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Old 22nd April 2006, 02:57 PM   #1
gy21 is offline gy21  Netherlands
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Default Need help with Tentlabs power supply

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I need some help with this power supply. I only get 2.63 V on pin 8.

I feed this circuit with 12.5 Volt, after the 7808 I measure 8 Volts. At the B of the transistor I measeare 3.2V The collectorhas 8 Volts.

If I measure straight over the 22k resistor (not from ground) I get 4,75V. If I measure straight over the 56k resister I get 3,2 Volts Wich is ofcourse the same as the basis at the transistor.

What am I doing wrong here?
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Old 22nd April 2006, 04:06 PM   #2
poynton is offline poynton  United Kingdom
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Default Re: Need help with Tentlabs power supply

Quote:
Originally posted by gy21
Click the image to open in full size.

I need some help with this power supply. I only get 2.63 V on pin 8.

I feed this circuit with 12.5 Volt, after the 7808 I measure 8 Volts. At the B of the transistor I measeare 3.2V The collectorhas 8 Volts.

If I measure straight over the 22k resistor (not from ground) I get 4,75V. If I measure straight over the 56k resister I get 3,2 Volts Wich is ofcourse the same as the basis at the transistor.

What am I doing wrong here?
Blown transistor ? Have you tried changing it ?
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Old 22nd April 2006, 04:12 PM   #3
float is offline float  England
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Just change the 22k for 2.2k and the 56k for 5.6k. That should sort it. Tip courtesy of Guido himself.

HTH
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Old 22nd April 2006, 06:22 PM   #4
gy21 is offline gy21  Netherlands
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Quote:
Originally posted by float
Just change the 22k for 2.2k and the 56k for 5.6k. That should sort it. Tip courtesy of Guido himself.

HTH
Yup that fixed it.

Thanks Float!

P.s. I Got 4.6V now, is that close enough to 5 V that is needed for the clock to work correctly?
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Old 22nd April 2006, 07:50 PM   #5
gy21 is offline gy21  Netherlands
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I read on the tentlabs site that the clock needs 5V +-5%. So that means 4,6V is to low.

Any suggestions to raise this voltage? Raising the 5,6K?
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Old 22nd April 2006, 09:30 PM   #6
float is offline float  England
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I'd adjust the res's to suit; the dac spec calls for 4.7-5.3v.

I got 5.01v when I built mine; maybe the transistor's slightly out of spec?

Also see here can't get 5V from tent clock XO sch
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Old 23rd April 2006, 09:17 AM   #7
gy21 is offline gy21  Netherlands
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ok, lowered the 2k2 res to a 1k5.

got 5.15 now on pin 8.

that should do it I think.

thanks for your help Float.
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