I am repairing an Alpine MRP-M1000 car amp that uses a very strange type of Class-D amplifier. in fact, im not 100% sure it is even class-D, it is more like FM??
So working backwards looking at the schematic, we have output mosfets running on pretty standard bipolar +/-45v power supply rails.
feeding the mosfets we have IR2010 gate driver IC's. feeding that is a Quad 2-input AND gate that is fed from a pair of MC14069 Hex Inverters.
now I have seen PWM done with Hex inverters before. but where it get's weird is the function of the NJM2137 opamp. this seems to be forming an Integrator/Differentiator?? Converting the incoming sine wave to a square wave that feeds the whole chain.
In all of the Hex inverter based PWM units I have seen there is a traingle wave generator that feeds the Hex Inverter and then you have some means of adjusting the duty cycle. But that doesn't seem to be how this circuit is working???
I am very confused as to how this works. Can anyone explain it to me, or point me to some tutorials of this technique or at least other examples of this in use??
Zc
So working backwards looking at the schematic, we have output mosfets running on pretty standard bipolar +/-45v power supply rails.
feeding the mosfets we have IR2010 gate driver IC's. feeding that is a Quad 2-input AND gate that is fed from a pair of MC14069 Hex Inverters.
now I have seen PWM done with Hex inverters before. but where it get's weird is the function of the NJM2137 opamp. this seems to be forming an Integrator/Differentiator?? Converting the incoming sine wave to a square wave that feeds the whole chain.
In all of the Hex inverter based PWM units I have seen there is a traingle wave generator that feeds the Hex Inverter and then you have some means of adjusting the duty cycle. But that doesn't seem to be how this circuit is working???
I am very confused as to how this works. Can anyone explain it to me, or point me to some tutorials of this technique or at least other examples of this in use??
Zc
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I would say the OP-AMP does just act as integrator (two-pole). I guess the hex inverters then act as delay and comparator.
I assume the schematic has been intentionally drawn in this cluttered fashion im order to obscure its working principle in some way.
Regards
Charles
I assume the schematic has been intentionally drawn in this cluttered fashion im order to obscure its working principle in some way.
Regards
Charles
I still don't quite understand where the "clock" for the switching frequency is generated? or why they would need to delay the signal. very very strange circuit. and a very problematic one at that. there seems to be a lot of these amps that are broken!
I'd say its a Self Oscillating topology, a cross between UcD and the IRS2092 delta sigma scheme(the dual capacitor integrator with the resistor to ground)
I have no oscillation! I suspect that IC9701 is bad.
If I apply a 100hz signal to the amp, I have clean signal right up to the DC Blocking caps E9701,2 and If I look at Pin one output, or pin 7 output of IC9701 opamp I have no signal and 6vdc(service manual says 2.13V) then a slight sine wave appears and then a large negative going spike pops, then it starts over again.
Thank you very much for the info. you guys rock! I googled Delta Sigma Class-D and found the http://www.irf.com/technical-info/refdesigns/iraudamp1.pdf
From this I was able to learn how this works and Now I understand what is happening in the amp I am working on a bit better. The pulsing I am seeing is the self start system trying to get the system to oscillate! But no go! No oscillation! So I need to just keep at it a bit more.
The IC9701 opamp is a NJM2137V SSOP-8 high speed opamp that no one seems to have. everyone is out of stock of them. 400mhz bandwidth and the fastest digi has is that package is 10mhz. not sure if that is fast enough for this application or not?
If I can find the 2137V I think I will order some and some hex inverters and cmos gate's and just shotgun them and see if that brings it back to life?
Zc
From this I was able to learn how this works and Now I understand what is happening in the amp I am working on a bit better. The pulsing I am seeing is the self start system trying to get the system to oscillate! But no go! No oscillation! So I need to just keep at it a bit more.
The IC9701 opamp is a NJM2137V SSOP-8 high speed opamp that no one seems to have. everyone is out of stock of them. 400mhz bandwidth and the fastest digi has is that package is 10mhz. not sure if that is fast enough for this application or not?
If I can find the 2137V I think I will order some and some hex inverters and cmos gate's and just shotgun them and see if that brings it back to life?
Zc
Ok I can Dead Bug in a TLO82 and see if will run.
I picked up another one of these amps tonight that runs and WOW I see why they fail! many parts in here run extremely hot! this amp really should have had a fan!! and the -10v VSS transistor will burn you to the touch (i found out the hard way)! I added a heatsink to the top of the device and some thermal grease under it to try and help it survive a bit longer. I understand now why the leads are always discolored! and the IR2010 gate driver IC's and output inductors run so hot you can't touch them.
Not the most efficient amp either. at 170w@4ohms it was drawing about 50 amps which is the limit of my power supply.
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