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Royer Topology Achieves 100μVp-p Noise at 250V Output

This circuit's resonant Royer topology achieves 100μVP-P noise at 250V output by minimizing high frequency harmonic in the power drive stage. The self oscillating resonant Royer circuitry is composed of Q2, Q3, C1, T1 and L1. Current flow through L1 causes the T1, Q2, Q3, C1 circuitry to oscillate in resonant fashion, supplying sine wave drive to T1’s primary with resultant sine-like high voltage appearing across the secondary. T1’s rectified and filtered output is fed back to amplifier reference A1 which biases the Q1 current sink, completing a control loop around the Royer converter. L1 ensures that Q1 maintains constant current at high frequency. Milliampere level output current allows the 10k resistor in the output filter. This greatly aids filter performance with minimal power loss.2 The RC path to A1’s negative input combines with the 0.1μF capacitor to compensate A1’s loop. D5 and D6, low leakage clamps, protect A1 during start-up and transient events. Although Figure 2’s collector waveforms are distorted, no high frequency content is present.

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