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  1. M

    IC output help

    Here we go... I know there are easier ways, but isnt the idea to try and learn things you dont know? Anways - ideas about why the output is so low?
  2. M

    IC output help

    Hi guys. I have made a circuit that uses a UC3843 in order to run a 12v lamp and be able to dim the lamp. I can get an the voltage on PIN 1 of the chip (the ouput of its error amplifier) to vary between 0.8 and 7.26 volts (which I believe should be enough to vary the output duty cycle between 0...
  3. M

    Variable PWM with chip

    Could someone let me know if the following setup on the UC3843 chip is actually going to produce a user variable PWM pulse to the MOSFET driver chip? Specifically, if the variable resistor doesnt work like this, how could I set it up? Thanks
  4. M

    UC3843 for a motor controller?

    Now that I think about it. If someone could explain to me how to setup a good current limit system, the PWM generator based on the dual opamp in another thread could probably be used. The PWM would be used to drive a half bridge driver at this stage. Later I may go to a full bridge, but not...
  5. M

    UC3843 for a motor controller?

    I was going to use the UC3843BN from ON. It's cheap and easily available for me. How about the above questions? Is there a better chip for providing a variable duty time PWM signal with current limiting around (that I can actually get in NZ)?
  6. M

    UC3843 for a motor controller?

    I am tossing around a few ideas as to making a motor controller for an electric wheel chair type thing (it'll need to handle a fair current from a 24v motor). I was thinking that pehaps the UC3843 would be a good PWM generator for this. My reasons for thinking this (which may be incorrect) are...
  7. M

    Soft start on a 555 timer

    Can a soft-start being implemented on a 555 timer through the control voltage pin (number 5). What I am after is to start the 555 up at a low frequency and have it ramp up to a higher frequency slowly. This is what I have in mind so far My question is  - will this circuit addition mean that...
  8. M

    Coil gun charger circuit

    Okay, I made some changes to the circuit. The mosfet driver is now powered from the 12v supply. I also added a schottky diode to ground between the driver and the fet, and a small value resistor. This solved the heating problems. I also upped the bleeder resistors to 100k and a 5k pot. I added a...
  9. M

    Coil gun charger circuit

    Just to clarify, my circuit is a little different from the one the anotherforummember posted. Here is the latest schematic of mine. I understand the mosfet wont be heating during the off period (hence the advantage to a larger cap from the transistors base), however I am curious as to what...
  10. M

    Coil gun charger circuit

    Okay, now I am confused. I got a new mosfet of much lower resistance. This one has an Rds (on) of 0.19 ohms. It has a 20 amp rating. However. Once the capacitor reaches the preset charge level, the mosfet heats up even quicker than the last one. It reaches the preset charge very quickly (faster...
  11. M

    Coil gun charger circuit

    Actually, now that I think about it, could it just be that there is too much current passing through the mosfet. After all, it says for the IRF830 that the RDS(on) is 1.5 ohms. Am I right in assuming this means that when it is on, it is going to be passing 12/1.5 = 8 amps? Could I reduce this...
  12. M

    Coil gun charger circuit

    Righto, I changed some bits around. It is now running at 4.8 kHz with a 66% duty cycle. That seems to have fixed the limited voltage issue. I should merrily be able to blow up capacitors now :-) As far as that diode is concerned, I am using an MR856, which according to its datasheet should have...
  13. M

    Coil gun charger circuit

    Well, I built it. It all seems to work (after some intial diffuculties). However I have a few questions as to its performance. Firstly, with the pot wound right up, the best charge I can get out of the unit is 75 volts. I presume this has something to do with the frequency or duty cycle I am...
  14. M

    Coil gun charger circuit

    Hmm, the forum seems to be "resizing" it. Try this link, should be alot clearer
  15. M

    Coil gun charger circuit

    Hi guys. I have come up with a schematic for a coil gun capacitor charger circuit. It should run off a car battery (12v). It is currently set up to charge up a 50v capacitor but I designed it to go up to close to 500v (the max rating for the diode), by just changing R4. What do you think?
  16. M

    Boost converter capacitor charger

    Hi everyone. I have been trying to design a ciruit for a boost converter in order to charge up a big capacitor. I have come up with a schematic. I would welcome feedback on this circuit, specifically will it work, and what adjustments/additions would be needed to make it work (or work better)...
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