Several test power supplies

1. The soft-start power supply is mainly used in applications requiring small power supply shocks. The circuit diagram is shown in Figure 1. Many amplifier designs. Whether it is DIY or commercial circuit. When the power is turned on, it will generate a strong impact noise. This is usually caused by the power supply rising too fast. If it is a high-power amplifier, it is very easy to burn the horn. Of course, the general amplifiers have a delayed connection to the horn 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 rectifies D and filters C1. The zener diode DW provides a reference voltage and the output voltage is a minimum of 0.6V. According to the output voltage, two Zener diodes can be connected in series, and 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 turning on and off of the power supply. When S1 is closed, the voltage on the capacitor C2 takes approximately 1 second to rise to the operating voltage, and the output voltage follows the rise slowly. When the zener diode with a rising voltage breaks down, the output voltage stabilizes. When S1 is disconnected. Capacitor C2 discharges through the base of T1 and the voltage drop takes approximately 5 seconds. Switch S1 can be omitted if the amplifier design is not critical to power down.

The voltage on the capacitor C2 must not exceed 80V. If the voltage exceeds 80V, the capacitor with higher withstand voltage needs to be replaced. The pressure drop of the T3 tube must be selected to meet the requirement. Can not be too large to avoid wasting power. Generate heat. Ideally, the sum of the voltage drop caused by T3's tube voltage drop load and the fluctuation of the power supply voltage plus 2V. When the load is not connected, the pressure drop of the T3 tube is allowed to be as large as 10V. T3 must add the heat sink. T2 is also best to add heat sinks.

2. The balanced power supply is mainly used in applications where two sets of positive and negative symmetric power supplies are required. The circuit diagram is shown in Figure 2. In addition to providing a set of positive and negative symmetric supplies (±1), this circuit also has the ability to provide another set of positive and negative supplies (±2). The voltage of this set of power supplies is higher than that of the (±1) set and the output current is also smaller. Visible by the schematic. It is possible to use the main power winding to obtain an auxiliary power supply.

Assume that the output voltage of the transformer is 2V, and the voltage drop of the rectifier diode is ignored, then the voltage of the main power supply (±1) is ±√2v1, and the capacitor C3 is charged by C1 through D2 in the positive half cycle. Charge capacitor C4 through D3 in the negative half cycle. The corresponding ±2 point voltage is ±2√2v1. The rectifier in this circuit uses IN400 series, according to the amplitude of the output voltage. The value of the capacitors C1 to C6 can be 100 to 680 μF.

3. A winding can output positive and negative power supply circuit 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 section 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. It must be ensured 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.