As a good engineer, circuit protection scheme are engineers according to the protection grade products and working voltage, current and power values of actual design, protection scheme is effective in addition to design and an important factor -- electronic protection device selection. Then? In the selection of ceramic gas discharge tube, are required to have what to choose the correct ceramic gas discharge tube? What the engineers how to choose and match the correct GDT? Following it, lightning protection, anti-static, anti over voltage, over current protection expert tage electronic circuit with lightning protection device of ceramic gas discharge tube as an example, detailed to explain the GDT if correct selection of gas discharge tubes. The following are the five major factors for selection of gas discharge tubes:
The selection of ceramic gas discharge tube:
1), in the rapid pulse, GDT gas ionization requires a certain amount of time (usually 0.2 ~ 0.3 s, the fastest also has about 0.1 s), which has a higher amplitude spike will leak to the back. To curb the sharp pulse, there are several ways: A, in the discharge tube or shunt capacitor varistor; transmission line B, in the discharge tube after the series inductance or stay length is appropriate, the sharp pulse attenuation to the lower level; C, using two levels of protection circuit to discharge tube as the first stage in TVS tube or semiconductor discharge tube as second grade, two grade with resistance, inductance or self recovery fuse isolation.
2), DC breakdown voltage Vsdc choice: the DC breakdown voltage Vsdc minimum value should be greater than the maximum power supply peak voltage or the maximum signal voltage of 1.2 times.
3), the impact of the discharge current choice: according to the line may appear on the maximum surge current or the need to protect the maximum surge current selection. Discharge tube impulse discharge current should be calculated according to the nominal impulse discharge current (or half of the single impulse discharge current).
4), ceramic gas discharge tube for breakdown voltage error is large, generally do not make use of parallel.
5), continuous flow problem: in order to make the normal arc discharge in shock after the breakdown in the possible freewheeling place (such as active circuit), in the discharge tube series varistor or self recover fuse limit continued flow, make it less than the holding current discharge tube.
The ceramic gas discharge tube:
Ceramic gas discharge tube is a kind of lightning protection devices are currently the most widely used, both AC and DC power supply lightning protection lightning or various signal, can play a very good protective effect. Ceramic ceramic discharge tube is encapsulated inside by two or more band gap metal electrodes, filled with inert gas argon, neon, when added to the two extreme voltage electric to gas discharge tube gas breakdown when the gas discharge tube to discharge from a high impedance into a low impedance, the surge voltage quick short-circuit to near zero voltage and overcurrent release into the ground, thus protecting the subsequent circuit.