Hello, I apologize if this question is trivial

My robot uses 2 DC motors as wheels and is controlled by a PIC18. I am using the L298 Dual Full-Bridge driver. My voltage supply is 10x1.5 V alkaline batteries in series and I then produce the 12V input to the L298 using a 7812 regulator. The L298 is capable of providing 1A (more if properly sinked) per bridge, however the maximum current the 7812 can provide is 1 A.

My concern therefore is how to limit the current drawn by the motors. Do I do this with PWM? I researched the datasheet of the L298 and there is a current sensing resistor, however this only allows me to measure the current supplied to the load, not to limit it. 500 mA per motor should be enough, but how do I limit my load currents to this value?

Thank you for your help

 

To controlle the current use transistors simple.You can use current mirrors circuits ?

Good Luck

 

Well, if you can measure it then you can control it and keep it at a desired level by controlling the PWM duty cycle.

 

Thank you for your help. It turns out the motors will actually draw 600 mA each when loaded, which is fine for the L298 but a problem for my 7812, as it can supply 1A max. Can this be fixed by PWM? E.g. if I have a 50% duty cycle, to the 7812 will it seem as if each motor draws only 300 mA?

Alternatively, do you know any 12 V regulators rated slightly above 1A? (2A is likely enough; I was looking at other threads and someone suggested a Toshiba 7.5 A, but I prefer something economical if possible and 7.5 A is more than I will need).

Thank you

 

Thank you for your help. It turns out the motors will actually draw 600 mA each when loaded, which is fine for the L298 but a problem for my 7812, as it can supply 1A max. Can this be fixed by PWM? E.g. if I have a 50% duty cycle, to the 7812 will it seem as if each motor draws only 300 mA?

No, it won't be fixed by PWM because it is the average values that matters. However, you can control the current by using PWM as not to exceed 500mA. The drawback of this is a reduction in the output torque.

Alternatively, do you know any 12 V regulators rated slightly above 1A? (2A is likely enough; I was looking at other threads and someone suggested a Toshiba 7.5 A, but I prefer something economical if possible and 7.5 A is more than I will need).

There are regulators rated for more than 1A.
Have a look here: www.national.com

If you want, you can use a 1A regulator per motor.

Have a look at switching regulators too.