DC-DC positive and negative dual power supply circuit diagram

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In the design of the radio compass detector, a positive (+12V), negative (-8V) DC dual power supply is required to power the relevant circuits. The detector is powered by a 27V DC power supply on the aircraft. This requires the conversion of the 27V DC power supply into a positive and negative dual power supply, and both the detector and the working circuit of the detector must be grounded. The author consulted a large amount of information and found that it is not difficult to convert the 27V DC power supply into positive and negative dual power supplies. However, due to the skin of the aircraft connected to the 27V DC power supply on the aircraft, it is necessary to realize 27V DC power supply, positive and negative dual power supply, and detection. The common working circuit of the instrument is relatively difficult, and it is easy to make the positive and negative dual power circuits short-circuit to the ground through the working circuit of the detector. Therefore, a dedicated DC-DC (DC-DC) positive and negative dual power supply circuit is specially designed.

1. Basic working principle The DC-DC positive and negative dual power supply principle circuit is shown in Figure 1.


The 27V DC voltage is regulated by the three-terminal integrated regulator block MC7812K, resulting in a stable voltage of +12V. C1 and C2 in the circuit are the filter capacitors at the input and output terminals respectively. In order to achieve a common ground output of -8V voltage and +12V voltage, an inverter circuit is used in the circuit, wherein the oscillation circuit is realized by NE555. The +12V voltage is supplied by the oscillation circuit composed of NE555. The oscillation frequency is determined by R2, RW1 and C4. The oscillation signal is rectified by C5 and D2 is half-wave rectified and sent to the input terminal of the voltage regulator circuit constructed by the three-terminal integrated regulator block MC7908K. , get a stable output voltage of -8V. In the circuit, D3 provides a path for the positive half cycle of the oscillating signal, and C6 and C7 are the filter capacitors at the input and output terminals of the voltage regulator circuit. In this way, the 27V power supply, +12V power supply, -8V power supply and radio compass detector can achieve common ground.

2. Design Considerations Due to functional requirements, the above positive and negative dual power supplies are + 12V, - 8V. If a ±X dual supply, or + AV, -BV (A < B) dual supply is required, the circuit needs to be adjusted. For example, if ±12V is required, the power supply voltage of the oscillating circuit needs to be increased. The design circuit is shown in Figure 2. The MC7815K supplies the power supply voltage to the NE555 oscillator circuit. In addition, the power of the power supply circuit is different depending on the needs. When designing the power supply circuit, the power margin should be fully considered, and the model of the three-terminal integrated voltage regulator block should be properly selected; and the three-terminal integrated voltage regulator block must be provided with a suitable heat sink.

It should be noted that DC-DC positive and negative dual power circuits already have ready-made integrated circuits (such as Marcos's MAX742, MAX743, etc.), but because of their output voltage is not adjustable, or output current, output power Smaller and more expensive, often fail to meet specific design needs. The DC-DC positive and negative dual power supply circuit designed in this paper is suitable for power supply from DC single power supply, but some working circuits need positive and negative dual power supply and the three must be common ground. This situation is in electronics, communication, Navigation equipment is very common. The voltage value of the power supply DC single power supply can be determined by the actual power supply. The voltage values ​​of the positive and negative dual power supplies can be designed according to the actual circuit operation requirements.