Kain

Ok, I thought so about the feedback but wasn't sure - no enough time to analyze this circuit anyways, but this is why we have Audioguru here ;D! I measured the negative input of U2 and it was quite enough to force the output to max so it does make sence. I am about to replace the 3 power BJTs now. Hopefully i won't see the smoke again... ::)

I actually found the problem. As I said I was assembling the PSU and what happened was that one of the 2N3055 was not hooked up correctly. I exchanged the base and the emmiter so when I loaded the PSU on 7A I blew all of the 2N3055 transistos and the TIP31A one (Q2). I think I might have blown something else too. I haven't placed the parts back yet but I am getting maximum output on pin 6 of U2 - no regulation possible. I replaced the chip too and result is still the same. The output on pin 6 U1 is 11.2V so I think this is acceptable. U3 is working fine too. U2 is acting like this even without Q2. Any idea what else might be blown? I was thinking Q1 maybe.

Ok, I finally managed to blow this PSU up. I burned Q2 and it was quite obvious since R15 begun to smoke. The output current was 7A at 2V when this happened. Any idea why it burned? I haven't replaced Q2 yet, and I don't wan to if it is going to burn on me again since this is not a fix obviously. I still coldn't figure out how i burned Q2 neither... The datasheet says that the max collector current is 3A. I think I haven't reached this value.

Hi fish2005, I am not sure if the dual power supply is also floating. One can think of the common as floating but in the case of laboratory PSU the common is very often ground as well, and as ground I mean earth. Even if it is not, the center point is called ground and positive and negative voltages are adjusted with respect to it. You can connect two of this in series without a "big boom" but I believe that the catch is that the current through them has to be the same if you want to use the full swing from 0-60V. If you use them as dual PSU I think still each stage will be on its own so you shouldn't have problems. I have done it actually.

I know that this is a bit out of topic since it is not directly related to the PSU, but can anybody here suggest a good CAD to draw a cover label for the face pannel of the PSU? I finally put it together - now it is going all the way to 30V/6.9A with fan cooling. The ripple problem is solved - audioguru was right about the proper star grounding technique. I shortened all wires as much as possible, and avoided crossing them too to avoid inductive coupling. After I make the label I will post the picture of the final result which I think looks quite nice even now (and works quite nice too

Thanks for the reply - it surelly was a good information. What does the information on the LITZ wire in parantesis indicate though (e.g. 1X15X,1)?

The article where I took this data from is basically the application of HID lamp controller made by TI. There is an inductor and a transformer that I am willing to try and build but one problem is that I don't quite know where I can buy the transformer core from. Here is the article in PDF. The way I understand the transformer data is: RM10PA250-3F3 PHILIPS - transformer core 10T PRIMARY LITZ(2X10X,1) - primary winding is 10 turns, but LITZ(2X10X,1)....I have no idea it might be wire data?? ::) 60T SECONDARY LITZ(1X15X,1) - secondary is 60 turns, and again LITZ(1X15X,1).... The winding sequence - I just don't understand it at all. HID.pdf

I was looking at some SMPS and saw the informaton about the winding sequence of the transformers and inductors. Can anybody here explain the meaning of the information below? This is what is typed in the datasheet: L2 RM10PA250-3F3 PHILIPS 10T PRIMARY LITZ(2X10X,1) 60T SECONDARY LITZ(1X15X,1) WINDING SEQUENCE (PRIM-10T, SEC-30T, PRIM-10T,SEC-30T, PRIM-10T) Oh and by the way, Happy New Year to everybody!!! ;D

Oh ok. It seems like the best of the 3 is the MAX038 anyways. Good thing I got it as sample some time ago ;D

Audioguru, where do youfind datasheet for XR20x6? I tryed to google it, but nothing came up... ::)

One more thing - I recommend you to experiment first with transient responces of RC and RL circuits so you can notice few things, sich as inductors are dead short to DC once they build their magnetic field and capacitors act as nearly open circuit once they charge up. Cheers :)

Connecting a stright wire and an inductor is not the same thing. A wire has some ammount of inductance but it is very small on first place. Another thing to consider is that every wire that you get your hands on has some resistance - it's a resistance derived from the resistivity of the material and the longer the wire is the more resistance you will have. The primary coil of a step down transformer has higher resistance than the secondary as well and thus limits the current through the coil (coils are made of wire too). If you hook up a short wire stright into the plug between the phase and neutral then you short it 100% since this wire has very small resistance (you most likely blew your fuse ;D). I would recommend you to use low voltage sin wave generator for resonance experiments - it's less dangerous and it has built in current limiter and so on, so there is no chance of you blowing yourself up or blowing the coil up or something else ;D. Capacitors are dead short at the first moment (this is for very short ammount of time) this is why people tell you that you need to hook up a series resistance. The series resistance will limit down the very high inrush current in the very beginning when you connect the LC circuit.

To get 12V rectified you will need a step down trasformer to get 12V AC and then you use full wave bridge rectifier (if your transformer does not have center tap) to get these 12VRMS to DC voltage. Keep in mind that the output will be the peak voltage of the secondary - 2 X Rectifier Diode voltage drops. You can achieve better efficiency if you use center tapped transformer and 2 diodes - in this case you will get DC value lower only with 1 diode voltage drop instead of 2. For most Si diodes the drop is about 0.7V if they are PN junction. For shotky Si the drop is about 0.5V. For Ge diodes it's about 0.3V. Hope this helps. :)

I just downloaded TINA - it has few things that DXP doesn't, such as 555 simulation. I also found the simulation model for TLC555 which is the linmos version of the 555 timer chip, but yet I cannot figure out how to create the simulation ready part ::) Ok, I understand that we can get some sim models but this still doesn't answer the real question - how do we make simulation models if we can do it at all...

I've been playing arround with DXP2004 evaluation software lately and with Orcad student edition, in particular with simulations ;D. I've noticed one thing for DXP 2004 but I assume that it is the same for any simulation software out there - we have limited number of simulation ready parts, thus I sort of wonder how do they make the simulation ready part? I digged some info for DXP 2004 and found out that we can basically make any part we want and we can assign an appropriate simulation model to it and it will make the part simulation ready. However, we have still limited number of models... So the question still remains - how do we create simulation models either in DXP or OrCAD or any other circuit simulation software? I believe this is more than handy to know ;D

Hi EdwardM! True about the rates, but don't you think those contacts will not last with all this high discharge current and arcing? Considering they will be opening and closing from 5 to 20 times/s with all this arcing....oh well, just my thoughts :)

Yes this is correct. I have a question though - is this button with normally open or closed contacts? On the picture it looks more like normally closed...

You are right - you cannot use AC to power those up. However, one simple thing that you can do is voltage doubler or multiplier (depending on where you live). If your outlet AC is 220RMS then a doubler would do and of course you will need to limit the charge up current otherwise you might get more than just flashing ;D. The problem with fluorescent bulbs is their intensity mostly. In fact, if you want to flash them fast you will still need high voltage to ensure that each pulse will break down the gas... I believe that there are relays that can open and close at this frequencies, but having in mind the current through its contacts when it closes I am sure its lifespan will be short overall. You can use SRC's or high voltage transistors instead, in combination with opto-couplers to insulate your pulse generator from the high voltage part of your circuit.

Hi. What sort of lamps are u planning to use? If you want to achieve a proper strobe effect u need to use discharge lamps like the ones used in photoflashes. Those have 3 electrodes - Anode Cathode and controlling electrode. The way it works is by applying high DC voltage between the Anode and Cathode and pulsing few kV voltage on the controlling electrode. Usually the voltage across the Anode and Cathode is delivered from a capacitor that is fully charged to the required working voltage. I have personally done some of those 5 years ago with 2 and more lamps. If you want to use a regular fillament lamps it will not work or it will be a poor effect because fillament lamps do not turn off fast enough (the wire inside is still hot and glowing) meaning that one can't switch them fast enough to achieve strobe effects well. Another thing is that flashing fillament lamps will kill them fairly fast.

Hi again. I have been playing arround with the scope lately and it is not too hard to figure out that in order to make a correct phase difference measurement when we feed 2 signals we should always have the same time base, and this is where I wonder

Ok now, I decided to try this once again before I totally change my mind about the circuit design and so far is seems like Aidioguru hit the jackpot ;D. I tryed the exact same circuit with a bypassing capacitor of 100nF across 1 and 8 as close as I can hook it and another capacitor of 100uF electrolic across the same pins. I have triggered this thingy about 50 times so far trying to burn it hard but it refuses ;D. Maybe 20V would do :P Just kidding but yes - it seems that the bypassing capacitor is needed, indeed. Oh, and about my previous post - I checked again about the bypassing of CMOS versions of 555 and it seems like I misread it sometimes ago - they still need to be bypassed but the value of the bypassing capacitor can be much smaller. I guess it was one of those nights when I was pulling all-nighter and didn't quite know what I was reading when I did ;D

Alun: "What are you trying to do?" I am trying to use 555 as a delay-on timer. In this particular circuit when there is nothing applied to the base of the transistor it shorts out the capacitor which causes pins 2 and 6 to have positive with respect to ground - the output on 3 is low. Once we connect the base of the transistor to ground the capacitor is allowed to charge exponentially, thus eventually we get high on 3, untill we remove the ground from the transistor's base, in which case the transistor quickly discharges the capacitor and the output 3 is forced to low. Audioguru: "I suspect that the supply voltage is too high because with only a 12V supply, the LED would look dim with only 1mA or less. Did you exceed the absolute max supply voltage of only 15V for National's or 18V for TI's Cmos IC? Is a relay or something connected to its output?" The supply voltage was 12V when I tested it and current limited to 15mA, so no - I didn't overvolted the chip. For now it drives an LED which lights up bright at 1mA even so I haven't tryed to source even 10mA , thus I haven't exceed the secifications in this way at least. :D Also if the diode is trying to remove any excess negative voltage from the capacitor I am not sure if it can do lower than about -0.7V (Si) thus if this is enough to burn the chip .....oups. Just a guess though. I haven't tryed to bypass the chip and see if it burns again but I have the feeling that I am about to waste another chip by doing it. The bypassing is normally suggested for the bipolar version of 555 but the manufactors claim it's not necessary for CMOS types. I hope I won't burn another ... ::)

Here is a circuit that I tryed yesterday. I first tryed with NE555 which is the regular 555 timer but then I wanted to have less power consumed so I decided to try with TLC555 which is same timer but CMOS (LINMOS) version from Texas Instruments. While the NE555 seems to work ok, the TLC555 burned out right away

Oh, so they mean capacitors reactance by saying impedance... Ok, makes sence. ::)

Ok, how about this? If the impedance of a capacitor is the sum of the real and imaginary part then if we know that the impedance of a capacitor that is given in catalog is 0.01Ohm then this means that the sum of the ERS and the imaginary are 0.01Ohm at most, meaning that ESR has to be even less than that. Is this correct?