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Connection of Vref (Reference Voltage) causing my drive faulty

Dear all,

I'm designing a circuit and currently facing some problems.

My circuit is basically designed to obtain 4 signals (namely A, B, C and D) from 4 testing points of a CD drive and do calculation to obtain output ((A+D)-(B+C))/(A+B+C+D). All the 4 signals and output must be connected to Vref as a reference point instead of GND. Apart from that, the Vcc and Vee of the op-amps used are also connected to the Vref.

Vref and GND mentioned above are both points on the CD drive also . When we take GND as the reference point, everything works perfectly. However, if Vref is taken as the reference point, some component(s) which are in between Vref and the GND is/are burnt.

My question is that how can we take Vref as the reference point without causing damage to the CD drive while getting a desirable results? Hope to get your response soon. The Vref for different drives are different.

Fyi, the requirement is to take Vref as the reference point. I'm not sure my explanation here is clear. If not, please feel free to highlight to me. I'll try my best to make the picture clearer.

Sorry that my circuit diagram is not yet ready in soft copy. Thanks.

Regards, Albert

Reply to
albertleng
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Well. Based on the testing requirement of my circuit, the A,B, C and D signals are to be taken with reference to the Vref point.

What i mentioned in the previous post only meant that the [(A+D)-(B+C)]/(A+B+C+D) can be applied but it's not the final output we want. What we want is the calculation done for the A,B, C and D signals with reference point of Vref.

Reply to
albertleng

Suppose you have 5 voltages, all measured with respect to GND. Call them Vref and Va, Vb, Vc, Vd.

A= (Vref-Va), B= (Vref-Vb), C= (Vref-Vc) and D= (Vref-Vc).

(A+D) - (B+C) (Va+Vd) - (Vb+Vc) ------------- = ------------------------ (A+B+C+D) (Va+Vb+Vc+Vd) - (4*Vref)

The minus sign in the numerator means that the Vref(s) cancel out, and you only need to change the denominator when dealing with GND-referenced voltages.

--
Tony Williams.
Reply to
Tony Williams

This is happening because you have no understanding of basic DC circuits and your so-called reference point for the measurement is ultimately connected to the CD GND which shorts out your Vref. Take your question to sci.electronics.basics, skip the abstraction bs, and just describe the circuit.

Reply to
Fred Bloggs

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