"MikeN" wrote in message
...
Not infrequently regulated power supply circuitry is found with NPN
pass transistors like the 2n3055, in the negative supply line,

I'm curious to know what are the pros and cons of putting the pass
transistors in this way, as against the more common topology of
putting them in the positive supply line?

Just think about where you are going to get the base drive if the pass
transistor is in the positive lead. You'll need a voltage considerably
higher than the output voltage. This may demand that the rectifier put out
more voltage than you'd really like, which means more drop across the pass
transistor and thus more dissipation (lower efficiency).

It's easy to get the supply for the base of the pass transistor if it is in
the return lead, without increasing the rectifier output voltage above the
minimum required to always overcome the drop in the pass transistor.

"MikeN" wrote in message
...
Not infrequently regulated power supply circuitry is found with NPN
pass transistors like the 2n3055, in the negative supply line,

I'm curious to know what are the pros and cons of putting the pass
transistors in this way, as against the more common topology of
putting them in the positive supply line?

Just think about where you are going to get the base drive if the pass
transistor is in the positive lead. You'll need a voltage considerably
higher than the output voltage. This may demand that the rectifier put out
more voltage than you'd really like, which means more drop across the pass
transistor and thus more dissipation (lower efficiency).

It's easy to get the supply for the base of the pass transistor if it is in
the return lead, without increasing the rectifier output voltage above the
minimum required to always overcome the drop in the pass transistor.

Power supply topology question
 

Not infrequently regulated power supply circuitry is found with NPN
pass transistors like the 2n3055, in the negative supply line,

I'm curious to know what are the pros and cons of putting the pass
transistors in this way, as against the more common topology of
putting them in the positive supply line?

Thanks

MikeN

MikeN wrote:

Not infrequently regulated power supply circuitry is found with NPN
pass transistors like the 2n3055, in the negative supply line,

I'm curious to know what are the pros and cons of putting the pass
transistors in this way, as against the more common topology of
putting them in the positive supply line?

Thanks

MikeN

One possible benefit is transistor is connected collector grounded.
There is no need
insulate the transistor and heat conduction is improved.

Possible problems may be in cases where for some reason the regulation
transistor fails,
unregulated and higher overvoltage can get to load if there is any
return path from ground to
unregulated negative line. Possibly transistor in negative line has
infinite
resistance when failed.

Some sort of overvoltage protection could be useful if the load is
sensitive to overvoltages.

rgds Kari B

MikeN wrote:

Not infrequently regulated power supply circuitry is found with NPN
pass transistors like the 2n3055, in the negative supply line,

I'm curious to know what are the pros and cons of putting the pass
transistors in this way, as against the more common topology of
putting them in the positive supply line?

Thanks

MikeN

One possible benefit is transistor is connected collector grounded.
There is no need
insulate the transistor and heat conduction is improved.

Possible problems may be in cases where for some reason the regulation
transistor fails,
unregulated and higher overvoltage can get to load if there is any
return path from ground to
unregulated negative line. Possibly transistor in negative line has
infinite
resistance when failed.

Some sort of overvoltage protection could be useful if the load is
sensitive to overvoltages.

rgds Kari B

R J Carpenter wrote:

"MikeN" wrote in message
...
Not infrequently regulated power supply circuitry is found with NPN
pass transistors like the 2n3055, in the negative supply line,

I'm curious to know what are the pros and cons of putting the pass
transistors in this way, as against the more common topology of
putting them in the positive supply line?

Just think about where you are going to get the base drive if the pass
transistor is in the positive lead. You'll need a voltage considerably
higher than the output voltage.

Could you specify what you mean by "considerably higher"?

This may demand that the rectifier put out
more voltage than you'd really like, which means more drop across the pass
transistor and thus more dissipation (lower efficiency).

It's easy to get the supply for the base of the pass transistor if it is in
the return lead, without increasing the rectifier output voltage above the
minimum required to always overcome the drop in the pass transistor.

R J Carpenter wrote:

"MikeN" wrote in message
...
Not infrequently regulated power supply circuitry is found with NPN
pass transistors like the 2n3055, in the negative supply line,

I'm curious to know what are the pros and cons of putting the pass
transistors in this way, as against the more common topology of
putting them in the positive supply line?

Just think about where you are going to get the base drive if the pass
transistor is in the positive lead. You'll need a voltage considerably
higher than the output voltage.

Could you specify what you mean by "considerably higher"?

This may demand that the rectifier put out
more voltage than you'd really like, which means more drop across the pass
transistor and thus more dissipation (lower efficiency).

It's easy to get the supply for the base of the pass transistor if it is in
the return lead, without increasing the rectifier output voltage above the
minimum required to always overcome the drop in the pass transistor.