Several good field effect transistor power amplifier circuit diagrams

Several good circuit diagrams

Field effect transistor multi-tube parallel output, 500W.

The biggest difference between field tubes and conventional power tubes is that field tubes are driven by voltage, and there are some differences in the driver stage. I have never tried a field tube power amplifier, so the sound quality depends on your design and craftsmanship!

IRFB33N15D is a very good MOS tube, with an internal on-resistance as low as 56mΩ, a maximum current of 33A, and a withstand voltage of 150V. It is often used in DC/DC converters. Of course, it is also often used in digital power amplifiers. .

It also has shortcomings. Its input capacitance is 2020pF. Like common MOS tubes, when driving it, a special circuit must be used to drive it. Just like the parallel circuit of R29 and D3 in your circuit, it is also a common method in the industry. The function is:

When there is no R29, the gate of Q7 is directly connected to the previous IC pin, and the inside of it is a totem pole circuit. Since it is a capacitive load, oscillation will occur, causing the driving waveform to ring. The resulting , the MOS tube is not opened enough, the internal resistance is large, and the efficiency is low. Adding R29 in series can eliminate this oscillation. The time constant between it and the subsequent MOS tube input capacitance (Ciss) is much smaller than the MOS tube turn-on time of 13ns, and the time constant of 4.7Ω 2020pF is 9.5nS, which meets the requirements.

When IRFB33N15D is driven by a standard circuit (equivalent to R29 being 3.6Ω), its recovery time is as long as 130nS. This is also a common problem of MOS tubes. In order to speed up the turn-off (to gain this 9.5nS time), when turning off, it is hoped that the gate The resistance is 0, so Schottky diode D3 (its operating frequency can be close to GHz) is connected in reverse parallel to R29 to accelerate the discharge.

The VGS of IRFB33N15D is between 3.0V and 5.5V. When actually driven, it depends on the working voltage of IRS2902S, which is actually around 10V. The forward voltage drop of Schottky diode D3 is only about 1.2V (the current is 1A, but its ΔV /ΔI is about 0, the dynamic internal resistance is extremely low), it can already ensure that Q7 and the gate are below VGS, and it has no effect on turn-off. In addition, you need to learn the meaning of dynamic internal resistance. Just like a power supply, its voltage drop may be 5V, but its internal resistance can be as low as more than ten milliohms.

The two field effect transistors in this circuit cannot be turned on at the same time, so when they are working, they must turn off first and turn on slowly. D3 and D4 diodes can quickly release the gate junction voltage of the field effect transistor when the driving voltage drops, thereby greatly shortening the time for the tube to return from the on-state to the off-state. When the driving voltage rises, the gate junction capacitance of the tube is charged through R29 and R27, thus delaying the conduction time of the tube. In this way, the function of priority of shutdown and slightly slower conduction is realized, which greatly avoids the situation that one tube has not exited conduction and the other tube has entered the state of conduction.