Can a regulator diode really regulate voltage?

Can a regulator diode really regulate voltage?

As we all know, the regulator diode is in the reverse breakdown time, in a certain current range (or within a certain power loss range), the terminal voltage is almost unchanged, showing the characteristics of voltage regulation. This sentence reveals two meanings:

The regulator diode is connected in reverse to the circuit

It must operate within a certain range (up to Iz) to regulate the voltage

At this time, it is necessary to understand the main parameters of the regulator diode:

Vz—Stable voltage.

Refers to the stable voltage value generated across the regulator tube when passing through the rated current. This value varies slightly with operating current and temperature. Due to the difference in manufacturing process, the regulator value of the same type of regulator tube is not completely consistent.

Iz—Stabilizes the current.

Refers to the current value through the regulator tube when the stable voltage is generated. Below this value, although the regulator tube is not unable to stabilize, the voltage stabilization effect will deteriorate; Above this value, as long as the rated power loss is not exceeded, it is also allowed, and the voltage regulation performance will be better, but more power is consumed.

Rz—Dynamic resistance.

It refers to the ratio of voltage change to current change across the regulator tube. This ratio varies with the operating current, and generally the larger the winning current, the smaller the dynamic resistance. For example, when the operating current of a 2CW7C regulator tube is 5mA, Rz is 18Ω; When the operating current is 1OmA, Rz is 8Ω; Rz is 2Ω at 20mA, and remains at >20mA.

Pz—Rated power consumption.

It is determined by the allowable temperature rise of the chip, and its value is the product of the stable voltage Vz and the allowable current Izm.

CTV—voltage temperature coefficient.

is a parameter that describes the influence of the stable voltage value by temperature.

IR—Reverse leakage current.

Refers to the leakage current generated by the regulator diode at a specified reverse voltage.

Here mainly focus on three parameters Vz, Iz, Pz, here take 1N4728A as an example, the tube Vz=3.3V, Iz=76ma, Pz=1000mw.

For this tube, if you want to use it to stabilize the voltage to 3.3V, the current I requirement is 76mA = < I<< Imax, Imax = 1000/3.3 = 303ma, if it is lower than this value is also possible, but the voltage will also drop slightly, but too much lower is not good, if I is only 10ma, then the voltage output is very low; Imax is only a theoretical current value, and the actual use is lower than this value; Secondly, the voltage added to the tube must be greater than Vz, that is, 3.3V, if it is too small, it will not reach the breakdown state.

As shown in the above circuit Vin=10.943V, I=73.138ma, it can be seen that Vout=3.299V, because I does not meet the requirements of Iz=76ma, so Vout is slightly less than 3.3V, but it is also acceptable.

Therefore, the regulator diode is not very simple to achieve "voltage regulation", it has relatively high requirements for input voltage (can also be said to input current), and the current can not be too large, the conditions are very harsh, in most cases it is only as a protective role, such as single-chip IO port plus 3.3V (or 5V) regulator diode to prevent surge voltage, if it is 5 to 3.3V, it is recommended or LDO, but if you do not have high current requirements (within 200ma), you can still use the regulator diode plus a holding capacitor to achieve.