Low-pass Filter?

[audioguru2]

There are two ICs used in the fixed and improved circuit.
Go to www.google.com or www.datasheetarchive.com and look at their datasheets.

 

[MP1]

Hi! im joseph

 

[arteka]

can someone post a corect scheme of this inverter with sinusoidal output plz?

 

[audioguru2]

This is a simple square-wave inverter. Its output transistors switch fully-on then fully-off to reduce their heating.
A sine-wave inverter is completely different and much more complicated. If you use a linear amplifier to drive the transformer then the transistors would heat nearly as much as the load. We talked about sine-wave inverters on another post.

 

[indulis]

Show me the math.................

A Butterworth filter, irregardless of order, only has poles in it's transfer function, so could you explain....

"A Butterworth two-pole active filter uses a form of positive feedback to hold the output up just before the cutoff frequency."

 

[audioguru2]

A Butterworth filter has a Q of 0.7 to provide its flat response, then its sharp drop at cutoff. If you connect two RC networks in series (buffered, so they don't interact), then they are a Bessel filter, the Q is only 0.5 and the response is sloppy and droopy. ;D

 

[indulis]

That doesn't show me the math or answer the question.

 

[audioguru2]

The math is in a text book or on the web.
Here's an example of a Butterworth lowpass filter showing the positive feedback:

View attachment 38076

 

[indulis]

John

I 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?

 

[audioguru2]

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.

View attachment 38077

View attachment 38078

 

[ECET0purdue]

why not use a fir filter? is there a difference? 

 

[audioguru2]

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

 

[ECET0purdue]

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?

 

[audioguru2]

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.

 

[indulis]

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???

 

[audioguru2]

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. View attachment 38081

View attachment 38082

 

[ren_ADD]

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 .......

 

[renaldo]

can i upgrade thats 500w to 5000w with a 110 and a 240 output ac

 

[audioguru2]

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.

 

[ray99mond]

Can i use the 1N5401 for the diode ?
the voltage at the primary side of the transformer should be 12V AC right ?