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Published byElena Corpe Modified about 1 year ago

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UJT transistor circuit template Unijunction Transistor Circuit Templates This presentation is partially animated. Only use the control panel at the bottom of screen to review what you have seen. When using your mouse, make sure you click only when it is within the light blue frame that surrounds each slide.

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UJT transistor circuit template current meter 0 current meter 0 volt meter 0 + + + + + 0 volt meter n n p pn junctions This transistor is in conduction collector base emitter current meter 0 + 0 volt meter n p pn junction This diode is forward biased anode cathode 1 pn junction 2 pn junctions

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UJT transistor circuit template 2 pn junctions 1 pn junction current meter 0 + 0 volt meter n p pn junction This diode is forward biased anode cathode emitter Base 1 Base 2 e b2 b1 + + + + + b2 n p e b1 UJT

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UJT transistor circuit template Low voltage signal applied to emitter A UJT (unijunction transistor) is a voltage-controlled switch that does not amplify the current in the load circuit. emitter Base 1 Base 2 e b2 b1 UJT p nn 0 Low current flow from base 1 through base 2 emitter p nn current meter 0 + + base 1base 2 Low voltage signal applied to emitter current meter OFF

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UJT transistor circuit template Low voltage signal applied to emitter emitter p nn current meter 0 + + emitter Base 1 Base 2 e b2 b1 UJT p nn 0 0 Low current flow from base 1 through base 2 base 1base 2 applied to emitter High voltage signal current meter OFF ON High current flow from base 1 through emitter base 1 A UJT (unijunction transistor) is a voltage-controlled switch that does not amplify the current in the load circuit. emitter

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UJT transistor circuit template + + + B2 Current flows into this circuit branch until voltage at node becomes high enough to stop the flow. p n n B1 + + capacitor Always a small flow of current in this branch of circuit. But not enough to turn the light on. Unijunction transistor in a light flasher circuit

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UJT transistor circuit template Current flows into this circuit branch until voltage at node becomes high enough to stop the flow. + + B2 p n n B1 + capacitor (This charging current continues its flow into the capacitor until the capacitor becomes fully charged and node reaches the threshold voltage value.) Always a small flow of current in this branch of circuit. + + When node voltage reaches threshold value, the capacitor discharges current through the emitter to B1 circuit v threshold Light is ON while capacitor discharge current is flowing. Unijunction transistor in a light flasher circuit

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UJT transistor circuit template v threshold When node voltage reaches threshold value, the capacitor discharges current through the emitter-B1 circuit + + B2 Unijunction transistor in a light flasher circuit capacitor Always a small flow of current in this branch of circuit. + + Voltage across capacitor drops as capacitor current discharges Light is ON while capacitor discharge current is flowing. Light is OFF when capacitor voltage is + p n n below UJT’s threshold voltage value. B1

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UJT transistor circuit template + + B2 Unijunction transistor in a light flasher circuit B1 capacitor Always a small flow of current in this branch of circuit. + + Voltage across capacitor drops as capacitor current discharges p n n When voltage across capacitor drops low enough current starts following in this branch again and cycle repeats itself. +

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UJT transistor circuit template

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B2 Unijunction transistor in a light flasher circuit B1 capacitor + + + + + p n n

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