Little knowledge of battery: the basic principle of DC stabilized power supply

　　The little knowledge of battery: the basic principle of DC voltage stabilized power supply

　　The basic principle of DC stabilized power supply

The DC stabilized power supply consists of a power frequency transformer, a rectifier filter circuit and a voltage regulator circuit. The basic block diagram is as follows. The role of each component:

　　 (1) DC stabilized power supply [2] The function of the power frequency transformer is to convert 220 V AC voltage into AC voltage, which is rectification Required for filter circuit.

　　 The power ratio between the secondary side and the primary side of the transformer is P2/P1u003dη, where η is the efficiency of the transformer.

　　 (2) Rectifier filter circuit: The rectifier circuit converts the AC voltage Ui into a pulsating DC voltage, and then the filter circuit filters out larger ripple components and outputs.

　　 small ripple DC voltage U1. Commonly used rectification and filtering circuits are full-wave rectification and filtering, bridge rectification and filtering.

　　 Each filter capacitor C satisfies RL-Cu003d(3~5)5T~(2), the medium T is the period of the input AC signal, and RL is the rectifier filter circuit Equivalent load resistance.

　　(3) Three-terminal integrated voltage regulator: commonly used fixed three-terminal regulator and adjustable three-terminal regulator. Commonly used adjustable positive voltage integrated regulator.

　　 CW317 (LM317) series, its output voltage can be adjusted from 1.25V-37V, only need fixed resistance and minimum circuit external components

　　 Potentiometer. It has on-chip transition, overheating and safe working area protection. The maximum output current is 1.5A. Its typical circuit is shown in the figure. The output voltage UO

　　 The expression is: UOu003d1.25 (1＋R2/R1)

　　 Generally speaking, R1 needs 120? 240 ohms, and the voltage difference between the output and the regulator is the reference voltage of the regulator (typical value is 1.25 V).

　　2. Performance indicators and test methods of regulated current

　　The technical indicators of DC power supply[1] can be divided into two categories: One is the characteristic index, including allowable input voltage, output current and output voltage regulation.

　　 range, etc.; another indicator is used to measure the stability of the output DC voltage, including the voltage stability coefficient (or voltage regulation rate) and output resistance.

　　 (or current regulation rate), ripple voltage (surrounding and random drift) and temperature coefficient. The test circuit is shown in Figure 3.

　　2. Performance indicators and test methods of regulated current

　　DC power supply[1] has two technical indicators: one is characteristic indicators, including allowable input voltage, output voltage, Output current and output voltage regulation

　　 range, etc.; the other is the quality index, used to measure the stability of the output DC voltage, including the voltage regulation factor (or voltage regulation rate) , Output resistance

　　 (or current adjustment rate), ripple voltage (surrounding and random drift) and temperature coefficient. The test circuit is shown in Figure 3.

　　Figure 3　regulated power supply performance index test circuit

　　(1) Ripple voltage: superimposed on the output voltage AC voltage component. The peak-to-peak value observed with an oscilloscope is generally in the order of millivolts. AC millivolt can also be used

　　meter to measure its effective value, but because the ripple is not a sine wave, there is a certain error, the ripple voltage of the general DC power supply VP-P≤ 10mV.

　　 (2) Voltage stabilization coefficient: Under the condition that the load current and ambient temperature remain unchanged, the relative change of the input voltage causes the relative change of the output voltage, namely:

　　(3) Voltage adjustment rate: the relative change of output voltage when the relative change of input voltage is ±10%, the voltage regulation coefficient and voltage adjustment rate both indicate the input power

　　The effect of voltage changes on the output voltage, so you only need to test one of them.

　　(4) Output resistance and current adjustment rate

　　 The output resistance is the same as the output resistance of the amplifier, and its value is when When the input voltage is constant, the absolute value of the ratio of the output voltage change to the output current change.

　　Current adjustment rate: produced when the output current changes from 0 to the maximum The relative change value of the output voltage. Both the output resistance and the current regulation rate show the influence of the load current change on the output voltage, so only one of them needs to be tested.

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