1uF @ 120V and 4H @ 60mA store the same energy, 7.2mJ
that's a place to start
-Lasse
-
Categories
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Need design for 120VDC 60mA constant current supply
1uF @ 120V and 4H @ 60mA store the same energy, 7.2mJ
that's a place to start
-Lasse
W
whit3rd
[ use two power supplies, and a class G type amplifier that
takes current from both]
The selector coil is floating, nicht wahr? A sense resistor on
the (-) terminal to ground is all it really needs, your low
voltage supply will power op amps and a grounded-base
transistor (base to +12V in this case) is the level
translation to the HV pass transistor.
J
James Arthur
James said:
Gee, no bites. Doesn't anyone like talking circuits?
Here's another hysteretic bucker, from scratch:
+120v
-+-
| D2
.-----------------------------o-----------|<----------------.
| Q1 | |
| 2n5401 | |
o------------. .-----o------)----o------------------. |
| e \ / c | | | | |
| --- | | - L1 _) |
| ___ | b .-. | ^ D1 4H _) |
0-----|___|----o | | R3 | | 55r _) |
| R1 | | | 1.8M| === | |
. | . 2.2k .-. '-' | GND | |
\ . | | | | | |
\ . SSR | | R2 | | o-----'
. | . '-' 5.6k | | |
| | | | |
.-. .----)-------' | |
| | R11 | | C1 | |
| | 680k | | || 470p | ___ |
'-' | o-----||-------)---|___|--. |
| | | || | R8 | ||--+
| ___ | |/ \| 47k | ||<-.
o--|___|--o--| Q2 Q3 |--------o .-----||--+ Q4
| R4 | |>. .<| | | |
| 39k .-. | | | | ___ |
| | | '------o-------' '--|--|___|--o-------.
| | | R5 | | R9 | |
| '-' 10k .-. | 15k .-. |
| | | | R7 Q2-3: | | | R10 --- C2
| === | | 470r 2n5550 | | | 33r --- 100n
| GND '-' MPSA42 | '-' |
| | | | |
| === | === ===
| GND | GND GND
'-------------------------------------------'
(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)
LTSpice says it draws about 3mA average, 5mA worst case.
This version is meant to be driven by the solid state relay (SSR)
IC1 shown in the OP's circuit here:
http://www.animats.com/nagle/aetheric/connecting.html
C2's kind of optional--it simplified analysis.
I don't think it gets much simpler than this. I did another
version using an IC switcher, but you still need a level shifter,
high-side switch, and Q4, so using an IC doesn't save much more
that a transistor and some discretes.
Cheers,
James Arthur
~~~~~~~~~~~
(Oh, I just used whatever diodes and such I had models for.
The 1n4148 isn't suitable; use a higher voltage diode.)
Version 4
SHEET 1 1520 680
WIRE 304 -192 -144 -192
WIRE 448 -192 304 -192
WIRE 832 -192 512 -192
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SYMBOL pnp 144 -32 M270
WINDOW 0 111 66 VLeft 0
WINDOW 3 80 84 VLeft 0
SYMATTR InstName Q1
SYMATTR Value 2N5401
SYMBOL diode 640 16 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL ind 720 -16 R0
SYMATTR InstName L1
SYMATTR Value 4H
SYMATTR SpiceLine Rser=55 Rpar=220k Cpar=1nF
SYMBOL res 720 464 R0
SYMATTR InstName R10
SYMATTR Value 33
SYMBOL npn 32 272 R0
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SYMBOL voltage -272 -80 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
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SYMATTR Value 120
SYMBOL res -176 336 R270
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WINDOW 3 0 56 VBottom 0
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SYMATTR Value 39k
SYMBOL res -48 336 R0
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL voltage -464 352 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value PULSE(0 120 10mS 100uS 100uS 20mS 40mS)
SYMATTR InstName V2
SYMBOL res 0 -32 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 2.2k
SYMBOL diode 512 -208 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL res 80 -16 R0
SYMATTR InstName R2
SYMATTR Value 5.6k
SYMBOL npn 368 272 M0
SYMATTR InstName Q3
SYMATTR Value 2N5550
SYMBOL res 192 368 R0
SYMATTR InstName R7
SYMATTR Value 470
SYMBOL res 608 416 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R9
SYMATTR Value 15k
SYMBOL res 192 -48 R0
SYMATTR InstName R3
SYMATTR Value 1.8meg
SYMBOL cap 240 192 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
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SYMATTR Value 470pF
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SYMATTR InstName R6
SYMATTR Value 47k
SYMBOL cap 800 496 R0
SYMATTR InstName C2
SYMATTR Value 100nF
TEXT 848 232 Left 0 !.tran 0 .2s 100uS 2uS
TEXT 888 -32 Left 0 ;Driver for a Teletype Model 15 selector\nmagnet
(L1).\n \n12-Mar-2009 by James Arthur
J
James Arthur
Jim said:
Your question was quasi-answered up thread.
The energy needed to charge to inductor is 60mA into 4H.
1/2 * L * i^2 = 0.5*4H*(0.06)^2 = 7.2mJ
1uF at 120v has the same, so that's ballpark. That's what
Nobody used. Whether you need more or less cap depends on
how you plan on using it.
The problem is charging that cap efficiently. I figured
to just skip that step and charge the inductor directly.
As to duty cycle and rep rate, IHNI--I was depending on
the OP. It seems they run at about 50 baud:
http://www.baudot.net/teletype/M15.htm
Cheers,
James Arthur
J
John Nagle
Right.
It looks like we have some good designs for an efficient driver
which requires an external 120VDC supply. The next step is to get
rid of the high voltage supply, and use some kind of up-converter
to charge up a capacitor with the 7.2mJ needed to pull in the
selector magnet. At 45.45 baud, one bit time is 22ms. Even
better, there can only be one 0 to 1 (SPACE to MARK) transition
every two bit times, so the charging system has maybe 1.8 bit times
or so to charge the capacitor. 75 baud is as fast as the mechanical
Teletypes ever got, so a 13ms bit time is the worst case, giving a
charging time of 23ms. So design for a 20ms charging time and a
1-2ms discharge time.
This is something like a "hammer driver" for a daisy wheel printer.
It would definitely be convenient to run the whole thing off
+5VDC. Right now, 90% of the hardware volume is the open
frame 120VDC 200mA supply.
John Nagle
J
John Nagle
James said:
Tried that in SPICE. During ON periods, the current through the selector
magnet is usually 60mA, but there are 1uS spikes to 200mA every
3ms. Not clear what's happening.
John Nagle
N
Nobody
That's the 1nF parallel capacitance specified for the inductor.
The 120V voltage pulses have a rise time of 1uS, with a peak slew rate of
~140V/uS, giving 140mA through the parallel capacitance, on top of the
60mA inductor current.
Yep, that's right. The real selector magnet will have considerable
capacitance. I didn't know the value, so I took a wild guess.
As far as getting rid of the 120v supply entirely, boost topology
off say +12v on the "hot" end of the coil, FET to GND on the cold end,
open the FET to dump the coil quickly?
That is, you might initially load up the boost coil (L1) to the
desired total energy, then let it fly back (single impulse)
through a rectifier, charging an appropriate capacitor to a
desired voltage, e.g. 1uF to 120v. The capacitor then decays
into and charges the selector magnet to the desired current.
In steady-state, maintain desired current with a low voltage supply
through a diode and resistor, as before, or switchmode, via SW1.
Open FET to dump the coil (L2).
Like this:
L1
.-.-.-. D1
+12v>----| | | |---o--->|-----o------.
| | |
SW1 \ C1 --- _) L2
| --- _) selector
=== | _) magnet
GND === | coil
GND |
||--'
||<-.
------||--+
|
===
GND
Cheers,
James Arthur
N
Nobody
LTSpice version:
Version 4
SHEET 1 940 680
WIRE 16 -144 -96 -144
WIRE 192 -144 96 -144
WIRE 288 -144 192 -144
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SYMATTR Value 5V
SYMBOL ind 0 -128 R270
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SYMATTR Value 630mH
SYMBOL sw 192 160 R180
SYMATTR InstName S1
SYMBOL voltage 320 128 R0
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SYMATTR Value PULSE(-1V 1V 20ms 1us 1us 20ms 100ms 5)
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SYMATTR InstName C1
SYMATTR Value 0.47µF
SYMBOL ind 736 -80 R0
SYMATTR InstName L2
SYMATTR Value 4H
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SYMBOL res 528 -64 R0
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL cap 624 -48 R0
SYMATTR InstName C2
SYMATTR Value 1µF
SYMBOL sw 752 304 R180
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SYMBOL voltage 880 256 R0
WINDOW 3 24 104 Invisible 0
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WINDOW 0 32 32 VTop 0
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SYMBOL schottky 704 112 R90
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SYMATTR InstName D2
TEXT -40 432 Left 0 !.model SW SW()
TEXT -130 506 Left 0 !.tran 500ms
J
James Arthur
Nobody said:
<snip>
Nice. I like your dump-snubber. Here's my reply (below).
I envision S1 being triggered on the rising edge of data,
with its ON-time controlled either by time (a 290uS one-shot)
or by a current sense limiter.
S2 would be controlled directly by the data level (high
= ON).
Cheers,
James Arthur
Version 4
SHEET 1 940 680
WIRE 16 -144 -96 -144
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SYMATTR Value 12v
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SYMATTR Value 1µF
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TEXT -40 432 Left 0 !.model SW SW()
TEXT -128 504 Left 0 !.tran 500ms
J
James Arthur
John said:
+5v is a pain--you can't charge the boost inductor quickly, and then
you need to stagger the switch timing. +12v wastes a little power,
but it makes the control circuitry simpler and faster.
Cheers,
James Arthur
J
James Arthur
Jim said:
Sure--it needs to be meaty, but that's standard switchmode
stuff these days.
It's low duty, low frequency. This toroid might be pushed
to 5.7A (we'd have to review the datasheet sat curve, but
20% reduced inductance at high current wouldn't hurt a
thing here):
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=M8842-ND
Cheers,
James Arthur
J
James Arthur
Jim said:
Me too. Gapped is the way to go. Here I just searched for
whatever Digikey had handy--saved me the calcs for a home-rolled.
Mouser's search is impossible for this -- slow, and won't permit
even a small subset of the range of Idc to search 3-7A chokes ...
grrr.
Cheers,
James Arthur
N
Nobody
Yeah, that makes more sense. I was thinking 1:1 current; don't know why.
I don't know how much of an issue the peak current will be, but you can
just increase the pulse width and inductor size if that's an issue. E.g.
2ms and 7.2mH gives 1.3A peak, 146mA RMS.
Also, I'm using 5V, which ISTR is what the OP said.
Regarding the current spike, the capacitor is also worth worrying about.
In the event that the capacitor fails open, the next pulse is going to
produce a rather nasty voltage spike.
That certainly makes the timing simpler.
J
James Arthur
Jim said:
Good point--this <50Hz app is pretty similar. I wonder how laminated
iron cores would stack up for this inductor. Surely spark coils
use 'em for good reason...
Peak current here could be reduced by raising the inductance,
but that's just as demanding on the inductor.
Everything else being the same, doubling turns gives:
o 4x inductance,
o 2x amp-turns per amp, cutting Isat rating in half
0.5 (4L) * (i/2)^2
------------------ = 1, so, no add'tl energy is stored by
0.5 (L) * (i)^2 just adding windings on a given core.
Cheers,
James Arthur
J
James Arthur
Jim Thompson wrote:
[snip]
That's pretty much what Nobody and I've been up to,
with a few variations. If John Nagle (the OP) doesn't
mind scrounging or winding an inductor, our work is done.
I Googled 'lightly' for laminated core inductors and learned
that those wound with hard-drawn copper _sound_ better too.
Something about added 'crispness' and 'brilliance,' I think.
So that's nice to know.
Cheers,
James Arthur
[snip]
That's pretty much what Nobody and I've been up to,
with a few variations. If John Nagle (the OP) doesn't
mind scrounging or winding an inductor, our work is done.
I Googled 'lightly' for laminated core inductors and learned
that those wound with hard-drawn copper _sound_ better too.
Something about added 'crispness' and 'brilliance,' I think.
So that's nice to know.
Cheers,
James Arthur
J
James Arthur
Nobody said:
Yep, and it's more power efficient during the steady-state.
I used +12v for speed and convenience.
It a) is, and b) will. A nice film cap should do well and last forever.
Cheers,
James Arthur
J
James Arthur
John said:
As one option your large +120v supply could be replaced with
a much smaller unit at this point.
If the selector coil can take it you could even cobble a 1:1
isolation transformer out of back-to-back wall warts or some
such, and use +170v. That'd be easy, with parts that are
widely available. A 1:1 audio transformer might even do for
just a few mA (check the ratings carefully first!). The switcher
uses jelly-bean parts as well--nothing that's hard to get.
The boost-inductor circuits are simpler and slick, but you might
have to scrounge for or make the boost inductor. JT was right
that--8mJ inductors are available, but not quite as dirt-common
as I'd thought.
Cheers,
James Arthur
J
James Arthur
James said:
Hey, here's one: 900uH, 6.7A, $1.95.
http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=9585
James Arthur
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