L298 Back EMF - Electronic Circuits Projects Diagrams Free

pittuck · 19th November 2004, 06:30 PM

Hi i have a problem and wanted to check somming.

I am using a L298 to drive 2 DC motors, but i missread/understood the datasheet and did not realise the diodes were needed.

Now my question, would it be possible to 'blow' the L298 without the diodes in?

Half the bridge is not working (well it is able to run a LED but not a motor) and the second half runs the motor very slowly. When i apply the 7.2V to the motor terminsals they work, so its not a motor problem.

The L298 has worked b4 in this setup so its not wiring... Oh and it blew my 18F452, the CCP2 module is broken and logic high is measured as 2V (dont worry i got a new one comming).

any ideas? I am buying a new chip but i want to make sure i have solved the problem.

Regards,

- Martyn

jrz126 · 19th November 2004, 06:39 PM

sounds like it is the chip, if you havent changed anything else and it just quit working, and you double checked the motor.

On a side note, I used one of these IC's once and I shorted something out, the chip exploded and the IC and my breadboard caught on fire :shock:

pittuck · 19th November 2004, 06:40 PM

ok well i will put the diodes in and use a cap on the driver ic next time!!!

me = dumb sometimes, but i did not get electricuted, so it was a pretty good day on thw whole.

jrz126 · 19th November 2004, 06:46 PM

When I put in my electronics orders, I'll usually buy enough for 2 circuits in case of situations like this. Because I know I'll screw up and be up a tree without a paddle.

fabbie · 20th November 2004, 03:34 AM

just wan to confirm something. Are L298 drivers capable of accepting PWM signals?
Never seem to mention anything in the datasheet

pittuck · 20th November 2004, 07:10 AM

http://www.iitk.ac.in/eclub/Circuit/l298.htm

http://www.dprg.org/projects/1998-04a/
You use in1 & in2 for direction and enablea for pwm for motor 1
You use in3 & in4 for direction and enableb for pwm for motor 2

Looks like it

I had these links on my scrath pad as i had the same thought yesterday. I noticed that DPRG uses a 1000mF cap on the Vs (motor supply) and GND lines, i will follow. I will also get a 0.1Ohm resistor for the current sense (will have to be wirewound as i cannot find normal 0.1Ohm resistors that are not SMD)

**Nigel Goodwin** · 20th November 2004, 08:03 AM

Quote:

Originally Posted by pittuck

I had these links on my scrath pad as i had the same thought yesterday. I noticed that DPRG uses a 1000mF cap on the Vs (motor supply) and GND lines, i will follow. I will also get a 0.1Ohm resistor for the current sense (will have to be wirewound as i cannot find normal 0.1Ohm resistors that are not SMD)

You don't have your location filled in!, but in the UK 0.1 ohm metal film resistors are available from RS Components - I keep them in stock at work!.

pittuck · 20th November 2004, 09:07 AM

well i know RS and farnell do em. But they dont accept solo cards. Doh! I will stick with rapid electronics as they accept solo cards.

fabbie · 20th November 2004, 10:03 AM

I thought of building my own H bridge cct from scratch for the experience but looks like the best way to solve this is to use the IC drivers. sigh. For this L298 driver, the maximum current rating is at 2 Amp per channel. Motor stalling can be rather dangerous for my 12V motor. Any suggestion for protective ccts? or should i just place a buffer interface to act as my fuse.
Also, dont really understand the current sensing pins. When it said limits the current, does this mean that it wont go above the Vs/R or Vs/R constant current? THX ALOT.

**Nigel Goodwin** · 20th November 2004, 10:31 AM

Quote:

Originally Posted by fabbie

I thought of building my own H bridge cct from scratch for the experience but looks like the best way to solve this is to use the IC drivers. sigh. For this L298 driver, the maximum current rating is at 2 Amp per channel. Motor stalling can be rather dangerous for my 12V motor. Any suggestion for protective ccts? or should i just place a buffer interface to act as my fuse.
Also, dont really understand the current sensing pins. When it said limits the current, does this mean that it wont go above the Vs/R or Vs/R constant current? THX ALOT.

Presumably the datasheet will explain how it works?, but (as far as I know) the current sensing resistor monitors the current, the chip will current limit depending on the voltage dropped across it.

fabbie · 20th November 2004, 01:06 PM

According to the datasheet, the maximum quiescent supply current,Is to the motor is in mA. Do we need a resistor at the Vs pin then?
I dont find it logical on how does a few mA able to output a maximum current of 2A.

pittuck · 20th November 2004, 01:19 PM

Ok well quiescent current is when its not driving anything. So if u put enable low it will only use 4mA, assuming a resistor of 0.1Ohm is used:

P = iir = 16r = 1.6mW

But at the peak current of 2A

P = iir = 4r = 0.4W

So thats where the numbers come from...

fabbie · 20th November 2004, 02:03 PM

Um...the resistor of 0.1ohm where are u referring to? at the Vs? i dont think it is required or at the current sensing?
By the way, pittuck, pls dont mind teaching me how to use the current sensing. How do u know the value of resistance to place. and what current isit tryin to limit?

pittuck · 20th November 2004, 02:27 PM

its for the current sense pin.

this pin enables u to read the current which is being supplied to the motors. which can be handy...

fabbie · 20th November 2004, 02:53 PM

According to the website you provided,
http://www.iitk.ac.in/eclub/Circuit/l298.htm
It said here that the current sensing here will control the current according to VS/R and will be provided to the load.

If the Vs is 12V. wouldnt the current be EXTREMELY big? 120Amp.
Mind teaching me how u did u attain the value of 0.1ohm?

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19th November 2004, 06:30 PM	(permalink)
pittuck	L298 Back EMF Hi i have a problem and wanted to check somming. I am using a L298 to drive 2 DC motors, but i missread/understood the datasheet and did not realise the diodes were needed. Now my question, would it be possible to 'blow' the L298 without the diodes in? Half the bridge is not working (well it is able to run a LED but not a motor) and the second half runs the motor very slowly. When i apply the 7.2V to the motor terminsals they work, so its not a motor problem. The L298 has worked b4 in this setup so its not wiring... Oh and it blew my 18F452, the CCP2 module is broken and logic high is measured as 2V (dont worry i got a new one comming). any ideas? I am buying a new chip but i want to make sure i have solved the problem. Regards, - Martyn

19th November 2004, 06:39 PM	(permalink)
jrz126	sounds like it is the chip, if you havent changed anything else and it just quit working, and you double checked the motor. On a side note, I used one of these IC's once and I shorted something out, the chip exploded and the IC and my breadboard caught on fire :shock: __________________ Jeff Zimmerman To the optimist, the glass is half full. To the pessimist, the glass is half empty. To the engineer, the glass is twice as big as it needs to be.

19th November 2004, 06:40 PM	(permalink)
pittuck	ok well i will put the diodes in and use a cap on the driver ic next time!!! me = dumb sometimes, but i did not get electricuted, so it was a pretty good day on thw whole.

19th November 2004, 06:46 PM	(permalink)
jrz126	When I put in my electronics orders, I'll usually buy enough for 2 circuits in case of situations like this. Because I know I'll screw up and be up a tree without a paddle. __________________ Jeff Zimmerman To the optimist, the glass is half full. To the pessimist, the glass is half empty. To the engineer, the glass is twice as big as it needs to be.

20th November 2004, 03:34 AM	(permalink)
fabbie	just wan to confirm something. Are L298 drivers capable of accepting PWM signals? Never seem to mention anything in the datasheet

20th November 2004, 07:10 AM	(permalink)
pittuck	http://www.iitk.ac.in/eclub/Circuit/l298.htm http://www.dprg.org/projects/1998-04a/ You use in1 & in2 for direction and enablea for pwm for motor 1 You use in3 & in4 for direction and enableb for pwm for motor 2 Looks like it I had these links on my scrath pad as i had the same thought yesterday. I noticed that DPRG uses a 1000mF cap on the Vs (motor supply) and GND lines, i will follow. I will also get a 0.1Ohm resistor for the current sense (will have to be wirewound as i cannot find normal 0.1Ohm resistors that are not SMD)

20th November 2004, 09:07 AM	(permalink)
pittuck	well i know RS and farnell do em. But they dont accept solo cards. Doh! I will stick with rapid electronics as they accept solo cards.

20th November 2004, 10:03 AM	(permalink)
fabbie	I thought of building my own H bridge cct from scratch for the experience but looks like the best way to solve this is to use the IC drivers. sigh. For this L298 driver, the maximum current rating is at 2 Amp per channel. Motor stalling can be rather dangerous for my 12V motor. Any suggestion for protective ccts? or should i just place a buffer interface to act as my fuse. Also, dont really understand the current sensing pins. When it said limits the current, does this mean that it wont go above the Vs/R or Vs/R constant current? THX ALOT.

20th November 2004, 01:19 PM	(permalink)
pittuck	Ok well quiescent current is when its not driving anything. So if u put enable low it will only use 4mA, assuming a resistor of 0.1Ohm is used: P = iir = 16r = 1.6mW But at the peak current of 2A P = iir = 4r = 0.4W So thats where the numbers come from...

20th November 2004, 02:03 PM	(permalink)
fabbie	Um...the resistor of 0.1ohm where are u referring to? at the Vs? i dont think it is required or at the current sensing? By the way, pittuck, pls dont mind teaching me how to use the current sensing. How do u know the value of resistance to place. and what current isit tryin to limit?

20th November 2004, 02:27 PM	(permalink)
pittuck	its for the current sense pin. this pin enables u to read the current which is being supplied to the motors. which can be handy...

20th November 2004, 02:53 PM	(permalink)
fabbie	According to the website you provided, http://www.iitk.ac.in/eclub/Circuit/l298.htm It said here that the current sensing here will control the current according to VS/R and will be provided to the load. If the Vs is 12V. wouldnt the current be EXTREMELY big? 120Amp. Mind teaching me how u did u attain the value of 0.1ohm?