TL431 is a cost-effective common shunt voltage reference with a wide range of uses. In layman's terms, it is used to generate a very stable reference voltage source. For example, when using AD for voltage acquisition, if the reference voltage is not stable enough and interference from the power grid is received, it will cause errors in the measurement results. At this time, it is necessary A very stable reference voltage source. There are many similar voltage reference chips on the market, but the TL431 is very cost-effective, so it is widely used.

The TL431 data sheet is available on alldatesheet. The chip has 3 main pins: CATHODE (negative), ANODE (positive), and REF (reference voltage). TL431 has many application scenarios, I only use it as a reference voltage source.

The following figure shows a PT100 temperature resistance detection circuit:

The left half is the signal generating part, and the right half is the signal amplifying circuit. Just look at the left part. The voltage, current, and resistance in the circuit are clearly marked. By adjusting the sliding rheostat to change the resistance of Ra and Rb to achieve the purpose of adjusting the output voltage, the output voltage calculation formula of TL431 is:

Vout = (Ra+Rb)*Vref/Rb (where Vref is the internal reference voltage of TL431 2.5V)

It is stipulated that the value of Rc should meet:

1mA "(Vcc-Vout)/Rc "500mA (I didn't find the value of 500mA in the data sheet)

When there is no load, that is, when Rd is positive infinity, Ib is approximately 0mA, and Ia must be greater than Ib. As long as Ia is greater than 1mA, the expected voltage value can be obtained by adjusting the sliding rheostat. At this time, if the load is added, Ib will increase. If the resistance of Rc is too large, Ia <Ib will be caused. This is not correct. At this time, the output voltage will decrease and the correct expected voltage cannot be output. At this time, a reasonable value of Rc resistance must be obtained through calculation.

According to the knowledge of electricians, Ia=Ib+Ic+Id, Id is a fixed value and small, can be ignored, then Ia=Ib+Ic, so Ia》Ib, and Ib=Vout/Rd, Ia=(Vcc-Vout )/Rc, then (Vcc-Vout)/Rc》 Vout/Rd, the value of Rc should be based on this formula. For example, if Rd is set to 1000Ω, Vout is set to 4.096V, then Ib≈4mA, then Ia》(Vcc-Vout)/Rc, namely Rc》(Vcc-Vout)/Ia, Rc<(5-4.096)/4mA=226Ω, take A standard resistance slightly less than 226 ohms is enough, but not too small, because the range of Ic is 1mA~100mA. If Rc is 5 ohms, then Ia=(5-4.096)/5=180.8mA, but at this time Ib The current is only below 10mA, and Ic=Ia-Ib=about 170mA, which exceeds the Sink-Current range of the chip's cathode pin of 1~100mA, which is not allowed! If this VREF is also used in other places, then the value of current Ib is the sum of the currents of all parts.

What is the difference between tl432 and tl431

They are all controllable precision voltage regulator sources. They are all three-terminal voltage regulators with adjustable voltage values, and the entire series is divided into Type A and Type B. The main difference is the voltage range:

The TL432 reference voltage is 1.25v.

TL431A: ±1% of typical accuracy, minimum voltage 2.475V, maximum 2.525V, typical 2.495V.

TL431: +/- 2% of the accuracy of the typical value, the minimum voltage is 2.445V, the maximum value is 2.545V, and the typical value is 2.495V. Other indicators are the same, and the pins are compatible.

A voltage stabilizing circuit refers to a circuit that can maintain a constant output voltage when the input voltage, load, ambient temperature, circuit parameters, etc. change. This circuit can provide a stable DC power supply and is widely used in various electronic devices.

There are many ways to classify stabilized power supplies. According to the type of output power supply, there are DC stabilized power supplies and AC stabilized power supplies; according to the connection mode of the stabilized circuit and the load, there are series stabilized power supplies and parallel stabilized power supplies; according to the adjustment tube The working status is divided into linear stabilized power supply and switching stabilized power supply; according to the circuit type, there are simple stabilized power supply and feedback stabilized power supply, and so on.

Such a variety of classification methods often make beginners confused and wonder where to start. In fact, it should be said that these seemingly diverse classification methods have a certain level of relationship, as long as this level is clarified, the types of power sources can naturally be distinguished.