DIY Power supply Question

[djmiyta]

Ok so I'm gonna build another power supply (its been years since I built my last one. A power supply for my 9volt pedals only. Finding info on the web is tedious and sometimes confusing so my question is ...
1 - I have an 18v (on the secondaries) transformer most directions to build a power supply say to use a 12 volt transformer. Anything wrong with using an 18 volt? and

2 - If theres is no problem using it would there be anything extra I'd have to do to a (or the ) circuit because it's 18v instead of 12v?

I know I'm asking without posting the scheme I'd be working from since I have'nt decided which one I'll try just asking in general

Thanks in advance for any guidance on this

 

[temol]

With 18V AC you have around 24V DC after rectifier. Assuming 2V voltage drop on a 7809 voltage regulator you still have some volts to drop... in a form of a heat on the regulator. Use TO220 package and see later if you need a heatsink.

 

[djmiyta]

With 18V AC you have around 24V DC after rectifier. Assuming 2V voltage drop on a 7809 voltage regulator you still have some volts to drop... in a form of a heat on the regulator. Use TO220 package and see later if you need a heatsink.

Thank you for the reply
I know Google is my friend but
Could you tell me how to get the voltage down to 9 volts , possibly?

 

[PunchySunshine]

Thank you for the reply
I know Google is my friend but
Could you tell me how to get the voltage down to 9 volts , possibly?

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[djmiyta]

Thank You very much

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[temol]

You have couple options here. It all depends on the load - how many mA are you going to draw. You can use it as is - but voltage regulator may get hot. Maximum input voltage for the 7809 in TO220 package is 35V. So you are within limit with 24V. Remember, the higher the input voltage, the more heat will be released.
You can also lower the voltage before the regulator using a resistor. Several dozen ohms, 3-5W. But again this is a waste of energy, converting it into heat.
Another possibility - use 18V regulator and then add DC-DC converter with adjustable output voltage. They're cheap.

 

[djmiyta]

You have couple options here. It all depends on the load - how many mA are you going to draw. You can use it as is - but voltage regulator may get hot. Maximum input voltage for the 7809 in TO220 package is 35V. So you are within limit with 24V. Remember, the higher the input voltage, the more heat will be released.
You can also lower the voltage before the regulator using a resistor. Several dozen ohms, 3-5W. But again this is a waste of energy, converting it into heat.
Another possibility - use 18V regulator and then add DC-DC converter with adjustable output voltage. They're cheap.

temol thank you for the response. Since it's for my pedals and I'd like to squeeze as many 9v jacks as I can into the box I naively assumed about 1 amp would handle alot but my salvaged transformer from a Fender Frontman amp is 1/2 an amp from the (frontmans scheme where I got that from) AND I have not done my homework on how many mA each of my pedals use (which I change out constantly) I just tried to shoot high. I figured on etching a board with 10 - 16 9v outs just not populate the board fully until I found or acquired and finally possibly buy a 12v 2 amp transformer. So I was just trying to find out if the transformer I do have actually can be used. Since I always seem to see power supplies for pedals typically at 100 mA I again assumed 1 pedal per.

so this time I attached a scheme. Does it still seem doable with the transformer I have? I'm thinking no problem but ...... I have been wrong a time or 3.