Master the Basics: Supply Dual Voltages

One of the most common challenges for electronics beginners building circuits with operational amplifiers (Op-Amps) is supplying dual voltages—that is, both a positive and a negative voltage relative to a common ground.

Why Do Op-Amps Need Dual Voltages?

Op-Amps can only output voltages that fall within their power rail limits. If you’re designing a circuit where the Op-Amp needs to output AC signals (which swing both above and below ground), then your Op-Amp must be powered by both positive and negative supply voltages.

Let’s walk through three beginner-friendly ways to supply dual voltages for your circuits.

1. Using a Benchtop Power Supply (The Easiest Way)

Benchtop power supplies are ideal for dual-voltage applications. They typically offer:

• A positive output terminal
• A negative output terminal
• A common ground terminal

For example, if you configure the power supply to output ±5V, the left terminal gives you +5V, the right gives –5V, and the middle is ground.

Breadboard Setup Tip:

• Connect the common ground to the inner ground rails on both sides of your breadboard.
• Connect +5V to the left red rail.
• Connect –5V to the right black rail.

This layout gives you symmetrical voltage access across your circuit. But what if you don’t have a benchtop power supply?

2. Using a DC-DC Converter Chip

If you're working with a single voltage power source—like a battery or wall adapter—you can generate a negative voltage using a DC-DC converter.

A great example is the TC7660H chip by Microchip. It takes a positive voltage (1.5V–10V) and generates the corresponding negative voltage. So if you input +5V, the chip outputs –5V.

⚠️ Note: These chips often require external capacitors to function correctly. Always refer to the chip’s datasheet for the correct configuration.

3. Creating a Virtual Ground (Budget-Friendly DIY Method)

Don’t have a benchtop power supply or converter chip? You can create a virtual ground using a simple voltage divider.

How It Works:

• Use two equal resistors (e.g., 1 MΩ each) in series between the positive and negative terminals of a battery.
• Tap the middle point—this becomes your virtual ground.
• For example, with a 9V battery:
• Virtual ground = 4.5V (middle of the divider)
• You now have +4.5V and –4.5V relative to this virtual ground.

Problem: Load Imbalance

If your circuit draws current from the virtual ground, the voltage may shift and become unstable.

Solution: Buffer with an Op-Amp

A voltage follower (unity gain buffer) Op-Amp solves this. It:

• Maintains the virtual ground at a stable level

• Has high input impedance (won’t disturb your divider)

• Has low output impedance (can drive loads)

This setup lets you safely use dual voltages for your circuit—even with a basic 9V battery.