S
server
Guest
message unavailable
Navigation
Install the app
How to install the app on iOS
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
More options
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
G
George Gonzalez
Guest
On Friday, September 1, 2017 at 1:56:39 AM UTC-5, John Nagle wrote:
Very long ago I found a AM radio by the side of the road in a pile of junk. It was a very cheap GE transformerless radio.
From it I salvaged the audio output transistor, a TO-66 style case. This transistor was fed right from the 120 VAC rectified power line so it was capable of handling 160 volts. I used it to switch the selector magnets on my Model 15 TTY, I forget if I wired it up as 20 or 60 mA. Anyway, that transistor worked just fine for years. Oh and for current limiting I had a resistor capable of dropping about 120 volts from the 160 volt DC power supply, so it must have been around 2K or 6K or so. So anyway, you don\'t need a constant-current driver so much, a resistor should work just fine.
On 08/31/2017 11:56 AM, Phil Hobbs wrote:
On 08/31/2017 02:33 PM, John Nagle wrote:
Is there anything later than the TL783 in a high-voltage (125V or so)
linear regulator? That\'s all DigiKey lists, and the TL783 is from 1981..
John Nagle
On the plus side, if you can handle the dropout voltage, it\'s a pretty
good chip.
Cheers
Phil Hobbs
It\'s the huge dropout voltage that\'s the problem. There has to
be about 15V between IN and OUT for it to work.
Linear Technology has some \"high voltage\" parts, but they top
out at 80V.
On Semi has a NCP781 150 V, 100 mA Very High Voltage Linear
Regulator, but the output voltage cannot exceed 15V.
Some other vendors have 60V parts. The TL783 is the
only part I can find that can regulate up to 120V.
There are some parts good up to 450V, but they require big
input/output differentials. They\'re for getting a little bit of
+5 directly from the AC line.
(The application is a driver for Teletype selector solenoids.
The upstream circuitry charges up a 2uf cap to 120V to provide
pull-in against the huge inductance, then dumps that into the
output. After discharge, a sustain supply takes over. I have
all that working for 220 ohm 5.2 henry selector magnets.
The problem is that there are several different magnets,
with different resistances and inductances. All of them need
60mA, and the big jolt from the cap will overcurrent the low
resistance solenoids. The higher resistance ones don\'t need
this protection. So I want to put current limiting to 60mA on
the output. It has to work over the voltage range 12-120VDC.)
John Nagle
Very long ago I found a AM radio by the side of the road in a pile of junk. It was a very cheap GE transformerless radio.
From it I salvaged the audio output transistor, a TO-66 style case. This transistor was fed right from the 120 VAC rectified power line so it was capable of handling 160 volts. I used it to switch the selector magnets on my Model 15 TTY, I forget if I wired it up as 20 or 60 mA. Anyway, that transistor worked just fine for years. Oh and for current limiting I had a resistor capable of dropping about 120 volts from the 160 volt DC power supply, so it must have been around 2K or 6K or so. So anyway, you don\'t need a constant-current driver so much, a resistor should work just fine.