Method for obtaining a lower DC voltage by a higher voltage power supply

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

1.5PF SOT23-6 Low Capacitance 5V Breakdown Voltage 6V SRV05

Shunuo varistor / ESD varistor / product complete / Sunlord first-class agent

Overview:
The 78XX Series Regulator (DC / DC) is a three-terminal regulator widely used in electronics. For more complex circuits, each module circuit sometimes requires a different supply voltage to provide energy separately. In this case, if only one set of single output transformers is used to generate a voltage, after rectification, the requirements of the DC/DC modules of the latter stage cannot be reasonably satisfied. Because the input voltage range of different values ​​of DC / DC module is required, if the voltage input to the DC / DC module does not meet the specified requirements (for example, the input voltage exceeds the specified range), the conversion efficiency is often too low. The DC/DC module can even be burned out due to excessive power consumption. In this case, the usual method is:

1) Different step-down transformers are used to generate the AC voltages suitable for the DC/DC modules of the latter stage, and then rectified and stabilized separately. Thereby generating a DC power supply voltage required for each module circuit;

2) The secondary multi-tap step-down transformer is used to generate the AC voltage suitable for the downstream DC/DC module, and then rectified and stabilized separately.

Although these two methods are feasible, they are not reasonable if they are produced as products. Because, for the production company, not only must consider the product performance, but also consider the price and production operability (production process). That is to consider the performance price ratio of the product. The higher the price/performance ratio, the stronger the competitiveness of the market.

For the first method, if the latter stage circuit requires two DC power supply voltages, such as 5V, 12V, and is regulated by 7805 and 7812 respectively, then two power transformers and two-stage rectifier circuits are required. This will inevitably increase material costs, production costs, etc., while increasing the board area and product volume.

For the second method, if the latter stage circuit requires two DC power supply voltages, such as 5V and 12V, and is regulated by 7805 and 7812 respectively, the secondary of the power transformer is required to have at least three taps, respectively, which are suitable for two types. The AC voltage required by the 7805 and 7812 is then rectified and regulated by two stages. Such power transformers are rarely sold in the market, and the price is high, which is not good for the price/performance ratio of the products. These shortcomings are even more pronounced if the types of power supplies required for the latter circuits are increased.

The following describes a circuit that does not increase the cost but also meets the electrical performance requirements. This circuit can achieve a lower DC voltage from a higher supply voltage, and the conversion efficiency is high, and will not burn out because the input voltage of the DC/DC exceeds the specified range. Therefore, a single step-down transformer with a double tap is required, and after rectification and then supplying different DC/DC modules, different DC power supply voltages can be generated.
(Please read the PDF for details)