Hello I am attempting to design a discrete class D amp as part of a project and as the title of thread suggests I don't really know what I'm doing. Unlike most of the posters here I am not concerned with brilliant efficiency or high fidelity just a functioning amplifier. It would be greatly appreciated if anyone could give me a little guidance and hopefully some re-assurance I'm going in the right direction. Currently I'm trying to work out the output stage which is a full bridge design as shown below.
*the load is an 8ohm speaker
If I have a PWM signal at 250 kHz alternating between +/- 5V what would be the best way to drive the MOSFET's? I know from what I've read that using N-channel MOSFET's for both the high and low side gives better results but the additional circuitry for level shifting seems a bit beyond me.
*the load is an 8ohm speaker
If I have a PWM signal at 250 kHz alternating between +/- 5V what would be the best way to drive the MOSFET's? I know from what I've read that using N-channel MOSFET's for both the high and low side gives better results but the additional circuitry for level shifting seems a bit beyond me.
MrDude,
Zetex used to have an eval board for their driver chip, using complementary pairs in a full bridge arrangement like you want.
Try locating zxcd50steval.pdf.
Blank out all the protection circuitry and notice how the pairs are driven via two caps from a 12V PWM signal.
E
Zetex used to have an eval board for their driver chip, using complementary pairs in a full bridge arrangement like you want.
Try locating zxcd50steval.pdf.
Blank out all the protection circuitry and notice how the pairs are driven via two caps from a 12V PWM signal.
E
One way of doing it using a triangle wave generator and audio signal going into a comparator. The output is then level shifted into a phase splitter for the two pwm signals.
Your concept schematic is only suitable for high supply voltages because it works as a power "voltage follower".
Swap N-ch and P-ch, and D and S connections, and analyze the resulting circuit.
Swap N-ch and P-ch, and D and S connections, and analyze the resulting circuit.
Thanks for the replies, I had a look at the data sheet for the mosfet driver Nigel suggested and though I can't be sure I think maybe using just n-channel mosfets may be easier. I drew out a little diagram to try and get my head around what the driver actually did and how I could use it. Hopefully my understanding isn't too flawed.
Thats for a half bridge, I don't know how a full bridge would be connected. I'm guessing you have a second driver but with the low and high outputs connections reversed or something. Also I couldn't see anything about it on the datasheet but does it have ample dead time? I noticed that this driver can handle very high voltages, I take it that it works fine with 5V or does it need a higher supply voltage? What sort of n-channel mosfets should be used with these drivers? Sorry I'm asking so many things but these things don't seem to mentioned on the datasheet.
Thats for a half bridge, I don't know how a full bridge would be connected. I'm guessing you have a second driver but with the low and high outputs connections reversed or something. Also I couldn't see anything about it on the datasheet but does it have ample dead time? I noticed that this driver can handle very high voltages, I take it that it works fine with 5V or does it need a higher supply voltage? What sort of n-channel mosfets should be used with these drivers? Sorry I'm asking so many things but these things don't seem to mentioned on the datasheet.
The easiest way to get into class D is find a reference design for your controller of choice and copy it. It will help you get to grips with the complexities and generally give you a layout to follow, as class D and SMPS's require the correct layout to functio and not pollute the world with EMI noise.
mrdude,
you may want to check out this thread on a simple design using a complementary pair:
http://www.diyaudio.com/forums/class-d/207535-just-fun-ucd-shoestring.html
-E
you may want to check out this thread on a simple design using a complementary pair:
http://www.diyaudio.com/forums/class-d/207535-just-fun-ucd-shoestring.html
-E
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