Precision voltage and current regulated power supply

　　(1) Working principle of CV/CC power supply CV/CC power supply is usually a power supply constructed based on the linear regulation principle. Figure 1 is its typical circuit. In the figure, the error amplifier AU is in the voltage control path, and AI is in the current control path. Their outputs are connected to the base of the output adjustment tube through an "OR" gate composed of diodes. This "OR" gate ensures that the adjustment tube is driven by the error amplifier AU or AI with a higher output voltage. When the output current Iout of the CV/CC power supply is not high, that is,

　　Figure 1 Typical circuit of CV/CC power supply

The voltage stabilization part works. In the formula, U'r is the reference voltage of the amplifier AI in the current path. By changing this voltage, the set value Io of the output current can be changed. At this time, the amplifier AI has no output, and the adjustment tube is only controlled by the amplifier AU. The output voltage will be stable at the value given by formula (7-4)

Where Rf is the feedback resistor.

　　Once the output current Iout exceeds Io, amplifier A1 starts to work. The power supply enters the steady current working state. At this time, the steady current control of the circuit is effective, and the stable load current is

　　It can be seen that changing Rf and Ur in the circuit can smoothly control the output voltage and output current in a wide range; automatically converting from voltage regulation (CV) to current regulation (CC) or from current regulation (CC) to voltage regulation (CV). Because the opening voltage of the diode "OR" gate is only 0.5~0.7V, if Au and AI use high-gain operational amplifiers, only a small level shift at the input end is required to achieve voltage regulation and current regulation control.

　　(2) High-stability regulated power supply In precision measurement, the stability of the power supply is sometimes required to be equal to or better than 10-6 (10min). In order to achieve such high stability, some special measures are often taken when designing and manufacturing the power supply. Figure 2 shows the block diagram of the optoelectronic regulated power supply.

　　Figure 2 Block diagram of optoelectronic regulated power supply

　　In Figure 2, the standard battery E is connected in series with the galvanometer and then connected across the output voltage. Under normal circumstances, the current in the sampling and comparison circuit is 0, and the small mirror and photosensitive element of the galvanometer are in a balanced position. When the output voltage fluctuates, the equilibrium state is destroyed, the current in the sampling and comparison circuit is not 0, the galvanometer deflects, and the light and shadow irradiated on the photosensitive element change, thereby generating a deviation signal. The adjustment circuit is controlled by this deviation signal, forcing the output voltage to return to the normal value, thus achieving voltage stabilization.

　　Figure 3 is a circuit diagram of a photoelectric voltage-stabilized power supply in actual use. It is mainly composed of a rectifier filter circuit, a pre-stabilization circuit, a photoelectric amplifier circuit, an adjustment circuit, a relay protection circuit and a galvanometer light source system. VT2, VT3, etc. constitute a pre-stabilization circuit, VT4 is a pre-stabilization error amplifier, VT1, VD5 and R2 are the constant current source loads of VT4, which are used to increase the amplification factor of the amplifier circuit. VT9, VT10, etc. constitute an adjustment circuit, VT11 is an error amplifier, VT8, VD8 and R8 are the constant current source loads of VT11. The comparison reference of the error amplifier is composed of R15, R9~R12 and the voltage regulator tube VD7, and the output voltage is sampled by Q2, R13 and Q3, R14. VT7 and R16 in the circuit diagram are used for overcurrent protection; the protection system composed of VT5, VT6, Q1 and the relay is used to protect the galvanometer and the standard battery. When the sampling comparison circuit is overloaded, the light deviates from the photosensitive transistor, the relay protection circuit is activated, and the switch in the sampling circuit is automatically cut off.

　　Figure 3 Circuit diagram of photoelectric voltage regulator