L293D - When drive 5mA resistive load, voltage dropping to 0.5V

Arun Soman

Intellectual 400 points

Other Parts Discussed in Thread: L293D

When load the current of 5mA resistive load the voltage at the output is dropping to 0.5V.

Please help me

over 11 years ago

0 Avi Chami1 over 11 years ago

Mastermind 7395 points

It is rather strange. Could you provide schematics of your circuit? Did you check Vcc integrity?

Best regards

Avi

0 Arun Soman over 11 years ago in reply to Avi Chami1

Intellectual 400 points

Hi avi,

Thank you.

Attached the schematic

L293D Circuit.pdf

0 Avi Chami1 over 11 years ago in reply to Arun Soman

Mastermind 7395 points

Hi,

VCC1 is going to the devices through a 10K resistor. I don't know if it is a good idea, try replacing it by a 0 Ohm resistor.

0 Shankarbabu M over 11 years ago in reply to Avi Chami1

Prodigy 20 points

Dear Mr. Avi,

We have already tried without resistor for the VCC1 but still there is a drop of 0.5 to 0.75V on the output.

Kindly revert back us on this issue on high priority.

Thank you in advance.

Best Regards

Shankar

0 Avi Chami1 over 11 years ago in reply to Shankarbabu M

Mastermind 7395 points

Hi,

Only to be on the safe side, it is not without a resistor but with a 0 Ohm resistor instead, I hope I didn't confuse you. . I also didn't understand what is the value of the series resistors at the output, but I guess you are using low values. Regretfully, I didn't see anything wrong with your circuit.

Regarding priority, I cannot change that, I am a community member, I guess some TI moderator will take care of that.

0 Shankarbabu M over 11 years ago in reply to Avi Chami1

Prodigy 20 points

Hi,

The series resistor on the output is 4 Ohm resettable fuse. We have even tested without the resettable fuse but still the behavior is ame.

Output drop is 0.5 to 0.7V.

We have planned SOP in this month but we have struck with this issue.

Kindly help us in solving this problem.

Thank you

0 Avi Chami1 over 11 years ago in reply to Shankarbabu M

Mastermind 7395 points

Now I am a bit confused.

At the beginning you wrote that the output drops to 0.5V.

Now, if I understand you well, what you are saying is that the output is 4.25V-4.5V?

Well, if that is the case there would be no problem, look at the datasheet, for Vcc2 = 24V the typical output drop is 1.4V. If it is an issue for you, could you use a higher voltage for Vcc2, namely 6V?

As a side note, the driver uses emiter follower, namely transistors on active zone (not saturation), so you would expect to have voltage drops like those you are measuring.

0 Ron Michallick over 11 years ago in reply to Shankarbabu M

TI__Guru*** 139846 points

Shankarbabu,

Please se the typical output schematic on page 4 of the data sheet.
Notice that the VOH drive is a emitter follower. This topology has a very low output impedance but there a voltage drop as a side effect.

0 Ron Michallick over 11 years ago in reply to Ron Michallick

TI__Guru*** 139846 points

Shankarbabu,

The L293D has diodes on all the output pins so the external diodes will not be required.

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L293D - When drive 5mA resistive load, voltage dropping to 0.5V