appearance, but all require you to identify the output
terminals and settings before connecting a circuit. A number beside A may be
the current-limit setting, not current that is actually flowing. Use the
output-status and constant-voltage/constant-current indicators to interpret the
display on your specific supply.

Voltage is a difference in electric potential. Write it with two points:

Voltage between two points

If the red meter lead is at +5 V and the black lead is at 0 V ground, the
meter reports about +5 V. Reverse the leads and the magnitude remains about
five volts, but the sign becomes negative.

The red voltmeter lead is on +5 V; the black lead is on −5 V. What voltage
should an ideal meter report?

2

2 · Voltage, current limit, polarity, and ground

7 min

Four ideas organize a DC-supply setup:

- Voltage setting: the potential difference the supply tries to maintain.
- Current drawn: the circuit determines this from its resistance and behavior.
- Current limit: a maximum chosen to protect the circuit and supply. It does not force that current through the load. If the load tries to draw too much, the supply reduces its output voltage or enters current-limited operation.
- Reference or ground: the point defined as 0 V for the circuit. Circuit ground is a chosen reference; it is not automatically the same as protective Earth ground.

Choose a limit from evidence, not by guessing. First estimate the circuit's
normal current—for a simple resistive load, use I = V/R. Then consult the
component, wire, connector, and supply ratings. A suitable teaching-lab limit is
usually modestly above the expected normal current, but below the smallest safe
rating in the path. Follow the local manual or instructor when it specifies a
limit. In CV (constant-voltage) operation the supply maintains the selected
voltage; in CC or current-limit operation it reduces the output voltage to
keep current at the limit. A circuit that unexpectedly enters CC therefore may
receive much less than the selected voltage.

Reference and meter polarity

DC supply and voltmeter connected with red lead on plus 5 volts and black lead on ground, showing a positive five-volt reading and noting that reversing the leads reverses the sign.

The meter reads red-lead potential minus black-lead potential. Lead color helps
you remember the intended polarity, but the actual connections determine the
sign.

A supply is set to 5 V with a 0.20 A current limit. A healthy circuit needs
only 0.012 A. What should the current limit do during normal operation?

Optional theory for a future physical supply

No physical supply is needed here; all required measurements happen in Hive.
For a later supervised laboratory, start with the output disabled or the supply powered off. Set the intended
voltage and a current limit justified by the expected load and equipment
ratings. Verify polarity and ground, inspect for a direct short, then enable the
output while watching the actual current and the CV/CC indicator. Disable power
before changing wiring or investigating an unexpected reading. Do not short the
output merely to set or test the current limit unless the supply manual or
instructor explicitly requires that procedure and provides a safe method.

3

3 · Measure two real supply outputs

10 min

You will open two saved Hive setups. Each already connects a DMM across the
positive supply terminal and ground in DC-voltage mode. Do not move the wires or
change instrument mode.

First predict the two results: approximately +5 V and approximately +15 V.
Real measurements may differ slightly in the final digits.

Measure +5 V relative to ground

  1. Open Hive and wait for the saved +5 V setup.

  2. Inspect the two wires: one reaches the supply output and one reaches ground.

  3. Open the DC Power Supply instrument and identify the configured +5 V output.

  4. Open the Multimeter and confirm DC-voltage mode (V⎓).

  5. Select Perform Measurement (Realizar medición in Spanish) once and wait for the result.

  6. Record the signed number and unit in the +5 V row below.

Measure +15 V relative to ground

  1. Open this second saved setup and wait for the +15 V circuit to appear.

  2. Confirm that the DMM remains connected between the positive output and ground in DC-voltage mode.

  3. Select Perform Measurement once.

  4. Record the signed number and unit in the +15 V row below.

Complete exactly two rows after the measurements. The voltage unit is fixed as
volts (V), so enter the signed number, including a minus sign if one is
shown. Format-only example: a possible +5 V row is
+5 V | GND (0 V) | +5.01 | yes. Replace +5.01 with your own Hive reading.
Leave any extra blank rows unused.

DC supply measurements

Complete the two fixed rows after using the corresponding Hive setup. Record the configured output, the reference node, the signed measured value, and whether the polarity matched your prediction.

Configured output Black-lead reference Signed measured voltage V Matches prediction?

Calculate the magnitude of the difference between your two measured voltages.
Enter the number in volts, then show the subtraction using your two table values.

4

4 · Optional theory: safe first power-up

7 min

No physical supply or circuit is required. Use this hypothetical sequence to
prepare for a later supervised physical lab, where power is a controlled
step—not the starting point:

1. Output off: keep the supply output disabled while wiring.
2. Inspect: check voltage, polarity, ground, rail assignments, and likely shorts.
3. Protect: estimate normal current and set a limit modestly above it but below the lowest applicable circuit or lead rating, following the manual or instructor.
4. Connect: use leads with intact insulation and no exposed accidental contacts.
5. Enable and watch: observe current and the circuit immediately.
6. Stop if unexpected: disable power before touching or changing connections.

Which actions belong in a safe first power-up? Select all that apply.

In a hypothetical future lab, you expected +5 V, but a physical DMM shows
about −5 V. From the theory alone, explain what the negative sign most likely
says about the lead/reference orientation and what you would check before
changing the supply setting.