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Alex Tsekenis

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Everything posted by Alex Tsekenis

  1. Do people use UJTs any more? I think is an obsolete technology...Even in its time it looks like a purpose specific device. I had to read up on UJT operation, and I dont know exactly how R2 helps in temperature compensation. From the formula given here for R2: http://mysite.du.edu/~etuttle/electron/elect10.htm it seems that R2 is related to the bias voltage of the E-B1 junction. You could say that as temperature increases, the thermal voltage of the E-B1 pn junction will increase thus making it harder to thrigger the UJT. On the other hand, the value of R2 will increase as temperature increases according to its temperature coefficient and the temperature change thus decreasing the standing voltage on the n side of the E-B1 junction hence making it easier to trigger the UJT. But the value or R1 will also increase by the same percentage therefore the voltage on the n side of the E-B1 n-p junction will be the same as this is like a potential divider.
  2. Hello, I believe that the first thing you have to aim for is enthusing / motivating your son and you in the subject. For this reason I would recommend more practical work than theory for starters. There are these kits that you can build 100s of circuits with. I grew up with this one: http://www.thamesandkosmos.com/products/ew2/ew2.html But it was named just Kosmos 300 or something back then. I particularly like these ones as they have a breadboard-like working area rather than springs. It comes with a manual that shows you how to build the circuits and also some very basic theory behind, transistors, resistors and capacitors usually using the water analogy. After having completed the circuits, you can have a look at transfering them on a breadboard and possibly on matrix board to begin using a soldering iron etc. At this stage you will also get to know your local part supplier. That would be a great way to start I believe. If you wish, you can also buy a book on basic theory. The best thing you can do is visit your local bookshop and find one that matches your level and learning expectations. In any case try to go in small steps and not too fast as you risk losing your son's enthusiasm who I believe is rather young.
  3. Also remember to record the state of the charge level of the battery as internal resistance will increase as the battery is drained.
  4. No, it is not that simple. In fact, you could do a research degree on this. But some deviation from perfect is acceptable. I see the IGBT you are using is a power device. Generally, driving an IGBT is like driving a MOSFET. In you case is a big MOSFET with 1.56nF of gate capacitance. Do a search on driving high power IGBT or Mosfet with MCU. You say threshold is 3V. Have a look at figure 1 of the datasheet on ST. You will need to charge the gate up to 10-15V to fully turn on the device. At the threshold voltage the igbt will merely be conducting. Another consideration is how quickly you can deliver gate charge to the gate capacitance. You thus need a high current driver for this device that has a high gate capacitance. The current required will be porportional to the frequency you will be switching the igbt at. The MCU is not capable of such outputs. You can use external transistor amplifiers controlled by the MCU to drive the gates, but I think even better is to use a so called 'low-side mosfet driver' Have a look on IRF, National, Micrel, Linear, Analog, Microchip, you will find a lot of devices. I came across a Microchip app. note a while ago on selecting the right driver for your application. What is your application by the way? Regarding the MCU, the only thing on Farnell was 1455065 which is not yet in stock and very expensive. Nothing on RS. Atmel does samples, possibly you could try that. Also search under Contact Us>sALES Support and select your region. There are many other distributors but this looks like a low demand part. Consider finding an alternative that is in stock. Elektor Electronics (the magazine) very very recently published a massive list of retailers that you could find useful.
  5. Hello, I avoided calling it a star ground as this is not for ground. It is like a 'star ground'. Google that. The idea is that all subcircuits that draw a small amount of current are not affected by the circuits that draw large currents. If they were sharing the same connection (not star), then a circuit that draws large current will create a voltage drop on the copper tracks. This voltage drop will also be seen by the low current circuits, possibly affecting them. If however all circuits went to a single point and at that point there was a large energy storage and low impedance from the power supply then sensitive subcircuits will be less affected, if at all. The same idea applied for a star positive supply, although it is not refered like that. Digital circuits are more tolerant to this but this IC has an analogue front end (the PHY part) that draws a lot of standby current. Audio amplifiers use this extensively. Power planes radically reduce this problem but nothing can eliminate it completely as the impedance to the power source will never be 0.
  6. The idea with this IC is to use one decoupling capacitor per VDD line and then connect them all together to VDD using a star connection.
  7. If you are into software, consider an RJ45 module with built in magnetics, MAC/PHY and ARM microcontroller. Alternatively, the circuit that you have been putting together can be bought ready made here: http://uk.farnell.com/microchip/ac164123/board-pictail-plus-ethernet/dp/1439831
  8. That is in the Microchip datasheet for that MAC/PHY chip with SPI interface. Winding your own transformers for Ethernet is silly. Wurth Electronic (Midcom), Coilcraft and many others have hundrends of standard models to suit ANY application and wiring layout. Good luck with the TCP/IP stack.
  9. Hello Mark. Please do not interfere with the battery in any way at this stage. Remove the battery and take the laptop apart. Locate the damaged PCB and take a good quality picture of it (<3000kB) and post it here. We will have a look at the board and tell you what to do.
  10. I just had a better look at the final circuit. The zener voltage is too low which makes me think that you are operating them far away from the zener region. As suggested, reduce R2,R4. You can also measure and include in your resistor calculation the C-E saturation voltage of Q1, Q2 although that will be tiny compared with Vpower-Ground. Also in a previous post you say that you will keep a high side on and pulse the low sides. Careful, you will blow a pair up on either the first or second pulse.
  11. If everything is fine and the heating is purely due to the Mosfet being a P-type, I can reccomend an excellent 8-pin IC to drive an N-channel device on the high-side by using a capacitor charge pump topology and an internal oscillator, gate driver.
  12. Try including some dead-time between switching bridgeA and BridgeB ON.
  13. Go to your local bookshop and buy a book on digital image processing and digital signal processing. The best way I can think of.
  14. I dont think that will work as the battery is not just a battery, it is a 'smart battery' with integrated safety interlocks and monitoring circuits. Your laptop expects to be able to communicate wth the circuits on the battery to turn ON. If you connect just the battery positive and negative (maybe there are more than 2 power connections) your laptop will most likely not switch ON at all. The best thing to do is take the laptop apart while taking pictures of the disassembly process. Locate the damaged board and try to repair that. If it is broken or badly damaged you could connect two small wires bringing the PCB power connector to the outside where you have a small connector that mates with the power supply of the laptop. The second approach allows you to maintain portability as well.
  15. You should spend time on this since you are dealing with 12 lead-acid batteries in series. The issue I see is that your cables and coil that have some resistance will heat up too thus changing your current limit. Use liquid nitrogen for your resistor will affect its resistivity so you will have to use a higher resistance value to compensate. Does it have to be KEPT at 40A maximum or you want any value up to 40A? In the first case you should use a current source, in the second a fuse. Whare do you get your liquid nitrogen from?
  16. Guys dont bother with Kevin, he is a post bot to generate search engine hits.
  17. I see. It happens that I am working on something similar but more complex (diagram attached) at the moment. It will be very hard to fit all the functions in the rectangle on such a small PCB but it is marginally possible given the low power that the circuit must handle. I would like to help you but I am up to my neck at the moment so I can't take on the whole project on my own. I might be able to squeeze some of the subcircuits in my schedule though or provide guidance on the development, something that you can do on this community board too. Hope this is of some help. Visio-POD_SPS_Gen.2_Block_Diagram_Rev3.pdf
  18. Hello again. Please understand my reluctance to give out my email address like this. If possible, share what you are trying to do with the community. You don't need to include any confidential details if any. In your first post you say "manage the battery pack for water cooling pump" which is not very clear. For example, do you want to develop a battery charger, a discharge cut-off circuit, a battery monitor...what is it more or less? Maybe your problem has a very straightforward solution.
  19. Hello, could you provide some further information on what exactly you want to do?
  20. I say you have more chances of success if you are honest when advertising.
  21. http://www.elektor.com/magazines/2006/october/ecg-using-a-sound-card.58566.lynkx There is no need for additional formatting.
  22. Hello, thank you for suggesting these. Have you developed these? I only refer to datasheets when I need specifications. But I can see the benefit of having a quick look at key characteristics. How about a stock database for a home electronics laboratory? This will include location of components, state (new, used, salvaged etc) key specifications, possibly pictures? You could do it with Excel or with a front-end to an SQL database. What do you think?
  23. It is posible as the IC acts just as the controller in the circuit. The power switch, voltage divider, current sense, inductors,capacitors are external so by recalculaing their value (full details in the datasheet) you will be able to produce your required output. Also have a look at this app. note: http://www.national.com/an/AN/AN-1484.pdf You could use the output divider to tweak the output voltage but vary it over such a range. Also you can use LTSPICE to simulate it.
  24. Ah, I am with you now. Maybe the best/easiest thing is to switch off the HV PSU before firing the SCR.
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