600w Mosfet Amplifier PCB
High power amplifier for use in DJ's, Public Address systems and other professional applications.
With output short Circuit Protection.
Q10, Q12, Q13 Must be Fitted together on a Heatsink / piece of Aluminum.
Only experienced / advanced users should make this one.
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 of Q1 & 65, working as differential amplifier.
Input signal received at the base of Q1 is amplified and sent to VAS from collector. Negative feedback (NFB) received at the base of Q6 from output determines overall gain and balance of the amplifier.
Constant Current Source (CCS) is made of 2 transistors Q2 & Q5 to increase the linearity.
Constant current by it is supplied to the LTP and VAS.
Collector currents of LTP transistors is balanced by Current Mirror (CM) made of Q3 & Q4.
In simple words input signal is amplified by the input pair Q1 & Q6 and sent to VAS for further amplification.
Voltage Amplification Stage (VAS)
As the name suggests, all the voltage gain of the amplifier is achieved in VA Stage.
The VA stage is Darlington (Beta Enhanced) which has better performance then single transistor VA stage.
Signal received from input stage at the base of Q8 is amplified via Darlington pair Q8 & Q11. Voltage amplified signal sent to the base of driver transistor Q13 from the Collector of Q11.
Current limiting circuit made of Q7, R16, R19 is added to VAS, it protects Q11 from overloading.
Constant current is supplied to VAS from CCS made of transistor Q7.
Biasing circuit is made of transistor Q10, which works as voltage divider. With preset RV1, Gate Voltages of output MOSFETs can be precisely adjusted.
Important to note that the biasing transistor Q10 must be fitted on the same heatsink along with Driver transistors Q12 & Q13 to ensure thermal tracking and feedback.
In simple words signal received from input stage is amplified by Q8 & Q11. voltage amplified signal is sent to output stage.
Output Stage ( OPS )
This circuit has Class AB output stage, so each half of the signal is amplified by N-Channel and P Channel output Mosfets.
Driver Transistors Q12 & Q13 work as buffers to prevent excessive loading of VAS and provide input to the output MOSFET's Q14, Q16, Q18 and Q15, Q17, Q19 respectively.
Complementary Feedback Topology ( CF ) is used at OPS. CF Stage is more linear due to local NFB and Thermal tracking is possible with driver transistors.
Output Short Circuit Protection - this circuit monitors current flow across Drain resistors and load, in case of output is shorted to ground the excessive current flow through the resistors will cause the Q20, Q21 to turn on and take away the signal from the driver transistors.
it is advised not to use 2Ω Speakers with this amp.
Zobel Network - made of R338 & C9, provides protection against high frequency oscillations.
In simple words signal received from VAS is given to the output MOSFETs via driver transistors. Output MOSFETs conduct high current to drive the speakers load.
Output power 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.