Attention should be paid when using voltage regulators

When using a voltage regulator, we need to pay attention to the following aspects. Firstly, it needs to be reversed in the circuit to stabilize the voltage. That is to say, the negative pole of the voltage regulator is connected to the high potential in the circuit, and the positive pole is connected to the ground potential. If it is reversed, it will burn out the voltage regulator due to excessive current. The second point is that the voltage regulator diode must be able to stabilize the voltage when the power supply voltage is higher than its stabilizing value. The third point is that if one regulator cannot achieve the stabilizing value, multiple regulators can be used in series, but remember not to use them in parallel.

The voltage regulator diode is connected in reverse parallel at both ends of the load during use. If the input voltage does not exceed its regulated value, it will not conduct. If it exceeds its regulated value, it will break down and conduct. Generally speaking, the input voltage exceeds its regulated value. In practical use, it is necessary to connect a resistor in series with it to bear the voltage higher than the regulated value.

When selecting parameters for a voltage regulator diode, the first step is to determine the voltage regulator value, which is related to the load circuit. Since not every voltage value has a voltage regulator diode, and the voltage regulator value may have a certain degree of dispersion, when selecting the voltage regulator value, it is possible to choose a voltage regulator value that is close to the load situation. For example, a 5V load can choose a 5.1V voltage regulator diode.

After determining the voltage regulation value of the voltage regulator diode, it is necessary to determine the resistance value of the voltage divider resistor. The resistor here mainly serves two purposes: one is to provide the operating current of the voltage regulator diode, and the other is to limit the maximum current of the voltage regulator diode. When the current of the voltage regulator diode is low, it cannot function properly as a voltage regulator. If it is too high, permanent breakdown may occur. To calculate the resistance value of a resistor, two values need to be determined first: one is the input voltage range, the other is the range of load current variation, and the other two parameters are the minimum current and maximum current, which can be found in the technical manual of the voltage regulator diode.

Assuming the input voltage range is 15V-18V, the load current variation range is 5-15mA, the output voltage regulation value is 12V, the minimum current of the voltage regulator diode is 0.25mA, and the maximum current is 50mA.

According to the formula: (18V-12V)/(50mA+5mA) R (15V-12V)/(0.25mA+15mA), the range of resistance R can be calculated to be between 109 Ω and 196 Ω. Common resistance values within this range, such as 120 Ω, can be selected.