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A year ago, I was scouring for an amplifier for my subwoofer project. So I've read some of the class d threads here, and learned many ideas because of it. I've come across a sigma-delta class d amplifier, created my own layout, built it, and I liked the sound of the bass, better than most class AB Ive tried., but the amp was easily busted because I accidentally short circuited the outputs.
Since I know basic electronics and can make PCB layouts. I thought of a design that combines most of the desirable features of the existing ones freely distributed here.
One of the easily implementable and forgiving design I found on the forum are the derivatives of IRAUDAMP1, a self oscillating sigma-delta class-D, implementation of International rectifier. There are also loads of documentation/application notes that can be freely downloaded on the internet that's why I chose that for the PCB layout of my subwoofer amplifier project.
Here are some of the design considerations for my amplifier project.
- The first goal of my design is that the driver IC must be easily obtainable and cheap. Must be cheaper than IRS2092.
- Must be all through hole components and low parts count. All through hole so that the amplifier will be easily assembled and repaired by an amateur.
- Another goal for the design is that the power supply for the driver chip must be integrated on the PCB. I chose the LM350 regulator as the power supply because it can easily provide 2A of current for the mosfet driver. I included the circuitry in the PCB such that only an external AC voltage will be needed. Also when there's an external supply for the driver, the amplifier will accept wide voltage range for the rail supply. The driver supply should be mounted on a heatsink too. Heatsink is calculated based on dissipation.
- Another goal for the design is to have an overcurrent protection built in. One of the easy implementation I found is the low side current sensing using NE555 and LM311.
- Single sided PCB. I created a single sided pcb for my prototype. But my latest design uses double layer to reduce noise.
- No built in speaker protection with relay on board because based on my experience, it is difficult to replace a busted relay without (slightly) damaging the pcb board.
- Paralleled outputs. One of the original goal is to have parallel output. I tried it and it worked on my prototype but the driver IC and the regulator IC is heating up like hell. So based on actual use and my calculations, the reliability will be compromised, if there's no buffer for the gate driver. So my final design uses only 1 pair of output mosfets.
Here are some of the application notes that helped me in building this amp.
IR Class D Tutorials:
Class D Audio Amplifier Design
Designing Practical High Performance Class D Audio Amplifier
IR Design Tips:
DT04-4 Using Monolithic High Voltage Gate Drivers
DT97-3 Managing Transients in Control IC Driven Power Stages
DT99-7 Alleviating High Side Latch on Problem at Power Up
IR Application Notes:
AN-1071 - Class D Audio Amplifier Basics
AN-1084 - Power MOSFET Basics
AN-978 - HV Floating MOS-Gate Driver ICs
AN-1070 - Class D Audio Amplifier Performance Relationship to MOSFET Parameters
AN-1135 - PCB Layout with IR Class D Audio Gate Drivers
Here's the picture of my prototype. The bass is very good. But in full range, sound is just ok. Also when it is connected directly to my laptop, there's an audible hiss, but when I used other sources, there are no hiss. That's why in my final design, I used double layer for the PCB. And it solved the hiss problem :) .
The amp is beside by receiver. Interference on FM radio stations is also not a problem. Better than a mono 250W class D I bought on some ebay store, the one I bought makes the FM radio of my receiver unusable. But I haven't tried it on AM though.
One of the problems I encountered was the heating of driver IC and regulator IC. So on my succeeding design I provided ample space for the heatsink for the voltage regulator. I also avoided paralleling of mosfets.
I only have a 20mhz scope and ordinary probes. As you can see there is some minor undershoot.
Here's my second iteration of the design, I've added an SMD buffer totem pole to the gate drive to get the burden of driving the mosfets instead of the IR2110 IC.
But after reading an application note about the consequences of paralleling mosfets, and since I have a limited knowledge and testing tools to measure the amp would be, I realized that bridging is a better solution to get more power that's why I discarded my 2 pairs design.
Also the buffer totem pole SMDs is hard to solder and the price is relatively high, and is not easily obtainable.
This is the final design of the layout of my class D amplifier. As you can see, the top copper is used as shielding planes. Also I avoided to put the shielding plane on the noisy high side gate drive. Just to be sure, because I've read that some of our members here didn't get good results with filling the top layer with copper plane. I got good result with this one.
The hiss was totally removed by the layout. Also interference to FM radio at 1ft is negligible.
I also made the mosfet TO247 and TO220 compatible.
I used HEF4069 as hex inverter, and IR2110 as gate driver. :)
The amp was designed to theoretically handle 20A output.
nice work jlester have you managed to push it hard at +/-80v with a 2ohm load?
I don't have a stiff power supply at hand yet so I didn't push it hard.
I'll publish my power measurements after I received my power supply. (ETA about 2 weeks) :)
I'll gonna use +-75V rails.
Target output current will be 16A into 2 ohms and 11A into 4 ohms (500W RMS)
Actual results might be better :)
Theoretically you can use higher rails for this amp if you put 250V mosfets (IRFB4229) and replace the value of resistor for the regulator of TL071. You also have to use higher voltage value for the bus capacitors.
Nice work sir .. it is looks like drtex irs 1500 !!
I also added extra measures (circuit and layout) to avoid the possibility of high side latching during startup and transients. And strictly followed layout guidelines as much as possible :)
Here's the sample vid of my amp just after I finished it assembling.
JLAmp1000D Subwoofer Amp Running Without Heatsink - YouTube
jlester87 hello, I think it's great PCB design, a few months ago I did a very similar design and found problems with noise that you mentioned, as was working with a layer, the quickest solution was to increase the switching frequency at 450KHz but that has its counterparts.
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