1. Symbol packaging

The circuit symbols and packaging of voltage regulator diodes and TVS diodes are basically the same as those of voltage regulator diodes. Sometimes it is even difficult to distinguish which one is which from the appearance.

2. Circuit connection

Voltage regulator diodes and TVS diodes are both connected in reverse in the circuit, that is, using their reverse characteristics and using the avalanche effect of the PN junction. Before reverse breakdown, there is a critical voltage. When connected in reverse in the circuit, they both have a voltage stabilizing effect, but they are not exactly the same. The voltage regulator diode uses the input voltage to be fixed at a certain value, while the TVS diode mainly prevents transient high voltage from clamping on the subsequent circuit.

3. Response time

Voltage regulator diodes generally do not talk about response time, but focus more on the voltage stabilization value. However, it is different for TVS diodes. Its characteristics determine that it has different functions. TVS diodes have the function of suppressing high energy transiently. Therefore, it is required to absorb high energy instantaneously within a short time. Therefore, this time is very short and reaches the nanosecond level.

4. Power size

The power of voltage regulator diodes is generally not very large. Common voltage regulator diodes have 1W and 2W, etc. Its power is determined by the allowable temperature rise. In fact, it is the product of stable voltage and current. For example, for the voltage regulator diode 1N4742A, its maximum power is only 1W and its stable voltage is 12V, so the current passing through it generally cannot exceed 80mA, otherwise the tube will heat up badly; for TVS diodes, it pays attention to instantaneous pulse power This power value is very high and can reach thousands of watts, but this time value is maintained very small.

Voltage regulator diode

The voltage regulator diode is a kind of PN junction that uses the reverse breakdown voltage to basically remain unchanged, but the current can change within a certain range. The voltage regulator diode has a high resistance state before reverse breakdown and a low resistance state after exceeding this critical point. Voltage regulator diodes are widely used in various voltage stabilization circuits and voltage reference components. They can be used in series to obtain higher voltage stabilization values.

Voltage regulator diodes are commonly represented by “ZD” in circuits. The main parameters of voltage regulator diodes are: stable voltage value, power dissipation, maximum working current. These three factors must be fully considered when designing circuits. The following figure shows a resistor-capacitor step-down circuit with an output voltage of 12V using a 1N4742A voltage regulator diode with a stable voltage value of 12V and a power of 1W.

TVS Diode

TVS tube is a transient suppression diode and a semiconductor device with surge absorption capability. Its response time is extremely fast and reaches sub-nanosecond level. Therefore, once the circuit receives an instantaneous high-energy impact, it can suppress this energy by absorbing instantaneous large currents and high voltages from the circuit to clamp it down. The final result is to protect downstream equipment or circuits.

TVS diodes are divided into unidirectional and bidirectional types. Unidirectional types are mostly used in DC circuits and bidirectional types are mostly used in AC circuits. They are connected in parallel with the protected circuit in the circuit. Once the instantaneous voltage exceeds the normal working voltage of the circuit, TVS The tube will undergo avalanche effect and provide an ultra-low resistance path for instantaneous current, so that protected devices or equipment can avoid damage. Therefore, this type of TVS tube is very suitable for ESD-sensitive circuits and overvoltage circuits. As shown in the figure below, when connecting a unidirectional TVS tube to a circuit, its polarity must be opposite to that of the power input polarity so that the circuit can work.