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In the circuit diagram provided, the 555 timer is configured in astable mode, generating a square wave output at a frequency of 20 kHz with a 1:1 duty cycle. When pin 3 is high, capacitor C4 charges; conversely, when it's low, capacitor C3 charges. Diodes VD1 and VD2 ensure that neither C3 nor C4 discharges in the circuit. The maximum charge voltage reaches EC, while the B terminal is grounded, producing a dual power supply of ±EC at terminals A and C. This circuit boasts an output current exceeding 50 mA.
Below are several single-to-dual power supply conversion circuits. Figure 1 presents the most straightforward design. However, it suffers from high power consumption due to the small resistor values chosen for R1 and R2. Additionally, the circuit's load-carrying ability is weak when these resistors have larger values, making this configuration impractical.
Figure 2 modifies Figure 1 by replacing the resistors with large capacitors. This reduces power consumption to nearly zero, making it ideal for applications where the positive and negative power supplies share similar loads.
Building upon Figure 1, Figure 3 incorporates two transistors, increasing the circuit’s load capacity. The output current is determined by the maximum collector current (ICM) of transistors BG1 and BG2. A feedback loop ensures that the positive and negative power supplies remain balanced even when the loads are unequal. For instance, if Ub decreases due to uneven loading, Ua remains constant (as it is supplied by the fixed voltage from R1 and R2). Transistor BG1 turns on, BG2 turns off, and part of the current flows through BG1, causing Ub to rise again. When RL1 equals RL2, both transistors are off, allowing R1 and R2 to be increased.
The circuit in Figure 4 builds upon Figure 3 by adding two biasing diodes. These diodes help the transistors exit their inactive regions, improving feedback and leading to greater symmetry and stability. Alternatively, the diodes can be substituted with resistors of tens to hundreds of ohms.
Figure 5 improves upon Figure 4 by replacing R2 with a Zener diode and transistor, further enhancing feedback mechanisms and ensuring superior symmetry and stability.
Figure 6 introduces an operational amplifier wired as a voltage follower. Its output current is limited by the op-amp’s load capability. For higher output powers, a power amplifier like the TDA2030, which features enhanced open-loop gain, can be utilized. Despite its simplicity, this circuit outperforms earlier designs.
These circuits provide various options for converting a single power supply into a dual power supply system, each with unique advantages depending on specific application requirements.