100W amplifier circuit with bandwidth from DC to 100kHz

This is an ideal Class AB power amplifier with perfect over-current protection and precise gain. Its power reaches 100W and the bandwidth is from DC to 100kHz. The attached figure is its complete circuit. The
output stage uses power MOSFET tubes and is driven by a full-swing output (rail-mil) high-speed operational amplifier: the two form a transconductance amplifier, and its output current is proportional to the input voltage; the high and low ends of the circuit are symmetrically connected relative to the positive and negative power supplies.
In order to work in Class AB, the drive signal is a nonlinear current symmetrical between the high and low positions.
In order to improve the output characteristics, a feedback circuit and a PI (proportional/integral) control circuit are set up; the integrator of the PI circuit is used to control the gain error and DC offset caused by load changes and internal parameter changes to the minimum state. The entire circuit constitutes an inverting amplifier that amplifies 100 times from the DC signal.
The output can be obtained from ±2V to ±200V:
400Vp-p is output at a 200Ω load, and a flat characteristic from 1kHz to 100kHz can be obtained, and the high-order harmonics are only 0.05%.
In the transconductance amplifier composed of a high-speed operational amplifier and a MOSFET, R19 is used to convert the drain current of Tr7 into a voltage signal and feed it back to the inverting input terminal of IC4: the positive and inverting input terminals of the operational amplifier are connected to the positive power supply terminal respectively.
D6 and D17 form a feedback loop from the drain of Tr7 to the collector of Tr3. To prevent Tr7 from saturating when the input signal is too large; C6 is a phase compensation capacitor.
Amplifiers with high voltage output must be protected from short circuits at their output terminals to avoid damaging the output tube. For the output stage of the transconductance amplifier. Overcurrent protection can be set. Because the output current is proportional to the input voltage, it is sufficient to limit the input voltage. Here, the peak and average overcurrents are protected separately.
Peak protection: Use D12, D13, D1l, and D16 to clamp the output of IC3 to limit the current flowing through R22. Since the capacitive component Ci of D11 and D16 is connected in parallel with R32, the frequency characteristics of IC3 will deteriorate, so D12 and D13 are added to prevent this situation. D6, D12, and D13 in the figure should be selected with a small Ci.
Average value protection: Use R5 (R1) and C1 (C3) to convert IE flowing through Tr3 (T16) into voltage. When this voltage value exceeds the voltage regulation value of the voltage regulator diode D1 (D2), Tr9 (TrlO) is turned on to limit the current flowing through R22.
The frequency characteristics are corrected by the feedback loop. The change in frequency characteristics caused by load changes is suppressed through the OUT→H→IC2→IC3→R22 loop. The circuit of IC2 and IC3. Its phase delay is "0" near 10MHz. The gain curve is flat. IC2 and IC3 use op amps with gain-bandwidth products of 100MHz and 290MHz respectively.
In order to improve the load regulation rate and keep the output voltage stable, an integrator composed of ICl and C15 is added to the input of the circuit. Feedback is introduced from the output stage, and the integral constant (C15) is proportional to the load capacity, making the entire circuit very stable even when the capacitive load is 0.003μF to 0.22μF. The peak value of the frequency characteristic is kept within -3dB.