Connection of Vref (Reference Voltage) causing my drive faul

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

 

[Rich Grise]

On Wed, 19 Jan 2005 08:47:14 -0800, albertleng wrote:

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.

So, why do you want to do something that makes it _not_ work perfectly?

I'd say, if it works perfectly, you're done. Signed, sealed, and
delivered.

Or are you really merely wanting to milk your customer?

Thanks,
Rich

 

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.

 

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.

 

[Tony Williams]

In article <1106153234.096471.54090@f14g2000cwb.googlegroups.com>,
<albertleng@gmail.com> wrote:

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.

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.

 

[Fred Bloggs]

However, if Vref is taken as the reference point, some component(s)
which are in between Vref and the GND is/are burnt.

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.