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  1. Cirkit

    Ni-MH charging circuit query

    Thanks for your replies. The charging circuit just seems to consist of the transistor as a constant voltage source as described above. I do not think it regulates the current once the pack is fully charged?
  2. Cirkit

    Ni-MH charging circuit query

    I have replaced the entire pack and measured the charge current at 136mA.
  3. Cirkit

    Ni-MH charging circuit query

    The ~7.7V is measured after the diode and resistor which is then supplied to the unit. The batteries are AAA rather than AA.
  4. Cirkit

    Help identifying odd adapter

    You could buy these two and make your own voltage switchable supply: http://www.ebay.com/itm/Multi-Voltage-Power-Adapter-3v-4-5v-5v-6v-7-5v-9v-12v-DC-2-1A-Power-Supply-Plug-/391612248241...
  5. Cirkit

    Help identifying odd adapter

    What you'll need to look for is a power supply with a 2-pin DIN connector. Something like these: http://azsurplus.com/index.php?main_page=product_info&products_id=8272 http://azsurplus.com/index.php?main_page=product_info&products_id=5789 They are often used with outdoor or decorative LED...
  6. Cirkit

    Ni-MH charging circuit query

    The 7.7V source consists of a cheap SMPS with a rectifier diode and 4.7 Ohm resistor in series from one of the terminals of the secondary output on the transformer. This is the positive charge output terminal to the unit. There is also an electrolytic and ceramic capacitor across the positive...
  7. Cirkit

    Dvd need help

    The marking in the bottom corner of the PCB indicates that there should be a +12V, +5V and + 3.3V rail on the output connector (J2?). Testing an SMPS with your finger is not safe whether it is live or not. There are dangerous voltages present.
  8. Cirkit

    Ni-MH charging circuit query

    Sorry, I meant to say 4xAAA's in series. It's a 3xAAA pack and a single AAA connected together. I thought the sense circuitry would regulate the charging too but it seems that the base is driven by the zener voltage so there is no chance of that? Would it be worth adding a resistor in series...
  9. Cirkit

    Ni-MH charging circuit query

    I am trying to work out how a charging circuit for a Ni-MH battery pack is operating and determine why there are powder deposits on one of the terminals of the cells of the battery pack. I have been told that the unit is new so I'm surprised that one of the cells has powder on the positive...
  10. Cirkit

    Parallel LEDs - resistor needed?

    Great, thanks for everyone's advice on this. I just wanted to make sure that I wouldn't burn out the LEDs. I will heed the advice about separate resistors for each LED in future! I'm curious how the current is being limited though, is it as a result of the load and the voltage drop on the...
  11. Cirkit

    Parallel LEDs - resistor needed?

    I measured the total current into the parallel string and it is 21mA. The voltage drops to 2.76V when connected to the parallel string. After powering the LEDs for about an hour, the temperature of the 358 Op-Amp rose by 2ºC above ambient.
  12. Cirkit

    Parallel LEDs - resistor needed?

    I'm not too worried about uneven brightness. I tried connecting the LEDs directly and it seemed bright enough. Is there a danger of the LEDs burning out? Since all the LEDs have already been assembled in parallel, it's not possible to add a resistor in series with each now. Should I still...
  13. Cirkit

    Parallel LEDs - resistor needed?

    I'm sure this question or similar has been asked asked before but I just wanted some clarification. If I am connecting 7 LEDs in parallel with a forward voltage of 3.3V each to a supply of 3.6V, is a protection resistor needed? The datasheet mentions a maximum forward current of 25mA per LED...
  14. Cirkit

    CMOS 555 driving BC337 - base resistor

    The 555 is operating in monostable mode and the high output voltage is around 3V.
  15. Cirkit

    CMOS 555 driving BC337 - base resistor

    Hello, I am trying to determine the correct base resistor value to drive a BC337 transistor into saturation. The transistor is connected to the output of a CMOS 555 timer via the resistor. The transistor is driving a 3V solenoid which consumes around 200mA when active. The entire circuit is...
  16. Cirkit

    5V boost converter efficiency?

    Thanks for your reply. I am measuring the current between the battery positive terminal and the boost converter positive terminal. The meter has a logging function and it measures around 340mA average and over 400mA (max) for one of the boost converter boards.
  17. Cirkit

    5V boost converter efficiency?

    I purchased a couple of different 5V boost converter boards from eBay to power a 5V solenoid from 2xAAs. The solenoid normally draws about 120mA from a 5V power supply. If I use either of the boost converter boards powered by 2xAAs, the total current consumption (boost converter board and...
  18. Cirkit

    Hot air rework tool

    It looks identical to the 858D model? I have used the 858D, it has a blower fan integral within the hand piece rather than a compressor in the main unit. Would be useful to know what others on here use too?
  19. Cirkit

    No sound front panel audio jack (need help)

    If there is another audio header on your motherboard, try moving the front panel audio jack connector to that one. This post explains what to do: http://www.tomshardware.co.uk/answers/id-2711342/front-panel-audio-connectors-working.html
  20. Cirkit

    Hot air rework tool

    Thanks, for the suggestion. I don't use one daily either at the moment. Just for occasional use to remove parts or for heatshrink tubing.
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