Hello,

I seldom have to work with high voltage/high power hardware, so I am looking for the safest low-cost approach. I am working with a TI Evalution Board/Reference Design for a Voltage Source Inverter. It requires a 350-400 VDC input (1.7A). My main objective or focus is on the firmware and power control algorithm and less so on power hardware design.

I found this ebay 350VDC SMPS Power Supply which has a fixed output at 350VDC @4.29A (Switch Mode Power Supply). I would like to be able to ramp up its output safely into the TI evaluation board and in fact in the TI User's Manual procedures generally call to start out at 50VDC and check firmware watch variables etc... before going full on.

From what I can tell I do not need a very clean and tightly regulated input into the board so long as it is between 350-400 DC. The user's guide also suggests a 100 Ohm load on the output side of the kit. I am guessing there are important power chain considerations from the input to the output side of the board that I will probably miss unless I ask the wise.

I am considering a rectifier or a voltage divider (like a power potentiometer) but I am pretty sure the power design considerations and component selection will be either limited or super costly. Hoping, for some thoughts and experiences about this approach? I basically want to control the output of the 350VDC SMPS say between 50VDC and 350VDC.

 

I don't see where it says your 350 VDC supply is isolated. Is there a reason why you think this suggestion from the TI datasheet may be unnecessary? I also question why you would buy a power supply from eBay. I don't know if that supply provides the necessary control to do what you want to do. If it was me, I'd use an adjustable lab supply to set voltages in between 0 and the maximum 350 V output.

 

A 350 volt, 4.29 Amp, DC power supply is certainly going to require very careful use, as it is able to deliver about 1500 watts when powered up.
To check out that reference design, as normally the check-out starts with a lower voltage, and then increments upward in steps.
My suggestion is to borrow, buy, or rent, a variable voltage transformer such as a "powerstat" or a "VARIAC", and start with a half wave rectifier to try operation at the recommended starting level of 50 volts.

 

Thank you @Papabravo I did miss the isolated requirements. I am a small one person consulting show. I do not have access to lab grade HV/HP supplies. My first search for high voltage power supplies were upwards of a few thousand dollars. I suspect the isolated requirement will only increase costs. I generally do not mind investing in equipment but in this rare one-off case I am afraid I would not have use for such a big-ticket item beyond this one project.

Perhaps I searched in all the wrong places and the prices were multiple of thousands hence I desperately took to ebay. Any suggestions for "Affordable" high voltage isolated supplies?

@MisterBill2 I do have a Variac so perhaps a rectifier would work for me? I assume that a Variac would be Isolated because of its "transformer" nature or is this bad assumption?

Without an isolated supply I suspect I would not be able to take safe measurements due to ground loops? Or could I get by with a differential O-scope probe (which I have) if I went non isolated?

 

Thank you @Papabravo I did miss the isolated requirements. I am a small one person consulting show. I do not have access to lab grade HV/HP supplies. My first search for high voltage power supplies were upwards of a few thousand dollars. I suspect the isolated requirement will only increase costs. I generally do not mind investing in equipment but in this rare one-off case I am afraid I would not have use for such a big-ticket item beyond this one project.

Perhaps I searched in all the wrong places and the prices were multiple of thousands hence I desperately took to ebay. Any suggestions for "Affordable" high voltage isolated supplies?

@MisterBill2 I do have a Variac so perhaps a rectifier would work for me? I assume that a Variac would be Isolated because of its "transformer" nature or is this bad assumption?

Without an isolated supply I suspect I would not be able to take safe measurements due to ground loops? Or could I get by with a differential O-scope probe (which I have) if I went non isolated?

Lab grade equipment can be had for resonable prices from retired rental equipment.

 

Lab grade equipment can be had for resonable prices from retired rental equipment.

Understood but this has not proven true for voltages over 200 VDC so far.

 

You can get that kind of voltage using a transformer from old tube equipment, but not at that power level. Maybe from an amateur radio transmitter? Try surplus dealers, and local ham radio clubs or forums; hams are prone to hoarding old equipment and parts. Keep in mind that transformer secondaries can be wired in series for more volts, so you could potentially get there with a couple of isolation transformers, or several audio power amplifier transformers.

 

I did not recall the actual project current requirements. The bad news is that most variable voltage transformers ARE NOT ISOLATED. But depending on the required current a simple voltage doubler can provide over 200 volts from the 120 volts mains.
AND, depending on the circuit, that 350 volt DC supply might provide a lower output from a lower input, if it is not regulated. AND, if you have a standard transformer 120/240 volts, that will allow you to assemble a simple rectifier supply to power with your variac, and have it isolated, and get the higher DC or close to it, for the initial checkout.

 

I did not recall the actual project current requirements. The bad news is that most variable voltage transformers ARE NOT ISOLATED. But depending on the required current a simple voltage doubler can provide over 200 volts from the 120 volts mains.
AND, depending on the circuit, that 350 volt DC supply might provide a lower output from a lower input, if it is not regulated. AND, if you have a standard transformer 120/240 volts, that will allow you to assemble a simple rectifier supply to power with your variac, and have it isolated, and get the higher DC or close to it, for the initial checkout.

The board silk screen on the DC input side says "350-400V 1.7A" .... These are very helpful insights and much appreciated.

 

I did not recall the actual project current requirements. The bad news is that most variable voltage transformers ARE NOT ISOLATED. But depending on the required current a simple voltage doubler can provide over 200 volts from the 120 volts mains.
AND, depending on the circuit, that 350 volt DC supply might provide a lower output from a lower input, if it is not regulated. AND, if you have a standard transformer 120/240 volts, that will allow you to assemble a simple rectifier supply to power with your variac, and have it isolated, and get the higher DC or close to it, for the initial checkout.

Maybe this project is similar to the ideas you are sharing?

 

After you do the lower input voltage tests then you can use that 350 volt supply. Do you know if that 350 volt supply is regulated? If not, you may be able to adjust the output by changing the input voltage with the variac. That would be very handy.

 

After you do the lower input voltage tests then you can use that 350 volt supply. Do you know if that 350 volt supply is regulated? If not, you may be able to adjust the output by changing the input voltage with the variac. That would be very handy.

Are you asking about the 350 Volt Supply I linked to from ebay ? If so it is a switch mode power supply so from that sense it is regulated.

 

Not all switchers are regulated to a fixed voltage, and not all of them are regulated.
OR maybe you did not buy that one.

 

Not all switchers are regulated to a fixed voltage, and not all of them are regulated.
OR maybe you did not buy that one.

I have not ordered the one from eBay yet no. However, I am intrigued - I thought switch mode would mean the switching regulating circuitry was “set in the design” - say by using a set resistor - to output a regulated voltage ?

So how would I know if it is regulated or not? For example the eBay page does not specify “regulated output explicitly” but it does say “constant voltage / constant current output” and has a +-10% on the input markings so would I take that to mean regulated?

 

The non-regulated device will probably be in the form of a switching inverter, rather than the buck or boost versions.
Really, an inverter will probably be the best choice.