"Looking at the current market Hi-Fi amplifier, the output power is more than 100W amplification products, and the 50 ~ 100W amplifier has a considerable proportion. From the high-fidelity perspective, power reserves Of course, it is good, but if you look at the energy supply, it is worth considering. Since the efficiency of purel Amation is very low, there is more than 780% of the wonderful music. The electric energy becomes heat generation. One per channel output power is 50W pureroa power amplifier, if the efficiency of 30%, the static power consumption is 330W, saying that the joke is, it is "guard" The stove is eating watermelon. When the author is helping people, they often encounter such situations: Many people are touched by the tone of purel Alays, but they often have to be cut by their "high fever" work. The power consumption is also a fatal weakness of the electronic management power. The market economy is ruthless. The domestic manufacturer, such as Scark, Ou Bo, the big model has also launched his transistor amplifier, which proves This. According to China's national conditions, the living room area of the general working class is more than 20 square meters, and usually uses a living room or bedroom as an audio room. If the sensitivity of the speaker is more than 89dB, then 10 ~ 20W of pureroa Can meet the requirements of general appreciation. If our ears will have a big volume in the scene in the song hall, hearing will gradually decline. Again, noisy left neighbors must be peaceful, not suitable. So if you produce some The sound quality of the sound is better than about 15W, and the static power consumption is less than 100W. It will definitely have a market. Unfortunately, this type of power is a blank. The Japanese gold scorpion has a A20, and each channel is pure, 20W, the sound quality is awkward, but The price is expected. Now, the manufacturer of domestic production amplifiers seems to be compared, the power is more, the more weigh the weight, but the sales are not very good. Why not make some "delicious" power amplifier to put it What about the market? In this thought, we designed this 15W pure arm and try to do some attempts in this regard.
One circuit principle 1, power amplifier circuit
The differential amplification circuit is formed by VT1 and VT2, and the static current of each tube is about 0.5 mA. R3 is the collector load resistance of VT1, and the VT1 and the push-level VT4 are directly coupled. The output stage consists of the same NPN-type high-power transistors VT5, VT6 as the same type, and does not use complementary symmetric push-pull circuits. The output tube VT6 is a common emitter circuit for a load (speaker), and VT5 is an emitter output circuit, which is asymmetrical. However, the experimental test showed that the entire amplifier circuit was smaller in canceling a large loop negative feedback (short-circuiting R5 short circuit), and mainly even harmonic distortion. This credit should be attributed to the promotion level circuit. The driving circuit is the most distinctive circuit of this unit, and its role and effect have been compared with the traditional RC bootstrap circuit. The VT4 is a set-amplifier resolution circuit, which is respectively paired by a pair of sizes and an emitter output, respectively. VT4 is an emitter output circuit for the output tube VT6, and the voltage amplification is less than 1. The signal output from the VT4 collector is applied to the base of the output push tube VT3 by a light-emitting diode VD1 having a small AC resistance. The positive direction of VD1 is about 1.9V, which can be seen as a regulated diode having a small noise, which causes the DC voltage UEC at both ends of the emitter resistance R7 of VT3 to substantially change, and the voltage regulator value of VD1 is small. 0.7V. For AC signals, R7 is parallel to the emission junction of VT3. VT3 and VT5 form an same polar Dalinkon composite tube. Therefore, the push-pull upper arm is composed of one-stage co-amplifier circuit (VT4) and the secondary emitter output circuit (VT3, VT5), and the lower arm of the push-pull circuit is the primary emitter output circuit (VT4) ) And one-stage co-amplifier circuit (VT6), it is obvious that asymmetric push-pull amplifying circuits. Therefore, when selecting the magnifying tube, the current amplification coefficient of these tubes is not required. This is especially important in large quantities of factories, which can greatly reduce costs. The β values of the prototype were as follows: β1 = β2 = 110, β3 = 50, β4 = 90, β5 = 70, β6 = 90. That is to say, the tube having a large beta value is prioritized to VT4 and VT6. The open loop voltage of the power amplifier circuit is about 504, and the closed loop voltage is magnified by R4 and R5, about 15.7. The highest efficiency of the theoretical power amplifier circuit is 50%. The maximum valid value of the prototype is 11V. It is more than about 15W (8Ω), and the static power consumption is about 40W. Therefore, the highest efficiency is 37.5%. When there is no signal input, the efficiency is zero, and the 40W power is almost entirely consumed on two output tubes, so there is a sufficient area of the radiator and ensure that the ventilation is good. In short, this work is placed:
1. The current amplifier coefficient of the power output tube does not need to be paired;
2. The driving circuit designed by the author replaces the traditional bootstrap circuit, the frequency response is good;
3. The output voltage is large;
4. Simple circuit, easy to adjust, easy to make.
5, regulated power supply
Since the amplifier is an OCL circuit, the output is directly coupled to the speaker, so it is generally applied to the delay protection circuit, but since the machine uses a ± 17V dual voltage regulator power supply with short circuit protection and soft start function, this part is omitted. Circuit. The positive and negative regulated circuit uses the collector output to adjust the circuit, which is high and has a short circuit protection function, but it is not possible to start. VT7, VT9 composition composite power adjustment tube. VT11 is a sampling magnifier. Since the base of VT11 is grounded, the emitter potential must be -0.7V to make it working in an enlarged state. Therefore, the lower end of R19 cannot be grounded, but connected to -17V. Therefore, if the negative output power supply is shorted, the voltage between the emitter of VT11 and the base of the base is zero, thereby turning the VT11, so that the tube VT9 is adjusted, and the VT7 is not until the base current is also as close as possible. Make the positive output supply voltage is zero. Due to the positive and negative stasis circuits, the negative supply voltage is also zero when the power is shorted. The output of the power amplifier circuit has the reason for the speaker protection circuit. In case there is an output tube to break through the short circuit, the other output tube will not be able to receive the power supply voltage due to the above protection function, so that the speaker is not There is a large DC current, thereby effectively protecting the speaker. The output voltage of the power supply is basically determined by the voltage regulator value of the VD4, VD5, about 0.7V lower than the voltage regulator value (ie minus VT11, the emission of VT12), so Two stabilizers should be carefully picked up. Input filter capacitors use two 4700μF electrolytic capacitors in parallel, while the output end filter capacitor uses only one 10μF non-polar capacitor. Through the prototype measured, the ripple voltage when the output current is 2.4a (full load): the positive source side is 0.8mV, the negative source side is 1.25mV. Further, the waveform is not a 100 Hz serrated, but a wider noise shape with a wide spectrum. The voltage regulator performance of the power supply is better, and since the adjustment tube of the collector output regulator circuit has a certain number of voltage amplifications, the second is due to the sampling ratio of the sampling circuit equal to 1, the voltage variation of the output is passed directly through VD4. The VD5 is coupled to the emitter of the sampling magnifier VT11 and VT12. In order to eliminate the "" sound caused by the impact current of the speaker when the general OCL circuit is turned on, the power supply also designs a soft start circuit. The working principle is as follows: After booting, the positive voltage on the filter capacitor C3 passes the R10 to the C5 to C5, and the voltage on the C5 rises according to the index law. The voltage is applied to the positive power supply output by R12 and VD2 while providing current through the emitter of the VT12, so that the negative power supply is also started simultaneously. When the power supply voltage reaches the normal value, the positive output voltage provides a trigger voltage to the one-way thyristor VD3 via R14 to turn it on. After the VD3 is turned on, its anode voltage is lowered below 0.7 V, so the diode VD2 is turned off. The voltage on the C5 is discharged through R12 and VD3. The delay time is determined by R10, C5 time constant. In this example, this constant is 0.33 seconds, and there is no sound in the speaker when booting. The power supply is highly efficient, and the output voltage can remain stable when the voltage is adjusted to 1V between the adjustment tube collector and the emitter. If the market power is 220V, the input voltage of the regulator circuit is set to ± 22V (with rated load), and the regulated power supply can be operated at the optimum state when the power supply changes ± 10%. If the tube pressure drop is 7V, the charge is about 17W at full load 2.4a, so there is only a small heat sink, and the efficiency is more than 70%. When the adjustment tube pressure drop is 3V, the efficiency is 85%. In summary, the power circuit characteristics are: soft start function; with a positive and negative power supply, short circuit or simultaneous short circuit, can save speaker protection circuit; high efficiency, about 70 to 85% or more; low ripple coefficients.
Second, the production and adjustment points 1. Select power output pipe VT5, VT6 is used in Toshiba 2SC3281, and β between 70 and 110. Sanken 2SC 2922 was also selected during the experiment, but it was easy to generate high frequency self-excitement. The push tube VT4 was selected from 2SD401, the β value of 70 to 90, and VT3 was also used in 2SD401, β between 50 and 70. When the β value of the output tube is more than 100, VT3, VT4 can also be used to select domestic tube 3DG130 (3DG12). The input stage VT1, VT2 can be used with 9012 or 9015, etc., the β value is about 100, should not be too high, but require pairing; also uses a P-channel junction field effect transistor, but the pressure should not be less than 40V (due to hand no Such tubes are not experimenting). The power of the resistor R6, R10 should be selected 1W, R7, R16, R19 should be selected 1 / 2W or more, and the rest is not required. The resistor R9 is used in parallel with two 1W, 0.51Ω resistor, sampling as measurement. The regulator VD4, VD5 should optionally be 1W above power. Any model of one-way thyristor selectable 1A current. The VT7, VT8 of the power supply section selects MJ2955 and 2N3055 or other complementary parallel tubes, requiring β, preferably greater than 80. Push pipe VT9, VT10 selected medium power tube 3CK9, 3DK9, etc., the β value is between 50 and 80. The sampling magnifier VT11, VT12 is selected from 9014 and 9015, and the β value is greater than 100. It is also important to pay attention to the β value of the positive and negative power supplies should be similar, that is, substantially pairing. Capacitors C1, C6, C7 use polyester or polypropylene capacitance. The voltage regulated power input filter capacitor C3, C4 uses four 4700μF35V high quality electrolytic capacitors two or two. The power conversion power capacity of the power transformer should not be less than 100VA, the secondary AC voltage dual 18V, and the current 3A is above. The rectifier can be used with 1 N5401.
2. Adjust the point power supply section almost no adjustment. If the power cannot be started since start, the value of R10 should be appropriately reduced, but it should be as large as possible to increase the delay time when it is fully loaded. Adjustment of the amplifier portion can be attributed to two; one is that the adjustment R2 is equal to zero; the second is that the adjustment R6 makes the pressure drop on R9 equal to 0.3V, and the final static current is about 1.18A. Note that the current can be slightly smaller, such as 0.9A, and the like, then adjust to the above-described specified value.
3. The power discharge circuit is slightly changed to the OTL circuit. At this time, the voltage regulated circuit can save the negative power supply portion. Although the test results of the technical indicators are not as follows, the sound is not a flavor. Due to the use of an output capacitor, the OTL circuitry will affect the frequency of the frequency characteristics, but the safety of the speaker is guaranteed. It is limited to the space, and details will not be described here.
Third, the main technical indicators of this amplifier are as follows: The maximum output power is 15W (8Ω); the frequency response is 5Hz ~ 44kHz (-1dB, 10W, 8Ω); the voltage gain is 24dB; the input sensitivity is 0.7V (RMS) . After repeated audition contrast, everyone agreed that when the merit was played, the voice was generous and round, smooth and natural, and the expression of the singer was very good. The performance of the violin is uneven, and the analytical force is high. But for symphony with large dynamic range, this instance is not from the heart, but it feels that the low frequency is more moderate, and the profile of various instruments can be painted. Although it is inferior during great dynamics, because it is only 15W valid value power. Therefore, it is extremely suitable as a family appreciation of music and reaches the desired design purpose. "
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