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1. 0-1A Bidirectional Current Source

I'm trying to design a bidirectional current source for the purpose of measuring very small (0.0001 Ohm) resistances. I've come across this circuit: I can see that the transistors are there to 'boost' the current but I don't understand the purpose of the 1K resistors and the capacitor. I...
2. A Simple Ohmmeter - Design Dillema

I've been design a simple ohm-meter which can measure resistances in the range 0.001 to 100 Ohms. I am aiming for an accuracy of 3%. Here's the circuit (so far): The circuit is basically a programmable current source which can source a current of 100, 10 or 1 mA. At junctions Va and Vb...
3. Terminating and Routing SPI

I'm looking for some advice regarding how to terminate SPI signals which are going to an external PCB. I know that SPI isn't meant for board to board communication but in this case the connecting ribbon cable is short - about 6" max length. My frequency isn't high, just 2 MHz but I have...
4. Pulse Skipping - Calculating Frequency Limits

I'm trying to design my first switching regulator circuit. I require three voltage rails, 5V, 3.3V and 1.8V. But to get started, I'm just focusing on 1.8V. I've decided to use the LT3507 as it seems to be commonly available here. It also has 3 buck regulator outputs, so it's a one-chip solution...
5. External Power Supply or Put Regulator on Main PCB?

I'm close to finishing my first 4-layer board. Initially, we felt that keeping the power supply as a separate unit would be better. This was because we wanted to avoid having heat on the main PCB - mostly because the area where the device is intended to be used is very hot and also quite dusty...
6. Puzzled by MOSFET switch

I have the following circuit wired up on a protoboard. The datasheet for the BSS138 MOSFET is here. I'm puzzled regarding what I'm seeing happen with this circuit - when I apply 3.3V at the gate resistor, the MOSFET turns on fully and I see 3mV at the output. This, of course, is expected...
7. Decoupling Caps' Via Position

I'm designing a 4-layer board with a couple of CPLDs and a uC. The top and bottom layer are for signals and the 2nd layer is ground and the 3rd layer is 3.3V. I'm placing a 0.1uF X7R Ceramic cap in 0402 package on every Vcc/Gnd pair. The thing that confuses me is that I've seen several ways...
8. TVS Diodes for ESD Protection?

I'm developing a basic cable continuity tester. Essentially, the circuit drives a test vector onto the cable and reads back the output vector. The output has MOSFETs for buffers/drivers but the input is connected directly to the ICs (CPLD, in my case). My concern is ESD. Unfortunately, I have...
9. Interpreting MOSFET ID/Vds curve for a MOSFET Switch

Hello, I'm considering using a logic-level MOSFET as a switch in a design. The drain of the MOSFET will be connected to an IC. The IC works at 3.3V and the maximum voltage at which it's guaranteed to read a low is just 0.8V. Now, I think every MOSFET will able to satisfy this but I'm just...
10. What is a good Overdrive Factor for a BJT?

I've been looking some pre-biased dual NPNs to use as buffers. My criteria is to have a very small package (i would prefer their width be less than 3mm. 2mm is very good) and that they ought to have a max. collector current rating of 200mA. I may have found such an NPN in the...
11. Would a four layer board be beneficial for me?

I'm designing a circuit that consists of the following: AT Mega 128L 2 to 6 CPLDs SD Card Interface 100 to 200 MOSFETs Power circuitry I should add that I already have a 2-layer prototype of the board and it works well. However, the prototype does not have the MOSFETs and the SD...
12. Want to get started with CPLDs

I want to get started with programming CPLDs. However, I'm confused about which development kit to get? I have about \$200 to spend. I feel that Altera has slightly better software - their Web version is free, it seems. So I'm mostly interested in that but have my options open. I'm also...
13. Using MOSFET in Saturation (as a switch)

I'm trying to learn about MOSFETs in order to use them as a switch. (note: this is not a homework/school question). On my breadboard, I have the following circuit hooked up: I vary the gate voltage using a potentiometer. Here is what confuses me: according to wikipedia, the MOSFET is in...
14. PWM Drive to H-Bridge with IR2113

I am using 4 MOSFETs in an H-bridge. The H-bridge is controlled with two MOSFET drivers (specially IR2113). I aim to drive the H-bridge via PWM which is carrying a 50Hz sine wave. Note that, the load is not a motor. Instead, the H-bridge is being used as a inverter. My question is, does the...
15. Frequency Response from a Discrete Transfer Function

Homework Statement Find the DC Gain and the Frequency Response of the above discrete-time system. The Attempt at a Solution This isn't really a homework problem but something I've been struggling with for my exams. I am given a transfer function in terms of z and am asked to find its...
16. Engineering Induction Motor, Parameter Test

Homework Statement I just gave an exam where one of the questions was where I had to find the various parameters using the two forms of tests for an Induction motor: No load test Locked rotor. Now, I can do this question but there is one thing that is confusing me. I had to find the stator...
17. Push pull stage current gain?

I'm trying to figure out the currubt gain for a class ab push pull amp. I know that it's basically two emitter followers, so am I correct in assuming that the current gain is just Beta?
18. Difference between Power Amp and Preamp?

Hello all, I was wondering what the difference between a power amplifier and a preamplifier was. Someone told me that a power-amp provides current and voltage gain whereas a pre-amplifier only provides voltage gain. If this is the case, why are circuits like the following considered Class...
19. Improving Employability

Hi, I'm a college student in the UK whose half-way through his Elec. Engineering degree. I quite enjoy my field and I get quite good grades (so far, I have scored first class in all of my courses except one.) and have a overall average of 82%. However, I'm quite worried about my prospects when...
20. Why does a MOSFET heat up with slow rise/fall times at gate?

I have a pulse width modulator thats composed of a triangular wave generator and a comparator. This outputs a pulse width modulated signal, whose duty cycle I set by changing the comparator's V- voltage. I have measured the rise and fall times of my output waveform and they are 27uS (for...
21. Variance of experimental data, compared to Theory

I'm looking for a way to compare experimental and theoretical data and determining if it obeys a certain law. In particular, I'm writing a computer program that does this and at the moment what I'm doing is, I'm calculating the ratio of each reading with the theoretical result and calculating...
22. 555 Oscillator Frequency Fluctuating Rapidly

hey all, I've wired up a standard 555 timer, using two resistors, a capacitor and a diode to make a clock in order to feed a stepper motor controller. http://wolfstone.halloweenhost.com/TechBase/com555_555AnyDutyCycle.gif Its wired like the schematic above. My resistor values are the...
23. Stepper Motor Ratings

I've got a 12V, 2 Ohm/winding rated motor and I'm trying to figure out how much current it'll take. From Ohm's law 12/2 = 6A - and thats a lot! Is this much current needed to drive the motor? Can I use a lower amount of current? If so, how do I limit it? I don't have the datasheet for the...
24. Stepper Motor Controller only working on a particular power suppy?

I'm making a circuit around the stepper motor controller L297 on a breadboard, and I've got it working so far. I haven't connected it to the H-bridge and so obviously not to the motor either. But I'm checking the logic levels using 4 LEDs connected to the outputs and they corrospond with the...
25. Gain Margin, Open or Closed Loop?

Homework Statement I'm given a closed loop transfer function with a gain, K=1 and a plant H(s). I need to find the gain margin of the system. Homework Equations I know how to solve this problem: a) I find the frequency where the phase is -180 degrees. b) I find the gain at that...
26. Engineering Studying Astronomy after Engineering?

Do you folks suppose its wise to get an Physics + Astronomy degree after engineering? Would it be a good career choice? I'm currently about to finish my first year in electronic engineering. Due to a lot of factors, I was unable to choose Astronomy when I enrolled. However, I've been...
27. Energy of a Capacitor System with partially inserted Dielectric

Homework Statement The above is a capacitor system. A dielectric is inserted into capacitor C3 and I need to find the total energy of the system. The dielectric is not fully in, only partially (lets say a length x). The Attempt at a Solution I first found the capacitance of C3 with...
28. Drag on a Cylinder - Confused

Homework Statement I'm writing a lab report on drag on a non-rotating cylinder. The drag coefficient is calculated using the Pressure co-efficient. The problem I'm facing is that my lab states that the pressure on the cylinder can be predicted by \left(p-p_{0}\right)_{max} \times cos(\theta)...
29. Differential EQ of this RL Circuit

Hi, I have the above the circuit and I've ended up with the following differential equation. I've tried solving it by separating the variables, but am not sure if its the right answer. IR + L(di/dt) + IR = x(t) x(t) = 5V. But since IR = y(t) and di/dt = 1/R dy/dt. y(t) is the...