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555 timer alternative for short duty cycle?

dump it back into the high voltage supply?

Version 4 SHEET 1 880 680 WIRE 336 -336 -352 -336 WIRE -352 -320 -352 -336 WIRE -352 -224 -352 -240 WIRE -336 -160 -352 -160 WIRE 48 -160 -256 -160 WIRE 144 -160 48 -160 WIRE 240 -160 144 -160 WIRE -352 -128 -352 -160 WIRE 48 -128 48 -160 WIRE 240 -80 240 -160 WIRE 336 -16 336 -336 WIRE 192 48 192 0 WIRE 192 48 -112 48 WIRE -112 64 -112 48 WIRE 240 80 240 16 WIRE 240 80 -16 80 WIRE 336 80 336 48 WIRE 336 80 240 80 WIRE 240 160 240 80 WIRE 512 160 240 160 WIRE 576 160 512 160 WIRE 704 160 656 160 WIRE -112 176 -112 144 WIRE -16 176 -16 80 WIRE -16 176 -112 176 WIRE 144 208 144 -160 WIRE 512 240 240 240 WIRE 704 240 512 240 WIRE 144 288 144 272 WIRE 240 288 240 240 WIRE 240 288 144 288 WIRE 240 304 240 288 WIRE 192 384 -48 384 WIRE -48 400 -48 384 WIRE 240 464 240 400 WIRE -48 512 -48 480 FLAG -48 512 0 FLAG -352 -48 0 FLAG -352 -224 0 FLAG 48 -64 0 FLAG 240 464 0 SYMBOL ind 688 144 R0 SYMATTR InstName L1 SYMATTR Value 4 SYMBOL nmos 192 304 R0 SYMATTR InstName M1 SYMATTR Value FDS2734 SYMBOL nmos 192 -80 R0 SYMATTR InstName M2 SYMATTR Value FDS2734 SYMBOL diode 320 -16 R0 SYMATTR InstName D1 SYMATTR Value MURS120 SYMBOL voltage -352 -336 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 4.5V SYMBOL voltage -352 -144 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value 120V SYMBOL voltage -112 48 R0 WINDOW 3 -387 50 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value PULSE(0 10 10m 1u 1u 2m 50m) SYMBOL cap 32 -128 R0 SYMATTR InstName C1

SYMBOL voltage -48 384 R0 WINDOW 3 -387 50 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V4 SYMATTR Value PULSE(0 10 10m 1u 1u 12m 50m) SYMBOL diode 160 272 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMATTR Value MURS120 SYMBOL res -240 -176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL res 672 144 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 55 SYMBOL res 528 256 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R3 SYMATTR Value 1Meg TEXT -508 312 Left 2 !.tran .1

Reply to
Lasse Langwadt Christensen
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Here's a real-world scope trace from a similar circuit:

The circuit (traditional drive, a 120VDC power supply and a 2K resistor)

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An actual selector magnet. 2 coils, in parallel, each about

1 inch in diameter and 1 inch long.

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Multiple Teletype cycles on a scope:

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One selector magnet decay time:

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That's 100v/div (there's a 100x resistor voltage divider before the scope, and a 10x probe), the spike is about 220V. It's decaying in about 300us. The SPICE model for the selector has to be way off. The current SPICE params are

L3 Vselector 0 4H Ipk=100mA Rser=55 Rpar=1000000

Rser is the measured resistance. Ipk is the safe maximum continuous current for the coil. 4H is what some Teletype literature says is the inductances. Rpar is completely bogus chosen to keep the spike amplitude from going insane.

In practice, ringing isn't the problem. I just need to worry about the power supply end, not the load end.

What all this Teletype stuff is for:

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I have more Teletype machines now and need to build about three more power supply/controller units. I'd like to power them entirely from a USB port. That's that this design is about.

John Nagle

Reply to
John Nagle

s,

to

s.

are

he

e
.

Visible short arcs typically drop between 20V and 30V, so they don't dissip ate much energy. It typically takes a few kV to initiate them, but the glow

-to-arc transition only takes microseconds, as you are only heating up a ve ry thin surface layer to it's melting point. It doesn't do the surface any good - which is why spark plugs don't last forever - but an arc discharge c an carry a lot of current with a relatively low voltage drop.

--
Bill Sloman, Sydney
Reply to
bill.sloman

Do you remember this?

Reply to
Michael A. Terrell

Thanks, Michael! ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     |
Reply to
Jim Thompson

You're welcome. They are adding a lot of old databooks.

--
Never piss off an Engineer! 

They don't get mad. 

They don't get even. 

They go for over unity! ;-)
Reply to
Michael A. Terrell

The higher the voltage you can maintain across the coil during de-energising the quicker i drops. You could just pick a resistor that does 4mA at 120v = 30k 0.5W.

NT

Reply to
tabbypurr

In AoE III, Figure 7.10.B, page 429, we show a simple configuration for a CMOS 555, that gives a nearly 0 to 100% duty cycle adjustment range with one pot, with constant frequency.

--
 Thanks, 
    - Win
Reply to
Winfield Hill

Voltage-controlled duty-cycle at constant frequency would be nice ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     |
Reply to
Jim Thompson

30k and 6H is a time constant of 180mSec. 60 mA into 30k is 108 watts and 1800V peak. The coil has stored energy of 3 * .06^2 = 0.0108 Joules, or Watt-Sec. If the energy is dumped in 20 mSec the average power is 0.54 watts.

It might be possible to hold the voltage at 120V by using a zener of that value. The peak power would be 7.2 watts, and would dump the energy in about

15 mSec.

Paul

Reply to
P E Schoen

I thought the coil took 4mA

certainly a faster option.

NT

Reply to
tabbypurr

out

use a diode and dump it back into the 120V supply

-Lasse

Reply to
Lasse Langwadt Christensen

How do you get 180msec? I make it 200 micro-sec. T=L/R

piglet

Reply to
piglet

You are correct. But I think my other calculations show that a 30k resistor is impractical, because of the 1800 volts. And the 108 watts would dissipate the 0.0108 J in 0.0108/108 = 100 uSec if the voltage were maintained.

Thanks for catching the error.

Paul

Reply to
P E Schoen

For a first switcher a 555 may not be the best option. Have a look at the UC3842-45 family they are nearly as cheap and plentiful as 555s and will do a beautiful boost converter with a lot less agony and heartache than a roll-you-own controller. Under-voltage lockout, cycle by cycle current limit, tight regulation and a 5V reference you can use for a few milliamperes of aux power are features hard to bolt on to 555 but come free with a UC3842!

piglet

Reply to
piglet

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