HKTREE2018 - 無線充電裝置

線路說明

無線充電的接收器連接線路圖左方的輸入端,直接連接超級電容 C1 進行充電。電容上的電壓由數字式電壓表量度。S1 為微動開關,按下後, 超級電容便會透過電阻 R1 放電。放電狀態透過紅色的發光二極管 L1 監察,放電初期 L1 會發光,當 L1 熄滅後,電容上仍殘留有約1.5 V的電壓,繼續按下一分鐘可以使電容放電至約0.3 V。開關 S2 的功用是選擇電路的運作模式,若 S2 處於彈起的狀態(如線路圖所示),電容便會直接連接 J1 上的馬達,若電容上有足夠的電壓,馬達便會轉動,綠色發光二極管 L2 亦會亮起。

正常比賽時,開關 S2 應處於按下狀態。這時候電容連接了自動觸發線路,當電容充電至由參賽者選定的電壓後,電路便會自動向馬達供電,直至電容上的電壓下降至約 0.3 V或以下。Q1 是 P 通道的場效應晶體管,其運作方式很簡單,當閘極 G 的電壓為高時,S 與 D 之間的通道為關閉狀態,相反,當 G 的電壓為低時,通道便會打開,S 及D 之間便能通電;因此,場效應晶體管可以視為一個由電壓控制的開關。Q2 及 Q3 皆為 N 通道的場效應晶體管,與 P 通道 Q1 的分別在於控制其開與關的電壓相反,即閘極 G 的電壓高時 S 與 D 之間的通道通電,電壓低時不通電。

電容一開始充電, Q1 的閘極 G 透過電阻 R3 接至較高電壓的電容上,因此 Q1 不通電,馬達不會轉動 。Q2 的閘極 G 連接至可變電阻 VR1 上,VR1 接駁成為分壓電路,因此,隨著電容上的電壓因充電而上升,Q2 的閘極電壓亦按比例上升,直至閘極電壓上升至約 0.7 V 時,Q2 便會通電。調節 VR1 可改變分壓的比例,從而控制電容充電至那一電壓水平才觸發 Q2 的導通。實際使用時,順時針方向轉動 VR1,電容便需要充電至更高電壓才會觸發線路通電,反之亦然。

當 Q2 通電後,Q1 的閘極 G 電壓便會下降至接近 0 V,所以 Q1 便會導通,供電給馬達。Q3 的功用是確保 Q1 保持在通電的狀態;若省去了 Q3,當電容因放電而電壓下降了一點,Q2 便會停止通電,從而令 Q1 亦停止通電;這樣,電容所儲存的電能便不能充分運用。由於 Q3 的閘極 G 透過電阻 R4 連接在電壓的輸出端,所以當 Q1 通電的時候,Q3 的閘極 G 電壓便會變高,Q3 便會通電,結果使 Q1 的閘極 G 電壓變低,這樣便可以確保當 Q1 一旦開始通電,便會繼續保持在導通狀態,直至電容上的電壓下降至非常低的水平為止。

若把 VR1 順時針方向旋轉至盡頭,線路便變成手動運作。因為當 VR1 順時針方向轉至盡頭,便等於把 Q2 的閘極 G 恆常連至 0 V,結果是無論電容的電壓充至多高,線路都不可能被觸發。這時候,便可以使用 SW2 作手動操作:充電時按下,充夠電時再按 SW2 使其彈起,馬達便會即時開始轉動。

注意事項

  • 必須要接上馬達,線路才可以正常運作
  • 接收線圈附有一片黑色的屏蔽貼,必須放在接收線圈後才可以正確充電
  • 發射線圈與接收線圈之間要保持最少2 mm 的距離,否則充電會不穩定
  • 參賽者可以自由選用合適的無線充電接收組件,唯需注意必須兼容大會供應的發射組件

比賽詳情及賽規請瀏覽 HKTREE 大會網站:http://www.hk-tree.org/tc/index.html


Description of circuit

At the left side of the circuit diagram, the receiver of the wireless charging circuit is connected to the input terminals, which is connected directly to the super capacitor C1 for charging. The voltage stored on the capacitor is measured by an attached digital voltmeter. S1 is a micro-switch that when pressed down, will discharge the capacitor through resistor R1. The status of discharge can be monitor by the red LED (L1). In the beginning, the LED will light up. When the light has dimmed out, about 1.5 V will still be found on the capacitor. Continue to hold down the switch for one more minute can discharge the capacitor to about 0.3 V. The function of the switch S2 is to select the working mode of the circuit. If it is at the pop-up state (as shown in the circuit diagram), the capacitor is connected directly to the motor via J1. If there is enough charge on the capacitor, the motor will start turning and the green LED (L2) will light up.

During the competition, the switch S2 should keep pressed down. In this way, the capacitor is connected to an automatic triggering circuit. When the capacitor has charged to a predetermined voltage, the circuit will power the motor automatically until the voltage on the capacitor has fallen to about 0.3 V or below. Q1 is a P-channel field effect transistor. Its operation is simple. When the gate (G) voltage is high, the channel between S and D is shut down. On the contrary, if the voltage at gate (G) is low, the channel will be opened, and current can passes through S and D. As a result, a field effect transistor can be considered as a voltage-controlled switch. Q2 and Q3 are N-channel field effect transistors, the difference between N-channel and P-channel is that they operated in the opposite way. i.e., when the gate (G) voltage is high, current can pass through S and D. They are not conducting when the voltage at G is low.

When the capacitor has started charging, the gate (G) voltage of Q1 is being pulled high by resistor R3. As a result, Q1 is not conducting and the motor will not turn. The gate (G) of Q2 is connected to the voltage divider formed by the variable resistor VR1, therefore, when the voltage on the capacitor is raising, the gate (G) voltage of Q2 will also rise in proportion. If the gate (G) voltage of Q2 has raised to about 0.7 V, Q2 will conduct. Adjusting VR1 can change the proportion of the voltage divider so that the triggering voltage can be set to any desired level. In practice, turning VR1 clockwise will increase the voltage for which the capacitor has to charge up before the motor is being triggered to run and vice versa. 

When Q2 conducts, the gate (G) voltage of Q1 will be pulled down to nearly 0 V, consequently, Q1 will conduct and supply current to the motor. The function of Q3 is to keep Q1 conducting. If Q3 is omitted, then Q2 will stop conducting when the voltage on the capacitor has felt a small amount due to discharge, causing Q1 to stop conducting. As a result, the charge stored in the capacitor will not be fully utilized. As the gate (G) of Q3 is connected to the output terminal via the resistor R4, when Q1 is conducting, the gate (G) voltage of Q3 will be high. Q3 will conduct, pulling the gate (G) voltage of Q1 low. Therefore, once Q1 has started conducting, Q3 will keep Q1 conducting, until the voltage on the capacitor has fallen to a very low level.

If VR1 is turned fully clockwise, the circuit can be used manually. Because when VR1 is turned fully clockwise, it connects the gate (G) of Q2 to 0 V constantly. As a result, no matter how high the capacitor has been charged up, the circuit will not be triggered. Therefore, the circuit can be used manually. Push down SW2 when charging the capacitor. Then push again to release SW2 to start the motor.

Important points:

  • Motor must be connected for the circuit to work properly
  • There is a shield (black in colour) that must be placed behind the receiving coil for correct charging
  • The distance between transmitting and receiving coil should be keep at least 2 mm, otherwise, the charging may be unstable.
  • Participants may use any wireless receiving unit. However, it must be compatible to the transmitting unit provided.

For further informations regarding the competition, please visit the official HKTREE website:http://www.hk-tree.org/tc/index.html

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補購查詢:歡迎致電《今日校園》訂閱部 2342-8298 (鄧小姐)
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