Power Supply

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Power Supply

Postby K9ACT » Wed Aug 25, 2010 10:05 am

In Steve's power supply, http://classeradio.com/power_supply_rev_d.pdf

What is the purpose of RY2 and R2?

Also, I was under the impression that some sort of step start was required for this sort of supply.

js
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Re: Power Supply

Postby kf1z » Wed Aug 25, 2010 2:47 pm

Ry2 is to provide switching of the DC supply. (DC side and AC side should both be switched, and NOT on the same relay)

R2 provides a means of quelling a spike (arc) when the relay closes or opens.

With the low power transformer from Steve, you will likely not need a step-start.

If you find you pop a circuit breaker on key up, then you do need to install one.
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Re: Power Supply

Postby K9ACT » Wed Aug 25, 2010 5:09 pm

kf1z wrote:Ry2 is to provide switching of the DC supply. (DC side and AC side should both be switched, and NOT on the same relay)

R2 provides a means of quelling a spike (arc) when the relay closes or opens.

With the low power transformer from Steve, you will likely not need a step-start.

If you find you pop a circuit breaker on key up, then you do need to install one.


Did you really mean key UP? What does up have to do with starting?

The other thing I do not understand is why I can't just leave the HV supply on all the time?

It works fine on my 48V version. When I unkey (key up), the relay opens between the mod and RF deck and nothing bad seems to happen while receiving. Does it have something to do with the fact that I am using a Kepco regulated supply?

js
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Re: Power Supply

Postby kf1z » Wed Aug 25, 2010 5:16 pm

Whatever
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Re: Power Supply

Postby K9ACT » Wed Aug 25, 2010 6:47 pm

kf1z wrote:Whatever


I wasn't trying be a wise guy. I am new at this solid state stuff and trying to make sure I understand what I am doing.

I see all sorts of exotic sequencers and need to sort things out.

When I see or hear "key up", I think of a telegraph key. This probably has something to do with being over 70.

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Re: Power Supply

Postby kf1z » Wed Aug 25, 2010 7:57 pm

Could be Jack.....

Thought the term probably DOES make more sense used in reference to the key as you put it.... "down" would be "on"....
Right or wrong, every time I hear it, it's "..key up the transmitter.." never hear "..key down the transmitter"... :D

Though I do hear the 11 meter guys saying "...key down bird watts.." :lol:



A sequencer of some sort is an absolute necessity.

Could be as simple as daisy-chained relays, where the next in line is actuated by the last, etc.

Or you can do a simple comparator and C/R ( ramped voltage ) 3 or 4 step deal.

There are some in expensive kits to accomplish it, but I have schematics that are pretty easy if anyone wishes.


The need is to get things on and off in the proper order. First on, last off.

With the HV DC being last one on, and first off.


As for leaving the PS on all the time....
Steve says it's a matter of the voltage from a linear supply tending to soar a bit too high with no load..
AND
More efficient to turn it off.


Also, less likely to burn and arc relay contacts if there isn't much voltage already on the filter caps when the transmit is actuated.
There is an easy, 4 component modification that can be done to slightly delay the "overload low" reset that delays the pulse-train from starting until JUST after the HV DC relay contacts close..
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Re: Power Supply

Postby K9ACT » Wed Aug 25, 2010 11:44 pm

Every HV supply I have ever built has a bleeder resistor in it, both for safety and to greatly improve regulation.

Seems like a "bleeder" is in order here also for the same reasons. I am not sure how much load it would take to keep it from soaring but I put a light bulb socket across the supply and will try different sized bulbs to find the min wattage needed.

I don't have enough caps to check it out but using about 2000 uF, the voltage only rises a few volts when I remove a 100W bulb. My guess is a 60 watt bulb will do the job and it won't exactly push my transformer for a 100W carrier.

Light bulbs are free and I have a really neat black light one that will provide the ambiance of a tube if it works.

js

BTW, "key the transmitter" takes the ambiguity out of it.
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Re: Power Supply

Postby kf1z » Thu Aug 26, 2010 8:16 am

There 'always' was a bleeder resistor in the PS schematic.

I wonder when and why it was removed?

The schematic I have says 15 to 25k ohm 2watt resistor.
From + to - of the DC supply...
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Re: Power Supply

Postby K9ACT » Thu Aug 26, 2010 9:28 am

kf1z wrote:There 'always' was a bleeder resistor in the PS schematic.

I wonder when and why it was removed?

The schematic I have says 15 to 25k ohm 2watt resistor.
From + to - of the DC supply...


Well, that covers the safety issue but it does not draw enough current to affect the regulation.

In a typical tube HV supply, you would have a 100K resistor for 2000V and dissipate 40W or 5% of the load.

For all practical purposes, 25K at 100V is no load at all.

My guess is that "efficiency" is the issue but I couldn't care less about that. It's only money.

What turns my crank is 150% modulation and I just wanted to see it happen.

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Re: Power Supply

Postby kf1z » Thu Aug 26, 2010 11:51 am

If things are sequenced correctly, there will be a brief moment (a few tens of milliseconds) when the DC supply relay is opened, and current will still be drawn through R1, because the PWM output board is still active.
So that draws the capacitor charge down a bit.

Then going from RX to TX... the PWM output board is made active JUST before the DC supply relay is activated, so there is already a load being drawn through R1.
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Re: Power Supply

Postby steve_qix » Wed Sep 01, 2010 12:04 pm

Wow, all this stuff :)

Ok - Grounds: The PWM output board has 2 main ground planes, and they are not connected together on purpose. The first ground plane is where the 18V power supply connects to the board along with the PWM signal coming from the PWM generator board. The ground point next to the +18V DC input should be grounded directly to the chassis or heat sink with a short lead. The other ground point is for the shield of the piece of coax carring the PWM signal from the PWM output board.

The other main ground plane is that formed by the damper diodes. There are several ground point thru holes on the board that will take a #14 wire. The wires from these thru holes to the actual ground plane (heat sink, usually) should be as short as practical.

A good, low ESR capacitors should be connected from the high voltage DC input, very near to the PWM output board, to the ground plane also. I use a 3uF 400 volt capacitor for the purpose, but the value is not particularly critical as long is it is a couple of uF or more.

Testing the PWM output board: With NO HIGH VOLTAGE, ground the PWM output board's output. That will bring the charge pump into operation. You can observe the output from the IXDD414 by looking at one of the gates of the modulator MOSFETs. You should see a reasonable square or rectangular waveform.
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Re: Power Supply

Postby steve_qix » Wed Sep 01, 2010 12:12 pm

Power Supply:

The power supply does not have a "bleeder" on purpose, other than a couple of fairly high value resistors, which are there to drain off the supply over a number of minutes (probably 20 or so) when things are turned off.

A traditional bleeder will be counterproductive for a number of reasons. First, you WANT the filter capacitors to stay charged between transmissions. This will significantly reduce stress on the rectifiers, relays and other components. 2nd, you do not want to add any more load to the supply than necessary. This is a capacitor input filter working into a pulse modulator. The less load on the supply, the better - except for the modulator iteslf. And, of course bleeder resistors make a lot of heat - another undesirable artifact.

If one needs to "drain" the supply quickly, simply turn off the AC to the high voltage supply while transmitting. The load will quickly drain the supply.

The DC output is disconnected ON PURPOSE during receive for a number of reasons. First, it's just safer, but more importantly, in the event of an overload, you DO NOT want to dump all of the energy stored in the power supply filter capacitor bank into whatever is going on to create an overload. The relays will disconnect the DC and the AC, and that's what you want. It isn't a good idea at all to leave either the power supply running all the time, under any circumstances. It should always be off when not transmitting. The pulse train is also killed when in receive and/or if there is an overload, assuming everything is constructed and connected (and adjusted) correctly.

Regards,

Steve
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Re: Power Supply

Postby kf1z » Wed Sep 01, 2010 2:40 pm

steve_qix wrote:Power Supply:

The power supply does not have a "bleeder" on purpose, other than a couple of fairly high value resistors, which are there to drain off the supply over a number of minutes (probably 20 or so) when things are turned off.

Steve



There used to be one shown in the schematics... but not in the newer version.....
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Re: Power Supply

Postby steve_qix » Wed Sep 01, 2010 4:21 pm

kf1z wrote:
steve_qix wrote:Power Supply:

The power supply does not have a "bleeder" on purpose, other than a couple of fairly high value resistors, which are there to drain off the supply over a number of minutes (probably 20 or so) when things are turned off.

Steve



There used to be one shown in the schematics... but not in the newer version.....


That is a mistake in the supply schematic. The resistor should be there. There is also no ground shown, but obviously everyone figured it out !

Thanks for pointing this out! I have corrected the schematic, and put the new version on the class E web site.

Regards,

Steve
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Re: Power Supply

Postby K9ACT » Wed Sep 01, 2010 11:49 pm

First of all, understand that I am not an engineer so many issues that are obvious to engineers are easily missed by my seat of the pants techniques. I have also learned over the years that many things engineers worry about don't necessarily cause grief if ignored. With that in mind, and the fact that what I am doing in this case seems to work for now (bang!), let's talk about this.....

steve_qix wrote:Power Supply:

A traditional bleeder will be counterproductive for a number of reasons. First, you WANT the filter capacitors to stay charged between transmissions.


Never thought of that but that assumes that you have a reason to shut off the supply between transmission. On a high voltage tube rig, this is always the way I design them, primarily for safety. It also turns out to be simple and straightforward up to a few thousand volts anyway.

Because of the issues of a cap input filter, there is a very good reason NOT to shut it off between transmissions, or more correctly, not to turn it on any more than necessary.

>This will significantly reduce stress on the rectifiers, relays and other components.

More reasons to leave it on.

>2nd, you do not want to add any more load to the supply than necessary.

A 25W light bulb across the supply with a 450VA transformer seems a small price to pay for the simplicity.

>The DC output is disconnected ON PURPOSE during receive for a number of reasons. First, it's just safer, but more importantly, in the event of an overload, you DO NOT want to dump all of the energy stored in the power supply filter capacitor bank into whatever is going on to create an overload.

It's not clear how an overload would occur during receive. In my setup, when I unkey, a relay opens the path between the mod output and the RF deck. With no load, there is nowhere for the HV to go during receive other than the light bulb which keeps the voltage from soaring.

Having said all this, keep in mind I am only running 100W and possibly, ignorance is bliss and it will blow up the next time I key it.

Your thoughts,

Jack
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