Brain teaser Interview Questions | Glassdoor

# Brain teaser Interview Questions

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## Brain teaser Interview Questions

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### Innovative Leadership Project Electrical Engineer 2014 (Analog) at Lutron was asked...

Nov 21, 2013
 Q2: A pnp transistor with its base connected to a voltage source, the V source is connected to a +10V source. The emitter of the transistor is connected to a resistance, and then to the same +10V source. The collector side is connected to a capacitor, which is not charged at t=0-. Given the graph of Vsource = 10 V stepping up at t = 0 to further, draw the graph of Vout. Vout is between the point of collector and capacitor. 3 AnswersANS: Vout should be constantly -10V until t=0, and will hit V=0 V linearly from V=-10 V after t=0.Hi, Can you explain why it linearly increases? Are you assuming that Collector is tied to -10V? The pnp transistor is completely cutoff for the given biasing. The only way the capacitor is going to charge is through leakage currents. It is very slow and takes a lot of time. Please advise me if my analysis is correct.I just made it back from Lutron's HQ and I was asked for the same question. My first approach will be identifying a PNP BJT, and elaborating all 4 BJT operating regions. Before t = 0, since q = 0, by using Q = CV, we can tell that the voltage across the capacitor is 0. Hence, Vo = -10V before t = 0. Recall the capacitor's current equation: I = C*(dv/dt), we can solve for the slope of changing voltage -> dv/dt = I/C. Here, I is simply the BJT's collector current, which can be found by looking at the BJT's emitter current. Given that the (beta) parameter is infinite, we see the base current to be 0. Now, at this point, we need to look for I_E. Since the R is given to be 9.3k, and VEE = 10V, it is natural to assume V_EB = 0.7V, and thus the voltage across R = 9.3V. Therefore, I_E = 9.3/9300 = 1mA. Voila, we now values for all currents: I_E = I_C = 1mA, and I_B = 0A. Plug the I_C value into the equation: I_C/C = dv/dt (C = 1uF). We know that the slope of the voltage change is 1000V/second, or 1 Volt per millisecond. Now, we know the capacitor voltage raises at 1V/ms from -10V, but we also need to know where is the upper limit. Looking back to the BJT basics about operating regions and BJT's 2-diode model, it is not hard to identify that this PNP BJT must operate in "Saturation" region (NOT IN "ACTIVE" REGION!). The boundary of that region is V_BC <= 0.7V (I hope everybody is able to solve for this). Hence, 0.7V will be the upper limit for capacitor voltage. At this point, you will have a flat line at Vo = -10V before t = 0. and raises at 1V/ms for 10.7ms and hit Vo = 0.7V. From t = 10.7ms and on, the Vo stays at 0.7V.

### Senior Client Services and Project Manager at Three Deep Marketing was asked...

Mar 20, 2013
 What is your idea of reasonable turn around time for a project?3 AnswersDepends on the clients ability to provide assets, and the scope of work.Reasonable would be the projected, based on original scope and estimated labor hours. The word reasonable in itself indicates the use of reason to determine the outcome.Just

### Systems Analyst II at AT&T was asked...

Mar 7, 2014
 How would you respond to a customer who encountered a problem with a product or service.1 AnswerFirst, try and reproduce the problem and if the problem could be reproduced acknowledge there was an issue, give thanks for bringing this to the company's attention, and apologize for the customer's encounter with the issue. Offer possible solutions or workarounds while the team worked to correct the issue.

### Supervising Production Engineer at WaferTech was asked...

Nov 17, 2012
 Only one tech question that wasn't a brain teaser- technical job related question was about line balance. There's 3 tools in a row with known stabilities. You know the second tool is very unstable but you need to meet demand.1 AnswerRun more product the previous day in the first machine the previous day.

May 17, 2010