upc1237 supply question

[Neutrality]

The datasheet states that VCC should be between 25VDC and 60VDC.

However from looking at various implemtentations, lower supply voltages should be usable as well. VCC as low as 12VAC(16VDC after rectificatiion and diode drop) is used in various implementations.

Should I expect it to work at VCC of 15VDC or are the designs with VCC of 12VAC(16VDC) flawed?

[Neutrality]

Anyone?

[Neutrality]

I'm still wondering about this and not really been able to find an answer. Google turns up nothing.

[sidiy]

According to the datasheet you must determine the value of R8 so that the voltage at pin 8 is 3.4V. From Fig.6 you can determine what the current is (about 2.8mA)...the rest is simple.

The circuit should work down to 3.4V but I have not looked if other components need to be recalculated.

[Neutrality]

Originally Posted by sidiy

According to the datasheet you must determine the value of R8 so that the voltage at pin 8 is 3.4V. From Fig.6 you can determine what the current is (about 2.8mA)...the rest is simple.

The circuit should work down to 3.4V but I have not looked if other components need to be recalculated.

You sure about that? The datasheet states VCC from 25V to 60V. Sure, you can calculate the resistance of R8 when using lower than 25V VCC values, but nowhere in the datasheet is mentioned if the chip will work below 25V VCC.

Do you have any practical experience with supplying the Upc1237 with VCC values below 25V?

[sidiy]

Well, the maximum voltage on pin 8 is 8V anyway, they recommend 3.4V. All you need is to pick the right resistor. I see no reason for the graph to become non-linear below 25V as long as the current is 2.8mA

[Neutrality]

Originally Posted by sidiy

Well, the maximum voltage on pin 8 is 8V anyway, they recommend 3.4V. All you need is to pick the right resistor. I see no reason for the graph to become non-linear below 25V as long as the current is 2.8mA

Hmm, at 60V VCC R8 should be around 20K according to the graph. That means that at 15V VCC, R8 should be around 5K.

[Greg Erskine]

I have found the uPC1237 datasheet to be quite confusing and I have read it many times.

Sorry to tag onto your thread but if you have generated a bit of interest someone may be able to help me.

Low pass filter for uPC1237 on pin 2

[sidiy]

I determined the formula to calculate R8 from the original graph: R8=(Vcc-3.4)/2.8 ; R8(kohm). Here is the same graph extrapolated.

To Greg: their formulas apply to a stereo amp, personally I think there's a caveat with this approach in the (unlikely, but still possible) event that one channel has a positive offset and the other a negative one. Pin 2 might see a voltage still within it's thresholds and do...nothing. I would use one per channel and readapt those formulas...
300uF seems large but only has to charge to +0.6V or -0.2V through ~28k. In my amps I have 100u and 120k//120k (and a 100k to gnd)

My experience with this circuit: more than 10 years ago, , I modified my old pair of Rotel 'monoblocks'...higher rail voltage meant new value for 'my R8'. The amps are still working today, never had the chance to trip the protection though.

BTW there is/was a replacement in case you come across the NTE7100.

[Greg Erskine]

Thanks so much sidiy,

Good point about having both channels feeding the filter circuit and canceling each other, I had not thought about that before.

Many speaker protection circuits use a NP or 2 polar caps in series (back to back) so they work on the negative cycle as well.

regards