# Current dumping Maxwell bridge

#### Erickuo

I don't know why, why the Maxwell bridge can eliminate the problem of crossover distortion.

Also, I measured that the current of Z3 is much higher than that of Z4, but normally, Z4 should be greater than Z3.

#### latala

i dont understand what you are asking the unit is an ic amp up to about0.6 amps then switches on the output transistors nothing new here

#### Erickuo

I don't know why,the AM4 is bigger than AM2.
I think that if VF1>0.7V, transistors is on,than current will dumping on the L1(AM2),but the Tina spice is not like this.

#### ejp

Because Z1 is absurdly low? And how large was Vin?

#### Erickuo

I try to let Z3=50 Ohm ,butis not consequent.
this is Vin=1Vpp,1kHz.

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#### ejp

So what is the design equation for the bridge?

#### Erickuo

I think it's to get rid of crossover distortion

#### Erickuo

That is maxwell bridge.
If C1*L1=Z1*Z3,that will balance.
but I don't know why balance can get rid of crossover distortion.

#### ejp

That doesn't make sense. The units of C*L are not the same as the units of Z1*Z3 which are R*R. It should be L/C = R*R, or L=RRC. Where did you get this from? It seems to me you should be considering Z1, Z2, Z3, and Z4. C1 is just part of a shunt Zobel network, and L1 is just a series inductance to the load, both being present for stability reasons. Neither is part of any bridge.

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#### Erickuo

C=1/wC , L=wL ,yes,the equation is L=RRC.
Add C1 because it needs to reduce high frequency oscillation,add L1 because C1 will cause circuit not balance,so need to add C1 and L1.
But I don't know why to add the Z3.

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#### jan.didden

Paid Member
i dont understand what you are asking the unit is an ic amp up to about0.6 amps then switches on the output transistors nothing new here
There's a lot new here, in the sense that the bridge components are calculated such that the output stage distortion is eliminated.

Jan

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• Current dumping - does it really work DCD.pdf
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#### Erickuo

I know bridges can remove distortion,but i don't know the principle.

#### ejp

Then look up Current Dumping Audio Amplifier, P.J. Walker & M.P. Albison, Wireless World, December 1975. But the correct equation here is (Z4*Z2)/(Z1*Z3) = 1, or L=RRC. Not your version: you have both the wrong capacitor and the wrong inductor in yours.

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#### Erickuo

I'm sorry for misplacing the circuit diagram.
But I used the correct circuit diagram or not the result.

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#### ejp

In the real 405 circuit, Z3=47R, Z1=500R, and the op-amp is inverting.

You still haven't answered where you are getting all this from.

#### Erickuo

I read the paper on current dumping.

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#### ejp

Still haven't answered that question. Where did you get your original circuit from? and that equation?

#### Erickuo

Still haven't answered that question. Where did you get your original circuit from? and that equation?

The equation is from his paper.
And the circuit diagram is modified from the original circuit diagram.

#### ejp

The equation is from his paper.
No it isn't. You gave C1*L1=Z1*Z. Where did you get that from?
And the circuit diagram is modified from the original circuit diagram.
Modified why?