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2thick4uni
Joined: Feb 20, 2009
Posts: 113
Location: UK
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 Posted: Sun Jul 14, 2013 10:09 am Post subject:
Voltages regulators on Yusynth VCO? |
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I'm going to build the Yusynth VCO but always like to get a good grasp of the theory of operation first. I'm struggling to understand the role of the 78L15 and 79L15 voltage regulators. Normally you need about 3 volts or more above regulation voltage (i.e 18v or more) for these to work, but here they seem to be used to provide a stable voltage for the VCO core from a +/-15v supply. 
I've read in an earlier thread that the +vcc and -vcc voltages are around 14.2volts, which seems to be a similar drop to using a diode? Does the vcc voltages not just mirror any dips in the 15V supply but 0.8v or so lower? How does this actually help?
Any explanation of how this stabilizes the VCO core voltage against fluctuations in supply voltage would be most helpful!
Thanks!
Allan |
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yusynth
Joined: Nov 24, 2005
Posts: 1314
Location: France
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| Posted: Mon Jul 15, 2013 11:26 am Post subject:
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I just quote what is written on the yusynth VCO page :
| Quote: | DESIGN NOTE :
I have received a lot of emails concerning the voltage regulators used in the circuit. Here is an explaination for the reason why they are there.
FAQs :
Are these two regulators useful here considering I am already using a regulated +/-15V ?
Considering that the 78L15 and 79L15 require an overhead of 3V to give the right voltage why are these for in this circuit ? Could not one just suppress them ?
The answer to these two questions is :
The aim of using these regulators is not to provide +15V and -15V as one would think first. As a matter of fact, because of the lack of voltage overhead and the low current draw they will rather deliver something like 14.2V and -14.2V. This is not a design error but was done on purpose : they are here to isolate the power supply circuit of the VCO core from the general power supply while providing a reference voltage of +/-14.2V. This helps very much in increasing the stability of the VCO.
As such, all the circuit of the VCO core was designed considering the voltage drop through the regulators, and it is a very important point. As such, if one would like to remove/bypass these regulators, one would need to recalculate many resistor values of the VCO core to have it working as expected.
In conclusion, they are there for a good reason  |
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Yves |
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2thick4uni
Joined: Feb 20, 2009
Posts: 113
Location: UK
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| Posted: Mon Jul 15, 2013 4:49 pm Post subject:
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Excellent, thanks Yves 
Now I have to work out how I read the VCO page and missed this! 
Allan |
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PHOBoS
Joined: Jan 14, 2010
Posts: 5947
Location: Moon Base
Audio files: 709
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| Posted: Mon Jul 15, 2013 11:41 pm Post subject:
Re: Voltages regulators on Yusynth VCO? |
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that doesn't really answer your question though:
| 2thick4uni wrote: | I've read in an earlier thread that the +vcc and -vcc voltages are around 14.2volts, which seems to be a similar drop to using a diode? Does the vcc voltages not just mirror any dips in the 15V supply but 0.8v or so lower? How does this actually help?
Any explanation of how this stabilizes the VCO core voltage against fluctuations in supply voltage would be most helpful! |
I can see how it isolates the power but I think it's only as stable as your 15V supply is and would fluctuate just as much.
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