L298 supply voltage - something strange going on

Thread Starter

Mike_Parks

Joined Sep 20, 2017
3
Hi,
I am using a couple of L298 H bridges controlled with an Arduino to control led Christmas lights which are wired with leds at alternate polarity.
One I have connected to a 12vdc regulated supply and that works fine.
The other I have connected to a 24vdc regulated supply but when connected to the L298 the voltage shows up as 35v - what is going on here ???
The power indicator led does not light up and the outputs don't work using the same inputs that work ok on the 12v bridge.
I know the second bridge is ok because if I connect it to the 12v supply it works fine.
I have removed the 12v jumper on the second bridge.
Any help much appreciated.
Mike
 

AlbertHall

Joined Jun 4, 2014
9,662
Are you sure it is reading 35V and not something like .35V?
Is the power indicator LED on the 24V power supply?
What is the output voltage of the 24V supply when not connected to your circuit?
 

Thread Starter

Mike_Parks

Joined Sep 20, 2017
3
Are you sure it is reading 35V and not something like .35V?
Is the power indicator LED on the 24V power supply?
What is the output voltage of the 24V supply when not connected to your circuit?
Hi, Thanks for the quick reply.
I have checked the voltage at the H bridge and it is definitely 35v.
The 24v supply is a DIY job using an L7824CV regulator chip with smoothing capacitor. The output is 24v when not connected to the bridge.
I removed the 12v jumper on the 12v bridge to see what happened - the voltage remained at 12v but the power on led did not light.
Would I cause damage to the 24v bridge if I inserted the 12v jumper ?
Thanks,
Mike
 

Thread Starter

Mike_Parks

Joined Sep 20, 2017
3
If you post a schematic of your circuit we'll have a better chance of diagnosing the problem.
Thanks for the interest in my little problem. I have come up with a solution to get round the problem.
I am running the second bridge at 12v also and taking the outputs to a bank of four SCRs which then switch the 24v to the leds.
 
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