Max DC voltage Motor Driver L298?

Hi there, I am driving two different DC motors with the [url][/url] - I dont need speed variations, but only direction control.

The default PWM frequency is set to 25Khz - and I am not sure why this is chosen. See [url][/url]

I experience about 40% lower speed from the motors compared to direct connected to the power source.

The power source is 12V and I need 12V to the motor, how do I achieve that?


@ njbuch - Hold the pwm pin high.

@ Mr. John Smith - does that mean modifying the driver and making pwmoutpit a digital output instead?

From what I understand, the driver chip itself will drop the voltage anywhere between 2-5 Volts (depending on current) due to inefficiencies. I think you can find this on the datasheet under “Total Drop” in the Electrical Characteristics section. There are other drivers that have less voltage drop like the TB6612, but I believe all of them will have some drop.

Edit: I guess that didn’t really answer the “how”. Besides the obvious of just using a higher input voltage, or using a more efficient driver chip, you could also look into an H-Bridge relay setup.

@ njbuch - Yea, try making it a OutputPort instead of PWM. As @ adaml said, there will be some inefficiencies from the drivers’ voltage drop.

Don’t connect a relay directly to any µC pins!

With PWM duty set to 1.0 the output is a near HIGH as you can get so should do the same.

Ok conclusion is clear: The voltage drop on l298 is about 4V and too much for my setup. New solution would be a polarity reversing relay module.

Any specific suggestions?

@ njbuch - power mosfets

Power MOSFET design (similar to the L298 output circuit) would give you silent control but a single DPDT relay and a single MOSFET for power on/off would allow you to control on/off and direction.

How often do you change direction? Relays these days are reliable but a MOSFET design would be a better solution and you could include current limiting if there was a short on the output.

@ Dave McLaughlin - I dont change direction very often, and physical wear would not be a problem at all.

I have found this MOSFET: [url][/url]

And this DPDT module: [url][/url]

Will try to wire that up, and see how it goes. Thanks so much for your pointers! :slight_smile:

@ njbuch - dont forget the heat sink

Just curious… How are you going to drive the P-Channel Fet? If via directly through a port pin that will not work (unless your output pin can be configured as Open Drain). If you want to minimize the part count go with a N-Channel, then you can use your port pin.

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@ VersaModule - Best tip of the day! Thanks

@ VersaModule - N Channel MOSFETs need a higher voltage than the supply voltage to switch on (charge pumps come in handy here). ST Micro makes one that apparently doesn’t need that.

This is why the L6470 requires those schotty diodes; to be able to tun on the mosfets.