Problem with. Astron RS-50M Power Supply
 

With the gear hooked to the supply, even with it turned-off, when I
turn on the supply, the voltage transient cleans or erases the
programming in the radios. It's not the radio, as it does it with 2-3
different ones.

Does anyone have any idea how to solve this problem, or if a faulty
component might be causing it?

I've worked on more than few of these supplies, and have never seen
this problem before.

I've E-mailed Astron, and did not even reply.
WB0VQP



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wrote:

With the gear hooked to the supply, even with it turned-off, when I
turn on the supply, the voltage transient cleans or erases the
programming in the radios. It's not the radio, as it does it with 2-3
different ones.

Does anyone have any idea how to solve this problem, or if a faulty
component might be causing it?

I've worked on more than few of these supplies, and have never seen
this problem before.

I've E-mailed Astron, and did not even reply.
WB0VQP


First, verify the problem. To do that, connect a switch
between the Astron and the equipment. Turn the supply on,
wait one minute, then turn the switch on. If you still have
the problem, it's not in the supply. If it eliminates the
problem, you could try adding an automotive relay in place
of the switch. Energize the relay from the 13.8 volts -
it will give you roughly 8 milliseconds delay between the
time you switch the Astron on and the time power is available
to the equipment. That doesn't fix the transient problem, but
it does bypass it. Another solution that doesn't fix the
problem (at its source, assuming it is a supply generated
transient) but does bypass it is a transorb diode rated at
15 volts, connected across the supply 13.8 v DC.

If the supply is creating transients causing the problem,
and you want to fix it at the source, you could try bypassing
things to ground with a bunch of .01 caps.



remove NoSpam to reply.

wrote:

With the gear hooked to the supply, even with it turned-off, when I
turn on the supply, the voltage transient cleans or erases the
programming in the radios. It's not the radio, as it does it with 2-3
different ones.

Does anyone have any idea how to solve this problem, or if a faulty
component might be causing it?

I've worked on more than few of these supplies, and have never seen
this problem before.

I've E-mailed Astron, and did not even reply.
WB0VQP


First, verify the problem. To do that, connect a switch
between the Astron and the equipment. Turn the supply on,
wait one minute, then turn the switch on. If you still have
the problem, it's not in the supply. If it eliminates the
problem, you could try adding an automotive relay in place
of the switch. Energize the relay from the 13.8 volts -
it will give you roughly 8 milliseconds delay between the
time you switch the Astron on and the time power is available
to the equipment. That doesn't fix the transient problem, but
it does bypass it. Another solution that doesn't fix the
problem (at its source, assuming it is a supply generated
transient) but does bypass it is a transorb diode rated at
15 volts, connected across the supply 13.8 v DC.

If the supply is creating transients causing the problem,
and you want to fix it at the source, you could try bypassing
things to ground with a bunch of .01 caps.



remove NoSpam to reply.

If the Astron overshoots, you can verify it with an oscilloscope. If indeed
it does that, you can modify the circuit to reduce that.

Why are you using a 35 Ampere power supply for such a small load? It would
be better to use a lower current rated unit. I use a 20 Ampere unit and
have no such problem.

Looking at the diagram, you can put in a capacitor across the reference
voltage at the IC to reduce the turn on speed.

On the other hand, it's possible the problem arises due to too slow a turn
on of the supply. You can do things to improve that also. Also, the supply
may be oscillating. Try connecting a dummy load of, say, a few amperes
across the output. An automobile headlamp can work for that.

Best to verify the actual cause with an oscilloscope before starting to make
modifications.

73, Bob K6DDX

If the Astron overshoots, you can verify it with an oscilloscope. If indeed
it does that, you can modify the circuit to reduce that.

Why are you using a 35 Ampere power supply for such a small load? It would
be better to use a lower current rated unit. I use a 20 Ampere unit and
have no such problem.

Looking at the diagram, you can put in a capacitor across the reference
voltage at the IC to reduce the turn on speed.

On the other hand, it's possible the problem arises due to too slow a turn
on of the supply. You can do things to improve that also. Also, the supply
may be oscillating. Try connecting a dummy load of, say, a few amperes
across the output. An automobile headlamp can work for that.

Best to verify the actual cause with an oscilloscope before starting to make
modifications.

73, Bob K6DDX

wrote in message
...
With the gear hooked to the supply, even with it turned-off, when I
turn on the supply, the voltage transient cleans or erases the
programming in the radios. It's not the radio, as it does it with 2-3
different ones.

Does anyone have any idea how to solve this problem, or if a faulty
component might be causing it?

Theory of LM723 operation (courtesy David Metz):
[An Astron schematic, when reading, is helpful]

The LM723 is a twenty some year old IC designed to be a universal voltage
regulator.
Being cheap and well understood it found in most of our bench supplies and
is the core of the popular Astron series.

Any bench supply consists of a transformer with a secondary of about 18
volts AC,
a rectifier block and a filter capacitor. With no load, the DC voltage
across the terminals
of the filter are going to be 18 to 30 volts.

Under load the voltage will sag due to the impedance of the secondary of
the power transformer. If it sags too far, the supply will loose regulation
and it will pass 120 Hertz ripple (hum) to whatever you are powering with
it.

Since the voltage across the filter capacitor can vary wildly as the load
changes
we need a method of regulating the voltage. The work of regulation is done
by
the pass transistors (Q2 to Q5). They in turn are controlled by the 723
regulator.

Lets look at the 723 in a little more detail now. Note that it has its own
filter power
supply made up from diodes D1-D4 and filter capacitor C2.

The 723 has its own internal highly regulated voltage reference supply (pin
6).
Internally the 723 compares this reference voltage to the output of the
power supply.

Voltage adjustment pot RV1 sets the "ratio" of the reference voltage to the
output of the supply.
This sets the output voltage from the supply.

The output of the 723 is pin 10. This voltage drives the base of Q1. Q1
acts as a simple amplifier to increase the current available to drive the
current hungry bases of the pass transistors.

As the load increases on our power supply, the voltage from the wiper of
RV1 drops as well.
When this occurs the 723 increases the voltage from pin 10 driving the pass
transistors harder through Q1.
The more base current through the pass transistors, the higher the output
voltage.

Thus we have regulation, the 723 continuously changing its output voltage to
meet the minute changes in load on the
supply. Remember, the 723 does the thinking, the pass transistors do the
work!

THE PASSING LANE
Let's look a bit at what the pass transistors do. The key thing here is
current carrying capacity and heat dissipation.
In our example, lets say your power supply uses the common 2N3055 NPN power
transistor.

This transistor can pass up to 15 amps of collector current. Note that it is
not wise to
run any device at its maximum rating. Thus for a 25 amp power supply you
would want to have more than
two 2N3055's in parallel. For the last supply I built, I used four.

If you used higher current rated transistors, you could get by with less of
them.
If you simply placed the multiple pass transistors in parallel,
slight differences in gain between them would cause unbalanced current flow.

The highest gain transistors would hog most of the current flow and most
likely fail.
To balance the current small value resistors called "Emitter Ballast
Resistors" are
added in series with the emitter lead of each transistor.
These can be between .01 to .1 ohms and should be of at least a five watt
dissipation.

wrote in message
...
With the gear hooked to the supply, even with it turned-off, when I
turn on the supply, the voltage transient cleans or erases the
programming in the radios. It's not the radio, as it does it with 2-3
different ones.

Does anyone have any idea how to solve this problem, or if a faulty
component might be causing it?

Theory of LM723 operation (courtesy David Metz):
[An Astron schematic, when reading, is helpful]

The LM723 is a twenty some year old IC designed to be a universal voltage
regulator.
Being cheap and well understood it found in most of our bench supplies and
is the core of the popular Astron series.

Any bench supply consists of a transformer with a secondary of about 18
volts AC,
a rectifier block and a filter capacitor. With no load, the DC voltage
across the terminals
of the filter are going to be 18 to 30 volts.

Under load the voltage will sag due to the impedance of the secondary of
the power transformer. If it sags too far, the supply will loose regulation
and it will pass 120 Hertz ripple (hum) to whatever you are powering with
it.

Since the voltage across the filter capacitor can vary wildly as the load
changes
we need a method of regulating the voltage. The work of regulation is done
by
the pass transistors (Q2 to Q5). They in turn are controlled by the 723
regulator.

Lets look at the 723 in a little more detail now. Note that it has its own
filter power
supply made up from diodes D1-D4 and filter capacitor C2.

The 723 has its own internal highly regulated voltage reference supply (pin
6).
Internally the 723 compares this reference voltage to the output of the
power supply.

Voltage adjustment pot RV1 sets the "ratio" of the reference voltage to the
output of the supply.
This sets the output voltage from the supply.

The output of the 723 is pin 10. This voltage drives the base of Q1. Q1
acts as a simple amplifier to increase the current available to drive the
current hungry bases of the pass transistors.

As the load increases on our power supply, the voltage from the wiper of
RV1 drops as well.
When this occurs the 723 increases the voltage from pin 10 driving the pass
transistors harder through Q1.
The more base current through the pass transistors, the higher the output
voltage.

Thus we have regulation, the 723 continuously changing its output voltage to
meet the minute changes in load on the
supply. Remember, the 723 does the thinking, the pass transistors do the
work!

THE PASSING LANE
Let's look a bit at what the pass transistors do. The key thing here is
current carrying capacity and heat dissipation.
In our example, lets say your power supply uses the common 2N3055 NPN power
transistor.

This transistor can pass up to 15 amps of collector current. Note that it is
not wise to
run any device at its maximum rating. Thus for a 25 amp power supply you
would want to have more than
two 2N3055's in parallel. For the last supply I built, I used four.

If you used higher current rated transistors, you could get by with less of
them.
If you simply placed the multiple pass transistors in parallel,
slight differences in gain between them would cause unbalanced current flow.

The highest gain transistors would hog most of the current flow and most
likely fail.
To balance the current small value resistors called "Emitter Ballast
Resistors" are
added in series with the emitter lead of each transistor.
These can be between .01 to .1 ohms and should be of at least a five watt
dissipation.

Well let's see, the size of the supply has nothing to do with the
problem I am experiencing!

The reason I am using an Astron 50 is because it also runs the HF rig,
and all the otehr 13.8 volt equipment in the shact with much reserve
current.

When I bought the supply (New) from AES to go with a brand new
TS-450S, I figured you only want to di this once, so I bought all I
thought I'd ever need.

Terry


On Fri, 11 Jul 2003 12:09:56 -0700, "Bob"
wrote:

If the Astron overshoots, you can verify it with an oscilloscope. If indeed
it does that, you can modify the circuit to reduce that.

Why are you using a 35 Ampere power supply for such a small load? It would
be better to use a lower current rated unit. I use a 20 Ampere unit and
have no such problem.

Looking at the diagram, you can put in a capacitor across the reference
voltage at the IC to reduce the turn on speed.

On the other hand, it's possible the problem arises due to too slow a turn
on of the supply. You can do things to improve that also. Also, the supply
may be oscillating. Try connecting a dummy load of, say, a few amperes
across the output. An automobile headlamp can work for that.

Best to verify the actual cause with an oscilloscope before starting to make
modifications.

73, Bob K6DDX

Well let's see, the size of the supply has nothing to do with the
problem I am experiencing!

The reason I am using an Astron 50 is because it also runs the HF rig,
and all the otehr 13.8 volt equipment in the shact with much reserve
current.

When I bought the supply (New) from AES to go with a brand new
TS-450S, I figured you only want to di this once, so I bought all I
thought I'd ever need.

Terry


On Fri, 11 Jul 2003 12:09:56 -0700, "Bob"
wrote:

If the Astron overshoots, you can verify it with an oscilloscope. If indeed
it does that, you can modify the circuit to reduce that.

Why are you using a 35 Ampere power supply for such a small load? It would
be better to use a lower current rated unit. I use a 20 Ampere unit and
have no such problem.

Looking at the diagram, you can put in a capacitor across the reference
voltage at the IC to reduce the turn on speed.

On the other hand, it's possible the problem arises due to too slow a turn
on of the supply. You can do things to improve that also. Also, the supply
may be oscillating. Try connecting a dummy load of, say, a few amperes
across the output. An automobile headlamp can work for that.

Best to verify the actual cause with an oscilloscope before starting to make
modifications.

73, Bob K6DDX