Power protection circuit (voltage regulator tube and transient suppression diode [TVS])
1, surge protection circuit: breakdown voltage regulator tube in accurate voltage, which makes it can be used as components to limit or protection, because the zener diode voltage can be various, therefore particularly suitable for this application. The zener diode in the D diagram as an overvoltage protecting device. As long as the power supply voltage exceeds VS the value of D voltage regulator diode conduction, the attraction of a relay J RL with separate power load.
The overvoltage protection circuit 2, the TV in the TV: EC is the main supply voltage when the voltage is too high, EC, D conduction, BG transistor conduction, the collector potential by the original high level (5V) to low level, through the control of the standby control line to enter the standby state television protection.
3: in the arc suppression circuit, inductance coil is connected in parallel with a suitable zener diode (you can also access a common diode principle as) then, when the coil in the conducting state is cut off due to the high voltage generated by the electromagnetic energy release is absorbed by the diode, so when the switch is off, switch arc also is eliminated. The application circuit used in industry more, such as some of the larger suction control circuit of electromagnetic power on the use of it.
4, series type voltage regulator circuit: in this circuit, the series voltage regulator tube D is the base of the voltage regulator diode BG clamp fixed at 13V, then its emitter on the output of a constant 12V voltage.
Transient suppressor diode is often referred to as the lightning protection tube, it is a kind of safety protection device. This device plays a role in shunt, clamp circuit in the system, can effectively reduce the pressure generated by the on-off switch circuit of lightning, lightning, high voltage pulse pulse, avoid damage to other devices.
Transient voltage suppressor diode has unidirectional and bidirectional two. Unidirectional Zener graphic symbols and similar TVS devices according to the polarity can be divided into unipolar and bipolar two; use can be divided into general and special type; according to the package and the internal structure can be divided into axial lead dual in-line diode, TVS array, patch type and high power [1] module etc.. Axial lead product peak power up to W, 500 400W, 600W, 1500W and 5000W. High power products are mainly used in power supply, low power products are mainly used in high density installation occasions. For high density mounting occasions, can also choose to dip and surface mount package etc.. Application circuit. When the input end of a high-voltage surge pulse is introduced, no matter how the pulse direction, TVS tube can quickly enter the state of breakdown, the input voltage clamp. The following table is used for the two-way TVS pipe parameters:
Model cut-off voltage
(V) breakdown voltage
(Vmin) the breakdown voltage (Vmax) test current (mA) maximum clamping voltage (V) peak pulse current (A) reverse leakage current (uA)
P6KE6.8CA 6.45 7.1410 10.5 58.11000 5.8
P6KE12CA 11.40 12.61 16.7 35.35 10.2
P6KE22CA 20.90 23.101 30.6 19.9 18.8
The following major factors should be considered when selecting TVS transient suppression diodes:
(1) if the transient suppression diode has the potential to withstand the peak pulse voltage (surge voltage) from two directions, it should be chosen bipolar, otherwise it can be used as a single pole.
(2) the Vc value of the transient suppression diode (s) should be lower than the maximum voltage of the protected element. Vc is in the off state voltage of the diode, is also in the impact of the ESD state by the voltage transient suppression diodes, it is not greater than the protected circuit can withstand voltage limit, otherwise the device is in danger of being damaged.
(3) transient suppression diode in the normal operating conditions do not be in the breakdown of the state, the best in the following VR, VR and VC should be considered in the two aspects of the requirements to select the appropriate transient suppression diode.
(4) if you know more accurate surge current IPP, you can use VCIpp to determine the power; if you can not determine the approximate range of IPP, then select the power of the larger TVS tube as well. PM is a transient suppression diode can withstand the maximum peak pulse power dissipation. In a given maximum clamp voltage, power consumption of PM is larger, the surge current capacity is higher; in the power PM under a clamp voltage VC is lower, the surge current capacity is greater. In addition, the peak pulse power consumption is also related to the pulse waveform, duration and environment temperature.
(5) transient suppression diodes are able to withstand the transient pulse is not repeated, the device provides the pulse repetition frequency (duration and duration of the ratio) is 0.01%. If a repetitive pulse occurs in the circuit, the pulse power should be considered, otherwise it may be damaged.
(6) for the protection of small current load, can consciously in the line to increase the current limiting resistor current limiting resistor, as appropriate, generally does not affect the normal work of the circuit, but the current flow resistance of interference is greatly reduced. However, it is possible to use a transient suppression diode with a small peak power to protect the small current load line.
(7) the capacitance C is determined by the transient suppression diode avalanche junction section, which is measured at a specific 1MHz frequency. The size of the C is proportional to the current capacity of the TVS, and the C is too general to cause the signal to decay. Therefore, C is an important parameter of the data interface circuit using TVS. The data / signal higher frequency circuit, the diode capacitance interference on the circuit is formed, noise or attenuation of signal intensity is large, therefore, need according to the characteristics of the capacitance range loop to determine the selected device. High frequency circuit generally select the capacitor should be as small as possible (such as LCTVS, low capacitance TVS tube, capacitor is not more than 3pF), while the capacitor requirements are not high, the capacity of the capacitor selection can be higher than 40 pF.
(8) in order to meet the international standard of IEC61000-4-2, transient suppression diodes must reach a minimum of 8 kV can handle (contact) and 15kV (air) ESD impact, some semiconductor manufacturers use a higher standard impact on their products. And for some special requirements of the portable device applications, designers can choose devices as needed.