Design Current Sources w/ DC Supply & Resistor/Transistor

In summary, designing a current source to meet the given specifications can be achieved by using a resistor with a high enough value and a power supply with a corresponding voltage in part (a). For part (b), using a transistor with a feedback loop or a voltage regulator can provide better control over the current. The key is to maintain a constant voltage drop across the load, regardless of the load resistance.
  • #1
mathman44
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0

Homework Statement



a) Design a current source using a simple DC power supply and a single large resistor. Assume
you want to supply loads which can vary between 1 k and 10 k and you want the current to stay within 5% of 1 mA.

b) Do the same thing using 2 DC power supplies and 1 NPN transistor with beta = 100 and
VBE = 0.6 V which will satisfy the same specifications. You are free to choose the values
of the power supply voltage and can use as many resistors as necessary.

The Attempt at a Solution



Just to make sure I'm understanding this correctly; if the load varies up to 10k ohms and we want the current to stay within 5% of 1 mA, then the load can only represent 5% of the total resistance, correct?

So the answer for (a) would be a 190k resistor connected to a 190V battery.

for b) I can put my load as a collector resistor, so the current it draws is independent of the load resistor value.

Am I going about this the right way?
 
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  • #2

I would like to offer some suggestions for designing a current source that meets the specifications given in the forum post.

For part (a), you are correct in understanding that the load can only represent 5% of the total resistance. In this case, the total resistance would be 20 times the load resistance, so a 200k resistor connected to a 200V power supply would work.

For part (b), using a transistor is a good idea as it allows for more control over the current. However, simply using a collector resistor may not be enough to ensure that the current stays within 5% of 1 mA. I would recommend using a feedback loop to regulate the current. This can be achieved by using a voltage divider with a potentiometer and connecting the output to the base of the transistor. This will allow you to adjust the base voltage and control the collector current. You can also use a second power supply to provide a fixed base voltage, if needed.

Overall, the key to designing a current source is to ensure that the voltage drop across the load remains constant, regardless of the load resistance. This can be achieved through various methods, such as using a feedback loop or using a voltage regulator. I hope this helps and good luck with your design!
 

1. What is a design current source?

A design current source is a circuit that is designed to provide a constant current output, regardless of changes in the load or input voltage. It is commonly used in electronic devices to power components that require a consistent current.

2. How does a DC supply affect the design of a current source?

A DC supply is necessary for a current source to function. The DC supply provides the necessary voltage for the circuit to operate and maintain a constant current output. The voltage of the DC supply will also determine the maximum current that the current source can provide.

3. What role does a resistor play in a current source design?

A resistor is used in a current source design to limit the current output and ensure that it remains constant. The value of the resistor is carefully chosen to match the desired current output of the circuit.

4. Can a transistor be used in a current source design?

Yes, a transistor can be used in a current source design to regulate the current output. A transistor acts as a variable resistor, adjusting its resistance to maintain a constant current as the input voltage changes.

5. What are the advantages of using a current source in a circuit?

There are a few advantages to using a current source in a circuit. These include a constant current output, which can help protect components from damage due to overcurrent. Additionally, current sources can provide a stable and accurate current, making them useful in precision electronic applications.

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