Series voltage stabilizing circuit outputting 40V to 80V

The attached picture is a DC series voltage stabilizing circuit with an output voltage of +40V ~ +80V. Since the output voltage can be adjusted up to +80V, and the power supply voltage of the integrated operational amplifier is not high, the integrated operational amplifier cannot be used, so the NPN transistor 2SC240 with Vceo=120V has to be used to form a differential amplifier to amplify the error. The differential amplifier tube is on the right side of the picture. A transistor Tr5 is also connected in series to the collector circuit of Tr7. Tr5 is connected to form a common-base amplifier circuit, and forms a common-base cascade amplifier circuit with Tr7. Its purpose is to improve the frequency characteristics of the error amplifier.

Tr1 is a high voltage field effect transistor. Its Vds=1OOV forms a constant current source with a current of 2mA in the circuit. This constant current source is the collector load of the common-base cascade amplifier circuit. Of course, the constant current source can also use a constant current diode E-202 with a current of 2mA. The maximum operating voltage of E-202 is 100V. Rated power is 300mW. can meet the circuit requirements.

The adjustment tube of the voltage stabilizing circuit uses NPN transistor 2SD1407A. The maximum output current of the circuit design is 500mA. The voltage values ​​marked at each point in the circuit diagram are measured when the output voltage is set to 42V. At this time, the input voltage of the circuit ranges from 45V to 60V. When the circuit is operating normally, the voltage drop between the collector and emitter of the adjustment tube Tr3 should be kept above 3V. If the set output voltage is not 42V but other values, the input voltage range will also change accordingly. The maximum value of the input voltage is determined by the power loss that the adjustment tube can withstand. If the input voltage is too high and the load current is large, it may cause the adjustment tube to overheat and burn out. Tr4 and surrounding resistors and capacitors form an overcurrent protection circuit. Tr4 is cut off during normal operation. When the current (load current) flowing through R4 is too large, the voltage drop on R4 turns Tr4 on, forming a bypass for the base current of transistor Tr2, thus playing the role of overcurrent protection.