Inferno #09 31 июля 2006

Железо

DIY - The scheme to protect your computer from the surge.

        For what and why


   This scheme protects your computer from the ne
renapryazheniya the chain of supply of +5 V, ie all
basic logic of the company. It allows you to
easy to use home-made pulse
nye voltage converters, as a rule
Lo-lowering type of high (with rectifier
mitelya secondary housing) to 5V.

   But to be fully effective protection of all
as necessary to fulfill certain requirements, and
This electronic unit only part of them!

   Let me remind everyone that the momentum transformation
converter (on) can seriously (c) save
electricity, which starts becoming ak
lectual and in our country, not (yet ve
sma) its inexpensive price. A Reliability
well-designed discrete blocks are not conditions
Tupa good integral analogues and
comparable with conventional stabilizers, although
more cumbersome, and options with a decreasing
transformer are inferior (in fact, only)
weights and dimensions, providing even greater
decoupling network, security and reliability
sequence. Therefore, if the data deficiencies you
are not confused, then think about the implementation
Pulse bloka.Eto will provide you with pain
Shay usefully spend headroom
transformer, using trance with (from
relatively) high voltage, which
(Possibly) long are you without cause, and
seriously alleviate the temperature regime (in
If internal power supply), not govo
series is already an excess of capacity for expansion.
But this later ...

   It is no secret that many fans of electro
nicks and experiments with it, which took place
school experience, and not associating it with the theory,
and lumped lumps fatal results
will not produce a pulse
power supply. The most reasonable of them
want to jeopardize their (fed)
technique, from a lack of proper knowledge
the design / manufacturing unit. Bo
more daring can practice at the camp
dard published, this scheme
and not worry about the security company. A
the most suspicious (and lazy) just settlement
tavyat Krenke - threelegged integral hundred
stabilizer - and forget about all these topics, wasps
vobodivshis of minuses, and rejecting the possibility
nye plyusy.K latter include those
who buys a modern UPS from your PC, and my
including. But why would I then write about
this? Because I have such a unit, and he
I was never led, and the stock of its powerful
STI to me is enough.

   A matter of principle ... First, I like
electronics and its effective application.
Secondly, my system (future) need
its own power, with an electronic UPRA
resistivity, but I do like it on the basis of
(I think) Polish UPS watts to 100, and then
lko at 12 V, ie I still have a transformation
Vatel from 12 to 5 and, of course, without unnecessary
losses. Impulsnik made himself perfectly, with
multistage input / output filtration
to her, e-governance and natural
cooling (silent), and do not want to
reduce its parameters (as a whole is ready
second, separate unit) simple pulse
lyapom. But as a cautious man, I can not
exclude any and all damages and disturbances
zhnost surge and should protect
complex from an annoying, albeit accidentally, Nep
redskazuemogo (not that ridiculous) vyho
let down. Using modern components
components are very affordable, you can build
it is very effective and simple transformations
transducer with elements of protection, but the quality
implementation is determined by the manufacturer and
does not guarantee (of course, cases
marriage is very rare, but you would like to see on
such a case you fell?). Also, can not be used
be disconnected damage statics delivery
(You do not personally accompanied the chip). Therefore,
not in vain in modern electronics (the most
different - but firm, well-known brands)
a lot of protection circuits - literally limit
fuse, the currents, even milliamps!
Which one can conclude? .. Pra
correctly! Use, duplicate protection, in
than do it as competently, and then
Then can create a new, albeit unknown and
this, albeit not as polished, but
Always refer to the protection and well-
Analyze the results of her work!

   We return to our teme.Hotite his impu
lsnik or vending simple variant
ant at the current chip, and afraid for the naked
manual ultrasonic inspection - then Assemble yourselves, to 
work scheme We protect, implement them (they are all dostato

chno simple and therefore very reliable), and contributed
coin collect impulsnik!


                 Description


   Presented here is the protection scheme
is an independent unit, shunting 5-wills
tovoe power system at a certain threshold
govom voltage (overvoltage). Scheme
has a trigger effect, and sraba
tyvanii dramatically reduces the supply voltage,
so that system performance becomes impossible either
zhnoy (as happens to the closure of the food
but not short). Circuitry protection more
than the classical one, based on an analogue of the powerful
zener diode, formed a chain back
connection of collectors on the base of the transistor, Th
denote the actual zener, Koror open
is called when the voltage exceeds the avalanche
of controlled breakdown (according to their
technical parameters) and sets the base current
transistor, which, in terms of coefficients
its gain coefficient (of course Hfe) will
collector current. In general, an increase in
voltage above a certain value of
current from the power supply will flow through a powerful 
spectrum nzistor (past the loading waste). Steepness

dependence of current on voltage, prick
ladyvaemogo to the load will be very large
- Exponential, because voltage from
indoor zener almost unchanged and
the difference of voltage butts
is called a Bose-Einstein transition of the transistor, which
and this dictates the dependence of base current (and
equivalents, in proportion, and the current collector
torus) of napryazheniya.A since the transistor
powerful and can pass through itself Bechet
current, then, accordingly, this current can
burn the fuse (at the entrance of the PD
at work overload), unless he
BP will provide the current. Well, if
can not and will continue to work, the load
will still be protected, and the voltage
exceeds a critical value. True,
part of the energy will be useless drain -
dissipated as heat through the defense -
power transistor on the heatsink.

   It is worth mentioning that any such
protection is based on a minimum
overexertion. T.e.takom excess of nominal
tional stress at which memory device
to be stable rabotat.Eto voltage
less than the maximum allowable, but that itself
some excess already clearly defines the need
conductivity response zaschity.V our case
I decided to improve the scheme and to introduce
trigger effect. The fact that the effect
Response vysheopisanoy protection during probes
lemah almost (and most do) is not noticeable.
Well, pokontrastney was a picture, louder
sound (and barely) warm body system
theme (how long have you fingered it, and so it heats
Xia ...). Before the PSU completely fails / etc, can
Jette take a long time, and the care of the stress
tion to the next higher post may be
gradual and imperceptible at ekspluatatsii.Krome
Furthermore, if protection is a big shunt
current, dissipated power (very large
Shua) should be somewhere in a computer to dissipate,
nothing is overheating. Hence, increasing
dimensions of the radiator and, accordingly, all
Site zaschity.Ne very pleasant this shadow
energy consumption. There is also something chto.Bolshoy
shunt current (possibly Actuating
lines) in the chain of collectors require proportional
flax large base current and, accordingly,
high-power zener diode in its circuits, again, with
appreciable size. A normal,
pre-emergency operating voltage Th
cut it will ooze a significant current loss
(Referring to stress when he hundred
bilitron already broken, but on the basis of not dos
sufficiently high voltage and power transistors
transistors still closed).

   To eliminate these shortcomings, I can
modernized the scheme, adding a trigger effect
effect, and it has improved its performance. Those
Now Zener transition opens at tiri
transistor, and the one actuating almost closes base
and a collector of power transistor. As a result,
supply voltage drops, and the system
clearly for the protection operation, the permutation
em to work. Small voltage drop
on the transistor, with possible high current,
reduces power dissipation losses and
Greve, which allows us to host defense
more compact, although the dimensions of the thyristor
my take ... Since the control circuit
thyristor very low-current, it can be used
to use a weak diode, and losses
current node protection, until it does not work, bu
FLS small. And the opening, he distinguished thyristor
rzhivaet amps of current, being impulsive
key, and the maximum current at operation
protection can reach hundreds of amperes (in the chain
collector, a pulse from the discharge capacitor
operators in the food chain BP and companies), and stress
the mains will have a much lower limit
separately, will not damage the chip.


           Next of parasites ...


   Parasitic thyristor effect - is to
is positive feedback, which reduces the
their immunity. It is based on the parameters
razitnoy capacity in the semiconductor junction, as a result
As a result of which, with the rapid growth of the NAP
masking in closed thyristor formed
stray current impulse control (such as
charging the parasitic capacitance), which can
Jette open thyristor, in our case, entangled
Steve avalanche process operation
protection (if the voltage is suddenly very quickly
podskochet, albeit on a small value).
In our case, it can be regarded as
Plus, because when emergency long public key
Th in the UPS current and, correspondingly, the voltage
the load will rapidly increase,
and then should work site protection. But
to exclude the effect of noise is better
desc limit the speed of stress
of, and why are the capacitors on the circuit
IU. In any case, the electrolytes in the chain of pi
Tania limit the rate of change of voltage
tion, and can not take it for this pulsation
Lawn, as during normal and emergency
work on the surge may be similar or
gradually replace each other.

   According to the characteristics for this
voltage thyristor, there is defined
lenny current limit control, the excess
which cause avalanche process
opening. But few people know, though, apparently
it would seem, of course, that the shortage is
of control current (even small, ie
with the boundary value of current when it ma
Leucheni excess will open), ti
thyristor can maintain its closed coc
Toyan long as he wants. The point of
wearing a multiplication factor of the charge,
which directly depends on the control
current. In our case, this current depends on
voltage and slightly floating on the temperature
(Coefficient dependence on
stabilizing zener voltage and some
Thoraya temperature dependence of the transition
thyristor and power transistor. Transistor
torus affects the temperature stability
the fact that it cuts off the base transition
part of the fall of voltage in a circuit with
thyristor). And since the operation
temperature does not vary greatly (approximately
room), but the change itself (relative
dependence on temperature) is weak,
threshold is almost stable.
However, the base transition of power transistor
torus to trip closed with a low-impedance
resistivity, and after the operation no longer
important, as will float voltage of the order
temperature, all the same it will be low. Until
operation of energy loss through power
transistor no.


      Voltage triggering thresholds


   Some of the difficulty lies in the
choice of this threshold, so that to him
it was hard to get the operation. A
reach it helps oscillatory
CLC process in the output filter UPS, jointly
stno with fluctuations of load current.

   Peak voltage rise (in the process
normal operation) will have at the moment com
mutation of the current in the UPS (when the current maximum
LIMITED), provided that the load drops sharply
(With a maximum close to zero). Then ene
rgiya stored in the step-down and filtering
inductor begins charging the output concentration
capacitor, from which the current is almost out
(Almost no load). Natural jump
stress at this point should not exceed
shat hundredths in the (ideally, but in practice
in the schemes he is a few tenths of B,
not the best scheme). But in the following
periods of pumping energy shock continues
camping, t.k.shema comparison voltage (amplified
Tel errors) rather inertial (except for the case
teas with simplified schemes - a matter of
transistors, where all processes are synchronous).
Inertia (due to the capacitors, Shun
commuting error amplifier) ​​suppresses placed
chi and parasitic generation (except for schemes where
This generation is the basis of synchronous
surface).

   But in any case within 2-3 in the period
pump voltage peak of the jump pass. Necessary
necessary to know how much can during this time
bounce voltage, and provide
threshold above the maximum protection, worker
surge. I always try to de
lat output and input filters (capacity and
inductance) at the rate of vibration stress
multiplication by a hundredth of a volt. The simplest
way to boost immunity protection
(Reduce voltage drop) - add
running in parallel several electrolytic
optical condensers. If you know exactly
face values ​​of capacitors and inductors and
maximum value (peak rise) pa
bochego current UPS, the maximum jump
output voltage (switching
UPS and the fall of max load. to min.)
will be:



     ------------------------------
    | Uout ^ 2 * Cvyh Ipik + ^ 2 * (+ Lpon Lfil)
 U = |------------------------------ - Uout

    | Cvyh

    |


   Ipik, usually twice the maxim
lnogo load current.

   The formula takes into account the redistribution
energy from the inductor to the output capacitance
STI. But in fact, begin the vibrational
tive processes involving pre-filter
tanks. However, the peak increase in tension in
they do not exceed the calculated above, only
should be for him to add two more values
calculated similarly, but Lfil = 0, on
the case of the inertia error amplifier and
influence of feedback loops in the UPS, assuming
that the energy filtering (accumulated in
At full load) has been expended
Wang and no longer accumulates (load
almost none). In addition to this we must add
0.1 V as supply voltage variations on
stabilization of the curve, when the current
load all (or almost all) work
range. And the resulting increase in count in
mehoy, non-emergency, operating a nuisance, it must be
added to the nominal value of the voltage
of when working at high load. Think
it should be 5 V and has obtained values
chenie be minimal boundary sraba
tyvaniya protection.

   The maximum value should not be
greater than 5.5 V. Of course, modern cross
trajectories are normal (for ALS - 1533, for example,
measures: 5 V + / -10%), but already old bust
at 0.25 and even overheating (for 155). When
such overvoltages old series of work
exist in a serious mode, their characteristics (in
Specifically, immunity) are deteriorating
especially in 155 series, but by itself is
voltage will not hurt them at neprodolzhi
the tangent action.

   Anyway, you can collect just
nkuyu, nodal shemku that his Popi
skivaniem indicates the output voltage of
work area (+ -0.25 V). So much for
slow and small disturbances, the unsubstituted
tnogo for protection, but a serious uniquely
will trigger and lock power.
But, more importantly, the UPS must identify
drop output voltage on and off
by peregruzke.Eto can also arrange
a simple knot. Such action is necessary in chains
scrap to disable the fallback work
you if the current is insufficient to burn
fuse.

   Actually - what's the point off PSU
in case of failure it may be
Impossible - unless faulty electronics.
Of course, in case of failure of a powerful electro
magnetic pulse (imagine what it
should be), or leakage of capacitors -
loss of capacity, increasing the level of pulsations
(Quite possible) ... But it is a rarity, and
more real overload BP technical
twists, if you occasionally something comes
tsya be fed from the company, Connect and about
believe the new drives and other obvesku.Tog
Yes off-load, or when the case
Tea closure is justified. T.e.otklyuchenie
with unacceptably low voltages, the transition
unloading of, say, less than 4.5 V. Although already at
this voltage may not work, and
155 series will not be able to quickly cross-connected
logic, I think that this threshold is justified. Before him
difficult to reach during normal operation,
and of interference can be forgotten. Only preamplifier
For details, refer lock when you turn - when
supply voltage rises - and it is desirable
but a lock that will not reduce bys
trodeystvie this site after the inclusion
niya.T.e.cherez seconds after turning on the block
Kirovka should not in any way reduce the response to
achieve the lower threshold BP shutdown.
And, of course, such a shutdown should possess
to memory, but not "off himself,"
otherwise we get undefined of self
liruyuschiysya polukolebatelny process with
known future.

   I think the scheme off the lower threshold
gu - this is a topic of a separate article.

   But suppose you do not know the parameters
details, and you can not correctly calculated
assume a surge voltage at the output BP.Mozhno
say - everything is very simple. Indeed
- Judge for yourself.

   Would you like to protect the PC? Probability
but, yeah, once you've read this far ... You Hoth
it would seem to expose the scheme companies exposed
voltage exceeding 5.5 V? I think not ...
Therefore, to determine the meaning of a surge in
voltage - in order to lower the threshold given
Noah my scheme. This is commendable. But remember,
that it is possible a smooth transition for the normal
limits, and better to collect a scheme indicating
to recognize this. If your
you UPS leads to frequent tripping
my scheme, then either you have to replace it
or alter, or try to raise
threshold of my design (add
a germanium diode or Schottky diode). But
the latter circumstance is not quite the mind
but because there is an emergency situation and need
do something, instead of avoiding its limit
elevated threshold. You should try to Doba
vit more capacitors on the output of the UPS or
(If you do not help) did his remake /
replaced by another.


              As it happens


   Let's look at options for UPS
and protection. Take a simple UPS brought down
general type, in several tranzistorah.Takie
typically work synchronously with the parasite to
vibration of the load, using this
to determine when to open and Zach
closing the klyucha.V their output ripple at
voltage is an integral part of RA
bots, and the more stress is smoothed
large capacity, the more spurious
effect becomes the operating frequency in these
blocks. Because the amplitude of the control drops, and
feedback is not the best (as
usually simplified).

   Unlike others, this is the most 'noisy
ing "blocks, and more than is necessary to put
their output LC filter. It's not only
in a very noticeable weakening of the interference (including
including the input LC filter), and that
current surges can greatly shift the burden
working phase control: in such simplified
blocks - and on several periods (synchronous
GOVERNMENTAL with fluctuating current in the load). The key will
children commute nedorazryazhennuyu inductive
vnost ajar and Schottky diodes, and it's you
Calling extra powerful noise and overheating in key
Cha, however, as variations on the original
voltage and transients including
chenii that are critical for simplified schemes. In
such moments, the output voltage parasite
but may pulsate (very low - not
operating frequency) and the trigger
protection.

   If such incidents continue some
Thoroe considerable time (without tripping over
shields), the key is in the end sdohnut.Tut WHO
 are possible options:

  - Break - supply voltage drops to 0
or so, the system is clearly no longer pa
 bot;

  - Closure - triggered protection, and the UNE
mummers falls. Key starts fade, and
fuse must die, but it can
 Jette turn into the latest version:

  - Conductivity, when the key turns in the
uncontrolled resistance continues
burn, and the load voltage is oscillating
tsya (if the defense did not work) or not less
varies (if worked), but the fuse
can not burn down - whichever is the current in the emer
organizations utilizing serial situation and depending on how 
you left the key and the system can continue to operate if

s of this current and the voltage is sufficient.

   As a rule, the latest version of the best ma
loveroyatny, and due to overheating is to
hlogo key, he finally ends (see ne
rvy option), although there are a return to the Deputy
As the whip - the second option.

   We are interested in the effectiveness of protection and
possibility of using such blokov.Dlya
improve reliability and reduce the probability
Tee aforementioned events should post
vit LC filter vyhode.Byvaet enough
pair of coils in a thick ferrite ringlet
(Cross-section of about a centimeter), but better increase
lichit to ten, is if you do not know na
The parameters of ferrite and can not be calculated
intelligently filter. And after a ringlet - pa
parallel load - to sculpt as Conde
ditch, as you see fit - it is reasonable
dozens mf.. While
as a capacitor to the ring as an integral
part of the UPS, it should be except that double
(Compared to the nominal value of the scheme, you
decided to repeat). With regard to the input LC
filter, it is, in fact, only extinguishes the mutual
nye RF interference network (from the secondary housing trance
rectifier) ​​and the UPS, which is desirable and
telen.

   But there is something else ... Fuse!
His choice determines the effectiveness of the protection
in tselom.Esli you just sum the shocks
blyaemuyu load capacity at higher
some stress on the UPS input and nakinete 50%
for losses and transients
you will get not just one denomination Fuse
ranitelya that will work well. You
with surprise may notice that he peri
quasiperiodic (sometimes too often) is the CDF
 host. The reasons can be three:

  - Absence of an input LC filter, or
its inefficiency (saturation is too small
logo of the cross section of the ferrite ring, nedos
 sufficiently coils - have tens);

  - The impact of the simplified UPS, which
with the inclusion of a large pumping capacity
current, not yet grown out of the second voltage
 Richco;

  - Inrush current secondary housing on the charge input
kondyukov (including most LC filters
pa).

   Therefore, you should put the input LC
filter, which together would save
energy loss of current at the input fuse
tele.V some cases, it allows lower
fuse into one or two par, but
not always because simplified scheme of UPS hara
kterny short overcurrent.

   Fuse is better to put the sequence
with respect to the input inductance (input
LC filter), where the current oscillations, according to
the physics of inductance will be the smallest.


                More


   Now recall that the most critical explosion
us to the closure regime in the key event of his
breakdown. Fortunately, this process is more than
Inertia, by lowering inductively
STI UPS. However, the fault can be
crack in the inductor, and then the velocity
rate of rise of current and voltage will be
very large. But in fact, still
process will be tightened as ferrite or
where all but disappeared. How do you think it is possible,
to ferrite suddenly split, and vysy
palsya, leaving a skeleton of the winding-up? On
true, not just possible, and
case the UPS must be traces of fur
mechanical, or other effects. More
actually short-circuit in the turns, but again, not about
one hundred so.

   But be that as it may, our protection scheme
worked, and did so before the stress
voltage across the output of the UPS has reached dangerous 
values radiation. But there was further drop in the UNE

masking output - due to trigger
effect, after which the voltage is again a
grow. Firstly, because the fuses
just do not burn, and the chain intact. Secondly,
because the key is first opened, and the current more
not fatally high, although probably already overestimated
sheng, a key is not completely croaked (only
chal). Also, because the inductance is not on
allows current increase rapidly. And, last
them - resistance of the host defense
causes a proportional voltage drop
of output, and though it is small, but growing
of the transmitted current.

   By the way, for simplified scheme in case
host defense response to noise (low
smoothing capacity) it would be a tragedy
for more live key. Because the voltage on
output fell, and the control scheme will leave
Key open, "hoping" that the voltage to
stignet threshold off key. But our
protection of this no longer tolerate. Then either
burn the fuse, if the current passes
my key will be large enough (and
the key itself will not have time to overheat, which is quite
actually a deliberate scheme), or burn
key itself, if not able to provide large
current or if the control scheme would not provide
desired current management and will not be blocked
Wang - quite an option for simple
UPS. Here we are again approaching the fault
key itself and the actual effect of the issue
vnosti protection.

   Suppose the key is hot, and he no longer
important current administration. Due to thermal
breakdown current through it became rasti.Struktura
semiconductor is destroyed, but it is unknown
as imenno.S one hand, the current will be able to limit
vysit critical and burn fuse
(Whether input or output), and accidents
ground state is over a cliff. On the other
hand, a rather burnt key can
become a heat gun and radiate - scatter
vat a lot of heat, missing a significant
current which will dissipate in a node for
shields. Shall not consider the option is not
controllable resistance, insufficient
for the protection operation. Firstly, there is
are failures of the system (from low power).
Secondly, it should detect the other
scheme. Third, the long it will last ...
The most dangerous is the peak of growth is
ka, when the key and the fuse has not yet DLS
Hlly. If the resistance nesdohshego key
is too low, the protection scheme is not
be able to keep the output voltage in normal
predelah.Konechno normal, this is unlikely,
but if you vlepit modern key (on the
example, IRFZ44), then anything is possible, then by
anxious to limit the current to individual
node, even in the same key with the restriction
on the condition of maximum upravleniyu.Glavnoe
used currents: the current protection schemes more
current limit circuit, and the current scheme is bounded
restrictions more current fuse. Hence
it is clear that in an emergency or burn
fuse or current will be limited
its nominal value.

   If you do not know how to limit the current,
Use at least a resistor - the simplest
option. Let's say you get from 12 to 5.
Then let the 1 on the heat dissipation
Power resistor (when converted to the maximum
The maximum load), and obtain the transformation
Vatel from 11 V to 5. Then at operation
protection and the closure of a key peak current
not exceed a 10-fold: 12 meals (yes
well if you do not sit down!) minus 2 in the scheme for
billboards - get 10 in the emergency mode
instead of 1 as usual. And it is already clear on what
current must be designed protection scheme (in
peak). Of course, the fuse will be
less current and will burn for tightened process
MAR. And if not, and the current will be less, we arrive at
tsya calculate the heat sink for the circuit protection
that it could long withstand such
emergency mode. Fortunately, the computer itself
in this case will not work - stress
underestimated, and the overheating of its chips are not
scary mikruhah currents are too small and not
dangerous even at high ambient temperatures
ture.

KSA-7G


           Selection of components


   If we analyze the parameters of parts
in my scheme, then you might think that it
collected without a second thought - of what came to hand. I
really took the transistor, has already fixed
lenny on the radiator and decided to use
this scheme as unnecessary. But the last
judged on the basis of the reference and measurement
its amplification factor - literally 10.
For high tranzyuka still small
Lovato will be, but if you take a big leak and
low speed, not too comfortable
using a key, except in special
Industrial modules of the last century (from
where he is). He told me just do not need, and
Why throw away - here will do. As a result,
The parameters and the current sink is
have been identified, I just compared them with
power dissipation - measured drop
voltage triggering. Which, when
current of 0.32 A was 1.4 V. Since
transistor was already well opened, and Tiris
operator could easily saturate it, I pointed out in
zmozhnoe drop 2 at full current - 6 A
By the way, if anyone noticed - I have a couple
parameters required for the transistor circuit as
equal basic - maksimalnym.Pri not
allowed continuous operation, but
should not forget that part of the energy scattered
Vaeth thyristor, and a real burden on the transit
Zyuk lower limit. In fact, the whole
current passes through tranzyuk, but part of it
through the base transition, and because Voltage
will - a few volts, can be long and
operate within the maximum power
surface.

   But in general here need a powerful low-frequency
LIMITED, a low-voltage transistor with a large
supply current - for effective rapid
reduce the voltage spikes during switching
research institutes, and perhaps more direct current, possibly 
because of low resistance breakdown key). With the specified 
tranzyukom scheme effective tive in nenavorochennyh companies 
requiring relatively weak power supply, rather than

advanced as PC-shnye. And if there Toko
Limits chain in the block may Brokers
remit logic with ultrahigh breakdown ...

   You can use germanium transistors
ki, old and powerful, but they are limited
current and therefore more effective in circuits
current limit. However, the dignity of germanium
efficiency of silicon - a low offset for the opening -
here is a disadvantage. They need
lower resistance in the base circuit, and
elevated because of this operating current node
protection reduces the speed uzla.No up
almost the same as that of silicon, it is
acceptable use.

   Transistors in a round housing demand
more space, and they are more complicated krepezh.No
efficiently, reliably cool, besides
their inner contact is welded a lot of Be
zotkaznee than the more convenient tranzyukov in
plastic housings. Therefore healthy
Disc tranzyuki - to protect the most endowed
PARTS (at least from our). Germany
curves transistors can significantly affect the
threshold (the spread between the series),
as open already from several hundredths of
lta - even before the threshold, which
becomes dependent on the temperature of BE junction
progress of these transistors.

   Thyristor, one of the most popular, so
also caught by the arm. Perhaps a couple of his
meters of the most embarrassing for us - the maxim
flax allowable voltage: hundreds of volts.
But especially to buy expensive LOW
nye thyristors inappropriate, they were quickly
the action is not strongly vyigryvaet.Po current as at
our value is quite normal - 10 A
that in the base circuit form a huge
current of collectors, or its saturation. Reason
is, the choice of the series will affect the threshold sraba
tyvaniya. Perhaps someone noticed a small
catch in the scheme. Why is the scheme by 6 A,
when he skips the thyristor
A whole 10? Why do not the transistor
throw it away and do not gather in one thyristor?
Of course, this may be possible to throw and
transistor and a resistor 10 ohms, and the resulting
scheme with a threshold of approximately 5.4 for fully
serves as a protection, but it is not universal, and I
would not rely on a very large
current. Thyristors - good keys, but they do not "
like "dissipate moschnost.Tranzistory th
Section effective to deal with it, and they
pulsed currents with a transistor circuit, as
performance node protection in general - a pain
above. Scheme on a single thyristor really
can be used but with limited pico
threshold current of 10 A (for example, as considered
rivalos above), and dissipated by the current defense, I
would not allow more than 8 A, and of course
but have to put the radiator. And in the transistor
reflex circuit you can use the transit
transistors, "to taste and combine instruments
under the desired current.

   Capacitors are chosen for their popularity
sequence and perform the main condition - they
should be much greater than the parasitic emkos
Tea in the thyristor.

   Resistor bypass transition thyristor
much smaller than its internal resistance
and sets the border operation by
significant imbalance in the current management
chain when it increased the voltage.

   Resistor shunt transistor transition
RA does not allow its opening to the tripping
tion of protection, eliminating excess leakage current and
waste of energy through the power transistor
before firing.

   The most significant is the diode on
Since it cuts off the voltage applied
to the scheme, leaving a balance of the thyristor and owls
Sem tranzyuku.Chem slightly lower than its resistance
resistance, the steeper the characteristic of its one hundred
stabilization and stable threshold
scheme as a whole. Our zener diodes are not the most
Top performance, and some do not
otherwise, as a disgrace not name, but for a given
Noah schemes you can use any - not tiny,
t.e.s shock to tens of mA and body pain
above, the resistor than 0.25. Such a margin
zvolit not somnevatsya the long-on
reliability and stability, not counting
Random braka.Voobsche, based on the infamous
characteristics of some of our stabilitro
electrons and their conditional designations of color,
it is difficult to believe that it is this
Zener - so-to.Vot and in this case
case, I took a glass diode, with a black
and white stripes, and the directory is defined
poured him as 2S133A, but measuring of stress
of it more like a 136-d (if such
exists at all). can not be excluded, and the operator
Chatcombe, t.k.spravochnik - is part of komerches
one publication (however, I many not only
to the commercial, the bug is). But the sense of
that rely on "blind" assembly
Site security is impossible, no matter what the details may be
whether, and to determine the threshold.
If it is very far from desirable, beneath
take it stabilitron or a chain of
and zener diode, or even two diodes
only the silicon - they are closer to stabisto
frames, which can also be used. In
any case should be limited to three
details, because more of them, the worse
temperature stability limit (although
She and weak). In general, try it with different
zener diodes, and even powerful (but
small in size).


       Arrangement for testing and tuning


   To accurately determine the threshold Gather
small circuit. Of course, it is possible and without
do if you use a laboratory
power supply with adjustable voltage and
limit the current (in series of 20 Ohm
2 W and above, or the security settings of the unit).
Obtained with several times the result can be
but considered quite accurate, but for the interest and
convenience is better with the scheme. You need a rectifier
mitel 12B. Of course, the best stabilizer, or
from the company, but fit and a rectifier, because
voltage is rarely changed to a large
value for a small time interval
intervals, and you can spend a few reliable
magnetic measurements. Still need a LED (any)
- To indicate the operation. He goes out
at operation protection. This will allow for
reach the threshold of "blind" and only then placed
We say napryazhenie.Obratite attention to pain
Shua capacity, better not underestimate, but it is
fit two capacitors on the 4700 uF. Re
transistors are powerful, some of these nominations
fishing, podstroechnik wire. If not,
first rough pick resistance, and to
that supplement scheme podstroechnikom acc
tstvenno connect it (something it is not
similar to the simple, convenient shemku). in practice
tick is not always available so powerful Seat
troechnye rezyuki, we can take from the old la
mpovyh telly, variables. I used
simple (probably poluvattny, brown on
getinakse), but the setting was so
bluntly, that I decided to connect the parallels
flax small podstroechnik at 4.7 ohms, and
almost without reducing its resistance, the substitution
raival them "exactly". Unfortunately, the scheme I
drew much earlier than he solved it
try, and did not dorisovyvat "exact"
podstroechnik - simply not appropriate.

   And now about the process itself. Recall that
When you set the voltage for the RC circuit process
recharge capacity is exponential
character, and at first the voltage on the capacitor
satori is changing rapidly, and then speed
changing the voltage drops to almost zero.
Considered to be transient Law
chennym if the voltage at Conder reached
2 / 3 of the set (or the difference between the
given and the former - depending on how you count). But
meaning that the voltage in Conder
managering end tends to infinity given
infinitely long, in fact it does not reach - current
through the capacitance is very small and voltage
This changes very little - in hundredths of a
Volts. Now imagine that for a given
RC circuit connected to one resistor - pa
parallel capacitance, then the stress to which
rum tends capacity will be determined
divisor to be received - by the resistance
resistances. At the end of a charge of almost the entire current
will flow through resistors, the voltage
established, but little current through the capacitance
will affect the share of current, and through
very long periods of time. As a result,
inertial digital testers can catch
accurately to measure the steady-state voltage.
In our case, the input resistors are regulated
are, and the output node protection is not regulated
camping, and the input we can install the NAM
mummers at the site of protection to be
seeks to charge kondendsator.

   Suppose we set the voltage is replaced
TNO below the threshold. Then, after
button is released, after a few seconds the voltage
mapping almost ceases to change - it went
to measure. And if you set the voltage
of much higher threshold, then a second
capacitor voltage, tending to him,
reaches the threshold, and the LED goes out - we
will not have time to measure precisely the time Actuating
niya.No now if we lower the mouth
certain established value - dropping him closer to
threshold, then the charging process at Conder otpu
Scania button will increasingly tighten
camping, and time to measure the exact value
will increase. Because the voltage on the line
capacitor will strive to exceed the threshold
on such a small value at which
charge currents are negligible and the rate of change
voltage equation tozhe.Opuskaya given on
voltage, adjustable podstroechnika arr
lizhaya him to the threshold, we displace the point of 
intersection cross the threshold voltage with a shallow part of

exponential curve of the charge, more
distancing it from the beginning of the transition process
- Tightening over time.

   In the end, be that for some
value (adjustable) LED will be quenched
nut after a certain - a stable time
after clicking knopki.Chem this time longer,
more accurately you can measure the threshold - connected
Chita tester and check the voltage, arrived
vte 0.01 V to compensate for the lag
measurement (in any case, this is a typical
error, because you'll be measured on the pre
towards DC 20V).

   And what if the scheme is triggered by interference?
What if the real threshold is still higher? Where
truth? In fact it is. While
on the verge of switching circuit responds to
any sufficiently powerful pulse interference and
fires in-sync with him, but the amplitude
it is much lower than the measured increase. AND
Still - how to make sure that the tripping
tion is not by chance that the true threshold is not
will be much higher? All the same, based on
exponent of the charge. Change the value of
(Resistor) - and get a stable CPA
batyvanie after some more or less
her short time. At the same time very stable
sequence indicates a certain point in
intersection curve of the charge and the direct threshold
though a stable thermal regime, and
properties of the capacitor can be changed in
time, and he bit through and tranzyuk
thyristor will be their warm, changing to
horn. But on the device you can easily track that
voltage does not exceed certain values
of, and the faster the circuit is triggered, the
measured value is less - and this may not mean
This means that noise has become more - agree!
Just the device does not have time to measure more
high and the correct value before operation.
However, for very precise selection of the resistor
and proximity to the high threshold (high
accuracy) can affect noise.
This will be reflected in the interim nestabi
lnosti tripping scheme - the sooner,
later, with a large spread in time, SDA
contraction defined continuous interval
during which the approximation to
threshold for the difference, close to the action
interference. But even here one can not exclude the influence
yanie thermal noise in the thyristor, stable
Ron and condenser, and the latter also
electrochemical defect of capacity.

   If you are not satisfied the threshold, within
0.1 V, then choose a site for resistance
shields. After soldering give details of cool - and
then there is a threshold check, otherwise false
izmerite.Esli spread even more desirable
- Pick Zener, try the options
with diodes.


               Prospects


   This protection scheme is easy to remake
another voltage - just placed
nyat, pick up another diode. For
Speccy with a weak unit is the only
difference. I, of course, about the protection of 12 V. With
important, again, when homemade and the names of
but the pulse unit. In the usual difference
input and 12 - is low, the load is too
small, and Krenek copes with
Heat rezhimom.Shema test too hell
ptivna - use Conder at 25 V and results
transistor per LED 1 k 0.5 W, the source
volts at 15 - 20. Resistors more than twice
powerful. But have longer hold the CCW
CDP for discharge Conder, or add on
delny resistor - 100 ohm (disconnect from a
k).

   If you needed even more highly
volt protection - recalculate the components of
you own. Note - the security node supermarket
flax, it can be used to protect the chain
drink with a negative voltage. Also can
zhno construct a circuit on the transistor PNP Tee
na and a thyristor with management on the anode -
all 4 types who need to - guess.

   Well, if you need a more powerful scheme
- Shunt still more current - place
other transistor and radiator.Togda you QS
zhete "protect" and the PTsshnyh BS with their Be
shenymi currents, it is also aktualno.Mne izve
stny event of their failure (literally
recently, a friend), with severe consequences
- Burned vinchester.Konechno, the assembly was not
filter and varistor, and with the jumper in place
rezyuka break wires. The result - a lot of faults
GOVERNMENTAL details, including k.z.v trance on duty
supply and fuse intact (6A! in the block
230 W). This is not the first negotiations
Rania ceramic resistor at the input
the fuse. Other devices
spaces also happens, poor collection
ki. By the way, the board of the PC PSU was to mark
mounting plate LEC-971.

   Finally affordable powerful tranzyuki
npn-type version of our scheme. Judge
themselves what to put and what for. But the maxim
flax worker (not an emergency), the current UPS USD
wives to be several times lower Ik:


   type P, W Ik, A



   KT802 50 5

   KT803 60 10

   KT805pl. May 30

   KT808 60 10

   KT808 70 10

   KT812 50 8

   KT819pl. 60 10

   KT819 100 15

   KT828 50 5

   KT834 100 15

   KT838 May 12

   KT839 50 10

   KT840 60 6

   KT841 50 10

   KT844 50 10

   KT845 40 5

   KT846 May 12

   KT847 125 15

   KT848 35 15

   KT854pl. 60 10

   KT857pl. 60 7

   KT858pl. 60 7

   KT863pl. 50 10

   KT864 100 10

   KT866 30 20

   KT872pl. 100 8

   KT878 100 8

   KT879 250 50

   2T886A 75 10

  KT908 50 10


   Of course, there are others. I have listed no
zkochastotnye, as well as high, for
greater choice. Have plastic, they
more comfortable - smaller, but they have less heat
and reliability of contacts within the shell of
this very carefully braze findings, it is better
do not bend them, connect the thick mnogozhil
nym wire (2.1 square meters. mm). I did not re
compute transistors "superbeta" (2 1)
because of their high cost and uselessness in a given
scheme. Of course, you can use them
but they are even less reliable. If you do not
transistor is large enough capacity and
much less powerful - use them. Soe
dinite parallel, but each base - separated
flax through a 1 ohm 0.25 W, and the total current and
power factor of 1.5 times less than the soybean
union of devices (including non-uniform
distribution, and better with more reserves
Som brother).


                   Total


   As I mentioned, this scheme is only part of the
full protection, as it protects the self
model powered devices, but can not protect
tit itself from overheating. So it's good for
Think of what can be expected in an accident
ynoy situation, if the device will be long
dissipate heat. You can put Fuse
ranitel with a current 2-3 times more nominations
lnogo.Tok in turn increases gradually,
and pulse overload is low, and the whole problem
small losses in the voltage at the fuse
cords, do not feel sorry for 0.1 V - put. 2-3-edge
tny stock will rely on the definition
divided by the power dissipation, which more
second fuse will not stand. This variant
ant is very simple and easy if you use
fuse in the circuit inductance of output
Nogo filter (current is almost constant), and to
ntrol voltage (stabilization) implementation
lyat already at the door, and then the loss limit
fuse will uchteny.No not all pulses
snye scheme so noble. And with good
implementation would be enough 2-fold
current value fuse. Even more
good variant - guard at the entrance,
also in the filter chain, also 2-3-fold
value of current consumption - here it is,
of course, will be even lower value, but
just not for simple circuits and for circuits with
soft start. You can use the scheme
off in case of emergency reduction, but that
She turned off if the key PSU broken? Can
use the scheme of current generators, vyho
dyaschie of saturation in emergency mode, but
a separate stati.Pomnite and of fixed assets
variable work at the threshold - should be indie
Katsia this state, and this is also a separate
article. On this for now.

22.12.2005 By KSA-7G