IXYS High Voltage current regulator

Adding a 100-ohm gate resistor stabilizes the 10m45s up to 120V (running at "10mA" with a 287-ohm resistor). From 120 to 200V it oscillated now and then at about 10-to-15MHz. This was using my Fluke meter as a load. With a non-inductive 15-ohms load resistor it's stable from RF oscillation to 260V where I stopped testing. It was also stable with drain voltage, only changing from 11.3 - 11.4mA from 10 - 260V. But I wonder, is it a bit persnickety for use with a sensitive radio?

In the T600 chassis, the 10M45 will be shunted to common by a 60uF at (+) and 20uF at (-), C41A and C41B. It is starting to sound like the oscillation is a result of a field effect adding additional poles into the loop around G-S.

Actually, my guess is it wouldn't oscillate in the radio application.

It's likely a better approach would be simply adding a gate resistor.

positive ------, 50mA high-voltage current source | d ,-- g | s --/\\/\\--+---- negative | 100 43 | '---/\\/\\--------'

The ixcp10m45s I measured has a substantially different Id-vs-Vgs plot than the dn2540n5, with a strong tailing- off of the drain current (and reduced g_m). This is a surprise, because the 10m45 apparently has a much larger die than the 2540, as is evident from its nice low 3.1 C/W thermal resistance, vs 8.3 C/W for the dn2540. On this basis alone the 10m45s would be preferred.

positive ------, 50mA high-voltage current source | d ixcp10m45s ,-- g | s --/\\/\\--+---- negative | 100 34 | '---/\\/\\--------'

I measured a nice stable 50mA current into a 15-ohm load (dropping 7.5V, similar to the string of tubes), over a voltage-drop range of 5 to 260 volts for the ixcp10m45s. There was no sign of oscillation with the 15-ohm load. (As reported, there was oscillation at high voltages if loaded only with a 1-ohm multimeter 200mA current-range.)

If one of these setups was used for a 90-volt drop, the FET would need to dissipate 4.5 watts without junction overheating, which would require a serious heatsink plus good airflow. It might be wise to add a 1k-ohm 10W power resistor in series to drop half the voltage.

Thanks for taking the time to make all those measurements, Win.

You're very welcome, Fred, the pleasure was mine. I'm sorry they dribbled out slowly over so many days, but I didn't have much time to spare for them. I've still got a few more badly-needed measurements to wrap up the scene.

Gents,

Have you seen this 50A1 substtute on eBay. This seller also offeres a 1L6 replacment.

Paul P.

eBay numner#

110164235153

Ah, I thought you knew about those, or had one. I purchased one last week, and it should arrive anytime now. I'll let you know how it's made.

I ran across more than few descriptions of that product in my search. It is based on the 10M45 and users say it works well. The seller has done a really good job with these and he has a website describing the design somewhere.

There may be several devices in the marketplace. The eBay fellow, eea101, has great looking stuff, and also he tells me he's a fan of AoE, so that's a good sign too!

I received it today and -- drumroll -- it's based on TI's high-voltage LM317, the TL783. It has a bridge rectifier, for ac operation, plus a 470-ohm 2W resistor, plus a TL783 and a 25-ohm current-setting resistor. I couldn't decipher the resistor's color coding (I suppose it said 24.9 ohms, but there was no red band), but it measured 25.0 ohms for a 50mA programmed current. Along with 470R, this means 25 to 150 volts of voltage-dropping operating capability.

eea101 uses the TO-220 package part, well suited to the serious heatsink he uses. But I note DigiKey has dropped the TO-220 version from their stocking list, as has Newark (why do they do that?), but Mouser has them, $1.60 ea.

I have seen the eBay offering before. I have been using

one for sale, last entry. It is based on the IXYS part. But he has been out of stock for a while.

Paul P.

What is he, a glass blower? Anyway, did you see my post late last night, in answer to Fred, wherein we learn that eea101's eBay item uses TI's TL783 chip,

TO-220 in stock at Mouser, p/n 595-TL783CKCSE3, $1.60

is the website of an old man nasmed Bill Turner who used to make replacement plastic dial covers for antique radios, along with other repruction parts. He has had multiple strokes over the past few years. You can find him on: news:rec.antiques.radio+phono newgroup.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

That's a great link, does he still sell and ship stuff? I'd like to place a nice order.

I have been calling him before placing an order. Like Mike mentioned there are some things that are out of stock due (I believe) to his recent stroke. Shipping is included in his prices.

Paul P.