L298N H-bridge test circuit

Jan 09, 2004 2 Replies

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Julia Goolia 22 years ago

Hi,

I am trying to assemble the test circuit for the L298N dual H-bridge from ST. The test circuit documentation is found on page 5 from the following:

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Basically, nothing happens. I'm working on input/output #4. However, I have made a few changes mainly because I don't have all the right parts and am wondering what the problem could be. I put diodes going from 1,15 to ground instead of wire or sense resistors (out of wire, and have no idea what a sense resistor is and/or how to use one). I'm turning on INPUT 4, ENABLE B and VSS (PIN9) via a BASIC stamp 2. Power source is a 12V, 200mA transformer which plugs into the wall (which always seems to be more than 200mA, but i don't know why). I check the voltage and current between the + of the power source and OUTPUT 4 and... NOTHING.

Any insight? Are my modifications messing things up? Are the recommended capacitors CRUCIAL to getting the thing to work?

Thank you so much!! Juliabean

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dan michaels 22 years ago

A schematic of your ckt would be nice. It's not clear from your description if you have it ... but you need to supply logic voltage

+5v to pin 9 to power the L298 chip, and also separate power to pin 4 to power the motor. This should be a different source than +5v logic.

And of course,

- all of the gnds need to be common.

- if you're not gonna use sense R's, then you can tie pins 1,15 straight to gnd.

- make sure your diodes aren't in upsidedown.

- also, use a fuse in the motor power line.

- also, not many motors will run on only 200 mA, so you should know if this source supplies adequate current.

- also, from the way you describe your control, the motor needs to be connected from pin 14 to **gnd**.

have fun,

- dan michaels =========================

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Julia Goolia 22 years ago

Thanks Dan! Your suggestions really helped and now I have something working. However, I cannot still get the motor to step. Basically, I'll put HIGH on INPUT 4 and LOW on INPUT 3 (and ENABLE B of course) and I can measure a voltage between OUTPUT 3 and OUTPUT 4. However, no current seems to be present. I really don't understand this, a voltage without current (I have an analog ampmeter who's lowest setting is 5mA and the needle does not move)... I feel like I'm so close!

Any insight would be greatly appreciated! Juliabean

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