indulis Posted December 7, 2005 Report Share Posted December 7, 2005 That doesn't show me the math or answer the question. Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 7, 2005 Author Report Share Posted December 7, 2005 The math is in a text book or on the web.Here's an example of a Butterworth lowpass filter showing the positive feedback: Quote Link to comment Share on other sites More sharing options...
indulis Posted December 7, 2005 Report Share Posted December 7, 2005 JohnI know the math...... for a second order, the transfer function solution is quadratic, but you're the "theory expert", so can you explain, in technical terms why the gain doesn't start to roll off a decade before the corner frequency? Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 7, 2005 Author Report Share Posted December 7, 2005 The gain doesn't fall off too soon because the positive feedback boosts it near the cutoff frequency. For a Butterworth filter, the frequency response is absolutely flat to near the cutoff frequency, no matter how many orders there are.As an example, I use a 2nd order highpass Butterworth filter with too much gain to give bass boost to my sound system. I used the same thing except with a 2nd order lowpass filter to give a 3.5kHz peak in telephone boardroom conferencing systems. Quote Link to comment Share on other sites More sharing options...
ECET0purdue Posted December 8, 2005 Report Share Posted December 8, 2005 why not use a fir filter? is there a difference? Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 8, 2005 Author Report Share Posted December 8, 2005 An FIR is a complicated digital filter. Maybe you are thinking of a switched capacitor filter, like I use in my ultra-low-distortion signal generator. I even use a switched capacitor notch filter in my distortion analyser circuit. They make great simple filters. ;D Quote Link to comment Share on other sites More sharing options...
ECET0purdue Posted December 8, 2005 Report Share Posted December 8, 2005 i belive its a fir it works really good, I downloaded it to a DSP Board. used a blackman window, its a band stop filter so when it reaches 60 hz it stops that frequency, pluged in a couple numbers and tested...so a fir filter will give better results? then a butterworth, or bessel? or is there something that makes them different? Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 8, 2005 Author Report Share Posted December 8, 2005 A FIR digital filter in a DSP board has a sharp cutoff because it effectively has many orders.A Butterworth analog filter can also have many orders. Maxim have some Butterworth switched capacitor lowpass filters with 8 orders. Square wave in, sine wave out. Quote Link to comment Share on other sites More sharing options...
indulis Posted December 8, 2005 Report Share Posted December 8, 2005 OK...... so what your "saying" is that, in a second order Butterworth low pass filter, there is gain just prior to the corner frequency due to "positive feedback"??? The transfer function only has poles and NO zeros, how can that be??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 8, 2005 Author Report Share Posted December 8, 2005 OK...... so what your "saying" is that, in a second order Butterworth low pass filter, there is gain just prior to the corner frequency due to "positive feedback"??? The transfer function only has poles and NO zeros, how can that be???The opamp provides the majical gain for some positive feedback and boost.In my example of a Sallen-Key lowpass 2nd-order filter that has equal component values:1) At low frequencies, C1 and C2 have a high impedance and don't affect the response which is flat.2) At high frequencies, C2 rolls-off the response so the opamp's output is lower than its input, then C1 also rolls-off the response.3) Near the cutoff frequency, C2 doesn't roll-off the response very much so there is positive feedback through C1 to the input which provides a boost.The boost is exactly the same as in my bass-boost circuit, except it is less because the opamp's gain is less. Quote Link to comment Share on other sites More sharing options...
ren_ADD Posted December 20, 2005 Report Share Posted December 20, 2005 hi, Im Ren from the philippines I just want to ask if the 500 watts power inverter is really working? and if so is it applicable to Television sets?Becuase I want also to build the power inverter if you wuold mine.Pls. give an assurance that the inverter will work?Thanks a lot :)....... Quote Link to comment Share on other sites More sharing options...
renaldo Posted January 19, 2006 Report Share Posted January 19, 2006 can i upgrade thats 500w to 5000w with a 110 and a 240 output ac Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 19, 2006 Author Report Share Posted January 19, 2006 Hi Ren,The modified 500W inverter is used in the Philippines to power fluorescent lights and TVs that work with an input from 85V to 250VAC.If you used many paralleled batteries, an enormous transformer, 8 to 10 times as many transistors, 8 to 10 times the size of the heatsinks and a few other things then it could be made for 5000W. Its custom-made transformer could have any output voltage you want. Quote Link to comment Share on other sites More sharing options...
ray99mond Posted February 19, 2006 Report Share Posted February 19, 2006 Can i use the 1N5401 for the diode ?the voltage at the primary side of the transformer should be 12V AC right ? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 19, 2006 Author Report Share Posted February 19, 2006 Can i use the 1N5401 for the diode ?For the modified 500W inverter project the 1N5401 diode is rated for 100V/3A so will be fine for D1 and D2.the voltage at the primary side of the transformer should be 12V AC right ?No. The primary has 24Vp-p so the transformer should be rated at 12V - 0V - 12V which is 24V center-tapped. Quote Link to comment Share on other sites More sharing options...
ray99mond Posted February 19, 2006 Report Share Posted February 19, 2006 Thanks for your great replyI measured the voltage between "12V to 0" and i get 24VACand same result for the "0 to 12V"I didn't connect to a transformer yet for safety purpose....so is the reading correct ? or should be 12VAC instead of 24VAC? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 19, 2006 Author Report Share Posted February 19, 2006 I don't know what your transformer is connected to. The mains? The project?I don't know what was not connected to a transformer yet.The project produces a square wave output that most meters won't measure accurately. Quote Link to comment Share on other sites More sharing options...
ray99mond Posted February 19, 2006 Report Share Posted February 19, 2006 sorry for confusing, I built this 500W inverter but not yet connect the transformer to that circuit yet. and the 24VAC is come from the circuit which should be connected to the transformer.sorry for drawing it wrongly. Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 19, 2006 Author Report Share Posted February 19, 2006 The project doesn't have a regulated output voltage. It will change with the load. Quote Link to comment Share on other sites More sharing options...
ray99mond Posted February 19, 2006 Report Share Posted February 19, 2006 the voltage will change with the load? the project is using 12v-0-12v to 220 transformer, so the circuit circuit should generate 12VAC at the primary side of the transformer right ? My problem is why i get 24VAC instead of 12VAC...Thanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 19, 2006 Author Report Share Posted February 19, 2006 With a 14V fully charged car battery, one 12V wire of the transformer will be driven to about 2V and the other 12V wire will swing to 26V. Then the oscillator reverses the voltages. So each transformer wire has 24Vp-p when measured from the 14V center tap.If you connect the high voltage winding to a 220VAC sine-wave, then each wire of the low voltage winding will be 12VAC which is 34Vp-p when measured from the center tap. Quote Link to comment Share on other sites More sharing options...
ray99mond Posted February 20, 2006 Report Share Posted February 20, 2006 I see... thanks for your explanation .. ;Dbtw I have a 3A step down transformer from 240VAC (primary) to 12v-0-12v (secondary) for the rectifier system, can i use it as the step up transformer for this circuit? 12v-0-12v become the primary side while the 240VAC as the secondary side? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 20, 2006 Author Report Share Posted February 20, 2006 If your transformer's 24V output is rated at only 3A then the transformer's max rating is only 72 VA. Using such a small transformer in a 500W circuit wastes many parts. Just the operating power of the circuit without a load will probably overload the transformer.Here is the modified project stripped down for a 100W load. With your small transformer its max is 72W. Quote Link to comment Share on other sites More sharing options...
ray99mond Posted February 20, 2006 Report Share Posted February 20, 2006 actually the transformer that i am using now is a 240V to 12V step down transformer for my rectifier circuit. I need this inverter for my UPS project, so this 500W inverter is suitable... so what kind of transformer i should get to support 500W output? 20A transformer? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 20, 2006 Author Report Share Posted February 20, 2006 actually the transformer that i am using now is a 240V to 12V Quote Link to comment Share on other sites More sharing options...
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