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| university:courses:alm1k:alm-lab-pv [16 Jan 2017 20:42] – [Procedure:] Doug Mercer | university:courses:alm1k:alm-lab-pv [20 Jun 2018 16:33] – The text is about the version on the left, not the one to the right Michel Walsh |
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| The regulated output voltage will be equal to the V<sub>BE</sub> of transistor Q<sub>1</sub> plus the forward drop of LED<sub>1</sub>. The current in the LED is set by the value of R<sub>1</sub> and the V<sub>BE</sub>. A range of output voltages are possible by choosing different color LEDs. The forward voltage drop can range from around 2 V for red and up to 3 V for blue or white. Even more output voltage values can be made by inserting the forward voltage drop of one or more standard Si diodes in series with the LED. | The regulated output voltage will be equal to the V<sub>BE</sub> of transistor Q<sub>1</sub> plus the forward drop of LED<sub>1</sub>. The current in the LED is set by the value of R<sub>1</sub> and the V<sub>BE</sub>. A range of output voltages are possible by choosing different color LEDs. The forward voltage drop can range from around 2 V for red and up to 3 V for blue or white. Even more output voltage values can be made by inserting the forward voltage drop of one or more standard Si diodes in series with the LED. |
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| Looking at the version on the right, NPN transistor Q<sub>1</sub> and collector resistor R<sub>2</sub> form a common emitter amplifier stage. PNP transistor Q<sub>2</sub> provides current gain. As soon as enough current is flowing through the LED and R<sub>1</sub> such that the voltage across R<sub>1</sub> is large enough to turn on Q<sub>1</sub> the circuit starts to regulate. Beyond the initial startup current in the LED, the majority of the current through the shunt regulator flows through Q<sub>2</sub>. The above explanation similarly holds for the complementary version on the right. | Looking at the version on the left, NPN transistor Q<sub>1</sub> and collector resistor R<sub>2</sub> form a common emitter amplifier stage. PNP transistor Q<sub>2</sub> provides current gain. As soon as enough current is flowing through the LED and R<sub>1</sub> such that the voltage across R<sub>1</sub> is large enough to turn on Q<sub>1</sub> the circuit starts to regulate. Beyond the initial startup current in the LED, the majority of the current through the shunt regulator flows through Q<sub>2</sub>. The above explanation similarly holds for the complementary version on the right. |
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| {{ :university:courses:alm1k:alm-lab-e2_a5.png?550 |}} | {{ :university:courses:alm1k:alm-lab-e2_a5.png?550 |}} |
