power supply

P

Peyter

Guest
I have a variable voltage, variable current power supply.
Had a quick look inside hoping to find the L200C, but
no, it's not there. Instead there is a bunch of op amps,
a variable zener diode and some fixed voltage ic's, such
as L7809 and L7812. I am trying to figure out why fixed
voltages are used, as the output voltage is variable. It
could be that they are used to power up the lcd displays
and are not used for the output at all, but I don't know.
Is it at all possible to do all this just with a few op amps?
(there are a few other active components as well but they
seem to be auxiliary items, not the heart of the system,
such as two bipolar transistors and just diodes.)
 
Peyter wrote:
I have a variable voltage, variable current power supply.
Had a quick look inside hoping to find the L200C, but
no, it's not there. Instead there is a bunch of op amps,
a variable zener diode and some fixed voltage ic's, such
as L7809 and L7812. I am trying to figure out why fixed
voltages are used, as the output voltage is variable. It
could be that they are used to power up the lcd displays
and are not used for the output at all, but I don't know.
Is it at all possible to do all this just with a few op amps?
(there are a few other active components as well but they
seem to be auxiliary items, not the heart of the system,
such as two bipolar transistors and just diodes.)
Click to expand...
It is very possible to build a lab supply without using integrated
regulators (except for ancillary functions). Most good
(indestructible) designs are discrete.
--
John Popelish
 
"John Popelish" <jpopelish@rica.net> wrote in message news:3FB5102C.6BC05D91@rica.net...
Peyter wrote:

I have a variable voltage, variable current power supply.
Had a quick look inside hoping to find the L200C, but
no, it's not there. Instead there is a bunch of op amps,
a variable zener diode and some fixed voltage ic's, such
as L7809 and L7812. I am trying to figure out why fixed
voltages are used, as the output voltage is variable. It
could be that they are used to power up the lcd displays
and are not used for the output at all, but I don't know.
Is it at all possible to do all this just with a few op amps?
(there are a few other active components as well but they
seem to be auxiliary items, not the heart of the system,
such as two bipolar transistors and just diodes.)

It is very possible to build a lab supply without using integrated
regulators (except for ancillary functions). Most good
(indestructible) designs are discrete.
--
John Popelish
Click to expand...
Can you see any reason why fixed voltage regulaors would be used
in a variable voltage power supply, or would that probably be for
the lcd displays, which I assume must have some fixed Vdd ?
 
programmerforhire wrote:
"John Popelish" <jpopelish@rica.net> wrote in message news:3FB5102C.6BC05D91@rica.net...
Peyter wrote:

I have a variable voltage, variable current power supply.
Had a quick look inside hoping to find the L200C, but
no, it's not there. Instead there is a bunch of op amps,
a variable zener diode and some fixed voltage ic's, such
as L7809 and L7812. I am trying to figure out why fixed
voltages are used, as the output voltage is variable. It
could be that they are used to power up the lcd displays
and are not used for the output at all, but I don't know.
Is it at all possible to do all this just with a few op amps?
(there are a few other active components as well but they
seem to be auxiliary items, not the heart of the system,
such as two bipolar transistors and just diodes.)

It is very possible to build a lab supply without using integrated
regulators (except for ancillary functions). Most good
(indestructible) designs are discrete.
--
John Popelish

Can you see any reason why fixed voltage regulaors would be used
in a variable voltage power supply, or would that probably be for
the lcd displays, which I assume must have some fixed Vdd ?
Click to expand...
The opamps that operate the supply need stable bias voltages. One of
the fixed regulators may even be used as a voltage reference for the
adjustable circuit.
--
John Popelish
 
"John Popelish" <jpopelish@rica.net> wrote in message news:3FB5652E.ADBC0000@rica.net...
programmerforhire wrote:

"John Popelish" <jpopelish@rica.net> wrote in message news:3FB5102C.6BC05D91@rica.net...
Peyter wrote:

I have a variable voltage, variable current power supply.
Had a quick look inside hoping to find the L200C, but
no, it's not there. Instead there is a bunch of op amps,
a variable zener diode and some fixed voltage ic's, such
as L7809 and L7812. I am trying to figure out why fixed
voltages are used, as the output voltage is variable. It
could be that they are used to power up the lcd displays
and are not used for the output at all, but I don't know.
Is it at all possible to do all this just with a few op amps?
(there are a few other active components as well but they
seem to be auxiliary items, not the heart of the system,
such as two bipolar transistors and just diodes.)

It is very possible to build a lab supply without using integrated
regulators (except for ancillary functions). Most good
(indestructible) designs are discrete.
--
John Popelish

Can you see any reason why fixed voltage regulaors would be used
in a variable voltage power supply, or would that probably be for
the lcd displays, which I assume must have some fixed Vdd ?

The opamps that operate the supply need stable bias voltages. One of
the fixed regulators may even be used as a voltage reference for the
adjustable circuit.
Click to expand...
I think you are right, because all of them have heat sinks. If they where just
for the lcd's they wouldn't need heat sinks. Thanks.

--
John Popelish
Click to expand...
 
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