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Posts posted by pyrohaz

  1. Hey Jack!
    I suppose one of the main points on the charge rate would be the battery capacity/chemistry type of the batteries. For example, the internal resistance of standard ni-mh batteries usually limits them (safely) at 3C, 3 times the capacity of the battery. For example, 1.2v at 800mAh would have a maximum output current of 2.4A with a voltage dropping proportionally.

    I think that if you try to charge the capacitors at a current of 1A to 1 time constant (63.2% charge) at 1A it would take about 6.4 minutes (T=RC, T(ms) = R(ohms)C(uF) 1A at 400V is a resistance of 400R, 400R x 970uF = 388000ms OR ~6 minutes)

    Unless you don't mind the quite long wait (if I worked that out correctly! XD) I think you will be in for designing quite a high current switching circuit. Even at 4A, the charge time will be 1.6 minutes for every time constant.

  2. Your absolutely correct there! Sorry. Yep two 120w Laptop power supplies it is then! I'm no longer able to make PCB's at school (Because I don't go there anymore!) Do you know where I can get single PCB's fabricated for suitable prices? OR kits that I can use (without a laser printer as I simply cannot afford one :P ) I think it would probably be better to design my own preamp to fit the specification of my amplifier instead of buying a prebuilt one. Also, I can customise it to my power supply.

  3. Thank you very much for your help as usual hero :) I would have asked the seller but after buying various items multiple times from China, the outcome is usually the same: Read the description. So instead, I looked through his shop and found a power supply section but I wasn't able to find a suitable pair or one :(. After doing some further browsing on eBay, I found a new revision of that board that accepts a Tapped transformer (20v, 0v, -20v) so I was just thinking, get an 18v, 0v, 18v Torroid, shove a switch and correctly measured fuse in the AC side and then be done with it? I'm just not sure on the VA rating I would need. Could you help me there please?

    Thanks guys :)

  4. Hey guys, im wanting to create a Bass amplifier head and for the amplifier section, I want to use the Philips TDA8920BTH, it can provide quite a high amount of power at 0.5% distortion in BTL mode. What I was wondering though was how do I create a mammoth PSU for this amplifier? I would have liked to use a switching power supply to reduce the weight of the head but if a transformer based one would be best, could you advise me on what would be required and how to make it?:) Thanks

    Amplifier: http://cgi.ebay.co.uk/Classic-D-philips-TDA8920BTH-digital-amplifier-2-100w_W0QQitemZ150446744622QQcategoryZ14973QQcmdZViewItemQQ_trksidZp4340.m263QQ_trkparmsZalgo%3DDLSL%252BSIC%26its%3DI%26itu%3DUCI%252BIA%252BUA%252BIEW%252BFICS%252BUFI%26otn%3D8%26pmod%3D150436324792%252B150436324792%26po%3D%26ps%3D63%26clkid%3D8209590715140814741

    PDF: http://www.nxp.com/documents/data_sheet/TDA8920B.pdf

    Sorry about the long URL's, I forgot how to shorten them XD

  5. Woo! I actually used a concept like this for my electronics tech product for my GCSE, I used a Piezo trigger (they convert vibrations into an electronic charge), I then amplified this signal massively so it goes from the small signal to a quite large pulse, then put this through a Schmitt trigger to "clean up" the signal, then into a diode based peak detector thing, to switch a relay. Since you say that you only have a small level of electronics knowledge, that might be a slightly too complex circuit and you may be better making a mechanical design, shown by Dionysus :)

    Good luck dude! :D

  6. The reason you were probaly not having as much heat as you wanted would probably depend on the power supply. At a voltage that low, I believe you'd need to increase the current as with a constant resistant, current is inversely proportional to voltage, as in: less current is required as more voltage is applied.

    If you were trying to power this small amount of wire with a battery, it would give a resistance (at 4 inches) of 0.556Ohm, which at 1.5v would require 2.7A - 1.5v/0.556Ohm

    Even if you were using a D cell, the internal resistance of the battery would limit the current massively.

    For an Energizer Alkaline D cell (a standard D cell battery), the internal resistance is between 150m and 300mOhm, already limiting the maximum current draw to 5A.

    Unfortunately, with a battery, when the current is that high, the cell voltage decreases proportionally to the current drawn.

    I think I might be thinking the wrong way round but if you get a thinner gauge wire, the resistance should increase but due to a decreased volume of nichrome, it should get hotter?

  7. I was originally going to use it to power an ETG gun but after having some extreme switching problems :P (couldn't find a thyristor or switching device with anywhere near enough current capability) I scrapped the idea and used the capacitors for different projects.

    Thanks to one of the users on this website, I picked up a load of them B stock off Rapid, I was really happy with the results and got some MASSIVE bangs out of creating molten flying aluminium sparks :P

  8. Hi Jack, when I was creating my capacitor bank (8000uF @200v) I was looking for a charging circuit and came across this website: http://sites.google.com/site/uzzors2k/boost_converter

    It uses some quite simple components (555 timer, power mosfet and inductor) and as it says on the website, can charge his bank up in 30 seconds. Hope it helps :)

  9. Well, remember that you will need to consider the self discharge of the capacitor (The capacitor 'looses' charge through leakage over time) you will obviously need some form of step down converter to a voltage useable by the LEDs, it might be quite hard to design a step down converter using discreet components and i'm personally not sure of any commercial step down converters (im quite sure they exist though :)

    To control the rate of discharge, you can vary the current flow from the capacitor.

    If you have a set discharge, you can just use a simple resistor and LED series configuration. While you probably won't be able to control the current through the LEDs too well, you could probably work out the rate of discharge from the current being drained from the capacitor. This wouldn't be a very efficient way of stepping down the voltage as the excess voltage will be given off as heat through the resistor. Also, since you stated a 300v difference in charge, teh resistor would either have to be configured for the highest voltage (1000v) or variable with the voltage.

    At 1000v with 1 LED, the value would need to be 56k at around 22w! Thats a lot of power dissipated as heat.

  10. Hi, assuming that you won't need to switch at half the frequency of the sine wave, (12v automotive relays probably cannot do this) You should be able to go:

    Half wave rectifier > Capacitor filter > Transistor switching Relay > Output!

    The transistor amplifier section should be able to take the 1.8v peak from the capacitor and use it to switch the relay.

  11. Hi Sam!

    Have you heard of Hall effect sensors? I'm not sure whether they would work with the 5m distance you are proposing but I do know that the output voltage varies with the level of magnetic field. Maybe a bit of research into these? I know that they are used within the twisting throttles of electric scooters and such products but whether they would would work for your job, i'm unsure about.

    Hall effect sensors can be bought off Rapid. :)

    Edit: For it to switch a stopwatch in your case, the output of the hall effect sensor would need to be amplified for a change (The magnetic field around it changing) and that small change being amplified, compared to its normal state. This can be achieved with a differential amplifier. The output of the amplifier could then be used in conjunction with a relay to switch your stopwatch.

  12. I calculated massively wrong then XD I dont understand how it got so loud then, was my speaker just massively efficient or was it overdriving but where I couldn't hear it? I was only using a single 12v Supply while my Bass amp (Hiwatt 10w blah blah...) seemed quieter :S And I had got the speaker wrong. After looking, it was 4 Ohm phillips speaker with tweeter, only a 5.25" speaker though :S Sealed enclosure....

  13. Thanks a bunch dude, you're a real help :) Right, how about if I modify it to:

    8" Speaker with tweeter (my dad uses them for his Denon integrated system lol)

    Use a TS555 instead (Please can you recommend what MOSFETS I should use? I haven't used mosfets yet, primarily because I just haven't got any!

    Replace the 741 with a TL071?

    What kind of output filter do you recommend?
    Inductors I have:

    For the speaker, I only called it hifi because thats what the sticker says :)

  14. Hey guys, i've been reading up on Class D amplifiers and how 555 timers can be used for Pulse width modulation. I decided to see how hard it would be to make a simple class d amplifier using a 555 timer.

    I've included a schematic of my circuit I have designed. Oh yeh, one mistake I did make in the schematic was: The speaker i'm using is 8R not 4R

    The 555 timer operated at 96KHz, Just below the 100KHz limit of the 555 timer. The first LC Lowpass filter is set at 10.7KHz using a 220uH Inductor and 1uF Tantalum capacitor. The second filter is set at just over 100KHz just incase any harmonics go over the first filter (more a safety precaution than anything). The output capacitor is only 1000uF because I didn't have any higher values at hand. I worked out that the reactance of this capacitor at 50Hz was 3.18R, not a major problem. I evaluated the bass response of this system with a sweeping track from 40Hz to 100Hz and after personally hearing, it sounded as if the peak was ~60Hz. I am using a JVC 8W 4" Hi-Fi Speaker. My power supply is a 16v 2.2A Supply with a 4mH Choke in series and 470uF Capacitor across the supply (After the choke) to lower supply ripple.

    Now! What I was wondering:

    1. I know that Class D amplifiers are meant to use Mosfets instead of transistors but I didn't have any at hand. Would using Mosfets benefit in any way? After doing a skin test on all the components, the heatsinked transistors were still cool enough to touch continuously and the 741 and 555 timer were the same temperature as when I started (the amplifier had been running for 1 Hour playing some music).

    2. Would I benefit from using a TS555 instead of a NE555? I read an Application Note from International Rectifier and it stated that reducing the dead time from 40nS to 15nS reduced THD by 1.92% so since the Rise and fall time of a NE555 is 100nS, the TS555's being 25nS rise and 20nS fall, would this really make a noticable difference?

    3. If I swapped out the 741 for a TL0x1 series, would it make much of a difference?

    Thanks in advanced guys :)


  15. I made a simple amplifier with the TDA2030 in a tech lesson at school, after looking around at what parts my school had, I found an old unsoldered TDA 2030, after soldering some solid core wires onto it, I made a 5W or so audio amplifier out of it, I know this is probably not the way to do it but I:

    1. Connected the +Vs to my 12v Supply and the -Vs to 0v.
    2. Biased the Non-Inverting input half way between the supply voltage using a simple resistive divider (two 10k's and a 100uF capacitor to make sure I got no ripple)
    3. I then wired it up as a standard Op-amp based audio amplifier, 10k resistor between the input capacitor and the inverting input, then a 100k resistor between the inverting output and the output for a gain of 10. Before the input capacitor, instead of directly inputting the the sound source into the amplifier, I made a simple Preamplifier based on the LM741 (I know you guys aren't too fond on the chip but it worked fine for this project!)
    4. I added a Miller circuit (? I forgot the name of the actual circuit lol) 1R resistor in series with a 100nF capacitor on the output, I think the increases stability or something?
    5. I placed a 2200uF Capacitor between the output from the chip and the speaker, my speaker was a single 4R speaker with a built in crossover and tweeter.

    The sound was actually quite impressive, after trying it with my bass guitar and comparing the sound of that amplifier to the sound of my standard amp, I was quite impressed at how small my distortion levels were.

    Obviously, there were some problems with this design such as: Negative feedback for the whole design I think? I will obviously keep that in mind for when I next build a circuit like this again.

    Audio, I don't think that he was intending to use them bridged, just using each chip for each channel.

    All I can personally say is I don't think you will be able to get much power as the TDA2003 at full power will cause quite a bit of distortion (10% at 10w through a 4ohm speaker) so if you did end up using the TDA2003 and TDA2030, you'd have to limit the TDA2030 to a much lower level.

  16. Wow! 4 Hours! that would be brilliant, I only expected 2!

    So as Hero said, how about:

    Joule Thief bootstrapping a 555 Timer, acting as a PWM oscillator at a given frequency, with a switching output?

    That circuit would be ok right because I know the joule thief can supply atleast 20mA (to light an LED)

  17. Hi there hero! thank you very much for your help and reply. If you re-read my spec, it was 0.2A our, not 1A at 5V. I just wondered if the input current could be kept below 1A because thats the maximum current supplyable by a D cell alkaline battery!

    Now, I definately do like the switching circuit that you designed for me, what is the switching frequency? (I didn't put this into the specification but i did want it to hopefully be above >25kHz, out of the audible range BUT thats not important :D.

    Thank you very much for the help, would you possibly be able to run through with me how you designed that circuit please for future references?

    Thanks again!

  18. Since the 4047 is in the 4000 series, I assume it doesn't work down to 1.5v? I thought their voltage range was just 3v-15v? Also, I thought that with boost converters, if the duty cycle is higher than 50%, the efficiency can be increased by matching the duty cycle to the frequency and inductor's inductance?

  19. Howdy guys, hope you all had a good Christmas and new year, I haven't been here in ages! Right, i've come across the question of... can somebody help me in designing a circuit that can complete my specification:

    DISCREET! No maxim or national semiconductor IC's please.
    1.5v to 5v, no more than 1A input current
    5v output current at 0.2A (preferably 0.5A but not urgent)
    Assuming 1A input current and Output current of 0.2A, hopefully an efficiency above 66%?
    Output can be zener regulated or shunt regulated etc...
    Hopefully using boost converter (inductor based) circuitry OR if anybody can devise a high current switched capacitor circuit, any ideas are welcome! I originally designed one using a transistor multivibrator but when testing in real life, it sagged to 3v with a 100R load!

    I was thinking, a pulse width modulating RTL inverter style thing, I will attach a schematic for the sort of oscillator i


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