# Can I use diodes to protect power supply outputs?

(Note, this is my first question on this site, please point out if there is something that I am doing wrong here.)

I have a thyratron that requires two separate power lines to attach to it. The two power lines meet at a single terminal on the thyratron tube.

One of the lines is a -100 volt DC and 100 milli-amp bias.

The other line is a series of 200 V pulses that are sent out at a frequency of 10 hertz. The pulses last for 0.4 micro seconds and have a rise and fall time of 1.5 kV/uS (the 200 V needs to be reached in 7.5 uS or less). Please also note that the pulses are only positive, so there are just 10 of these every second.

Since the pulses would probably mess up the DC bias, it seems reasonable that I would put a capacitor between the terminal and the pulse source and an inductor between the DC source and the terminal.

My question is, how should I calculate the capacitance and inductance that will be needed?

Also, could I just use a diode to protect the DC and pulse source?

Here is link to the basics of a thyratron: https://en.wikipedia.org/wiki/Thyratron

simulate this circuit – Schematic created using CircuitLab

• Welcome to EE.SE. A schematic is better than words. You can add one in using the CircuitLab button on the editor toolbar. Double-click a component to edit its properties. 'R' = rotate, 'H' = horizontal flip. 'V' = vertical flip. Note that when you use the CircuitLab button on the editor toolbar an editable schematic is saved in your post. That makes it easy for us to copy and edit in our answers. You don't need a CircuitLab account, no screengrabs, no image uploads, no background grid. – Transistor Jul 6 '19 at 18:49
• @Transistor Thanks for the advice, just put it in. Its a really cool feature, I think I'll use that for my own designing! – James Li Jul 6 '19 at 19:07
• Good work, but it doesn't clear up much. Where's the thyristor? (CircuitLab has one at the bottom of the component library.) When you say "thyristor tube" what exactly do you mean? (It sounds like something made of glass.) Have you got a part number and a link? What is the circuit supposed to do? – Transistor Jul 6 '19 at 19:21
• @Transistor I got two things confused, I should have said "Thyratron," not thyristor. The node labeled "terminal" in the diagram is found on the thyratron. It is a CX-1538 R made by English Electronics. One of the things that the thyratron needs is the bias voltage and the trigger pulse voltage to be applied to the same place. I don't have a detailed diagram of the thyratron. – James Li Jul 6 '19 at 19:26
• Hit the edit link again to correct the thyristor error ... Add in a link to a good introductory text to educate those of us (including me) that have never heard of a thyratron. The 100 mA source may be OK. What's the source impedance of the square wave? – Transistor Jul 6 '19 at 19:38