For circuit protection, protection schemes are engineers according to product protection grade and actual working voltage, current and power values of design, selection of protection scheme is effective in design and an important factor - electronic protection device. What engineers how to choose the ceramic gas discharge tube? The lightning protection anti-static, over-current, over voltage protection expert tage electronic circuit with lightning protection device of ceramic gas discharge tube as an example, for the selection of the friends to explain in detail the GDT!
(radio frequency protection circuit)
The selection of ceramic gas discharge tube:
GDT [UN3E5-90LM] DC nominal voltage: 90 + 20%V, impact current (8/20 S): 5kA, the capacitance value of < 1.5pF, resistance value > 1G;
GDT [UN3E5-90MM] DC nominal voltage: 90 + 20%V, impact current (8/20 S): 10kA, the capacitance value of < 1.5pF, resistance value > 1G;
Transient suppressor diode (TVS)
TVS [Vrwm:3.0V] ESD03V32D-LC; Vb:4.0V; anti-static capacity (contact / air): 8KV/15KV; junction capacitance (f=1MHz): 1.2pF; package for SOT-323
In the fast pulse under the impact of ceramic gas discharge tube 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.
The selection of the DC breakdown voltage Vsdc: the minimum value of the DC breakdown voltage Vsdc should be greater than 1.2 times the maximum power peak voltage or the maximum signal voltage.
Impulse discharge current selection: to be based on the line may be 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).
The ceramic gas discharge tube for breakdown voltage error is large, generally do not make use of parallel.
The current 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.
(radio frequency protection circuit diagram two)
In this regard, if you do not understand or do not understand how the selection of ceramic gas discharge tube, according to the above five points are given to you from the electronic selection required, can contact us, for you one by one to answer the questions in the heart and brain fog of confusion. Thank you for reading this article.