Is it correct?

[alexsoad]

Hello,
I need to command 2 DC motors with a L298N H driver.
I have a few questions , because my electronics skills are only basic .

1. I will supply the board with 9V from a transf. Then i will use a 1n4148 diode to limit the current. Here is the first question: Will this diode grant me a maximum of 2A? I need 2A at maximum for the L298N for not to burn it.
From the output of the diode i will also put a voltage regulator, to provide me 5V for the rest of the circuit (uC-dspic30f3014 ... and others), but this is another story and i do not need help here.
The motors work well with L298N because they were used by someone else in this configuration. But I do not know how much A and V they need .
So, the main problem is not to burn the L298N. I would prefer the 1n4148 to crack instead, if the motors will ask for more then 2A. So, is the ideea good?

2. The second problem is that the driver schematics found by me on the internet allways came with some diodes connected to the outputs of the driver. I do not understand their need. Are they optional? I just want 4 wires to command two dc motors. All i need is the 4 outputs of the driver.

Please someone explain me this two problems. Thank you very much


ps: here is a link to the schematic of the driver:
https://www.electro-tech-online.com/custompdfs/2010/12/36721.pdf

 

[audioguru]

The 1N4148 diode has a max allowed current at room temperature of 300mA continuously, 1A for only 1 second or 4A for only 1 micro-second. Its voltage loss is over 2V at high current.

A series diode does not limit the current. The current in the diode will get higher and higher until something in the circuit blows up.
A DC motor draws a very high current when stalled or when starting to run. The high current might blow up the diode, or blow up the L298, or blow up both.

Resistors to ground at pin 1 and pin 15 of the L298 can limit the current or drive a shutdown circuit when the current gets too high.

The very important diodes shown on the schematic of the L298 prevent the very high flyback voltage when the motor is turned off from blowing up the L298.

 

[alexsoad]

ok . i understand. the diodes are very important, and also i need to put those sensing resistors to prevent blowing up L298.

what value for the sensing resistors should i choose?

and , on more question :
this is the power supply part of the schematic:
**broken link removed**

from "V9" i am willing to supply the pin 4 (+VS) of the L298. should i supply pin 4 with 9V after the current is passing through the 1n4148 (D1 in the schematic) ? or should i supply pin 4 with 9V without the current passing through the 1n4148 diode?

the current rating of the PWR2.5 is 4A.

ps: thank you very much for the first answer audioguru

 

[audioguru]

1) A 9V transformer has an AC output. Instead you need 9VDC from a rectified and filtered transformer.
2) Get rid of the 1N4148 diode that simply reduces the 9VDC to 7VDC or less.
3) The LM340T-24 is a 24V voltage regulator IC that needs an input of at least 26V or more. Instead you need an LM340T-5 5V regulator.

The L298 has a voltage loss of 5V max when its load current is 2A so your motor will get only 4V. The 4V is reduced by the voltage loss of the current sensing resistors.

 

[Boncuk]

Hi,

just go along with the data sheet.

Pin4 of the L298 has to be supplied with the desired motor drive voltage (max. 46V).

Pin9 is for the logic supply which is meant for 5V typically and 7V max.

Diodes D1 through D4 protect the IC from EMS pulses generated by the inductive load (motor).

You might omit those diodes on your discretion without guarantee of a working IC for a long time.

Omit D1 of your power supply. It's just there to increase cost.

Boncuk

 

[alexsoad]

Thank you both for the responses

I already bought this diodes: SPC TECHNOLOGY|1N4001|DIODE, POWER RECTIFIER,35V,1A | Farnell România

Are they good instead of the shottky diodes?

 

[alexsoad]

i use STMICROELECTRONICS|L78S05CV|V REG +5.0V, 78S05, TO-220-3 | Farnell România as a regulator.
That block from schematic was used by me because they both have the same footprint.

But thank you for the observation

 

[audioguru]

Since you posted a schematic with the wrong part number shown then I won't look at your schematics anymore.

 

[alexsoad]

sorry my mistake. i just couldn't find the part number that i needed in the altium 's library :|
i just checked if the footprints are the same.

but, if you don't want to respond to my problems, very well then. i respect your decision and i thank you again for your responses. you helped me very much!

so, for anyone who can help me, i want to know if these diodes can be used instead of shottky...
SPC TECHNOLOGY|1N4001|DIODE, POWER RECTIFIER,35V,1A | Farnell România

 

[Boncuk]

You need fast revovery diodes with trr of ≤200ns.

A rectifier diode is too slow!

Boncuk