### Fast Facts: Analysis of Line Regulation of Different Voltage Regulators Unraveled

Voltage regulators (as the name implies) regulate a certain amount of input bias to a specified voltage level. A zener diode is the most basic of all voltage regulators, though it is characterized by a significant amount of voltage drop across it. If we want a low voltage drop across our regulator, low drop-out (LDO) voltage regulators are available. They may come in a variety of packages and even offer extra features (such as the TPS7333QP which offers an extra "reset" function to shut down its load (microcontroller) in the event of an undervoltage condition).

One important characteristic to look at in voltage regulators is their line regulation. Line regulation (as the name implies again) is a measure of how well the line voltage is maintained with respect to a varied input bias. For example, if we feed a voltage regulator with 7 V, it yields a 5 V output. But when we feed it with 13 V, line voltage/output becomes 5.3 V. Thus we can say that our sample voltage regulator has bad line regulation (compared to standards) - that is 5.3 V - 5 V = 0.3 V (neglecting current).

Let us look at some voltage regulators and compare their line regulation using NI Multisim.

Here we have the LM109H voltage regulator, swept from 0 to 17 V and given a load of 1 mA. Observing the curve, we find that the output stabilizes at 5 V given an input of 7 V. I want to characterize its line regulation at 7.5 and 15 V. Using the cursor function, we see that the difference is 1.5186 mV.

Now I want to compare it with another voltage regulator that regulates at 5 V too, say the MC7805BT. We simulate it with the same working conditions as the LM109H.

Once more, by the cursor function, we find that the line regulation between 7.5 V and 15 V is 2.9216 mV. Therefore, if we are strict with line regulation in our design, we reject the MC7805BT and choose the LM109H (of course, MC7805BT may have other characteristics that are more favorable than LM109H depending on the demand of the circuit).

On the test bench, when measuring line regulation, we sometimes place bypass capacitors at the input and output to filter out AC or high frequency components (since a shunt capacitor acts as an LPF). Also, it is important to be cautious when using a sinking current source as a load to your regulator. At undervoltage condition, the curve may be erroneous since the load would constantly be pulling the same amount of current (which is equivalent to a lower resistance). Putting a delay on your measuring instrument may make things complicated, so it is more advisable to use a passive component (a resistor) or an electronic load (if one is available).

### Calculator Techniques for the Casio FX-991ES and FX-991EX Unraveled

In solving engineering problems, one may not have the luxury of time. Most situations demand immediate results. The price of falling behind schedule is costly and demeaning to one's reputation. Therefore, every bit of precaution must be taken to expedite calculations. The following introduces methods to tackle these problems speedily using a Casio calculator FX-991ES and FX-991EX.

►For algebraic problems where you need to find the exact value of a dependent or independent variable, just use the CALC or [ES] Mode 5 functions or [EX] MENU A functions.

►For definite differentiation and integration problems, simply use the d/dx and integral operators in the COMP mode.

►For models that follow the differential equation: dP/dx=kt and models that follow a geometric function(i.e. A*B^x).

[ES]
-Simply go to Mode 3 (STAT) (5)      e^x
-For geometric functions Mode 3 (STAT) 6 A*B^x
-(Why? Because the solution to the D.E. dP/dx=kt is an exponential function e^x.
When we know the boundary con…

### Common Difficulties and Mishaps in 6.004 Computation Structures (by MITx)

Updated:
May 6, 2018
VLSI Project: The Beta Layout [help needed]Current Tasks: ►Complete 32-bit ALU layout [unpipelined] in a 3-metal-layer C5 process. ►Extend Excel VBA macro to generate code for sequential instructions (machine language to actual electrical signals).
Current Obstacles/Unresolved Decisions:
►Use of complementary CMOS or pass transistor logic (do both? time expensive, will depend on sched.
►Adder selection: Brent-Kung; Kogge Stone; Ladner Fischer (brent takes up most space but seems to be fastest, consider fan-out) [do all? time expensive, will depend on sched.)
►layout requirements and DRC errors