voltage regulators ?

can somebody point me in the right direction ?

i bought 2 regulators today

one is 15V the other is -15V

i have wired them to a 20v power supply

they both have 3 pins

pin1 input power (20v) pin2 gnd pin3 output power

i expected to see 15V and -15v on pins 3

but i got 20v !!!!

any suggestions - I am sure i have sone something stuipd

To use the +15v and -15v regulators you need independent +20v and -20v supplies.

The +15V regulator should work as you wrote, with perhaps the addition of decoupling capacitors on the input and output (check the datasheet). The -15V regulator needs negative voltage input power.

Ordinary regulators can't produce voltages outside the range covered by their input power supply. However there are DC to DC converters which can produce negative voltages from a positive input - eg. the Recom RB-0515D converts +5V & 0V into +15V, 0V & -15V.

thanks for the advice guys (i guessed that was the problem)

i will look into a power supply that produces positive and negative power

regards

tim7: The +15V regulator should work as you wrote, with perhaps the addition of decoupling capacitors on the input and output (check the datasheet). The -15V regulator needs negative voltage input power.

Ordinary regulators can't produce voltages outside the range covered by their input power supply. However there are DC to DC converters which can produce negative voltages from a positive input - eg. the Recom RB-0515D converts +5V & 0V into +15V, 0V & -15V.

that RB-0515d is a neat little product, i always think it is like magic if you can create a negative voltage from a positive one - is there an inverter inside it ?