How to reduce voltage of a bipolar power supply

[guidoilieff]

Hi, i'm making CA tremolo and I have a +12/-12 300mA power supply lying around that I want to use. I need to lower the -+12v to -+6v so I end with 18v. Which way is the best? Thanks 


http://www.diystompboxes.com/smfforum/index.php?topic=111202.0

[mth5044]

Whaaat? Lower +/-12v to +/-6 to get 18? Wuh?

I don't undersnd, but you can rectify and use 7806 and 7906 to get your 6V. Not sure what the 18V is you want?

[guidoilieff]

Haha, never mind.

So I can use 7806 and 7906 no matter the voltage input? Should I use heat sinks?

Thanks

[GibsonGM]

Whether you need to use a heat sink or not depends on the current you intend to draw from the regulators.  Since you're dumping 1/2 your supply, I would assume you should heat sink them, just to be on the safe side. 

If I was going to do this, I might estimate the draw, and use a resistor at the regulators' outputs to simulate the circuit itself...then see if they get hot.  But there is no harm in just sinking them.    Bet they'll get hot

There's a mathematical way to calculate the heat they'll dissipate, but I don't go there - I just sink them for anything more than the most basic circuits that I can 'hand evaluate'!

>>Read the regulators DATA SHEETS. They will tell you the max input voltage you can apply.  In your case, taking +12 and -12, and sending thru respective regulators, is fine I am sure.  They tend to be limited more to about 30V. 

[slacker]

Why do you want +-6 Volts? The circuit wants +-9 Volts, I would do what PRR suggested in your other thread and use 7809 and 7909 regulators.

[guidoilieff]

Why do you want +-6 Volts? The circuit wants +-9 Volts, I would do what PRR suggested in your other thread and use 7809 and 7909 regulators.

He said : "Do NOT go over 6VAC! This already gives +/-8V, 16V total"


I think 6vAC is more than 6vDC or something like that...

[davent]

Why do you want +-6 Volts? The circuit wants +-9 Volts, I would do what PRR suggested in your other thread and use 7809 and 7909 regulators.

He said : "Do NOT go over 6VAC! This already gives +/-8V, 16V total"


I think 6vAC is more than 6vDC or something like that...

Two different supplies, regulated and non-regulated supplies.

The two regulators would prevent maximum voltage being exceeded.

Without regulators as shown in Pauls diagram, a transformer bigger then 6VAC would result in voltages greater then the IC can handle.

[Ice-9]

Do Exactly as PRR says in your other thread.