Everything You Need To Know To Find The Best high voltage diode

#1 November 11, , 05:07:54 PM Last Edit: November 11, , 05:11:02 PM by klugesmith Didn't know they came in SMD.  In one kind, the round wires from traditional axial package are formed into a kind of J-lead, and molded plastic shape is prismatic.  The other kind appears to be a MELF.


So here are questions, not answers, for you.  Would you solder SMD parts to each other, or to some circuit-board-like substrate?   What's your plan for cooling the diodes?  How will you meet air gap and surface creepage spacing rules for the working voltage? 
Are you making a high frequency rectifier, and are 1N diodes fast enough?

[edit] For applications where long string of 1N's is appropriate, stacking those MELF parts in an insulating tube without solder could be very handy. Must consider contact pressure, cooling, and corrosion.

Quote from: klugesmith on November 11, , 05:07:54 PMstacking those MELF parts in an insulating tube without solder could be very handy.

That's such a simple and brilliant idea! Have to remember that one. Probably works for resistors, too.


Kind regards,
Max

Quote from: klugesmith on November 11, , 05:07:54 PM


So here are questions, not answers, for you.  Would you solder SMD parts to each other, or to some circuit-board-like substrate?   What's your plan for cooling the diodes?  How will you meet air gap and surface creepage spacing rules for the working voltage? 

I plan solder that with thin and put them in oil

Quote from: klugesmith on November 11, , 05:07:54 PM

Are you making a high frequency rectifier, and are 1N diodes fast enough?

Is necessary use fast diode for CW multiplier?

Quote
Is necessary use fast diode for CW multiplier?

It depends on the frequency. As far as I know, Cockroft and Walton got their high voltage without high frequency. i might ask if anybody here know the dynamics of HV vacuum rectifiers. But the answer is on the Internet for self discovery.

Quote from: klugesmith on November 12, , 05:44:35 AM

It depends on the frequency. As far as I know, Cockroft and Walton got their high voltage without high frequency. i might ask if anybody here know the dynamics of HV vacuum rectifiers. But the answer is on the Internet for self discovery.

I plan use a ZVS that frequency affect the diodes? I'm not a CW voltage multiplier expert. I've only built one, although it is a nice 14-stage one. You can see info about it in this section. I also use a ZVS driver. The ZVS driver in combination with a flyback transformer merely forms a high voltage oscillator to drive the multiplier stack. The diodes need to be fast enough to respond to the driving frequency. High voltage diodes with reverse recovery times of 100 ns are commonly available and work well with typical driving frequencies. That's what I use. I believe that matching and balancing is only an issue for diodes in parallel. In a series configuration it doesn't really matter as long as the individual diodes are the same type. Diodes in a series connection is the standard method of implementing a high voltage diode. As an example look at the HV rectifier circuits for X-Ray transformers. They consist of many diodes in series.

Quote from: MRMILSTAR on November 16, , 04:57:27 PM
I believe that matching and balancing is only an issue for diodes in parallel. In a series configuration it doesn't really matter as long as the individual diodes are the same type. Diodes in a series connection is the standard method of implementing a high voltage diode. As an example look at the HV rectifier circuits for X-Ray transformers. They consist of many diodes in series.

Can't find the thread now but there was lengthy discussion about diodes in series for HV in a 4hv thread from long ago, here's a related post. Right click and open image in new tab to see the text.

Here is a simple way to check and verify if a high voltage diode is good or bad. We'll be checking a HVR-1X-3 that came from a microwave oven in this case. First, let's find the data sheet for reference on the HVR-1X-3. A quick search on Google, and I came upon a link from alldatasheet that described this as a 12,000 volt diode, rated at 500mA.

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High voltage diodes cannot be accurately tested with the diode test function of a DMM. Basically a high voltage diode is comprised of several lower voltage diodes placed in series, to increase the operating voltage. Since they are in series, you won't be able to see the 0.6 volt forward voltage as you would in a conventional single diode test on a DMM. So, we need to find another way to test the diode.

For this you will need a variable power supply with adjustable current limiting (any typical bench supply, such as a 0-24 volt would test most high voltage diodes).

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For the first step, we are going to try and forward bias, or turn on the diode in question. On your power supply, the first thing you will want to do is set the current limiting to 100mA (remember this is a 500mA diode and we want to be less than that amount). Next, turn the voltage all the way down on the power supply. Hook up the diode as shown in the diagram below. Place the meter to show the current if the power supply only has one display. Now, slowly turn up the voltage while watching the current draw. If the diode is good, at some point you will see the current rise to 100mA and stay at that value (the current limiting has activated on the power supply). Right at the point the current limits to 100mA, the diode is forward conducting or turned on. Depending on the voltage rating of the diode, the power supply will be showing something on the order of 6 volts, 12 volts, or more. If you happen to have a current draw immediately when you hook up the diode (power supply will basically be at zero volts as you try to increase the supply voltage), it is probably shorted.

Next, we'll just check the reverse bias condition of the diode. Turn the voltage back down on the power supply. Now 'flip' how the diode is hooked up to the leads. Again, slowly raise the voltage on the power supply. This time you should not see any current draw on the power supply as you raise the voltage all the way up to the maximum amount. This indicates the diode is not showing any leakage in the reverse bias condition.

This makes a quick and easy test on most high voltage diodes, and you don't need any special equipment to accomplish this. Just remember to limit the current to the diode accordingly when you do this test.