Designing a +10V Supply with Transistors: A Practical Approach

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In summary, the task is to design a +10V supply with the following specifications: Iout = 0-100mA, Vout = 10V, and Vin = 20-25V (unregulated supply with ripple). The circuit diagram is attached and the book being used is The Art of Electronics. The author emphasizes practicality and suggests not worrying about precise calculations when using 10% resistors or 20% capacitors. The solution involves starting at the output voltage and determining the base and zener voltage, which should equal the collector voltage plus 0.6V. The base current is 1/100 of the collector current, and the output current is limited to 100mA. The zener also
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irishhockey
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Homework Statement


Design a +10V supply with the following specs:
Iout =0-100 mA
Vout =10V
Vin=20-25V (unregulated supply w/ ripple)

The circuit will have the diagram attached.

The book I am using is The Art of Electronics, which is very "practical" the author says things like why worry about calculating something to 1 in 100, when you will then reach for a 10% resistor or 20% cap.

Homework Equations


Ibase * beta = Icollector
Iemitter = Ibase (1+beta) = Ibase + Icollector
Iemitter=Ibase +0.6V

The Attempt at a Solution


I start at the output, 10V and 0-100mA. The Voltage at the base and also zener must be equal to collector voltage +0.6V. The current in the base is 1/100 the collector current, and output current is 100mA(max) so I base = 1mA and Icollector=100mA. The zener also requires a constant 10mA, which is needed to keep the dynamic resistance under control. My issue is now the resistors.

So, I know that the resistoprs have 25V on the side facing the power supply, and for R, the voltage on the base/zener side is 10.6V. Does this mean I can say the voltage drop across the res is 14.4 V (using 25V and planning for worst case)? If so, can I just say IBASE + Izener=11mA, asnd the use V/I=R? if so Ic an figure everything else out I belive.

Thank you
 

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  • #2
You are on the right track but is 25V the worse case? What does the zener current fall to if the input is 20V instead of 25V.
 

What is a transistor emitter follower?

A transistor emitter follower is a type of transistor circuit that is commonly used to drive high impedance loads. It is designed to have a high input impedance and a low output impedance, allowing it to amplify a signal while maintaining its voltage level.

How does a transistor emitter follower work?

A transistor emitter follower works by using a transistor to buffer the input signal. The input signal is applied to the base of the transistor, and the output signal is taken from the emitter. The input signal is amplified by the transistor and the output signal follows the input signal with a slight voltage drop.

What are the advantages of using a transistor emitter follower?

There are several advantages of using a transistor emitter follower. Firstly, it has a high input impedance, which means it does not load the previous stage or circuit. Secondly, it has a low output impedance, which allows it to drive high impedance loads. Additionally, it has a high voltage gain and low distortion, making it suitable for audio applications.

What are the applications of a transistor emitter follower?

Transistor emitter followers have a wide range of applications in electronics. They are commonly used in audio amplifiers, where they can drive high impedance speakers. They are also used in voltage regulators and power supplies to provide a stable output voltage. In addition, they are used in digital circuits as buffers to isolate different sections of the circuit.

What are the limitations of a transistor emitter follower?

While transistor emitter followers have many advantages, they also have some limitations. One limitation is that they have a low current gain, which means they cannot provide a large output current. Additionally, they have a limited frequency response, making them unsuitable for high-frequency applications. Finally, they are not suitable for use as a switch, as they do not have a fully on/off state.

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