Exam 1 Flashcards
What will happen if you use a PIN photodiode in a photoconductive mode?
Less sensitive. Generates very low current.
Signals with frequency lower than 100 Hz
High-pass
Signals with frequency higher than 10 kHz
Low-pass
How to know if strain gauge is compressed vs stretched
Increase in resistance = stretched
Decrease in resistance = compressed
Why photodiode is more popular than photoresistor?
Linear response.
Identical sensor output regardless of input current (or voltage).
What is the purpose of using an op-amp for the LED circuit in a forward bias?
To protect the LED from unnecessary high current.
The output current from the op-amp will be capped.
Voltage Divider Relationship
Used for resistors in a series.
Vout = (Vin)(R2/R1+R2)
Current Divider Relationship
- Used for resistors in parallel.
- I1 = (Iin)(R2/R1+R2)
- I2 = (Iin)(R1/R1+R2)
What is voltage “droop?”
A small decrease in voltage as the load current increases.
How to back calculate size of Resistor in DMM with measured Vout.
Rdmm = (R)(Vout/Vin-Vout)
Draw the I-V curve for typical diode as well as Zener diode.
Zener diode has less rapid breakdown
How does a voltage regulator (using a Zener diode) work?
To maintain a stable output voltage, even when the input voltage or load conditions fluctuate.
Zener Diode equation
Ir = (Vin - Vz) / (R)
How is the emitter current controlled by the base current in an NPN transistor?
Current flows due to electrons moving from the emitter to the collector, and the transistor is active when the base is positive relative to the emitter.
Why do you need an op-amp to protect your LED and Zener diode? If you are not using an op-amp,
how can you prevent a large amount of current flowing through your LED and Zener diode?
For dynamic control and feedback regulation Without one, protect LEDs and Zener diodes using simple series resistors, preventing damage from excessive current.
Why do you need a 1-Ω resistor to measure ILED and Izener, assuming that you only have a voltmeter?
Creates a measurable voltage drop proportional to the current flowing through the diode. This allows you to calculate the current with a voltmeter which only measures voltage.
Why is zener diode the most popular to measure temperature?
Simplicity, compact size, and stable reference voltage although it may not be as sensitive or accurate as thermocouples or thermistors in measuring temperature over a wide range.
In the zener diode temperature sensor circuit shown in Chapter 4, what will happen if a very large
input current (> 1 A) is applied?
Can lead to overheating, thermal runaway, component failure, voltage instability, etc.
Why does the voltage drop when holding a zener diode with your finger?
The heat from the finger increases the diode’s temperature. The Zener voltage drops due to its negative temperature coefficient.
What is a Wheatstone Bridge?
Electrical circuit used to measure a very small change in resistance, not readily detectable by a typical DMM. Consists of four resistors arranged in a diamond configuration.
How does a strain gauge measure strain?
Detects changes in its electrical resistance as it deforms in response to applied stress
What is a cantilever biosensor?
A strain gauge used to monitor biological reactions. When an analyte binds to them, they begin to bend.
With the measured Vbd, can you identify whether the strain gauge was compressed or stretched?
The Wheatstone bridge was initially balanced.
Yes.
Positive = stretched
Negative = compressed
Why does the voltage output of an op-amp saturate?
Due to the inherent limitations of the op-amp’s design and the conditions of the circuit
