1. Design of DC stabilized power supply
Design of Rectifier Transformer
The design of the three-phase rectifier transformer includes: the connection method of the primary and secondary windings, the calculation of the secondary side voltage, the calculation of the primary and secondary side currents, the calculation and determination of the capacity, and the selection of the structure form. Among them, the connection method of the primary and secondary windings and the determination of the secondary side voltage are the contents of our key analysis. This article takes the design of three DC power supplies of a stepper motor driver as an example to introduce in detail
2. Determination of secondary side voltage
The secondary voltage is not only related to the load voltage (that is, the DC voltage stabilized power supply voltage to be designed) and the rectifier circuit, but also related to the voltage stabilizer device. For the bridge-type rectifier circuit with high requirements, the capacitor filter voltage regulator and the voltage regulator can be used for voltage regulation. As shown in Figure 1, the +7V low-voltage drive is mainly used for phase locking, its current is small, the voltage is low, and the voltage fluctuation has little effect on the working state of the drive power supply, so no voltage regulation is required; +110V is used for high-voltage drive, intermittent High frequency power supply and high frequency, large current and current change rate will produce high overvoltage, so electrolytic capacitors should be used for voltage regulation and resistance current limiting; +12V is used for computer and integrated circuit power supply, with small current and low voltage, However, it requires stable voltage and small ripple coefficient, so two-stage voltage regulation with capacitors and three-terminal voltage regulators is used. For different voltage stabilization methods, the secondary voltage has different determination methods. In theory, the calculation formulas of these three voltages are the same, that is, U2=Ud/2.34 or UL=Ud/1.35, the calculated three secondary voltages The voltages are: 5.2V, 81.5V and 8.9V, but the results of this calculation are not suitable in practice. Therefore, some quantities must be determined by engineering estimation formulas. For example, the three-phase irreversible rectifier system generally uses the formula UL=(0.9 ~1.0)•Ud estimation, if the DC side is filtered by electrolytic capacitors, the average output value will increase, generally estimated by the formula UL=Ud/2½; Voltage range, Ud should generally be increased by 3 ~ 6V, and then use the formula UL = (0.9 ~ 1.0) • Ud to estimate. The three secondary voltages thus determined are: UL7=0.9×7=6.3V,
UL110=110/2½=78V, UL12=16×0.9=14.4V.
3. Rectifier circuit design
Three-phase rectifier circuits usually include three-phase half-wave rectifier circuits and three-phase bridge rectifier circuits. Because the output average voltage of the three-phase bridge rectifier circuit is high, the voltage ripple is small, and the quality factor is high, bridge rectifier circuits are often used. The selection of the diode type on the bridge arm is mainly determined by its rated voltage and rated current, and the rated current and voltage are determined by the average load current and voltage. The calculation formula is: ID=(1/3) ½•Id, ID( AV)=ID/1.57, UDn=(1～2) 2½•U2, the type of rectifier can be determined by checking the diode manual by ID(AV) and UDn.
