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Working of PWM regulator LM3524

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Badal

New Member
Hi!
I am building a single phase DC-AC inverter using PWM controller IC LM3524. While testing the PWM chip I find that both the outputs are in phase instead of 180 degree out of phase. Is my understanding about the outputs to be out phase wrong?
 

JimB

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While testing the PWM chip I find that both the outputs are in phase instead of 180 degree out of phase.
How did you test the outputs?
Did you use an oscilloscope?
How did you set the triggering?

JimB
 

alec_t

Well-Known Member
Most Helpful Member
Is my understanding about the outputs to be out phase wrong?
No. They are driven out of phase. If you're seeing them in phase then check for a short-circuit between them.
Welcome to ETO!
 

Badal

New Member
Yes JimB, I have used an oscilloscope. Triggering was set at 50%. Thanks for your quick response.
 

chemelec

Well-Known Member
Is that a Dual Trace Scope so you can view Both out puts at the same time?
 

dr pepper

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I wonder if you have feedback messing up the circuit, though that wouldnt give perfect in phase.
 

Les Jones

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If you look at FIGURE 6. on page 7 of the data sheet you will see that the PWM signal drives both output transistors in phase. (It is the output enable signal that drives them in anti phase.) Also if you look at typical applications on paged 8 to 10 you will see in most cases the output transistors are connected in parallel so they must be in phase.

Edit. I have just realised that from figure 6 only one output transistor can be active at a time so the comment about them being shown in parallel is not relevant.

Les
 
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dr pepper

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I was thinking when I made my last post, I'm sure I've seen a circuit that switches from sequential drive to parallel drive as a means of reducing the power, thats obviously how its done, probably a sense resistor and a tranny switching the enable line on the ic.
 

spec

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Hi Badal,

It is impossible for the two output transistors of the LM3524 to be in phase, as far as I know.

I suspect that your scope triggering is set to alternate trigger.

If you can't set your scope to trigger off just one channel, you should have an external trigger input.

Connect one of the output transistor emitters to the external trigger input of your scope and select external trigger.

Alternatively you can set your scope to chop if the signal frequency is low enough.

spec
 

JimB

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Most Helpful Member
I suspect that your scope triggering is set to alternate trigger.
That was what I was thinking when I asked earlier what Badal was using.

JimB
 

ronsimpson

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I think it is the time zone difference.
There are times when we are not in the same day.
 

spec

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Bed time here. The clocks went back an hour on Sunday night/morning so it is 12:50am officially, but 1:50am bodily.

spec
 

Badal

New Member
Hi spec,
Your suggestion is wonderful. After getting up in the morning I saw your suggestion and tried immediately. I found the trigger set as alternate. When I change it to single, output is perfect. Extremely thankful, spec. Thanks to all others also for their suggestions. Wonderful community!
 
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