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Design Project: DC Voltage Regulator
5 questions By Tony R. Kuphaldt
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Question 4 of 5
Make a rough calculation of the power your circuit’s final output transistor(s) must dissipate when carrying the full 2 amps of current. Will the power dissipation be greatest at maximum voltage (20 volts) output or minimum voltage (3 volts) output? Explain why.
Reveal answerThe answer to this question may surprise you, being somewhat nonintuitive. You may find that power dissipation is the most significant technical challenge to overcome in this circuit design: how to ensure your circuit will not be damaged by excessive heat.
Notes:Having students recognize this design problem and engineer solutions to it is very important part of this project, and it will greatly enhance their practical understanding of transistor circuits as well!
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Question 5 of 5
The best regulator designs use feedback to ensure “tight” regulation of voltage over a wide range of load currents. Explain what this “feedback” is, and how it works to improve voltage regulation.
Reveal answerWith “feedback,” the output voltage is sampled and “fed back” to a prior stage in the transistor circuit, so that any load-induced change in output voltage elicits a response from the amplifier to counter-act that change. In other words, feedback makes the circuit “aware” of its own output.
Notes:Many voltage regulator circuits employ operational amplifiers (using negative feedback) to accomplish this very design goal: improved voltage regulation. Your students may find a perusal of an op-amp based design helpful when considering how to build their regulator circuits out of discrete components.
