![]() Resistor R1 and transistor Q1 behave like a bias potential divider for Q2 base and likewise resistor R3 and transistor Q2 perform the bias base for the transistor Q3. The base bias of Q1 is implemented by resistors R2 and R5. The below discussed three stages are directly connected. RV1 works like a volume control and hooks up with the amplifier stage by means of C1. It operates using a battery supply as low as 4.5V. The circuit shown below makes use of just 3 transistors, is able to amplify with an output transformer, and provides an output power between 100 -200mW. When power output, harmonic, distortion, frequency response are not considered critical for an amplifier, for example in small radios receivers, applying a class 'A' amplifier becomes a favorable choice. In the above paragraphs we learned how to build a class A amplifier using MOSFET, now we will learn how a simple class A amplifier circuit could be built using only bipolar transistors or BJTs. If high current supply is used, make sure to use an appropriate heat sink for the FET. A resistor value of between 22 and 100 ohms can be a decent selection for testing. Practically any resistor could be utilized in place of R2 provided that the maximum current and power ratings of the FET aren't surpassed. If we put a a voltmeter across the Q1 drain and the ground of the circuit, and we fine-tune R3 to get a meter reading of half the power supply voltage. Essentially, the voltage across Q1 and the load resistor have to be the same for the working of class-A amplifiers.Ī 100K potentiometer (R3) along with a 1M fixed (R1) constitute a straightforward adjustable gate-bias circuit. In this condition no current moves from the load resistor, R2. Having zero gate bias employed, Q1 acts similar to a switch which is in the switched off state. ![]() The IRF511 (Q1) is wired like a most simple class-A audio-amplifier circuit, as shown in the figure below. The bias was via a pot of 100K along with resistor of 1M.Ĭare should be taken to adjust the pot only for so long as half of the DC gets over the load resistors and MOSFET. To filter and smooth the power we used 10000♟ capacitors and Hammond make 10mH choke of 5 amp over pi filter setting. The power supply used for this single MOSFET class A power amplifier circuit is 18VAC and 160VA EI transformer attached to a bridge rectifier of 25 amp to generate DC power of 24 Volts. The heat-sink used for the mosfet was of 0.784 ☌/W. Please note, the device would be hot and susceptible to burning during idle mode, hence caution is utmost important.Ĭlass-A can never be an ideal option for a high efficiency amplifier design, but as we are applying the idea in this setup, we had to use more than 20 Watts power to generate a modest 4.8 Watts audio. However, to achieve total resistance of 15 ohms, the resistors are wired on a series of two, which makes 30 ohms and furthermore setting up the sets in parallel. ![]() To manage the load, we used four non-inductive wire wound resistors of 10W. This is used to couple the input and on the output a large electrolytic along with polyester bypass capacitor of 10♟. The capacitors that we used in this experiment is that of Sprague. The amplifier we are building is built by incorporating the device 2SK1058 N-Channel MOSFET from Hitachi. To build the circuit we need: A MOSFET, some capacitors and resistors and a sturdy power supply which has to be properly filtered using large filter capacitors.
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