The function and performance index and test method of special power supply

one,Special power supplyThe basic principle of

The special power supply is composed of a power frequency transformer, a rectifier filter circuit and a voltage regulator circuit. The functions of each part are:

(1) The function of the special power frequency transformer is to transform the 220V AC voltage of the grid into the AC voltage Ui required by the rectifier filter circuit. The power ratio between the secondary side and the primary side of the transformer is P2/P1=η, where η is the efficiency of the transformer.

(2) Rectifier filter circuit: The rectifier circuit transforms the AC voltage Ui into a pulsating DC voltage. Then filter the larger ripple component through the filter circuit, and output the DC voltage U1 with smaller ripple. Commonly used rectification and filtering circuits include full-wave rectification and filtering, bridge rectification and filtering.

(3) Three-terminal integrated voltage regulator: The commonly used integrated voltage regulators include a fixed three-terminal regulator and an adjustable three-terminal regulator. Commonly used adjustable positive voltage integrated voltage regulators are the CW317 (LM317) series. Their output voltage is adjustable from 1.25V to 37V. The simpler circuit external components only need a fixed resistor and a potentiometer. The chip has protections for transition, overheating and safe working area, and the maximum output current is 1.5A. The expression of the output voltage Uo of the typical circuit is: Uo=1.25 (1＋R2/R1)

In the formula, R1 generally takes 120-240 ohms, and the voltage difference between the output terminal and the adjustment terminal is the reference voltage of the regulator (typical value is 1.25V).

2. Performance indicators and test methods of the special power supply

The technical indicators of special power supplies are divided into two types: one is characteristic indicators, including allowable input voltage, output voltage, output current and output voltage adjustment range, etc.; the other is quality indicators, which are used to measure the stability of the output DC voltage. Including voltage regulation coefficient (or voltage regulation rate), output resistance (or current regulation rate), ripple voltage (surrounding and random drift) and temperature coefficient.