How do I properly connect a bench power supply to a pulse generator for testing?

[kelly0303]

Hello! I am sorry if this questions is silly but I really don't know much about electronics.

I have a pulse generator (this one) and I want to test it with a low voltage for now. I have a bench power supply (something like this). I am confused about how to make the connections. For the pulse generator

I have a +HV and a -HV input. If I want to just use the +HV I understand that I need to ground the -HV. The bench power supply has 3 outputs: positive terminal, negative terminal and ground. Usually if I set a voltage on the bench power supply, that voltage gets applied between the positive and negative terminals. Does this mean that, if I set, let's say, a voltage of 20V on the bench power supply, the positive terminal will output 10V, the negative one -10V and the ground, by definition, 0V?

So if I want to use my pulse generator, I would need to connect the positive terminal to +HV, the ground to -HV and the negative one won't be connected to anything? And this also means that the voltage sent to the pulse generator will always be half of the one displayed on the bench power supply? Does this make sense or am I miss-understanding everything?

One more question: How do I make sure that the ground of the pulse generator is the same as the ground of the bench power supply? Is this because I plug them in the same AC source (the normal wall socket)?

 

[Baluncore]

Read the manuals.
• Risk of lethal electric shock. Do not touch the output or load while the PVX-4140 B is operating. This instrument produces LETHAL levels of electric current at its output.
• DO NOT OPERATE THIS INSTRUMENT UNLESS ANOTHER PERSON, CAPABLE OF RENDERING FIRST AID OR RESUSCITATION, IS PRESENT.
• SAFE AND PROPER OPERATION OF THIS INSTRUMENT IS THE RESPONSIBILITY OF THE USER.

How do I make sure that the ground of the pulse generator is the same as the ground of the bench power supply?

You MUST connect all earthy ground and 0V terminals together.

The pulse generator can produce a maximum 3.5 kV pulse between the +HV and -HV terminals. If you ground the -HV terminal, you get a positive 3.5 kV pulse from +HV, referenced to ground. If you ground the +HV terminal, you get a negative 3.5 kV pulse from -HV, referenced to ground.

 

[kelly0303]

Read the manuals.
• Risk of lethal electric shock. Do not touch the output or load while the PVX-4140 B is operating. This instrument produces LETHAL levels of electric current at its output.
• DO NOT OPERATE THIS INSTRUMENT UNLESS ANOTHER PERSON, CAPABLE OF RENDERING FIRST AID OR RESUSCITATION, IS PRESENT.
• SAFE AND PROPER OPERATION OF THIS INSTRUMENT IS THE RESPONSIBILITY OF THE USER.You MUST connect all earthy ground and 0V terminals together.

The pulse generator can produce a maximum 3.5 kV pulse between the +HV and -HV terminals. If you ground the -HV terminal, you get a positive 3.5 kV pulse from +HV, referenced to ground. If you ground the +HV terminal, you get a negative 3.5 kV pulse from -HV, referenced to ground.

Thank you for your reply. I read the manual of the 2 devices individually, I am just not sure how to connect them. Given that the bench power supply can supply at most 30 V, I will go nowhere near 3.5 kV (for now I want to do a test at low voltage).

As far as I understand, the pulse generator has the ground from the AC power supply. I am not sure how to then connect this ground of the pulse generator to the ground of the bench power supply.

Basically I didn't understand from the manuals how to connect the 2 devices (as each manual describe each device independently). I would just like to know how to connect the 3 output of the bench power supply (positive, negative and ground) to the 2 inputs of the pulse generator (+HV and -HV), assuming I want the -HV to be grounded.

 

[Baluncore]

It appears that the HV inputs and outputs are all coaxial connectors, with the outer screen connected to the grounded chassis.
Join ground and (-)ve on your DC power supply, to produce 0V and +V.
Connect 0V to -HV input, and +V to +HV input.
Connect the outer screen of the -HV input to 0V.

 

[Tom.G]

After reading the manual from the Directed Energy website
(https://directedenergy.com/wp-content/uploads/2020/02/PVX-4140-B-Operating-Manual.pdf)
the device is essentially a switch with fast pulse edges.

The Grounding is done with the 3-prong power cord, so be sure to plug it into a properly wired 3-prong outlet.

If you want Positive output pulses you will be using the + HV Input, then your Power Supply should have the -(Minus) connected to Ground and to the shell of the + HV Input connector on the DirectedEnergy pulser. The Power supply +(Plus) would then connect to the Center terminal of the + HV Input connector.

Note that the backpanel Output and HV Input connectors are type SHV, a little harder to find than their look-alike type BNC connectors. The SHV are necessary to handle the higher voltages.

The Output voltage is whatever voltage you feed it on HV Input connectors on the back panel.

You must supply a +5V level to the Gate input on the front panel to get an output signal.
See 4.3 Gate Input on pg. 6 of the User manual.

Note the requirement for a fast risetime for the pulse (<20 ns), and that the Gate input is a 50 Ohm load. You will need a Pulse Generator that meets these voltage, risetime, and 50 Ohm load requirements.

Have Fun!... (and I'm curious, what will you be using this for?)

Cheers,
Tom

 

[Baluncore]

https://en.wikipedia.org/wiki/SHV_connector
New SHV connectors can be expensive. You can get them from China via eBay.
For voltages below 50 V you might improvise by modifying a BNC or SNC connector.

 

[kelly0303]

After reading the manual from the Directed Energy website
(https://directedenergy.com/wp-content/uploads/2020/02/PVX-4140-B-Operating-Manual.pdf)
the device is essentially a switch with fast pulse edges.

The Grounding is done with the 3-prong power cord, so be sure to plug it into a properly wired 3-prong outlet.

If you want Positive output pulses you will be using the + HV Input, then your Power Supply should have the -(Minus) connected to Ground and to the shell of the + HV Input connector on the DirectedEnergy pulser. The Power supply +(Plus) would then connect to the Center terminal of the + HV Input connector.

Note that the backpanel Output and HV Input connectors are type SHV, a little harder to find than their look-alike type BNC connectors. The SHV are necessary to handle the higher voltages.

The Output voltage is whatever voltage you feed it on HV Input connectors on the back panel.

You must supply a +5V level to the Gate input on the front panel to get an output signal.
See 4.3 Gate Input on pg. 6 of the User manual.

Note the requirement for a fast risetime for the pulse (<20 ns), and that the Gate input is a 50 Ohm load. You will need a Pulse Generator that meets these voltage, risetime, and 50 Ohm load requirements.

Have Fun!... (and I'm curious, what will you be using this for?)

Cheers,
Tom

@Baluncore @Tom.G thanks a lot for your help! This makes perfect sense now. The power cord I am using is this one and I plug it into a wall socket (I am in the USA so it would be 110 V of AC at 50 Hz). One quick question, I see that you suggest I should connect the Ground of the DC voltage supply to the shell of the +HV input of the pulse generator. I assume that this is such that the 2 devices to have the same ground. However, for the DC voltage supply I am using exactly the same power cord and also plugging it in a wall socket. Shouldn't the 2 devices then automatically have the same ground (isn't this the point of having a ground in the wall socket, such that all devices have the same ground)?

I am using this to control a pulse valve (we are building an ion source and we want to release some gas at some fixed intervals of time). However, the valve only needs 28 V (at 0.4 A) so this device going up to 3.5 kV is a bit of an overkill probably, but we had it around in the lab so I decided to give it a try (and also learn how to use it meanwhile).

We do have some SHV around and I learned how to tell them apart from BNC. It is the MHV ones that always confuse me!

 

[Baluncore]

However, for the DC voltage supply I am using exactly the same power cord and also plugging it in a wall socket. Shouldn't the 2 devices then automatically have the same ground (isn't this the point of having a ground in the wall socket, such that all devices have the same ground)?

That is probable, but you do not want your power currents running through the PE, protective Earth circuit for your house.
You can never be certain that the PE will be connected inside an instrument, or in a wall power socket.

 

[kelly0303]

That is probable, but you do not want your power currents running through the PE, protective Earth circuit for your house.
You can never be certain that the PE will be connected inside an instrument, or in a wall power socket.

That makes sense.

In the BNC case, sometimes I use a 50 Ohm terminal to ground a given channel. Is there something similar I can use for the SHV output of the -HV channel (i.e. connect the pin directly to its shell)?

Also, are there other DC power supplies that can be more easily used for this application, ideally something that has coaxial outputs that I can directly connect to the pulse generator?

 

[tech99]

It strikes me that to use a 3.5 kV generator for something requiring 28 V is creating unnecessary risk. I don't think this would stand up in law if it were the UK.

 

[Tom.G]

I'm glad you didn't have to buy the Directed Energy device, it can supply only 0.05A (50mA) 0.1A (100mA) of output current!

You would be much better off just using a transistor or two as an amplifier after a pulse generator... especially as you would need a pulse generator to drive the Directed Energy device anyhow.

(Remember, projects can get complicated, but should not be more complex than needed. )

Cheers,
Tom

 

[kelly0303]

It strikes me that to use a 3.5 kV generator for something requiring 28 V is creating unnecessary risk. I don't think this would stand up in law if it were the UK.

I am not using a 3.5 kV generator. The DC voltage supply goes only up to 30 V, and that is as much as the pulse generator will go, too. 3.5 kV is the maximum I can go in voltage for the pulse generator if I need to, so I don't think there are any risks, no?

 

[kelly0303]

I'm glad you didn't have to buy the Directed Energy device, it can supply only 0.05A (50mA) of output current!

You would be much better off just using a transistor or two as an amplifier after a pulse generator... especially as you would need a pulse generator to drive the Directed Energy device anyhow.

(Remember, projects can get complicated, but should not be more complex than needed. )

Cheers,
Tom

Wait I am confused, in the manual it says:

The instrument features an output voltage swing of up to 3500 V, peak current of up to 25 A, and continuous current of up to 0.1 A.

Did I miss something in the manual?

 

[Tom.G]

Did I miss something in the manual?

No. I mis-remembered it while typing.
Now corrected in my earlier post.
Thanks for pointing it out!

 

[kelly0303]

No. I mis-remembered it while typing.
Now corrected in my earlier post.
Thanks for pointing it out!

But I am a bit confused now. In my case I need to generate pulses about 30 ms long, once every ~1s. Does this count as continuous current (0.1 A) or peak current (25 A)? (based on your comment I would say it is continuous, but I am not sure I understand why)

 

[Tom.G]

Unspecified therefore unknown, try it and see what happens... then please let us know the results.

 

[kelly0303]

Unspecified therefore unknown, try it and see what happens... then please let us know the results.

What would happen if I go over the current? I mean will the device beak, or it has something that prevents me to go over that value (as it is the case for bench power supplies)?

 

[rbelli1]

You have a multi thousand dollar device that may or may not burn up if you use it to drive the valve. If you switch to using a transistor and a diode, you can can have a sub one dollar circuit that will almost certainly work.

I would suggest starting out with the simplest circuit and then get more complicated if warranted.

BoB

 

[DaveE]

the valve only needs 28 V (at 0.4 A) so this device going up to 3.5 kV is a bit of an overkill probably

Probably?

It strikes me that to use a 3.5 kV generator for something requiring 28 V is creating unnecessary risk.

You would be much better off just using a transistor or two as an amplifier after a pulse generator.

You have a multi thousand dollar device that may or may not burn up if you use it to drive the valve. If you switch to using a transistor and a diode, you can can have a sub one dollar circuit that will almost certainly work.

I would suggest starting out with the simplest circuit and then get more complicated if warranted.

OK, I'll add the 4th (at least) vote. You are headed down the wrong path here. It's not that you couldn't make it work (maybe). It's just a bad, potentially dangerous, design. Sorry to be blunt, but I have never met a competent EE that would use a 3.5KV pulse generator to control a 28V device.

If you can't do this design at reasonable voltages, you aren't qualified to be dealing with very high voltages. Please be careful. Avoid unnecessary risks. In any case, since you'll probably ignore our advice, do a FMEA (Failure Modes and Effects Analysis). What will happen if your control circuit doesn't work the way you expect, what if parts break, what if there are issues you don't know about. Please design a robust system that simply CAN'T MAKE DANGEROUS VOLTAGES, particularly since we don't think you need them.

 

[Baluncore]

Please design a robust system that simply CAN'T MAKE DANGEROUS VOLTAGES, particularly since we don't think you need them.

The pulse generator can only output what is input. 30 V max from the lab supply.

I am using this to control a pulse valve (we are building an ion source and we want to release some gas at some fixed intervals of time). However, the valve only needs 28 V (at 0.4 A) so this device going up to 3.5 kV is a bit of an overkill probably, but we had it around in the lab so I decided to give it a try (and also learn how to use it meanwhile).

You could also buy a cheap 'DC solid state relay' to replace the entire 3.5 kV pulse generator box. But the way you are doing it with a 19" rack module will be a bit more impressive.

If the valve is a solenoid valve, then I would use a $1 N-channel MOSFET, with a fly-back diode across the solenoid to catch the turn-off spike. A logic level MOSFET could be driven directly by your gas inject signal, or a 555 timer chip.