National's 170w Class D amplifier


I am currently building National's 170w class D amplifier which uses the LM4651 driver IC and the LM4652 mosfet IC.

I just wanted to know if there is anyone out there who has attempted to build this amp or has any special tips to share with me.

I have searched the forums and only mr partyjups has attempted but not completed this amplifier.

Thanks in advance
Hi Jonas
The problem that im experiencing at the moment is actually getting the board done from the schematic but here is the link for the .pdf document that national supplies you with.


This document has a schematic diagram and the board layout but National also supplies you with a design guide. If you use this design guide you will definitely not be using the same layout. Im not sure what the correct link for the design guide is but if use google to search for it im sure youll come up with something. The design guide is really helpful and im almost complete with this project. It wasnt that hard but the main problem was sourcing the i.c's here in South Africa.

Please use google to search for "LM4651" and "LM4652". The 4651 is the driver ic for the 4652(which contains 4 mosfets).

Please feel free to email me as i dont visit the forum regularly.

hope i was of some help to u.
Interesting enough I just got some of those parts in the mail today. I was planning on building a pair as well.

Are you intending on using national's typical aplication? I was wondering how high a frequency one could get out of them. It's says it's a "subwoofer" amplifier, but by using a higher switching frequency one should be able to get better responce in the higher frequencies, correct.
I built an amp with these components and it seems to work as advertised but there are some issues to keep in mind when designing the board.
I ran into protection/shutdown problems and destroyed 3 of the transistor ICs because I had the wrong type of inductor. If possible, use the inductors specified in the reference design!!
Do NOT use a toroidal choke! I did and apparently it saturated too easily at these frequencies and caused too much current to flow thru the MOSFETs. Make sure you use a coil with a DC current rating of at least 10 amps to be sure. If the current rating is too low, the coils will overheat and also saturate and destroy the transistors. I have seen suitable coils in the digi-key catalog which I will try next, part M6346-ND.
The bandwidth seems to be limited to around 10k. Increasing the switching freqency will cause a decrease in the power output and will affect efficiency and increase distortion. It seems that the IC internally limits the bandwidth somewhat, and 20kHz operation is unlikely even with increased switching speed.
Keep the traces to the MOSFET module as short as possible and avoid crossing any low-level signal traces. The square wave control signal emits a lot of RF energy so the traces should be run over a ground plane if possible.
Why use National's output IC?

I ordered some samples of the controller IC, but I intend to make my own H-bridge output stage with larger mosfets. I'm considering possibly using IRFZ24 or IRFZ44 types. I have large quantities of N-channel mosfets to try out. I'll probably create the driver board separate from the output board so that I can try different output devices without too much hassle. Has anyone else tried this? It seems that National's ICs are always lacking when it comes to the ability to handle any real power.
Anybody build other class d amp full range

I wiah that i could find low cost full range class d amp with very high sw freq.

I have read that Texas instrument is one of the best in chips for class d. but I have been looking at this
from international rectifier

It look like it posible to make up very high power from these drivers and they come in DIP housing have anybody make up something with these parts?

Im looking for PA amplifire low cost high power
best regerds jc dk.