PDT Transistor

Conception Rules Pdt You want Ve = 0,1 Vcc then choose Re to get the desired Ie Then Vce should be 0,5 Vcc to keep the Q point in the middle of the Load Line. 0,1 Vcc + 0,5 Vcc = 0,6 Vcc , that means Vc = 0,4Vcc Rc = 4Re Constant supply Rule : Rth <= 0,01 * Beta * Re (Thevenin resistance from the base view). Stable supply : Rth <= 0,1 * beta * Re but as R2 is generaly lower than R1, we can use R2 <= 0,01 beta Re. V2 = Ve + 0,7 = 2,7v V1 = Vcc - V2 = 20 - 2,7v 17,3v R1 / R2 = V1/V2 , so R1 = V1/V2 * R2 R1 = 17.3 / 2.7 * 200 1.3k ohm Use the Lowest beta in the Datasheet of the Transistor. Verify that the power in the transistor is ok ! (Ie * Vce) Application. Vcc = 20v Ie = 10mA BetaDc = 100 to 300. Ve = 0,1 Vcc = 2V Re = 2 / 0,01 = 200 Ohms. Rc = 800 Ohms. Vce = 0,5 Vcc = 10V R2 <= 0,01 * 100 * 200 <= 200