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In the figure, the single-chip U2 drives 8 common cathode digital tubes through the CH452 and simultaneously scans 64 buttons. Because some digital tubes have reverse leakage at higher operating voltages, it is easy for CH452 to mistakenly think that a button has been pressed all the time. Therefore, it is strongly recommended to use diodes D1-D8 to prevent digital tube reverse leakage and improve the keyboard. The level of the SEG0~SEG7 input signal during scanning ensures that the keyboard scan is more reliable. When the supply voltage is low (eg VCC = 3.3V), these diodes should be removed to avoid affecting the display brightness.
If the CH452S chip uses both keyboard scanning and digital tube display functions at 5V, then a diode must be added.
Silicon TVS / TSS:
Diode TVS (Transient Voltage Suppressor), also known as Transient suppression diodes, is widely used a new type of high efficient circuit protection device, it has a fast response time (the nanosecond) and high surge absorbing ability.When it ends of stand moments of high energy shock, TVS can bring the two ends at high rate from high impedance to a low impedance between impedance values, to absorb a large current moment, put it at both ends of the voltage restraint on a predetermined value, thus protecting the back of the circuit components are not affected by the impact of the transient high pressure spikes.
Silicon TVS Transient Voltage Suppresso,Silicon TSS Transient Voltage Suppresso
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