EU Class Amplifier / Class EU Amplifier

The EU Class amplifier combines the advantages of the Class A amplifier and the Class B amplifier to produce a better amplifier design The purpose of any amplifier is to produce an output large enough to meet the needs of the input signal but meets the needs of the load attached to it. We found that the power output of an amplifier is the product of the voltage and current applied to the load (P = V*I), while the power input is the product of the DC voltage and current from the power supply. Although amplification of a Class A amplifier (where the output transistor transmits 100% of the time) can be high, the efficiency of the conversion from a DC power supply to an AC power output is generally less than 50%. However, if we change the Class A amplifier circuit to work in Class B mode (where each transistor transmits only 50% of the time), the collector current flows through only 180o of the cycle in each transistor. The advantage here is that the efficiency of converting from DC to AC is much higher at about 75%, but this Class B configuration causes the output signal to break down in a way that may be unacceptable. One way to produce an amplifier with a high-efficiency output of the Class B configuration, together with the low distortion of the Class A configuration, is to create an amplifier circuit, a combination of the previous two classes. The EU Class amplifier output floor then combines the benefits of the Class A amplifier and the Class B amplifier, minimizing the low efficiency and corruption issues associated with them. As we mentioned above, the EU Class amplifier is a combination of Class A and B, as the amplifier for small power outputs works as a Class A amplifier, but turns into a Class B amplifier for larger current outputs. This action is achieved by the front polarity of the two transistors in the output stage of the amplifier. Each transistor will then transmit between 180° and 360° of time, depending on the amount of current output and the pre-polarity. Thus, the amplifier output floor works as an EU Class amplifier. First, let's look at the comparison of output signals for different elevated working classes.

  • Class A: – Single-output transistor transmits for a full 360° cycle of the input waveform.
  • Class B: – Transmits only half of the input waveform of the two output transistors, that is, 180°.
  • EU Class: – Transmits two output transistors somewhere between 180° and 360° of the input waveform.

EU Class Amplifier Voltage Pre-Polaration

Here, the polarization of transistors is obtained by using a suitable constant pre-recess voltage applied to the soles of TR1 and TR2. Next, there is a region where both transistors are conductive and the small motionless collector current flowing from TR1 meets the small motionless collector current flowing from TR2 to the load. When the input signal is positive, the voltage at the base of the TR1 rises and produces a similar amount of positive output, which increases the collector current flowing from tr1 welding current to load to RL. However, since the voltage between the two bases is constant and constant, any increase in the transmission of TR1 will result in an even and opposite decrease in the transmission of TR2 during the positive half cycle. As a result, the transistor TR2 eventually shuts down and releases the forward-sided transistor TR1 to ensure all current gain to the load. Similarly, for the negative half of the input voltage, the opposite happens. That is, when the input signal becomes more negative, TR1 turns off, while TR2 sinks the load current. Next, when the input voltage IS ZERO, we can see that both transistors are somewhat conductive due to voltage pre-polarization, but as the input voltage becomes more positive or negative, one of the two transistors further reduces the source of the load current. Because the switching between the two transistors occurs almost instantly and is smooth, the crossover distortion affecting the Class B configuration is greatly reduced. However, incorrect polarity can cause sharp cross distortion elevations when switching two transistors. The use of a constant pre-polarization voltage allows each transistor to transmit more than half of the input cycle (Class AB operation). However, it is not very practical to have extra batteries in the upgrader's output floor design. A very simple and easy way to produce two constant front polarization voltages to set a stable Q point close to the transistor segment is to use a resistant voltage dividing network.

EU Class Amplifier Resistance Bias

When a current passes through a resistance, a voltage drop develops along the resistance, as defined in the Ohm law. Thus, by placing two or more resistances in series to a supply voltage, we can create a voltage dividing network that produces a series of constant voltages at the values we choose. The basic circuit is similar to the above voltage pre-redecry circuit, which transistors transmit during opposite half cycles of the input waveform of TR1 and TR2. That is, it transmits TR1 when vin is positive and TR2 when VIN is negative. The four resistors, R1 to R4, are connected along the Vcc supply voltage to ensure the necessary resistant polarity. The two resistors, R1 and R4, are selected to set the Q-point slightly above the cut, and the correct value of VBE is set to about 0.6V, so that if the voltage drops along the resistant network, it brings the base of the TR1 to about 0.6V. , and TR2's to approximately –0.6V. Then, the total voltage drop along the pre-redefinition resistors R2 and R3 is about 1.2 volts, which is just below the value required to fully open each transistor. By pressing transistors just above cutting, the value of the motionless collector current, ICQ, should be zero. In addition, since both switching transistors are connected effectively serially throughout the feed, the VCEQ volt drop in each transistor will be approximately half of the Vcc. While the resistant polarity of an EU Class amplifier works in theory, a transistor collector current is very sensitive to changes in the basic polarity voltage VBE. Also, the cutting point of the two complementary transistors may not be the same, so finding the right combination of resistance within the voltage dividing network can be laborious. One way to overcome this is to use adjustable resistance to set the correct Q point, as shown.

Adjustable Amplifier Pre-Polaration

An adjustable resistance or pocinciometer can be used to direct both transistors to the transmission threshold. The TR1 and TR2 transistors are then polarized via RB1-VR1-RB2 to stabilize their output and flow zero immobile current into the load. The input signal applied through the C1 and C2 capacitors is overlayed on the pre-polarity voltages and applied to the bases of both transistors. Note that the signal applied to each base has the same frequency and amplitude as the vin. The advantage of this adjustable front polarization arrangement is that the basic amplifier circuit does not require the use of complementary transistors with near-identical electrical characteristics or the full resistance ratio within the voltage dividing network, as the posiometer can be adjusted for compensation. Since resistors are passive devices that convert electrical power into heat due to the degree of power, the resistant polarity of a fixed or adjustable EU Class amplifiers can be very sensitive to changes in temperature. Any small change in the operating temperature of the pre-polarization resistors (or transistors) can affect the values of each transistor that produce unwanted changes in the motionless collector current. One way to overcome this problem with temperature is to replace resistances with diodes to use diode deflection.

EU Class Amplifier Diode Pre-Polaration

While the use of polarized resistors may not solve the temperature problem, one way to compensate for any change in temperature in the base-emitter voltage (VBE) is to use a pair of normal forward-sided diodes in the polarizing arrangement of the amplifiers, as shown. A small constant current flows through the serial circuit of the R1-D1-D2-R2 and produces voltage drops that are symmetrical on both sides of the input. When the input signal voltage is not applied, the point between the two diodes is zero volts. As the current flows through the chain, there is an forward voltage drop of approximately 0.7 V along the diodes applied to the base-emitter connections of the switching transistors. Therefore, the voltage drop along the diodes deflects the base of the transistor TR1 to approximately 0.7 volts and the base of the transistor TR2 to approximately –0.7 volts. Thus, the two silicon diodes provide a constant voltage drop of about 1.4 volts between the two bases, pressing them over the breakpoint. As the temperature of the circuit increases, so does the temperature of the diodes located next to the transistors. Voltage along the PN connection of the diode thus reduces the deflection of some transistor base current, which stabilizes the transistor collector current. If the electrical properties of the diodes closely match that of the transistor base-emitter connection, the current flowing in the diodes and the current in the transistors will be the same and create what is called the current mirror. The effect of this current mirror balances the changes in temperature that produce the required EU Class work, thereby eliminating any transitional distortion. In practice, diode polarity can be easily performed on today's integrated circuit amplifiers, as both the diode and switching transistor are produced on the same chip as the popular LM386 audio power amplifier IC. This means that both have the same characteristic curves during a wide temperature change that allows thermal stabilization of the sedentary current. The polarity of an EU Class amplifier output stage is usually adjusted to fit a specific amplifier application. The amplifier's still current is set to zero to minimize power consumption, as in The Class B process, or adjusted to the flow of a very small motionless current that produces a real EU Class amplifier operation, minimizing transition corruption. In the eu class pre-polarity examples above, the input signal is connected directly to the switched transistor bases using capacitors. However, we can slightly improve the output stage of an EU Class amplifier by adding a simple common emitter drive stage, as shown.

EU Class Amplifier Driver Stage

Transistor TR3 acts as a current source that adjusts the required DC pre-polaration current flowing through the diodes. This sets the silent output voltage to Vcc/2. Because the input signal runs the base of TR3, when TR2 is off, the positive half of the input cycle acts as an amplifier stage that runs TR1 and the negative half of the input loop running TR2, and the bases of TR1 and TR2. As with most electronic circuits, there are many different ways to design a power amplifier output stage, since many variations and modifications can be made in a basic amplifier output circuit. The job of a power amplifier is to provide the connected load with a reasonable degree of efficiency and a significant output power (both current and voltage). This can be achieved by running the transistor(s) in one of two basic operating modes, Class A or Class B. One way to operate an amplifier with a reasonable level of efficiency is to use a symmetric Class B output floor based on complementary NPN and PNP transistors. With an appropriate level of advanced polarization, it is possible to reduce any cross-distortion as a result of both transistors being cut for a short period of each cycle, and as we see above, such a circuit is known as the EU Class. Then by putting it all together, we can design a simple EU Class power amplifier circuit, as shown now, producing about one watt to 16 ohm with a frequency response of about 20Hz to 20kHz.

EU Class Amplifier

Summarize

Here we found that an EU Class amplifier is polarized for the output current to flow less than a full cycle of the input waveform, but more than a half loop. The implementation of EU Class amplifiers is very similar to standard Class B configurations in that each transistor uses two switched transistors as part of a complementary output phase that the input waveform transmits over opposite half loops before being combined in load. Thus, by allowing both switching transistors to transmit current at the same time for a very short period of time, the output waveform during the zero transition period can be greatly softened by reducing the transition distortion associated with the Class B amplifier design. Then the transmission angle is larger than 180° but much smaller than 360°. We also found that an EU Class amplifier configuration is more efficient than a Class A amplifier, but slightly less efficient than Class B due to the small still current required to direct transistors immediately above cutting. However, the incorrect use of pre-poaring can cause cross distortion spikes, which creates a worse situation. However, EU Class amplifiers are one of the most preferred sound power amplifier designs due to their combination of fairly good efficiency and high quality output, as they have low cross distortion and high linearity, similar to the Class A amplifier design.