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L298 Problems

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jstepheta

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Hi everyone, I am trying to build a robot on my own for the first time and am in need of a little help:

I have one DC motor (rated 12V I think) which I want to have bidirectional control of. To accomplish this, I selected the L298 dual H bridge as I had them handy.

CONNECTIONS:

I have made the following connections:
1 (Current Sense A)--not connected this should be ok right? this pin is only used for the logic circuit to determine how much current is flowing to your motor i think. . .
2 (Output 1)--red terminal of motor
3 (Output 2)--black terminal of motor
4 (supply voltage)--+12V
5 (Input 1)--either +5 or GND
6 (Enable A)--+5
7 (Input 2)--either +5 or GND
8 (GND)--GND
9 (Logic supply voltage)--+5
10 --not connected
11 --not connected
12 --not connected
13 --not connected
14 --not connected
15 --not connected

TESTING I HAVE DONE:
*Keep in mind that my enable is permanently tied to logic high.

Whenever I have the motor's terminals connected to the outputs, both outputs are the same voltage regardless of what the inputs are.

I suspected that somehow the motor was shorting together the two outputs, so I removed the motor and began changing the inputs again.

With no load, the outputs DO behave as expected. However, the chip doesn't behave like this when the motor is connected.

QUESTIONS:

How exactly does this chip work? As I understood it, the current should flow out of one of the outputs, through the motor and then into the other output pin. Then to go the other direction, reverse the inputs--and the current should flow out of the other output through the motor in the opposite direction and then into the first output pin.

Does anyone have any ideas?
 
jstepheta said:
CONNECTIONS:

I have made the following connections:
1 (Current Sense A)--not connected this should be ok right? this pin is only used for the logic circuit to determine how much current is flowing to your motor i think. . .
2 (Output 1)--red terminal of motor
3 (Output 2)--black terminal of motor
4 (supply voltage)--+12V
5 (Input 1)--either +5 or GND
6 (Enable A)--+5
7 (Input 2)--either +5 or GND
8 (GND)--GND
9 (Logic supply voltage)--+5
10 --not connected
11 --not connected
12 --not connected
13 --not connected
14 --not connected
15 --not connected

I solved my own problem--the above part is NOT ok. I had the concept of an H bridge correct in that the load current flows out of one output, through the motor and into the other output. However, if you look at the datasheet for the dual H bridge:

https://www.st.com/stonline/products/literature/ds/1773.pdf

You will see that the bottom of the H is simply tied together and has NOT been connected to ground. How will the current flow if there is no return?
 
Thanks Mike, I actually was just looking at the block diagram and figured that out a few moments ago. . . I had just assumed that the bottom of the bridge was connected to GND internally. . .

In any case, thank you for replying!
 
l298 output problem

hiii guys..........

i am a new member...
i am trying to create a mobile robot project.for controlling the dc motors i am using the l298.it will driven from the parallel port of my pc.
this are the corresponding voltages that are going into the l298 pins:---

1. 2.8mv
2.
3.
4. 12.58v
5. -0.7v
6. 5.13v
7. 2.4v
8. 3.1mv
9. 5.13v
10. -0.7v
11. 5.13v
12. 2.5v
13.
14.
15. 3.0v

as the 2,3,13,14 pins are the output pins.......i should be getting 12v as corresponding output for driving the motor.............IS IT OKK??? ......................................but i am getting nothing.

(as the 5,7,10,12 are the input pins i have given an instruction 80 where 2.4 v is the high & -0.7 is the low)

please someone help me getting the outputs as 12v for driving the motor................its really urgent
 
i want run a motor with l298n.

i have a amaron battery of 12v,9a.............

i think i have connected every pin connection right.............but there is still no output.

please can anyone help me????????i need help urgently........

atleast guide me about how much voltage/current is going to the 15 pins of l298?
 
If pin 1 or pin 15 are not connected to ground (maybe with a low value current-sense resistor) then the L298 IC will not work.
 
i have connected pin 1 & 15 to the ground..........


those are giving 2.8mv and 3.0mv respectively.......for driving 12 v battery how much output should i get?????

what will be the needed voltages/current for the 15 pins of l298????help me please
 
Last edited:
You said you had 3.0V at pin 15. You did not say pin 15 was connected to ground.
The outputs of the L298 have voltage losses as shown in the datasheet so with a 12V supply the motor gets only 6V to 9V.
 
i have already connected pin 1 and 15 to the ground................but the outputs are showing floating voltages ranging in mV.

what can be the problem??i am seriously confused............please help me

sorry for the mistake.............it was not 3.0v..........it was 3.0mV
 
Last edited:
The max allowed negative input voltage is -0.3V. Yours is more than double at -0.7V. Then maybe the inputs are burned out.
Why are the inputs a negative voltage??

Also your input high voltages at only 2.4V and 2.5V are very close to the minimum viltage. Try 3V to 5V.
 
i am giving the input from computer's parallel port.......

so the inputs coming from parallel port are like this.............high voltage is 2.5v................................low voltage is -0.7

how can i make the inputs to 5v(high) or -0.3v(low)???pls give me suggestions
 
as you have suggeested i have connected the input pins.............high pin to 4.4v and low pin to 0.4 mv

but still it is giving floating output.............what can i do now??
 
as you have suggeested i have connected the input pins.............high pin to 4.4v and low pin to 0.4 mv

but still it is giving floating output.............what can i do now??
Replace the L298 IC that was probably destroyed by the negative input voltage that was too high.
I assume that you have added four "'fast recovery diodes" as shown in the datasheet.
 
okk.....i can change the l298ic

but how can i get 5.0 (high) and 0(low) as inputs for l298 from the parallel port???

the parallel port outputs are 2.4v and -0.7v.................
 
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