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In the circuit depicted in the diagram, a 555 timer IC is integrated into an unstable configuration, producing a square wave at its output pin with a frequency of 20 kHz and a duty cycle of 1:1. When pin 3 is high, capacitor C4 charges; conversely, when it's low, C3 charges. Diodes VD1 and VD2 ensure that C3 and C4 charge but do not discharge within the circuit. The maximum charging voltage reaches EC, while the B terminal is grounded. Consequently, terminals A and C yield a dual power supply of ±EC. The output current of this setup surpasses 50 mA.
Below are several variations of single-supply-to-dual-supply circuits. Figure 1 presents the most straightforward design. However, it suffers from high power consumption due to the small resistor values of R1 and R2; larger values weaken the load capacity. Thus, this circuit isn't ideal for practical applications.
The circuit in Figure 2 modifies Figure 1 by replacing the resistors with large capacitors. This approach eliminates power consumption entirely, making it suitable for scenarios where the positive and negative power supply loads are equal or nearly so.
Figure 3 builds upon Figure 1 by adding two transistors, boosting the circuit's load-carrying capability. The output current relies on the maximum collector current ICM of transistors BG1 and BG2. A feedback loop ensures symmetry between the positive and negative power supplies even under unequal loading conditions. If one load decreases, causing Ub to drop, Ua remains stable, prompting BG1 to activate while BG2 deactivates, redirecting current through BG1 to raise Ub. With balanced loads, both transistors remain off, allowing R1 and R2 to increase in size.
Figure 4 refines the design of Figure 3 by incorporating two biasing diodes, which push the transistors out of their inactive zones, improving feedback efficiency. This results in greater symmetry and stability. Alternatively, D1 and D2 can be swapped with resistors ranging from tens to hundreds of ohms.
The circuit in Figure 5 offers superior symmetry and stability compared to Figure 4 by replacing R2 in Figure 4 with a Zener diode and transistor, further amplifying feedback effects.
In Figure 6, an operational amplifier is employed as a voltage follower, with the output current depending on the op-amp's load capacity. For higher output power, a power amplifier like the TDA2030, known for its enhanced open-loop gain, can be utilized. Although simpler, this circuit performs better than its predecessors.
These circuits provide various methods to convert single power supplies into dual ones, each addressing specific limitations and offering unique advantages in terms of efficiency, load capacity, and overall performance.