Click Here to download 600 watt mosfet amplifier circuit diagram
Input stage works as a transconductance amplifier ( voltage in - current out ).
This stage consist of Long Tailed Pair (LTP) made by Q1 & Q6 working in differential mode. Current flows from Constant Current Source (CCS) made of Q2 & Q5, two transistors are used to improve PSRR and Linearity. Current is balanced by Current Mirror (CM) made of Q3 & Q4,
In simple words input signal is amplified by the input pair Q1 & Q6, current amplified input signal is sent to VA Stage for voltage amplification.
Voltage Amplification Stage ( VAS )
As the name suggests all the voltage GAIN of the amplifier is achieved in VA Stage.
VAS of this circuit is Darlington ( Beta Enhanced ) so low GAIN transistors can be used.
Signal received from input stage is amplified via Darlington pair Q8 & Q11. Constant current flows from CCS made of Q9.
Biasing circuit is made of Q10, preset RV1 is to adjust output stage biasing voltage.
it is important to note that the biasing transistor Q10 must be mounted on the same heatsink along with Output transistors to ensure thermal tracking.
In simple words signal received from input stage is amplified by Q8 & Q11. voltage amplified signal is sent to output stage.
Output Stage ( OPS )
Output stage of this circuit is Class B, so each half of the signal is amplified by each pair of N-Channel and P-Channel MOSFETs.
Driver Transistors Q12 & Q13 work as buffer to prevent excessive loading of VAS as well as to provide input to the output mosfet pairs of Q14, Q16 and Q15, Q17 respectively.
Output Topology is Complementary Feedback pair which has improved linearity and better thermal tracking.
Negative feedback via R11 to the base of Q6 ensures overall amplifier performance and stability.
Zobel Network made of R34, C9 provides protection against high frequency oscillations.
In simple words signal received from VAS is given to the output MOSFET via driver transistors. output MOSFET conduct high current to drive the speakers in accordance with signal.
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Power output at various Supply Voltages -
Standard Test configuration for output power measurement -
PCB designed with thick copper tracks & large solder pads to facilitate straightforward placement and soldering of components.
* - Always use complementary NPN-PNP pairs.