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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →A dual-frequency Class E converter is designed to run at either of two switching frequencies, with its resonant network providing a useful operating condition at each one. Selecting a frequency can change the converter’s power state or output behavior; it is not simply a matter of doubling the switching rate. In a properly designed circuit, the transistor can turn on when its drain voltage is near zero at both frequencies, reducing switching loss.
What makes a Class E converter resonant?
A Class E converter uses a transistor as a switch, rather than operating it continuously as a linear amplifier. A shunt capacitor—often including the transistor’s output capacitance—and a resonant output network shape the switch’s drain-voltage waveform and the load current. A DC-feed inductance supplies comparatively smooth current.
The circuit is timed so the transistor turns on when the voltage across it is approximately zero. This is zero-voltage switching (ZVS). Some designs also arrange for the voltage’s slope to be near zero at turn-on, a stricter condition called zero-voltage-derivative switching (ZVDS). These conditions reduce the overlap of switch voltage and current during turn-on, which helps limit switching loss. They do not eliminate conduction, component, or other circuit losses.
How does it operate at two frequencies?
The resonant network is designed to provide a useful impedance or resonance condition at each of two selected switching frequencies. The control circuit chooses between those frequencies to select the intended operating state. For example, a frequency may correspond to a high-power state and the other to a low-power state. In another design, the two operating points may provide different output characteristics or support power and data on the same inductive link.
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Both frequencies must work with the circuit’s load, duty ratio, component values, and transistor capacitance. The design must satisfy its resonant and switching conditions at each operating point; merely changing the frequency does not guarantee ZVS or the desired output.
One switching cycle
- Switch on: The transistor conducts while the shunt capacitor is discharged or held near zero voltage. The DC-feed inductance supplies relatively smooth current.
- Switch off: The resonant network and shunt capacitance shape the drain-voltage excursion, while the output network carries the desired fundamental-frequency current.
- Energy exchange: Inductors and capacitors exchange energy at the selected operating frequency. At the second frequency, the network uses its other designed impedance or resonance condition.
- Timed turn-on: The controller waits for the drain voltage to return near zero before turning the transistor on again. In a ZVDS design, it also targets a near-zero voltage slope at that instant.
Actual waveforms depend on duty ratio, load or reflected load, resonator quality factor (Q), switch output capacitance, and the selected frequency. A change between operating states also involves control and circuit dynamics; the available examples do not establish one universal transition method or ripple level.
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Why use two frequencies?
- Select power states: A 2023 control method alternates between high- and low-power states while preserving ZVS and ZVDS in both. It describes a prototype operating over 4–8 MHz, with control-frequency operation reported up to 500 kHz; that control frequency is not the same as the converter’s MHz switching frequency.
- Shape output across load changes: A dual-band multi-resonant network can be designed for load-independent constant-current or constant-voltage output at its operating points.
- Carry power and data: A 2024 open-access study designed a dual-frequency impedance-matching network for wireless power and data transfer over an inductive link, reporting soft switching at both frequencies.
- Limit switching loss at high frequency: Class E operation uses resonant waveform shaping and soft-switching conditions to reduce switching loss at RF and MHz frequencies.
What published examples show
| Example | Frequency and reported figures | Purpose or reported result |
|---|---|---|
| Dual-band multi-resonant converter (IEEE paper; published online in 2024, in a 2025 journal issue) | 6.72 MHz and 8.1 MHz; 12 V input; 4.5–18.3 W output | Designed for constant-current or constant-voltage output; the paper reports ZVS at both operating points. |
| Two-state control method (Celentano, Pareschi, Rovatti, and Setti, IEEE Transactions on Power Electronics, 2023) | 4–8 MHz prototype operating range; control-frequency operation up to 500 kHz | Alternates high- and low-power states while preserving ZVS and ZVDS in both states. |
| Wireless power-and-data link (Results in Engineering, 2024) | 91.3% reported power-transfer efficiency for a design with an original resonant frequency of 1 MHz | Dual-frequency impedance matching for wireless power and data transfer; the study reports ZVS and ZVDS at both frequencies. |
These are results from different designs, not universal operating limits or a direct performance comparison. In particular, the 91.3% figure belongs to the reported wireless-link design; it should not be treated as a general efficiency for dual-frequency Class E converters.
What to compare when evaluating a design
- Frequency pair and separation: These determine the resonant conditions the network must support.
- Electrical operating range: Check input voltage, output power, load or reflected-load range, and duty ratio together.
- Design objective: Establish whether the frequencies select power states, provide constant-current or constant-voltage behavior, or separate power and data functions.
- Resonator behavior: Consider Q, bandwidth, and sensitivity to component tolerances, which affect how robustly each operating point can be maintained.
- Switch limits: Check device capacitance and drain-voltage stress as well as whether the design requires ZVS alone or both ZVS and ZVDS.
- Control behavior: Evaluate transition ripple and control frequency separately from the power-switching frequency.
What information is needed to design one?
The topic alone is not enough to choose inductor, capacitor, transistor, gate-drive, or timing values. A design needs, at minimum, the target frequency pair, input voltage, output power, load or reflected load, duty ratio, transistor output capacitance, allowable switch-voltage stress, and required regulation mode. Published prototypes and methods illustrate possible approaches; they do not provide a universal parts list.
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