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+15Vdc , -15Vdc and +5Vdc output

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shaneelal

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Hi, I'm using a 36V center tap transformer rated at 3A.
I need to obtain +15V and -15V dc for a current sesnsor.
I'm using a 7815 and 7915 for the +15Vdc abd -15Vdc respectively,also 7805 for +15Vdc.
Does anyone have a circuit design that may be able to help me.If you have any tips please tell me.
 

Hi,

I'm not sure exactly what you want to know. For some basic PSU information, try these links - the first is almost what you want (missing the +5V):

**broken link removed**
http://members.shaw.ca/roma2/supply.pdf

For the +5V, just add it on like the 7815.

You might need to watch the power dissipation on the 7805 - it is running with a big voltage drop, probably about 17V. How much current do your supplies need?

Any specific questions?

Cheers,
FoxyRick.
 

    shaneelal

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The 7805 will need to supply at most 100mA to the devices that require 5V. Can I use the +15V output as input for the 7805?
 

Using 15V to supply 5V regulator seems to be good option ..
 

7805 can supply between 5mA and 1A output current and the input voltage must be around 10V.
 

and the input voltage must be around 10V.
It is incorrect. The max input voltage is 35Vdc and minimum Vout+3V=8Vdc ..
 

    shaneelal

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IanP said:
and the input voltage must be around 10V.
It is incorrect. The max input voltage is 35Vdc and minimum Vout+3V=8Vdc ..

I meant you need 10V if you want a 5V output.
Anything lesser than 10V will give less than 5V at the output.
 

I am unable to obtain the 36V transformer. Can one 24V or one 18V transformer be able to provide me with +15V,-15V,and +5V?
 

You can use the 24 V transformer.
For the 7815 you will need about 22 V input to obtain a 15 V output so a 18 V transformer may not be a good option.
 

For the supply of a sensor and then 100mA @ 5V yopu can use one 18V transformer and 1 diode (half wave rectification) for each rail (+ and -) connected to top transformer secondary winding, the bottom becomes your 0V. Use smoothing capacitors >1000µ per rail. After rectification with caps connected you will have 18V * 1.4 ≈ (+/-)25V (with no load). For currents as you described it should work ..
 

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