Category: PWM

This article is a follow up to my last post regarding class D amp using LM319 but some of you may feel less enthusiastic about LM319 due to its one channel approach using it’s one comparator, while the other remaining one was used as square wave/triangular generator. Well, this article will fill in the blank of the missing channels that can be implemented using single LM339 up to three or four channels at your own will.

I mentioned three channels if one comparator is used as oscillator but can be made four channels in a single chip if the oscillator will be provided externally by using LM555 timer.

Fig. 1 shows single chip 3 channel amplifier schematic circuit of LM339 using MOSFET driver TC4420 to drive speaker. The blue rectangular box encircling 6 TC4420 can be replaced by high side/low side FET drivers like IR2110 shown in Fig. 2

Fig. 1

Three channel LM339 plus 6 pieces TC4420 in full bridge topology.

Fig. 2 shows single chip 3 channel amplifier schematic circuit using LM339 with mosfet driver IR2110 and N channel power mosfets to drive speaker. CD4049 inverting CMOS were used to split the single ended output of LM339 into complementary form as required by IR2110 to drive the half bridge topology in the power output stage. R19, R20, R21, R22, R23 and R24 together with corresponding In4148 fast turn off diodes are added to avoid shoot through during switching transitions of power mosfets. This deadtime implementation is much desirable compared to doing it at the gate of the power mosfet for sharper knee response.

This circuit configuration is also called general purpose switching amplifier. Numerous application in industrial motor control such as application that pops up on the creative minds include a 3 phase inverter or VFD (variable frequency drive) that can be used to drive industrial induction motors if the inputs will be driven by a 3 phase variable frequency signal instead of audio source. Volume control must be implemented at the 3 inputs to increase or decrease the power and RPM of the motor. The 3 phase variable source can be made sinewave or square wave.

Although I have not yet made this circuit project in a working prototype due to the nature of my job as seaman in a passenger cruise ship 19 years ago, (yes, I made this circuit during my idle time onboard) surprisingly I almost forgot this project to implement until I came across it on my laptop. The circuit shown on the schematic below may need further scrutiny and must be evaluated via a breadboard before any attempt to be made into a final PCB prototype. These may include the deadtime adjustment of the diodes and resistors at the inputs of IR2110 which maybe too small or too large in resistance based on particular application just mentioned. These can increase deadtime causing distortion in audio amplifier applications but for VFD 3 phase inverter application, the greater the deadtime the better will be.

Fig. 3 shows the internal schematic circuit of LM339

The

Finally! I`m back from long hiatus!

As the subject title implies, yes. LM319 is not a popular choice as integrator/differentiator combo due to it`s output pull-up resistor which is not good to directly drive capacitive load. Although it was being claimed by chip makers as fast comparator, they mean it’s fast enough as digital pulse generator for driving TTL/DTL logic gates. This means it can generate decent PWM pulses intended for class d amp purposes but at different, or should I called it harsh method as shown in schematic diagram of Fig. 1 below.

Continue reading “Class D amp using LM319 comparator”

Perhaps some of you have already seen my blog in DIY audio forum showing practical use of 555 timer as class d amp source. Indeed, the circuit is quite an interesting subject to exploit specially to some curious folks looking for cheap but good sound class d audio amp project. The same circuit is shown in figure 1. Continue reading “Active crossover network using 555 timer as class d amp”

Class D amp using TL494 DC to DC converter chip

It’s almost 5 years now since I published a topic regarding how to use TL494 as class d amp in a popular DIY audio forum. I think it’s quite good to include this article here also. By the way, before I publish that topic I thoroughly googled the said subject to see if there are some geek guys who have already done such a playful exploit of this chip but I simply got zero hit. This could mean that I am an early bird on this regard? Or maybe I am the only one who have a bizarre taste in choosing the right chip for such an application. Continue reading “Class D amp using TL494 DC to DC converter chip”

It’s more than one month now since I updated my last post and I regret that I couldn’t post anything within that length of time. This is due to the nature of my job. We left Tilbury last month and now we transferred here in Bremerhaven shipyard and our ship is still being dry docked for repair. Unfortunately we still don’t have any internet connection and our satellite is still under repair too. I just rely on outside wifi access so, this is my new follow up post as continuation for the unfinished topic for that post below. Hopefully, I will make a new post again if our internet connection will be restored soon.
My last article was still 555 timer so this is another neat idea how to get more useful circuit out of your 555 timer. I think it is not good to move on to another topic using another chip because every time I made a circuit out of this 555 timer, another idea pops-up in my mind to share. Continue reading “2 channel 555 timer class d amp source”

I’m almost in the process of preparing another article to post but my attention was diverted again to the previous 555 timer circuits I made. I simply couldn’t afford to leave the circuit that way. I am concerned that by changing the 2N3904 with the same type of transistor but of different hfe, the duty cycle changes accordingly and this is annoying. Continue reading “Bias scheme for 555 timer as class d amp”

Ok, I’ve been so busy for the past few weeks and I couldn’t make a follow-up from the last article of the 555 timer circuit. So here is another improvised model circuit that will eliminate the unwanted DC offset voltage from the output that affect the previous one discussed. By the way, all previous circuits that I discussed were intended as “low power” class d amp source that is adequate to drive head phones via a coupling capacitor. Continue reading “Full bridge class d amp using 555 timer”