VP VBB But VP If VD VP 1 Therefore T RCln Design of UJT Oscillator Resistor is limited to a value between 3 kilo ohms and 3 mega ohms. The upper limit on ‘R’ is set by the requirement that the load line formed by and intersects the device VBB ‘R’ ‘R’ characteristics to the right of the peak point but to the left of valley point. If the load line fails to pass to the right of the peak point the UJT will not turn on, this condition will be satisfied if , therefore . VBB RP R VBB IP At the valley point and , so the condition for the lower limit on to ensure IE IV VE ‘R’ turn-off is , therefore . VBB RV R VBB IV The recommended range of supply voltage is from 10 to 35V. the width of the triggering pulse . tg R CB1 In general is limited to a value of 100 ohm and has a value of 100 ohm or greater RB1 RB2 104 and can be approximately determined as . RB2 PROBLEM A UJT is used to trigger the thyristor whose minimum gate triggering voltage is 6.2V, 0.5mA, The UJT ratings are: 0.66, 3mA, leakage current I Iv RB1 RB2 p = 3.2mA, and . Oscillator frequency is 2kHz and capacitor C = Vp Vv Design the complete circuit.
VP VBB But VP If VD VP 1 Therefore T RCln Design of UJT Oscillator Resistor ‘R’ is limited to a value between 3 kilo ohms and 3 mega ohms. The upper limit on ‘R’ is set by the requirement that the load line formed by ‘R’ and VBB intersects the device characteristics to the right of the peak point but to the left of valley point. If the load line fails to pass to the right of the peak point the UJT will not turn on, this condition will be satisfied if VBB RP , therefore R VBB . IP At the valley point IE IV and VE , so the condition for the lower limit on ‘R’ to ensure turn-off is VBB RV , therefore R VBB . IV The recommended range of supply voltage is from 10 to 35V. the width of the triggering pulse tg R CB1 . In general RB1 is limited to a value of 100 ohm and RB2 has a value of 100 ohm or greater 104 and can be approximately determined as RB2 . PROBLEM A UJT is used to trigger the thyristor whose minimum gate triggering voltage is 6.2V, The UJT ratings are: 0.66, I p 0.5mA, Iv 3mA, RB1 RB2 leakage current = 3.2mA, Vp and Vv . Oscillator frequency is 2kHz and capacitor C = Design the complete circuit.
U3_L19-Gate-Triggering-Methods.docx