The working principle and simple introduction of DC voltage stabilised power supply
The typical circuit block diagram of a transistor series-type DC regulated power supply is shown in Fig. It consists of a rectifier filter circuit, a series-type voltage regulator circuit, an auxiliary power supply and a protection circuit.
The rectifier filter circuit includes the power transformer, rectifier circuit and filter circuit. Semiconductor circuits commonly used DC power supply 6V, 12V, 18V, 24V, 30V and other rated voltage values, while the grid voltage is generally 220V AC, to transform the grid AC voltage into the required DC voltage, first of all through the power transformer step-down, and then through the rectifier circuit will be turned into a pulsating AC DC, due to the rectified voltage there is also a large AC component, must be filtered through the filter circuit. The rectified voltage has a large AC component, which must be filtered out by a filter circuit to obtain a smoother DC voltage.
After the filter circuit after the DC voltage, although the pulsation is small, but the value of the voltage is still unstable, the main reason for three aspects: First, the AC grid voltage is generally about ± 10% fluctuations, and thus will cause the rectifier filter output DC voltage is also about ± 10% fluctuations; Secondly, the rectifier filter circuit there is an internal resistance, when the load current changes in the internal resistance to the voltage landing will also change, so that the output DC voltage is also ± 10% fluctuations. Will change, so that the output DC voltage also changes; Third, in the rectifier regulator circuit, due to the use of semiconductor device characteristics change with the ambient temperature, so also cause the output voltage is not stable.
Voltage regulator circuits can maintain the stability of the output DC voltage so that it does not change with changes in grid voltage, load or temperature. Series type voltage regulator circuit consists of adjustment link, comparison amplifier circuit, sampling circuit, reference voltage and other parts. The adjustment tube in the adjustment link is connected in series between the filter circuit and the load, so it is called series-type voltage regulator circuit. Adjustment tube is equivalent to a variable resistor, if the output voltage increases, the resistance value increases accordingly, so that the output voltage back down; Conversely, if the output voltage drops, the resistance value decreases accordingly, so that the output voltage increases. This adjusts the output voltage to keep it constant, you can achieve the purpose of voltage regulation.
The sampling circuit uses the method of resistor divider to sample the change of output voltage in a certain proportion for the sampling signal. The reference voltage is a stable and standard reference voltage. Sampling signal and reference voltage at the same time added to the comparative amplifier circuit for comparison, and then amplify the difference between the two, with the amplified voltage to control the base of the regulator tube injected into the current to change the regulator's DC internal resistance, adjusting the output voltage is stable and unchanged. In order to improve the performance of the regulator, the comparative amplifier circuit is often used two-stage differential amplifier, amplification is larger, stronger control capability, followed by the comparative amplifier circuit also requires a small zero drift, good temperature stability.
The above rectifier filter circuit and series-type voltage regulator circuit together, also known as the main power supply. The voltage regulator principle is this: if the output voltage increases due to grid voltage or load changes, the sampling voltage generated by the sampling circuit also increases, the sampling voltage is greater than the reference voltage, the difference is amplified by the comparative amplifier circuit, after the adjustment link so that the emitter junction voltage of the regulator tube decreases, the base current decreases, the DC resistance of the regulator tube increases, the tube voltage drop increases, thus making the output voltage Decrease, maintaining the stability of the output voltage. Similarly, when the output voltage decreases, through a similar process, so that the DC internal resistance of the regulator tube decreases, its tube voltage drop decreases, will also make the output voltage back up, so that the basic unchanged.
