78xx regulator for negative voltage

[lcsaszar]

What 78xx and 79xx compatible low noise voltage regulators (not LDO) are recommended?

 

[steveu]

79xx is NOT an EF output. Both 78xx and 79xx are primarily NPN transistors, so the negative regulator is a ~CFP/quasi circuit. Check the data sheet(s). This is one reason the pin-outs are different.

 

[egellings]

Output stage looks like a Darlington type to me.

 

[Arnolddew]

When using these type of configuration (image from post #44) of two positive regs in a sett-up you need single transformer windings. But can you now use other type of positive and real negative regs in that same set up/on that pcb which share the same ground but power different parts?

 

[tomchr]

The low noise regulators based on LT3045 are around £20 for +ve and £30+ for the +ve, that's a big difference.

If low noise is your goal, I suggest using a more modern regulator. The TPS7Axxxx from TI are very good. TPS7A3301 for example. They're not easy to solder by hand, but it can be done with a hot air tool.

Tom

 

[tomchr]

Both 78xx and 79xx are primarily NPN transistors

That's no surprise. The PNPs of the era utterly sucked. That's why they're only used in the bias circuits of the regulator. Some modern analog-optimized semiconductor processes have good PNPs, but most BiCMOS processes only support lateral PNPs which are awful. Beta of 10 on a good day.

Tom

 

[oxothuk]

we have LT3094 and TPS7A3301 TO-220 replace boards
https://www.ldovr.com/Ultra-Low-Noise-LDO-Voltage-Regulator-p/lt3094-79xx.htm
https://www.ldovr.com/product-p/tps7a3301-79xxg.htm

 

[Nick Sukhov]

IMHO the best +_ is TPS7A39 "all in one" [ https://www.patreon.com/posts/kit-fonokora-su-96595568 ] [

]

 

[jan.didden]

well spotted, correction should be like this ..... but is the 78xx going to work as negative regulator?

View attachment 1237934

This will work fine. It is still a positive voltage regulator but the way it is used it delivers a negative voltage to gnd.

Jan

 

[Arnolddew]

Jan, your superregs can be used the same way; connect two positives is series to create one pos and and one neg? Each with separate windings of course.

 

[RJM1]

I thought that You could not do this with a single winding
until I tried this.
Did I miss something?

 

[steveu]

I'm impressed! Yes, that seems to work just fine.
How did you create the LM7805 symbol and where did you put the symbol and comp files?
Only issue is the half wave rectifier ripple, but it works.

 

[jan.didden]

Jan, your superregs can be used the same way; connect two positives is series to create one pos and and one neg? Each with separate windings of course.

Yes. Ever since 1916, everything is relative ;-)
Think about why multimeters have two probes even if you want to measure just 'a' voltage!

The only thing a 15V reg does is maintain, accurately and free of noise, a difference of 15V between two terminals.
It only becomes a pos or neg voltage once you decide which terminal to ground.
Or to stack it upon another voltage somewhere.

Jan

 

[RJM1]

@steveu
That was a long time ago for LTspiceIV, I found the .lib file
dated 2010. The symbol is the LTspice LT1084 symbol renamed.
see attached (.txt added)