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

[shaneelal]

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.

 

[FoxyRick]

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]

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?

 

[IanP]

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

 

[usernam]

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

 

[IanP]

and the input voltage must be around 10V.

It is incorrect. The max input voltage is 35Vdc and minimum Vout+3V=8Vdc ..

 

[usernam]

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.

 

[shaneelal]

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?

 

[usernam]

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.

 

[IanP]

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 ..