NE555

Turn-off time less than 2μs
Max. operating frequency greater than 500kHz
Temperature stability of 0.005% per °C

 

PIN Configuration

Pin1 GND 地線(或共同接地), 外接電源負端VSS或接地, 通常狀況下接地

Pin2 TRI Trigger 低觸發端, 這個腳位是觸發NE555使其啓動它的時間週期, 觸發信號上緣電壓須大於2/3 VCC, 下緣須低於1/3 VCC A low voltage (less than 1/3 the supply voltage) applied momentarily to the Trigger input causes the output (pin 3) to go high. The output will remain high until a high voltage is applied to the Threshold input (pin 6).

Pin3 OUT Output 輸出端Vo, 時間週期開始時移至比電源電壓低1.7V的高電位, 週期結束時輸出回到OV左右的低電位, 高電位時的最大輸出電流大約200mA. In output low state the voltage will be close to 0V. In output high state the voltage will be 1.7V lower than the supply voltage. For example, if the supply voltage is 5V output high voltage will be 3.3 volts. The output can source or sink up to 200 mA (maximum depends on supply voltage)

Pin4 RES Reset 直接清零端, 低邏輯電位送至這個腳位時會重置定時器, 使輸出回到一個低電位. 當此端接低電平時, 時基電路不工做，此時不論TR, TH處於何電平, 時基電路輸出低電位. 該端不用時應接高電平

Pin5 CON Control Voltage 控制電壓端, 若此端外接電壓, 則可改變內部兩個比較器的基準電壓, 這個能夠小範圍調節穩態時的脈衝長度或非穩態時的頻率. 當該端不用時應將該端串入一隻0.01μF電容接地, 以防引入干擾. 這個接腳准許由外部電壓改變觸發和閘限電壓, 當計時器經營在穩定或振盪的運做方式下, 這輸入能用來改變或調整輸出頻率. You can control the threshold voltage (pin 6) through the control input (which is internally set to 2/3 the supply voltage). You can vary it from 45% to 90% of the supply voltage. This enables you to vary the length of the output pulse in monostable mode or the output frequency in astable mode. When not in use it is recommended that this input be connected to circuit ground via a 0.01uF capacitor.
Pin 5 is control, you can control the operation of the timer from an outside source. The Control is often used for audio modulation, but for a simple square wave generator it is usually not used. However, if you leave the pin unconnected, it can pick up electromagnetic waves that can cause a tiny bit of erratic behavior, which is often undesired. If you're only using the chip to flash an LED, for example, you probably don't need the capacitor. You probably won't see the difference. The .01uF cap is only there to eliminate the unwanted signals.

Pin6 TRE Threshold 高觸發端, 重置鎖定並使輸出呈低態. 當此pin的電壓從低於1/3VCC移至高於2/3VCC時啓動這個動做 In both astable and monostable mode the voltage across the timing capacitor is monitored through the Threshold input. When the voltage at this input rises above the threshold value the output will go from high to low.

Pin7 DIS Discharge 放電端, 該端與放電管集電極相連, 用作定時器時電容的放電. 這個接腳和輸出腳有相同的電流輸出能力, 當Pin3爲低電平時, Pin7對地爲低阻態(對地導通), 當Pin3爲高電平時, Pin7對於爲高阻態 when the voltage across the timing capacitor exceeds the threshold value. The timing capacitor is discharged through this input

Pin8 VCC 正電源電壓端, 外接電源VCC，雙極型時基電路VCC的範圍是4.5~16V, CMOS型時基電路VCC的範圍爲3~18V. 通常用5V供應.

應用電路1: Astable Operation 非穩態電路(多諧振盪器)

多諧振盪器又稱爲無穩態觸發器, 沒有穩定的輸出狀態, 只有兩個暫穩態. 在電路處於某一暫穩態後, 通過一段時間能夠自行觸發翻轉到另外一暫穩態. 兩個暫穩態自行相互轉換而輸出一系列矩形波. 多諧振盪器可用做方波發生器.
接通電源後, 輸出假定是高電平，則Pin7截止, 電容C充電. 充電迴路是VCC - R1 - R2 - C - GND, 按指數規律上升, 當上升到2/3 VCC時(Threshold端電平大於Vc), 輸出翻轉爲低電平. Vo是低電平, Pin7導通, C放電, 放電迴路爲C - R2 - T - GND, 按指數規律降低, 當降低到1/3 VCC時(Threshold端電平小於Vc), 輸出翻轉爲高電平, 放電管T截止, 電容再次充電, 如此周而復始, 產生振盪.
輸出高電平時間 T = (R1 + R2) * C * ln2
輸出低電平時間T = R2 * C * ln2
振盪週期 T = (R1 + 2R2) * C * ln2

使用麪包板和測試板對上面電路的測試. 用一個104(100k)的電位器代替R2, 測試不一樣的R2值下蜂鳴器的聲音. 在R2在0~10K範圍時, 是一種清脆的"滴"聲, 在大於50K以後聲音愈來愈悶, 逐漸接近於漏電時急促的"嗒嗒嗒"聲.

應用電路2: Less Than 50% Duty Cycle Astable MultivibratorAstable

前一個電路的佔空比只能在55%~100%之間調節, 下面是改進的電路, 能夠讓佔空比在 9%~100% 之間調節. 經過兩個1N4148二極管控制充放電時的電流流向, 當電位器觸點靠左時, 充放電的時間比爲1:10, 佔空比爲1/11約9%, 在靠右時, 充放電的時間比爲11:0, 佔空比爲100%. 經過下方的電容容量切換, 能夠顯著調節輸出的頻率.