LED control using L298 H bridge

I am trying to control led strings which only have two wires with each led at alternate polarity. A friend told me about the L298 H bridge and I sort of have it working.
I have led strings which run at 12v and others that need 24v. I have two H bridges. If I run either of them at 12v the leds behave exactly as they should with alternate leds lighting and fading. However if I run either bridge at 24v (removing the 12v jumper) then I get no output at all with the same input from the Arduino.
Anyone used the L298 to control led strings ?
Thanks,
Mike

When you say "no output", do you mean that your 24V led strips do not light, or that you have measured the bridge's output with a multimeter (or ideally a scope).

Thanks for the prompt reply.

I put the problem to my friend who put me on to the L298 bridge and he gave me the cause of the bridge not working at 24v.

I did not realise that if the 12v jumper has been removed you must connect pin 6 to a 5v supply as input to the chip.

Looked through lots of web pages on the L298 and none of them mentioned this.

All working as it should now.

Mike_Parks:
Looked through lots of web pages on the L298 and none of them mentioned this.

That's because the L298 chip doesn't have any jumpers, it's just a chip.

Anything you have that needs a jumper is an L298 module, an L298 chip on a board, an implementation of the chip in a way designed by the module maker. With those things you have to track down info on the specific module by make and model, since the pins and jumpers and power connections and whatnot will differ from module to module.