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1. The soft start power supply is mainly used in applications where the power supply is required to be small. The circuit diagram is shown in Figure 1. The design of many amplifiers. Whether it is DIY or commercial circuit. When the power is turned on, strong impact noise is generated. This is usually caused by the power supply rising too fast. If it is a high-power amplifier, it is easy to burn out the speaker. Of course, the amplifier is added with a delay to turn on the speaker circuit. The solution to this problem is to use a soft-start power supply with a slow start feature. In the circuit of Figure 1, the AC power supply is D-rectified and C1 filtered, and the Zener diode DW provides a reference voltage with an output voltage of at least 0.6V. According to the output voltage, two Zener diodes can be connected in series. The total voltage drop of the Zener diode can be selected from 28V to 63V. Switch S1 (in conjunction with the main switch) controls the power on and off. When S1 is closed, the voltage on capacitor C2 takes about 1 s to rise to the operating voltage, and the output voltage follows a slow rise. When the voltage-stabilizing Zener diode breaks down, the output voltage is stable. When disconnecting S1. Capacitor C2 is discharged through the base of T1, and the voltage drop takes about 5 seconds. Switch S1 can be omitted if the amplifier design is not critical to power outage requirements.
The voltage on capacitor C2 should not exceed 80V. If it needs to be exceeded, the capacitor with higher withstand voltage needs to be replaced. The tube voltage drop of T3 should meet the requirements. Not too big, so as not to waste power. Generate heat. Ideally, after the T3 tube voltage drop load is connected, the sum of the voltage drop and the fluctuation of the power supply voltage is 2V. When the load is not connected, the tube pressure drop of T3 is allowed to be as large as 10V, and the heat sink must be added to T3. T2 is also best to add heat sinks.
2. The quad-balanced power supply is mainly used in situations where two sets of positive and negative symmetrical power supplies are required. The circuit diagram is shown in Figure 2. In addition to providing a set of positive and negative symmetrical power supplies (±1), the circuit also provides the ability to provide another set of positive and negative power supplies (±2). The voltage of this group of power supplies is higher than the (±1) group supply voltage, and the output current is also small. Visible from the schematic. It is possible to obtain an auxiliary power supply using the main power winding.
Assuming the transformer output voltage is 2V, the tube voltage drop of the rectifier diode is neglected, then the voltage of the main power supply (±1) is ±√2 v1, and the capacitor C3 is charged by C1 through D2 in the positive half cycle. Charge D4 through D3 in the negative half cycle. Correspondingly, the voltage at ±2 points is ±2√2 v1. The rectifier tube in this circuit uses the IN400 series, according to the amplitude of the output voltage. The values ​​of the capacitors C1 to C6 may be 100 to 680 μF.
3. One winding can output positive and negative power supply circuits at the same time as shown in Figure 3. The positive power supply circuit is a conventional bridge rectifier circuit. For the negative power supply part, when the diode D3 is turned on. The potential at the positive terminal of capacitor C2 is approximately zero. The power supply charges C3 through D3, C1, C2, and D2, in order to ensure that the voltages on C1 and C3 are almost equal. Must ensure that D3 is always on. This requires that the output current of the positive power supply circuit must be greater than the output current of the negative power supply circuit. If the two are equal, a light bulb can be added to the positive power supply circuit and used as an indicator light.
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