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- Thread starter rhymeswthorange
- Start date

If not, the opamp will increase its output voltage in an attempt to get to 15.6V, and the collector of Q2 rises until its Q-B junction starts to reverse conduct, and the voltage across R4 goes up until there is no more voltage (or even reverse voltage) across the LED, it goes off.

Jan Didden

Also, when you use the equation R8 = R9*(Vout-Vref) / Vref , and substitute 890 for R8, 1130 for R9, and 6.0 for Vref; you get 12.33V for Vout.

Thanks for the help, can you guys think of anythig else that could be wrong? Seems like the voltage isn't being regulated as the output is about the same as the input voltge.

rhymeswthorange said:

Also, when you use the equation R8 = R9*(Vout-Vref) / Vref , and substitute 890 for R8, 1130 for R9, and 6.0 for Vref; you get 12.33V for Vout.

The LM329DZ as VRef will yield 6.9V, not 6.0V --

While it isn't a problem here, Jung pointed out in the TAA 2000 issue -- that there are occasionally dud LM329's so make sure that it is actually working.

PS -- Jan wrote one of the original series (1995) articles.

P.S. I have yet to check the other suggestions - have to get home first

You're still off on Vout. Across the 890 ohms there is 6.9 V. Therefore, across the 1130 there is 1130/890 * 6.9 = 8.76 volts. Therefore, Vout = 15.66V. Since the opamp needs some volts to operate, and you also loose some in the series transistor, you need probably a minimum of 20VDC input under load. Please check.

Jan Didden

janneman said:

You're still off on Vout. Across the 890 ohms there is 6.9 V. Therefore, across the 1130 there is 1130/890 * 6.9 = 8.76 volts. Therefore, Vout = 15.66V. Since the opamp needs some volts to operate, and you also loose some in the series transistor, you need probably a minimum of 20VDC input under load. Please check.

Jan Didden

you also lose across the LM317 pre-regulator -- (the version which I built did not incorporate this.)

I'm using a 1n5235 zener to the collector of Q2.

I'll measure voltages as soon as I get home.

Thanks again for all the help!

I'm not using R1, R2, you are.

In the Jung schematic where there are R1 and R2, I see a 1N4148 diode, not a zener. And in that diagram, Vout = 15,66, sorry.

How many volts is that zener?

What else is different?

Can you post a diagram of the one YOU buiilt? We may catch something that went unnoticed so far.

Jan Didden

Could anyone explain the variations in voltage across different loads? Thanks!

With no load, Pin 6 has 17.9V and there is 6V between +In and Output.

The voltage difference btween +In and Ouput are the same polarity - one isn't negative.

?

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