Reference voltage source circuit diagram

Reference voltage source circuit diagram (1)

TL431 is a reference voltage integrated circuit with excellent performance . It is used in voltage stabilization, instruments, adjustable power supplies and switching power supplies . It is characterized by: a large adjustable output voltage range of 2.5~36V; a small output impedance of about 0.2Ω, an absorption current of 1~100mA, and a temperature coefficient of 30ppm/ ℃. The graphical symbol of the device is shown in Figure (a). There is a 2.5V precision reference voltage source inside it.

Figure (b) is a voltage stabilizing circuit using TL431. The maximum stable current of the circuit is 2A, and the adjustment range of the output voltage is 2.5~24V. The light-emitting diode in the figure is used as a voltage regulator to keep the emitter junction of T2 constant, thereby making the current I1 constant, ensuring that when the input voltage changes, the TL431 will not be damaged due to excessive current. When the input voltage changes, the reference voltage UREF of TL431 changes accordingly. When the output voltage rises, the cathode voltage of TL431 decreases as UREF rises, and the output voltage decreases accordingly.

Reference voltage source circuit diagram (2)

The internal circuit of the MC1403 reference voltage source is very complex, but the application is very simple and requires only a few external components. The illustration shows its general application. In the figure, RP is a precision potentiometer , used to accurately adjust the output reference voltage value, and C is a noise elimination capacitor . When the input voltage Ui of MC1403 decreases from 10V to 4.5V, U0 changes by 0.0001V, and the change rate is only 0.0018%.

The output voltage of the circuit in the picture above is stable at 2.5V. If you want to obtain a reference voltage source higher than 2.5V, you can use the circuit shown in the picture below. In the figure, ICL 7650 is a chopper auto-zero precision operational amplifier , Rf is the feedback resistor , and R1 is the inverting input resistor. R1=Rf=20kΩ. The output voltage U0 is:

Reference voltage source circuit diagram (3)

The following is a very exquisite high-precision voltage reference circuit. The 431 in the picture can also be other reference sources (such as LT1004) or even a simple Zener diode .

Reference voltage source circuit diagram (4)

A Zener diode only provides its specified breakdown voltage when a specific test current Iz flows through it. Therefore, the size of the series current-limiting resistor in the figure below cannot be too large, and it is necessary to ensure that sufficient current flows through the diode.

For example, using a 9V supply and a 1N751A, the Zener diode has an I z of 20 mA, then the resistor value is (9-5.1)/20 mA = 195 ohms. The advantage of this solution is that the circuit is simple and the cost is relatively low.

Reference voltage source circuit diagram (5)

The most common one we have is the 7805 three-terminal voltage regulator. Such devices generally have output short-circuit protection and can tolerate wide fluctuations in load current more easily than a simple Zener regulator.