This is a MOSFET transistor based power amplifier circuit that can be operated between +35V to -35V range. The input voltage is pre filtered and pre amplified before applying to the MOSFET switch. The pre audio amplifier is a differential amplifier section with PNP transistor.What is differential amplifier? A difference amplifier is a type of power amp with two differential inputs which amplify the difference between two input signals. Here we are dealing with the circuit diagram and working of high voltage differential amplifier using IRF9530 and IRF530 MOSFET. You need a dual power supply circuit for this amplifier which I had posted earlier.
Recommended: MOSFET Working Animation
Don’t forget to have a look at other amplifier circuits in the related posts section at the bottom.
Circuit diagram of MOSFET power amp
Click on the circuit diagram for enlarged view
- Dual power supply
- Resistors ¼ watt (10Ω; 560Ω; 680Ω; 820Ω; 1.2kΩ; 2.2kΩ; 2.7Ωk x 2 4.7kΩ x 2; 10kΩ; 15kΩ; 47kΩ x 2)
- Preset (1kΩ)
- Electrolytic capacitors (47µF,16V x 2; 100µF,50V x 4)
- Capacitors (220pF; 68nF)
- Inductor (12 turns of enameled copper wire on a 1cm diameter plastic former- 0.1µH)
- Diode (1N4002)
- BJT transistors (BC556 x 2; BC546 x 2)
- MOSFET (IRF530; IRF 9530)
- Speaker (8Ω)
Working of 50 Watt amplifier
- Input audio signal is pre filtered using a low pass filter and applied to the differential amplifier based on transistors Q5 and Q6.
- C7 removes the high frequency noise signals and R16 limits the current through C7.
- The intermediate stage consisting of Q3 and Q4 acts as a driver to the next MOSFET stage.
- To adjust the quiescent current, a preset is connected at the base of Q3 transistor.
- The IRF530 and IRF9530 MOSFETs are important part of this amplifier.
- Here the two MOSFETs form a complementary push pull driver amplifier which is the output stage of our power amplifier.
- R14 and C8 reduce the unwanted noise occurring in the MOSFET amplifier.
- The capacitors C5 and C3 are power supply filters. The output speaker is driven via an inductor to make noise free amplifier.
Remember: Provide a suitable heat sink for MOSFETs.