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Connecting two rails, from DC power supply, to L7915 regulator pins

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nzkunal

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Hi am trying to create two rails +15V and -15V from a single +24V DC power supply.

I wanted to know what I should be connecting to which pin of the L7915CV regulator.

1 - +24V, C1(+), C2(+)
2 - GND, C1 (-)
3 - Output -15V & C2(-)

C1 and C2 are 10uF electrolytic caps.

For some reason I am getting +1.5V on the output pin

Any suggestions?
 

using lm7660

nzkunal said:
Hi am trying to create two rails +15V and -15V from a single +24V DC power supply.

I wanted to know what I should be connecting to which pin of the L7915CV regulator.

1 - +24V, C1(+), C2(+)
2 - GND, C1 (-)
3 - Output -15V & C2(-)

C1 and C2 are 10uF electrolytic caps.

For some reason I am getting +1.5V on the output pin

Any suggestions?
Click to expand...

A Negative regulator Only works on a Negative power supply.

Unless you connect the +24 to the Ground and use the -24 into the 7915, You only have a positive power supply.

And If you do that, than you don't have a Positive supply for the Positive regulator to work.

Where are you getting this 24 volts from?
Battery or a transformer supply?
 

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    nzkunal

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l7915 application circuit

Thanks for the response.

Ok. I am using a battery supply.

So there is no way to create a negative and a positive rail from a single DC power source?
 

l7915

nzkunal said:
Thanks for the response.

Ok. I am using a battery supply.

So there is no way to create a negative and a positive rail from a single DC power source?
Click to expand...

15 Volts is a bit high for this, But You can by using an LM7660 to create a negative supply.
Do a search for the data sheet and it will give you a schematic.

This Somewhat depends on How much current you need?
What are you trying to operate with the +/- 15 volts?
 

l7915 application schematic

Running a LM311 comparator.

I am currently running the comparator using +15V and ground but for some reason it is not giving me a very good output with an AC 2V peak-peak 40kHz signal. I thought maybe if I provide a -15V rail input to it it might work better.

The AC signal is a nice sinusoid but as soon as I connect it to the inverting and non-inverting inputs of the opamp it distorts the signal.
 

Re: L7915 design

nzkunal said:
Running a LM311 comparator.

I am currently running the comparator using +15V and ground but for some reason it is not giving me a very good output with an AC 2V peak-peak 40kHz signal. I thought maybe if I provide a -15V rail input to it it might work better.

The AC signal is a nice sinusoid but as soon as I connect it to the inverting and non-inverting inputs of the opamp it distorts the signal.
Click to expand...

Why are you using a 311 Comparator for an AC signal input?

What are you really trying to do?
What output do you want?

A High Slew Rate Op-amp would be more suitable, Especially at 40khz.
 

Re: L7915 design

I am trying to build a Zero Voltage Switching controller for an application. The output of the comparator would be used to drive some FET's.

Could you suggest any opamps that would be suitable for generating a square wave of 50% duty and the same frequency as the sine wave input into the opamp?
 

Re: L7915 design

nzkunal said:
I am trying to build a Zero Voltage Switching controller for an application. The output of the comparator would be used to drive some FET's.

Could you suggest any opamps that would be suitable for generating a square wave of 50% duty and the same frequency as the sine wave input into the opamp?
Click to expand...

Sorry I haven't done any zero crossing detectors, But manufacturers do make special Integrated Circuits for that specific purpose.

I would suggest you do a search for them.
(Possibly at Texas Instruments and On Semiconductor)
https://www.ti.com
https://onsemi.com

Hope this helps......Gary
 

Re: L7915 design

Hi,
Your input is getting distorted since it is exceeding the limit of -0.3V of the comparator on the negative side. Your -ve supply voltage idea will work, even if you give a -5V supply. But before that, you can try feeding the input signal through a resistor (say about 3.3K) and clamp the -ve peak of the input at the comparator using a diode connected to ground. You should connect the signal to +ve input of the comparator and -ve input of the comparator to be connected to ground through another 3.3k resistor.
You can also see the data sheet of LMV761 for your application.
Regards,
Laktronics
 

Re: L7915 design

Thanks.
Does this look right?
 

Re: L7915 design

Hi,
No, Please **broken link removed** to view the corrected circuit diagram in Pspice.

Regards,
Laktronics
 

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