A signal generator is an electronic test instrument that produces precisely controlled, repeating electrical waveforms—like sine, square, or triangle waves—at specific frequencies and amplitudes to stimulate and test circuits. When you are designing, building, or troubleshooting 12V/24V/48V power systems, inverters, or battery management systems (BMS), you cannot always rely on the actual battery bank or the AC grid to test your control logic safely. Instead of risking a blown MOSFET or a shorted lithium cell, a signal generator lets you inject a safe, adjustable bench signal into your control board to verify its behavior before connecting high-power sources.
What a Signal Generator Actually Changes on the Bench
Beginners frequently confuse a signal generator with a power supply or an oscilloscope. A power supply provides static DC voltage and current to run a circuit. An oscilloscope reads and visualizes electrical signals. A signal generator, however, creates the dynamic stimulus. It replaces missing or untestable real-world inputs—like a spinning alternator, a grid AC waveform, or a thermistor changing resistance—with a known, mathematically perfect waveform.
By injecting this known variable, you isolate faults in power control boards. If your solar charge controller is not firing its buck converter MOSFETs, you do not need to guess if the microcontroller is failing or if the gate driver optocoupler is dead. You bypass the microcontroller, inject a known square wave directly into the gate driver input, and watch the output on your scope. If the driver switches correctly, the fault lies upstream in the logic; if it does not, the driver stage is compromised.
Most benchtop signal generators have a 50Ω output impedance. If you set the generator to output 5V peak-to-peak (Vpp) and connect it to a high-impedance load (like a 1MΩ oscilloscope input or a microcontroller GPIO), the voltage will actually double to 10Vpp due to impedance mismatch reflection. This is the number one reason hobbyists fry 3.3V ESP32 GPIO pins when testing inverter logic. Always set your generator to 'High-Z' (High Impedance) load mode in the utility menu if you are connecting it directly to logic boards, or use a 50Ω BNC feed-through terminator.
Worked Numeric Example: Driving a 48V Inverter H-Bridge
Let us look at a real-world scenario: testing the high-side and low-side MOSFETs in a 48V DC-AC inverter H-bridge using an IR2110 gate driver IC. Before connecting the 48V LiFePO4 battery bank, you must verify the gate driver is receiving the correct pulse-width modulation (PWM) and translating it into the 12V gate-to-source (Vgs) signals required to fully enhance the power MOSFETs.
- Set the Waveform: Select a square wave on the signal generator.
- Set the Frequency: Enter 50 kHz. This means the total period (T) is 1 / 50,000 = 20 µs.
- Set the Duty Cycle: Dial in 50%. The signal will now stay HIGH for 10 µs and LOW for 10 µs.
- Set the Amplitude: Set it to 3.3Vpp with a 1.65V DC offset (so it swings from 0V to 3.3V), perfectly simulating the logic output of a 3.3V microcontroller feeding the optocoupler.
- Inject and Measure: Connect the BNC lead to the PWM input pin of the IR2110 test circuit. Probe the HO (High-side Output) pin with your oscilloscope.
If the circuit is working, your oscilloscope will show a 12V square wave switching at 50 kHz. Crucially, you must check the rise time. For hard-switching 48V inverters, the Vgs rise time must be under 100 ns to prevent the MOSFET from lingering in its linear region, which causes massive heat dissipation and catastrophic thermal runaway. If the signal generator proves the input is perfect but the rise time on the scope is 400 ns, you know you need to lower your gate resistor value or upgrade your bootstrap capacitor.
Where You Meet This in Practice
In the power and energy storage space, signal generators are indispensable for simulating physical phenomena that are otherwise difficult to control on a workbench.
- BMS NTC Thermistor Simulation: Battery Management Systems rely on negative temperature coefficient (NTC) thermistors to monitor cell temperatures. To test the BMS over-temperature disconnect logic without heating up a battery pack with a heat gun, you can use a signal generator paired with a voltage divider to sweep a DC voltage curve that perfectly mimics the resistance drop of a thermistor going from 25°C to 65°C.
- Solar Charge Controller MPPT Sweep: When designing the input stage of a solar charge controller, you can use a signal generator to output a slow-moving triangle wave into the feedback loop of your operational amplifier. This simulates the changing voltage of a solar panel moving through its maximum power point, allowing you to tune the PID controller response times on the bench.
- UPS Zero-Crossing Synchronization: Uninterruptible Power Supplies (UPS) must switch from battery-inverter power back to grid power exactly when the AC sine wave crosses zero volts to avoid massive inrush currents. You can feed a clean 60 Hz sine wave from a signal generator into the UPS zero-crossing detection circuit to verify the optocoupler triggers at exactly 0V, rather than relying on noisy grid power that might mask timing errors.
Benchtop vs. Handheld: Tool Selection Matrix
Choosing the right tool depends on whether you are doing precision inverter design or quick field troubleshooting on a solar array. Below is a comparison of standard options used by power electronics builders.
| Feature | Siglent SDG1032X (Benchtop) | FNIRSI SG-004A (Handheld) | ESP32 DevKit (DIY Code) |
|---|---|---|---|
| Best For | Inverter design, BMS logic tuning | Field testing, quick PWM injection | Permanent embedded stimulation |
| Max Frequency | 30 MHz | 100 kHz | ~40 MHz (LEDC peripheral limits) |
| Waveform Types | Sine, Square, Ramp, Pulse, Noise, Arb | Sine, Square, Triangle | Square (PWM), Sine (via DAC) |
| Amplitude Control | 1 mVpp to 20 Vpp (precise) | 0.1 V to 12 V (stepped) | 0V to 3.3V (fixed logic) |
| Approx. Cost (2026) | $350 - $400 | $35 - $45 | $8 - $12 |
For serious power electronics work, the benchtop unit's ability to output arbitrary waveforms and precisely control edge times makes it mandatory. The handheld units are excellent for verifying if a motor controller responds to a basic 5 kHz PWM signal, but they lack the amplitude precision required for logic-level simulation.
Frequently Asked Questions
What is the difference between a signal generator and a function generator?
In modern bench terminology, the terms are largely interchangeable, though 'function generator' traditionally referred to instruments that only produce basic repeating waveforms (sine, square, triangle). A 'signal generator' is a broader term that historically included RF (radio frequency) generators and arbitrary waveform generators (AWGs) capable of producing complex, non-repeating digital data streams. For testing 12V/24V/48V power systems, a standard function/arbitrary waveform generator is exactly what you need.
Can I use an ESP32 as a signal generator for inverter testing?
Yes, but with strict limitations. An ESP32's LEDC (LED Control) peripheral can generate highly stable square waves (PWM) up to roughly 40 kHz with precise duty cycle control, which is sufficient for testing basic buck/boost converter gate drivers. However, the ESP32's onboard DAC is limited to low-frequency, low-resolution sine waves, making it useless for simulating 50/60 Hz AC grid zero-crossings with the precision required by a UPS transfer switch. Furthermore, the ESP32 outputs 3.3V logic; if your gate driver requires a 5V or 12V logic threshold, you will need to add a level-shifter or optocoupler between the ESP32 and the device under test.
Why does my generator output read double the voltage on my oscilloscope?
This is the classic 50-ohm impedance mismatch. Signal generators are designed to drive 50-ohm transmission lines (like long coaxial BNC cables used in RF). To ensure the voltage at the end of a 50-ohm cable matches the screen readout, the generator internally outputs twice the set voltage, expecting half of it to drop across its own internal 50-ohm series resistor. If you connect the generator directly to an oscilloscope set to 'High-Z' (1 Megohm) input, no voltage drops across the internal resistor, and you measure the full, doubled voltage. To fix this, either change the oscilloscope's input impedance to 50 ohms (if supported and within voltage limits), use a 50-ohm BNC terminator at the scope end, or change the signal generator's utility settings to 'High-Z Load' so it stops doubling the output.
