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'[EE]: How to control a 24V solenoid with a PIC and'
2001\07\23@170446 by Edson Brusque

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Hello,

   I'm trying to turn a 24V solenoid (electro-magnet) with an NPN
transistor (TIP41) wired to a PIC. Here's the circuit:


                  24V-----------+
                            solenoid (with reverse diode)
                    C-----------+
   PIC----10K--+----B
               |    E
              1K    |
               |    |
              GND  GND

   It's not working. It seens the transistor have a much larger resistance
(when on) than the solenoid (about 5 ohms). When I disconect the solenoid,
the multimeter shows 24V ok when PIC pin is high. With the solenoid, it
shows below 1V (more like a hundered millivolt).

   Please, someone can help me?

   Thanks,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2138  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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2001\07\23@171552 by Douglas Butler

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Your drive to the transistor is rather weak.  Do you know how much
current the solenoid draws?  The part number of the transistor would
help too.  Can you give us the transistor voltage when it is turned on?
The first thing I would try is to reduce the 10K resistor.  Changing it
to 1K or even 220 ohms would drive the transistor harder and make it
turn on more completely.

Sherpa Doug

> {Original Message removed}

2001\07\23@172000 by Tom Messenger

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At 05:52 PM 7/23/01 -0300, you wrote:
{Quote hidden}

Sure. Try a little Ohm's law first. Desired collector current will be 24V/5
ohms = 4.8AMPS.

4.8AMPS divided by beta of transistor is how much base current you need. In
saturation, a "rule of thumb" is beta of 20; try optimisically with beta of
50... 4.8AMPS/50 = 96mAMPS

Pic at real 5 volts: (5-.6)/10k = 440 microamps.

Remove NPN, put in FET. Don't worry, be happy.
Tom M.

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2001\07\23@172211 by Brent Brown

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>     I'm trying to turn a 24V solenoid (electro-magnet) with an NPN
> transistor (TIP41) wired to a PIC. Here's the circuit:
>
>
>                    24V-----------+
>                              solenoid (with reverse diode)
>                      C-----------+
>     PIC----10K--+----B
>                 |    E
>                1K    |
>                 |    |
>                GND  GND
>
>     It's not working. It seens the transistor have a much larger resistance
> (when on) than the solenoid (about 5 ohms). When I disconect the solenoid,
> the multimeter shows 24V ok when PIC pin is high. With the solenoid, it
> shows below 1V (more like a hundered millivolt).

It looks like you need more base drive to turn the transistor on
harder, 10k is too high. Probably 470R would do it as I suspect the
TIP41 has relatvely low gain. This would give about 9mA base
drive. You wont need the resistor to ground for turning off the
transistor as this is done pretty well when the PIC output goes low.
Hope this does the trick.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  spam_OUTbrent.brownTakeThisOuTspamclear.net.nz

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2001\07\23@173257 by David VanHorn

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At 05:52 PM 7/23/01 -0300, Edson Brusque wrote:
{Quote hidden}

You aren't turning on the transistor much.
What's it's beta value?
You need to divide the solenoid current by that value, which will give you
the base current.
Then, re-calculate your 10k, to provide enough base current.
The pull-down resistor can be much larger, it only needs to swamp out the
max leakage from the PIC when it's in the low, or high-z state.
A series diode with the 10k may help assure an OFF off state.
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2001\07\23@173310 by David VanHorn

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>
>Remove NPN, put in FET. Don't worry, be happy.
>Tom M.

Beware, Vth needs to be below 4V, or you won't be very happy.

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2001\07\23@173322 by Douglas Butler

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If you put in a FET you still need to juggle the resistors.  For a FET
start by swapping the two resistors  You will need some resistor to GND
to stop the solenoid from firing while the PIC boots.

I think your TIP41 is fine with better drive.

Sherpa Doug

> {Original Message removed}

2001\07\23@181509 by Spehro Pefhany

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At 05:24 PM 7/23/01 -0400, you wrote:
>If you put in a FET you still need to juggle the resistors.  For a FET
>start by swapping the two resistors  You will need some resistor to GND
>to stop the solenoid from firing while the PIC boots.

Just a series resistor will do it. The gate charge will keep the MOSFET
reliably off for the few milliseconds while the PIC is starting, but it
doesn't hurt to put a 100K or so in there to take care of the case if the
PIC is unplugged. A logic-level MOSFET such as the IRLIZ44 will do this
with no heatsink (0.55W in a TO-220).

>I think your TIP41 is fine with better drive.

It's a bit marginal, but it could be made to work. Watch turn-off time
and the SOA limitations with an inductive load! Vce(sat) with a 6A
load is spec'd at 1.5V max. with 600mA drive. Using "typical" figures,
Vce(sat) is 0.4V at Vbe is about 1V at 5A/500mA drive. That's typical
2W dissipation (requires a heat sink) use, say, a 2N4403 to drive
the base current, and the PIC can sink the 25mA of base current the
for the drive transistor (forced beta of 20). The base resistor would
be around 7 ohms at about 2W, for a total loss of about 4W (typ).

P.S. That's a 120W solenoid. Either it is very large, or it is only
rated for intermittent duty.

Best regards,
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2001\07\23@192009 by Mike Kendall

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Try a HEXFET from Industrial Rectifier

----- Original Message -----
From: "Tom Messenger" <kristspamKILLspamTHEGRID.NET>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Monday, July 23, 2001 9:23 PM
Subject: Re: [EE]: How to control a 24V solenoid with a PIC and a
transistor?


{Quote hidden}

resistance
> >(when on) than the solenoid (about 5 ohms). When I disconect the
solenoid,
> >the multimeter shows 24V ok when PIC pin is high. With the solenoid, it
> >shows below 1V (more like a hundered millivolt).
> >
> >    Please, someone can help me?
>
> Sure. Try a little Ohm's law first. Desired collector current will be
24V/5
> ohms = 4.8AMPS.
>
> 4.8AMPS divided by beta of transistor is how much base current you need.
In
> saturation, a "rule of thumb" is beta of 20; try optimisically with beta
of
{Quote hidden}

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2001\07\23@195824 by Edson Brusque

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Hello David,

> >Remove NPN, put in FET. Don't worry, be happy.
> Beware, Vth needs to be below 4V, or you won't be very happy.

   what's Vth?

   Best regards,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2138  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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2001\07\23@195837 by Edson Brusque

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Hello Douglas, David, Tom et all:

> Your drive to the transistor is rather weak.  Do you know how much
> current the solenoid draws?  The part number of the transistor would
> help too.  Can you give us the transistor voltage when it is turned on?
> The first thing I would try is to reduce the 10K resistor.  Changing it
> to 1K or even 220 ohms would drive the transistor harder and make it
> turn on more completely.

   Yes, now I've tried to replace the 10K resistor with a lower one. With
220-470R the solenoid turns on, but the power dissipation on the transistor
is very high. It seens the transistor isn't saturating, so the C-E voltage
is high.

   When I designed the PCB I was thinking in using this transistor to
switch a lower current device, but the client decided to use this hi-power
solenoid, this is where my problem started. I would like to add a BC548 to
drive the TIP41, but I don't want to mess with the PCB. The TIP41 have HFE
(about 15 at 3A), so I'm thinking in replacing it with a high gain power
transistor (maybe a darlington one?) or a FET. What parts would be a good
suggestion?

   Regards,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2138  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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2001\07\23@200604 by David VanHorn

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At 07:05 PM 7/23/01 -0300, Edson Brusque wrote:
>Hello David,
>
> > >Remove NPN, put in FET. Don't worry, be happy.
> > Beware, Vth needs to be below 4V, or you won't be very happy.
>
>     what's Vth?

Threshold Voltage. If you can't get the gate above the threshold voltage,
then you can't turn on the FET.   In your case, you need to be
SIGNIFICANTLY above the threshold, or mister fet's going to get nice and
toasty.

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2001\07\23@201013 by David VanHorn

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>
>     When I designed the PCB I was thinking in using this transistor to
>switch a lower current device, but the client decided to use this hi-power
>solenoid, this is where my problem started. I would like to add a BC548 to
>drive the TIP41, but I don't want to mess with the PCB. The TIP41 have HFE
>(about 15 at 3A), so I'm thinking in replacing it with a high gain power
>transistor (maybe a darlington one?) or a FET. What parts would be a good
>suggestion?

A darlington would work well, as would a Sziklai pair, if you can find it.
You'd have to think upside down with the Sziklai though.

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2001\07\23@205205 by Eduardo Jr

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Boa Noite.

  Um transistor bipolar i uma boa solugco se o seu equipamento tiver espago
suficiente para acomodar um dissipador tirmico. Melhor ainda se o seu
solenoide for usado por curtos periodos de tempo.
  Para tanto devem ser tomados alguns calculos para garantir que seu
transistor ira conduzir na zona de saturagco, onde temos menor Vce (tensao
entre coletor e emissor) e por sua vez menor perda de energia por dissipagco
termica (P=V x I).

  http://www.fairchildsemi.com/pf/TI/TIP41.html

 Pelo datasheet na corrente Ic de 4,8A (24V/5 ohm), i indicado uma tensao
de Vcesat de 400mV.
 Logo a dissipagco em cima do TIP i da ordem de 19W (Vce x Ic). Nada mal
para um transistor que suporta dissipar  65W com a temperatura de
encapsulamento de 25 graus Celcius. Mesmo morando em Blumenau i difmcil
obter 25 graus em um encapsulamento dissipando quase 20 watts.
 UM ponto que impossibilita o uso do TIP41 no seu projeto i ele estar
operando prsximo do seu valor maximo de corrente de coletor.

 Suponhamos que ainda vai tentar um teste usando o TIP41 e ver se ele
"aguenta" mesmo. Vamos `s contas:

{Quote hidden}

Ic = 4,8 A
para esta corrente de coletor temos (datasheet):
Beta=40
Vce(sat) =400mV
Vbe(sat) = 1,2V

vamos calcular o valor de R:

Vh(pic) = Vcc - 0,6 = 4,4V
Ib = Ic/Beta = 4,8/40 = 120mA <==== o PIC nao pode fornecer esta
                                                     Corrente!!!

 Entco, SE ainda assim insistir em usar o TIP41, vc vai precisar de um
transistor adicional para fornecer a corrente de polarizagco como um booster
de corrente.


  Imagino que esteja com dificuldades para encontrar componentes,
principalmente aqui no Brasil, e esteja usando o material que tem ` mco. Sei
que i mais caro e difmcil encontrar POWERFETs, mas neste caso seria o
componente que eu usaria.
 Eu costumo usar POWERFETs em aplicagues de corrente acima de 3A com
acionamento por controladores. Os transistores da sirie IRLZ___ podem ser
acionados diretamente pelas portas do PIC.
 Espero ter ajudado em seu trabalho. Se quiser algumas paginas de como
projetar conexoes de saidas TTL e transistores FET posso indicar algumas.
Boa sorte

Eduardo Lopes.




{Quote hidden}

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2001\07\23@210715 by Olin Lathrop

face picon face
>     I'm trying to turn a 24V solenoid (electro-magnet) with an NPN
> transistor (TIP41) wired to a PIC. Here's the circuit:
>
>
>                    24V-----------+
>                              solenoid (with reverse diode)
>                      C-----------+
>     PIC----10K--+----B
>                 |    E
>                1K    |
>                 |    |
>                GND  GND
>
>     It's not working.

There are two good reasons for this.

1  -  The 10K and the 1K resistors form a voltage divider.  Even without the
transistor drawing any current and the PIC output at 5V, the voltage for the
base would be 5V * 1K / (10K + 1K) = 455mV.  That is just too little to turn
on the transistor more than a trickle at most.

2  -  Even without the 10K resistor, the base current with the PIC output at
5V is 4.3V / 10Kohms = 430uA.  I don't know what the gain of the TIP41 is or
how much current your solenoid needs, but this sounds way too small.  You
can usually assume a current gain of 100 for small signal transistors, 25 or
so for medium power (a few watts), and sometimes as low as 10 or 15 for high
power (many watts).

So, what to do?  Since you didn't give the pertinant values, I'll make up
some and you can adjust the result given the real values.  Let's assume the
solenoid requires 100mA.  You can easily find a transistor that can pass
100mA with 500mV C-E drop or less.  That means it will only dissipate 50mW
when on, which is no big deal.  Even a small signal transistor in a TO-92
package can do this, so let's assume you have a transistor that has a
current gain of 100.  That means it needs at least 1mA base drive to deliver
100mA to the solenoid and still stay saturated.  Figure the B-E drop at
700mV, so that leaves 4.3V between the PIC pin when it is high and the base
of the transistor.  Let's double the minimum base current to provide margin.
That means your base resistor is R = V / A = 4.3V / 2mA = 2.15Kohm, in other
words around 2K ohms.  This assumes you loose that base to ground resistor
(1K in your schematic).  There is no point for that resistor in this case.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, KILLspamolinKILLspamspamembedinc.com, http://www.embedinc.com

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2001\07\23@214652 by Herbert Graf

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The threshold voltage. In this sort of situation think of it as the minimum
voltage require to turn the transistor "on". TTYL


> {Original Message removed}

2001\07\23@214704 by Edson Brusque

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Hello,

   now I'm thinking about using a small signal transistor (BC548) to give
the TIP41 more current.

   Someone can point me how can I connect the two? May I use it the
Darlington's way?

   Regards,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2138  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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2001\07\23@215954 by David VanHorn

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At 10:45 PM 7/23/01 -0300, Edson Brusque wrote:
>Hello,
>
>     now I'm thinking about using a small signal transistor (BC548) to give
>the TIP41 more current.
>
>     Someone can point me how can I connect the two? May I use it the
>Darlington's way?

Sure, just make sure you have that turn-off resistor on the base of the
TIP, otherwise leakage from the first transistor may cause it to be
partially on, and get rather hot, when it should be off.

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2001\07\23@220501 by Eduardo Jr

picon face
Boa noite.

 Como havia dito voce pode usar um POWERMOSFET para acionar diretamente o
solenoide, diretamente do PIC.
 Como a maioria dos FETs tem o encapsulamento TO220 e a configuragco G-D-S
voce pode usar sem muita modificagco na sua placa. pois o TIP41 tem a
configuragco B-C-E.

o circuito ficaria assim:

            Vcc
             |
             R
             |          D ------  LOAD
   -----=----x--- r --- G
                        S --- GND


 Note que o resistor R i de pull-up para garantir que a saida TTL,
normalmente TOTEM-POLE consiga garantir o Vt mmmino para acionamento do FET
e para que ele opere na regiao de saturagco.

O resistor r i para garantir que o PIC nao va queimar em aso de falha no
FET. com isso o tempo que o FET leva pra ligar i maior e com isso i gerado
menos rumdo de comutagco e diminui o estresse no componente.

quanto `s paginas pode estudar este material:

6 INTERNATIONAL RECTIFIER.  IR Application Note AN-949 : Current Ratings of
Power Semiconductors.  California, 1991.  [online]  Disponmvel na Internet
via WWW. URL: http://www.irf.com/technical-info/an949/an-949.htm.  Arquivo
capturado em 15 de abril de 2001.

7 ___.  IR Application Note AN-937 : Gate Drive Characteristics and
Requirements for HEXFETs.  [s.l.], c2001.  [online]  Disponmvel na Internet
via WWW. URL: http://www.irf.com/technical-info/an937/an-937.htm.  Arquivo
capturado em 15 de abril de 2001.

11 MOTOROLA Discrete Applications. AN1102 : Interfacing Power MOSFETs to
Logic Devices. Por Ken Berringer.  Phoenix : Cahners, 1989. [online]
Disponmvel na Internet via WWW. URL:
http://www.web-ee.com/primers/primers-frm.htm/files/mosfet-logic.pdf. Arquivo
capturado em 15 de abril de 2001.



Mais uma vez boa sorte.
Acho que agora fica mais facil pra vocj projetar. O unico incoveniente i
encontrar FET com prego baixo. Aqui no Rio de Janeiro i dificil encontrar os
componentes que preciso e normalmente preciso encomendar FETs em Sco Paulo.
Normalmnte FETs de potencia com corrente de 40A estco na faixa de 8 a 10
Reais CADA!

Eduardo Lopes.
{Quote hidden}

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2001\07\23@222658 by Spehro Pefhany

picon face
At 10:45 PM 7/23/01 -0300, you wrote:
>Hello,
>
>    now I'm thinking about using a small signal transistor (BC548) to give
>the TIP41 more current.

See my previous posting where I suggest a 2N4403

(driven from push-pull PIC output, Low = ON)

                  +5   (500mA)
                 |/ E
PIC-----[160R]----|   PNP (eg. 2N4403)
                 |\
                  |
               [7R5 3W]
                  |
                  x---------> base of TIP
                  |
               [100R]
                  |
                  0V


I would suggest avoiding the Darlington connection at these levels,
as the output drop is more like 1.2V than the 400mV of the above circuit,
increasing the power loss in the TIP to 6W from the 2W in the above
circuit. OTOH, it won't draw 1/2 amp from your 5V supply so this is a
factor. Personally, I think at this current level, MOSFETs are a no-
brainer, with rare exceptions.

BTW, Vth is not really the MOSFET parameter you want to look at, rather
at the Vgs that the Rds(on) is guaranteed at. Vth is normally spec'd with
a fairly low drain current. "Logic" MOSFETs are normally spec'd at
Vgs of 4.5V or even lower.

Best regards,
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2001\07\24@052237 by Terry

flavicon
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At 10:45 PM 7/23/01 -0300, you wrote:

{Quote hidden}

Why not a TIP121 or TIP132 darlington with Min. hfe 1000? Same package and pinout so you won't have to change the PCB. If you have extra CPU overhead, turn on the darlington and switch over to a 500Hz 1/3 or more duty cycle to minimize power dissipation.


Cheers

Terry



Design Consultant

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2001\07\24@062606 by artstar

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A darlington like a TIP147 wouldn't be a good go because of the low Vce
voltage. A fet would be a better option here. The IRLZ44 (I think that's
the number ... just going off memory here) as was suggested earlier, I
think, would be the way to go.

Adios,
LarZ

---------------  TAMA - The Strongest Name in Drums  ---------------

{Original Message removed}

2001\07\24@082833 by Olin Lathrop

face picon face
> A darlington would work well, as would a Sziklai pair, if you can find it.
> You'd have to think upside down with the Sziklai though.

I don't like a darlington here because of the high on voltage.  Why not just
simply cascade them?  That way the output transistor can still be saturated.


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2001\07\24@082848 by Olin Lathrop

face picon face
>     Someone can point me how can I connect the two? May I use it the
> Darlington's way?

I doubt there are any laws against it, but I wouldn't.  Just cascade the two
resistors.  PIC drives base of Q1.  C of Q1 to +5V.  E of Q1 to B or Q2 thru
resistor.  E of Q2 to ground and C to solenoid.  Adjust resistor to obtain
suitable base drive for Q2.  Note that the voltage accross the resistor will
be 5V minus the two B-E drops, or about 3.6V.  The rest is Ohm's law.  Also
add a relatively large value resistor from Q1-B to GND.  Its only purpose is
to prevent small leakage thru Q1 from going thru Q2.  10Kohm should be fine.


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2001\07\24@093510 by Douglas Butler

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Look at a TIP120 darlington.  It has a beta of 1000 up to about 5A.
Like any darlington the saturation voltage is a little high so It may
need a heatsink if the solenoid is on for long, but I think it will fit
in your existing PCB.  It probably costs more than the TIP41 but less
than a Hexfet.

Sherpa Doug

> {Original Message removed}

2001\07\24@094800 by Douglas Butler

flavicon
face
I don't know the language, but this circuit will definitely fire the
solenoid while the PIC boots!  DO NOT USE THIS.

Sherpa Doug

> {Original Message removed}

2001\07\24@114633 by Lawrence Lile

flavicon
face

What's a Sziklai?  

Here are some dumb guesses:
A. A Russian drink made of beets and vodka

B.  A wild boar native to New Zealand

C.  A dangerous algorithm written in C, prone to memory leaks (see Windows)

{Original Message removed}

2001\07\24@191510 by Brent Brown

picon face
> What's a Sziklai?
>
> Here are some dumb guesses:
> A. A Russian drink made of beets and vodka
>
> B.  A wild boar native to New Zealand
>
> C.  A dangerous algorithm written in C, prone to memory leaks (see
> Windows)

I know it isn't B, because I live there, so I would go for A. My next
guess would be D: Some kind of two transistor configuration but not
a darlington pair. Would be interesting to hear what it really is and
what it is useful for.


Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  RemoveMEbrent.brownTakeThisOuTspamspamclear.net.nz

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2001\07\24@193547 by Spehro Pefhany

picon face
At 05:20 PM 7/24/01 -0700, you wrote:
>
>Why not a TIP121 or TIP132 darlington with Min. hfe 1000? Same package and
>pinout so you won't have to change the PCB. If you have extra CPU overhead,
>turn on the darlington and switch over to a 500Hz 1/3 or more duty cycle to
>minimize power dissipation.

The MOSFET I suggested looking at:
www.irf.com/product-info/datasheets/data/irliz44n.pdf
has compatible pinout to the TIP42C, and he can eliminate the heatsink.
Just change the resistor values eg. to 100R series and 10K "base to emitter"
(gate to source). It is a 55V/30A with 0.025 Ohm Rds(on) at 5V gate drive
and 0.035 Ohm Rds(on) at 4V gate drive (maximum). R-theta-JA is 65'C/W
for the fullpack device, so even at 0.035 Ohm (less than 200mV drop),
the 175'C maximum Tj won't be exceeded at 5A until the ambient temperature
is almost 120'C. (with no heatsink) That will be reliable. ;-)


Using a darlington (eg.
www.freetradezone.com/dc_images/85/16/D0258516.pdf
will work fine, but note the maximum Vce(sat) at 4A Ic
and 16mA base current is 2V, and at 6A Ic and a whopping 30mA of base
current it is only guaranteed to be < 4V. The SOA looks OK. But, even if
the output voltage is "only" 2V, that is 10W of power to dissipate, a
fairly large heatsink, which works against the lower price of the
darlington (about 60-70 cents US less in 100 qty). A cheaper MOSFET
with higher Rds(on) could be used, but a heat sink would likely be
required for reasonable Ta range.

The PWM idea is a good one, and if the chip has a built-in PWM module,
it could be put to use for this, provided the electrical and acoustic
noise was not troublesome. Just turn it on for 100msec or whatever, then
cut back for hold. The power dissipation in the coil will be greatly
reduced (but increased in the catch diode).

BTW, the catch diode will slow down the release of the solenoid, if
this is an issue.

Best regards,

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2001\07\24@195249 by Barry Gershenfeld

picon face
>What's a Sziklai?

1. Glad someone else asked, not me...

2. One word: "Yahoo!"

The first hit you get back will show you a circuit:

http://www.phys.ualberta.ca/~gingrich/phys395/notes/node97.html


(Sorry for the duplicate message, Lawrence...I wasn't looking
at the "reply to".)

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2001\07\24@202840 by David VanHorn

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face
At 10:46 AM 7/25/01 +1200, Brent Brown wrote:
> > What's a Sziklai?
> >
> > Here are some dumb guesses:
> > A. A Russian drink made of beets and vodka
> >
> > B.  A wild boar native to New Zealand
> >
> > C.  A dangerous algorithm written in C, prone to memory leaks (see
> > Windows)
>
>I know it isn't B, because I live there, so I would go for A. My next
>guess would be D: Some kind of two transistor configuration but not
>a darlington pair. Would be interesting to hear what it really is and
>what it is useful for.

Did my reply not make it?
Page 95 of HH has everything you need.
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2001\07\24@220616 by Brent Brown

picon face
> Did my reply not make it?
> Page 95 of HH has everything you need.

Sorry Dave, I may have missed your reply. But I did see Barrys
reply which gave:-
http://www.phys.ualberta.ca/~gingrich/phys395/notes/node97.html

And now I know what a Sziklai circuit is. Looks to me like VCE(sat)
would be at best 0.7V, which is this application is better than a
darlington but not as good as a MOSFET.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
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2001\07\25@021609 by Dale Botkin

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face
On Wed, 25 Jul 2001, Brent Brown wrote:

> > What's a Sziklai?
> >
> > Here are some dumb guesses:
> > A. A Russian drink made of beets and vodka
> >
> > B.  A wild boar native to New Zealand
> >
> > C.  A dangerous algorithm written in C, prone to memory leaks (see
> > Windows)
>
> I know it isn't B, because I live there, so I would go for A. My next
> guess would be D: Some kind of two transistor configuration but not
> a darlington pair. Would be interesting to hear what it really is and
> what it is useful for.

http://www.phys.ualberta.ca/~gingrich/phys395/notes/node97.html

About 20 seconds to fire up a browser and use Google to find this one.

Dale
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2001\07\25@072900 by Roman Black

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Brent Brown wrote:

> http://www.phys.ualberta.ca/~gingrich/phys395/notes/node97.html
>
> And now I know what a Sziklai circuit is. Looks to me like VCE(sat)
> would be at best 0.7V, which is this application is better than a
> darlington but not as good as a MOSFET.


Hi Brent, yep it's not that good, not as good as
a fet or even a high-side pnp driving a low-side
npn, especially for the solenoid circuit where the
high-side pnp can be driven from the 5v rail.
Some good NPN power transistors have very low sat
voltages, a circuit I built recently the NPN had
a Vce sat of only 19mV, that's like a relay! :o)
-Roman

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2001\07\25@074505 by Roman Black

flavicon
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Spehro Pefhany wrote:
>
>
> The MOSFET I suggested looking at:
> www.irf.com/product-info/datasheets/data/irliz44n.pdf
> has compatible pinout to the TIP42C, and he can eliminate the heatsink.
> Just change the resistor values eg. to 100R series and 10K "base to emitter"
> (gate to source). It is a 55V/30A with 0.025 Ohm Rds(on) at 5V gate drive
> and 0.035 Ohm Rds(on) at 4V gate drive (maximum). R-theta-JA is 65'C/W
> for the fullpack device, so even at 0.035 Ohm (less than 200mV drop),
> the 175'C maximum Tj won't be exceeded at 5A until the ambient temperature
> is almost 120'C. (with no heatsink) That will be reliable. ;-)


Excellent info! And a nice FET. I don't think any darlington
is a good choice with a 5A 24v load. I'm going to be picky
with your fet calcs <grin> remember 65'C/W is for free standing
TO220 pack with no parts around it, and a room temp PCB. For
most situations, especially if in a small enclosed box I would
derate that to say 85'C/W.

Assuming 0.035 ohm Rds, at 5A is 0.875W. So maybe 75'C rise
will be seen over ambient, FET will get to about 100'C.

Anything over 55'C total temp at the transistor will cause
failures, probably within months as the solder weakens and
goes through enough heat/cool cycles to get circle fractures.
This is the stuff I fix all the time in TVs, and having the
infrared thermometer now it's a big eyeopener, a TV with tran
at 50'C runs for years, models with transistors at even 65'C
fail repeatedly after a few months. With some models i've
been clamping bigger heatsinks on, or using better (lowsat)
parts, having to re-engineer their crappy product so the
poor customer gets more than 6 months MTBF. :o)

I suggest 0.3W max from an un-heatsunk TO220 pack.

One last point, FETs made for 5v drive, you won't get 5v
from a PIC output pin. PIC pins source 4.2v typical, down
to 3.5v once you are sourcing 10mA or more. This is an
important point for PIC newbies. The cure is fairly simple,
add a pull-up resistor from 5v to the PIC output pin, gives
5v at the FET when on. About 1k should be fine.

Sorry to be picky, but newbies especially should be VERY
conservative with all their ratings. The expert engineers
can start to push the limits... (but then a year later i'll
be fixing their product!) ;o)
-Roman

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2001\07\25@082254 by dr. Imre Bartfai

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Hi,

I'm a Hungarian. Sziklai sounds as a Hungarian surname. Unfortunately, I
never heard it before.

Regards,

Imre


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On Tue, 24 Jul 2001, Barry Gershenfeld wrote:

{Quote hidden}

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2001\07\25@082947 by Vasile Surducan

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Maybe A, but is done from pure alchool ( 99,99 % ), water on taste and
baked sugar. Don't even try it if you don't live in Siberia [he he..]

Vasile


On Tue, 24 Jul 2001, Dale Botkin wrote:

{Quote hidden}

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2001\07\25@100132 by Spehro Pefhany

picon face
At 03:50 PM 7/25/01 +1000, you wrote:

> I'm going to be picky with your fet calcs <grin>

Hi, Roman;-

Sure!

> remember 65'C/W is for free standing
>TO220 pack with no parts around it, and a room temp PCB. For
>most situations, especially if in a small enclosed box I would
>derate that to say 85'C/W.

Well, I was talking the internal Ta, but your box would have
to be pretty small (and sealed) to get that hot inside.

>Assuming 0.035 ohm Rds, at 5A is 0.875W. So maybe 75'C rise
>will be seen over ambient, FET will get to about 100'C.

Really worst case, and that is junction temperature, vs.
rated 175'C. Remember typically the FET will be more like
0.025 ohms or so with a drive from 5V.

>Anything over 55'C total temp at the transistor will cause
>failures, probably within months as the solder weakens and
>goes through enough heat/cool cycles to get circle fractures.

Yes, thermal cycling can kill the die eutectic bond.

>This is the stuff I fix all the time in TVs, and having the
>infrared thermometer now it's a big eyeopener, a TV with tran
>at 50'C runs for years, models with transistors at even 65'C
>fail repeatedly after a few months. With some models i've
>been clamping bigger heatsinks on, or using better (lowsat)
>parts, having to re-engineer their crappy product so the
>poor customer gets more than 6 months MTBF. :o)
>
>I suggest 0.3W max from an un-heatsunk TO220 pack.

That is extremely conservative by most people's standards,
I think my 600mW for industrial environments (up to 60'C
behind the panel) is pretty conservative for 24/7 operation,
and it's been shown to be very much ok in some high volume
products (> 10 years life 24/7). But I can't argue with
being on the safe side (unless I have to pay for the
safety factor.. ) There are some TO-92 (!)
packages that are sorta ok for consumer applications
at more power than that. eg. the 8550, not so conservatively
rated at 1W at Ta=25'C (normally, it's 360mW or so). Not
that I'd make crap like that, but if you look inside those
$10 amplified speakers..

>One last point, FETs made for 5v drive, you won't get 5v
>from a PIC output pin. PIC pins source 4.2v typical, down
>to 3.5v once you are sourcing 10mA or more.

The MOSFET gate draws 0.0mA, the gate-source resistor I
suggested draws 500 uA. So, the output will be darn close to
Vdd (150mV or so) With darlingtons, transistors etc. you
have to pay attention to this. Fortunately the drive goes
up at high temperatures where the transistor beta is
also higher.

For the MOSFET driver, your suggested pull-up resistor is
usually a bad idea because it will cause the solenoid to
come on if the PIC output is high impedance for any reason
(eg. during startup), or if the PIC is unplugged.
That's why I suggest a pull-DOWN resistor. The MOSFET can
also be damaged if it drifts into the linear region.

>Sorry to be picky, but newbies especially should be VERY
>conservative with all their ratings. The expert engineers
>can start to push the limits... (but then a year later i'll
>be fixing their product!) ;o)

Not a chance!

Best regards,
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2001\07\25@101108 by Spehro Pefhany

picon face
At 08:36 AM 7/25/01 +0200, you wrote:
>Hi,
>
>I'm a Hungarian. Sziklai sounds as a Hungarian surname. Unfortunately, I
>never heard it before.

I've been to Szeged if that counts, on my post-revolution tour of the
former Eastern Bloc (yes, I know Hungary was not really part of it..).
Home of fine paprika.

More seriously, here is the obit for the man (indeed a Hungarian, born in
Budapest) who died only a few years ago in Los Altos CA.

http://www.losaltosonline.com/latc/arch/1998/39/People/1pioneer/1pioneer.html

Best regards,
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2001\07\25@105748 by Roman Black

flavicon
face
Spehro Pefhany wrote:

> Really worst case, and that is junction temperature, vs.
> rated 175'C. Remember typically the FET will be more like
> 0.025 ohms or so with a drive from 5V.

Yeah, but I prefer to measure ten or so before
I really trust the makers specs. Being close to Asia
here brings a certain distrust of Asian specs, like I
bought some 65w autotransformers last month, to convert
240vac to 110vac. One I sold to a customer kept going
into thermal shutdown, I tested it into a resistive
load and at 52w it went into thermal shutdown after
about 1 hour at room temp. Dishonest crooks, some of
those Asian companies. :o(

Having said that, some of the better companies have
a higher respect for their specs, we use Motorola
diodes, many test at double the official performance.
Testing is the key. :o)


> >Anything over 55'C total temp at the transistor will cause
> >failures, probably within months as the solder weakens and
> >goes through enough heat/cool cycles to get circle fractures.
>
> Yes, thermal cycling can kill the die eutectic bond.

Yep, and just as often kill the circuit board solder joints,
especially with rigid-mounted vertical heatsinks, where the
expansion/contraction of a TO220 part causes vertical stress
on the solder joints. Very common.


> >I suggest 0.3W max from an un-heatsunk TO220 pack.
>
> That is extremely conservative by most people's standards,
> I think my 600mW for industrial environments (up to 60'C
> behind the panel) is pretty conservative for 24/7 operation,
> and it's been shown to be very much ok in some high volume
> products..

Yeah, I have stuff here running TO220s at 0.6w, when mounted
away from the board and in decent air convection boxes this
is ok without a heatsink. Even 1w can be done if you don't
mind it getting hot and smelly.


> For the MOSFET driver, your suggested pull-up resistor is
> usually a bad idea because it will cause the solenoid to
> come on if the PIC output is high impedance for any reason
> (eg. during startup), or if the PIC is unplugged.
> That's why I suggest a pull-DOWN resistor. The MOSFET can
> also be damaged if it drifts into the linear region.

VERY good point! I hope the newbies are watching before
they start posting "why does my solenoid operate during PIC
bootup"... :o)


> >Sorry to be picky, but newbies especially should be VERY
> >conservative with all their ratings. The expert engineers
> >can start to push the limits... (but then a year later i'll
> >be fixing their product!) ;o)
>
> Not a chance!


Hey Spehro, i'd buy your products without a second thought. :o)
Just some "engineers" worry me, as do some parts manufacturers
with dishonest specs. Sure it's ok being in the right, but try
explaining to the customer that it's NOT your fault, it's
the crooked Asian company that messed up... I had to do exactly
that last month.
:o)
-Roman

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2001\07\25@112707 by David VanHorn

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An observation:

Controlling things from microcontroller outputs, is not as simple as it
first appears.
I think I feel another web article coming on. :)

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2001\07\25@170524 by steve

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> For the MOSFET driver, your suggested pull-up resistor is
> usually a bad idea because it will cause the solenoid to
> come on if the PIC output is high impedance for any reason
> (eg. during startup), or if the PIC is unplugged.

One technique I have used is to switch the pull-xxxx resistor (or
schottky diode clamp) based on an I/O that goes high impedance
during reset. The pin needs to be actively set to enable the output
driver transistors, etc.

> >Sorry to be picky, but newbies especially should be VERY
> >conservative with all their ratings.

Both newbies and oldbies need to pay attention to the reset state
and what happens when a watchdog occurs. I've seen so many
products where this is ignored and some of them are really scary.

A typical scenario would be a fet that turns on while the micro is in
reset, attached to an under-rated power supply. Power comes up
at the normal rate, fet turns on, adding larger load onto power
supply, power supply sags, fet turns off, light load on supply,
supply recovers, power comes up, fet turns on,......
Net result = 50% PWM on solenoid controlling hydraulic ram.
Ouch !

A similar situation occurs a lot of the time when outputs are turned
on by the micro under software control. You might have a reset
generator that monitors supply voltage and adds a few milliseconds
of delay but that's not long in power supply terms. If you turn on all
your loads straight away you get a similar situation to that above.

Also in that category is misuse of watchdogs. Wonderful things but
should be regarded like airbags - only used when all else has failed
and should deploy in a useful way.
Ones that restart the system and do the same thing that led to the
watchdog in the first place are of limited use in many situations.

Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: stevebspamBeGonespamtla.co.nz      fax +64 9 820-1929
======================================================

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'[EE]: How to control a 24V solenoid with a PIC and'
2001\09\22@174451 by David VanHorn
flavicon
face
----- Original Message -----
From: "Lawrence Lile" <.....llile@spam@spamEraseMETOASTMASTER.COM>
To: <.....PICLISTRemoveMEspamMITVMA.MIT.EDU>
Sent: Tuesday, July 24, 2001 10:44 AM
Subject: Re: [EE]: How to control a 24V solenoid with a PIC and a
transistor?


> What's a Sziklai?
> Here are some dumb guesses:
> A. A Russian drink made of beets and vodka
> B.  A wild boar native to New Zealand
> C.  A dangerous algorithm written in C, prone to memory leaks (see
Windows)

Its described on page 95IIRC of Art of Electronics.
Its similar to a darlington, but different. In the Sziklai,  the small
transistor and the big one are different sexes.  Typically, the small one is
NPN, and the big one is PNP. All the base current in the big one goes to the
load as well, so its a bit more efficient.

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2001\09\22@181054 by Jinx

face picon face
> > What's a Sziklai?

> > B.  A wild boar native to New Zealand

True. It's big and it's flightless so it's here

> Its similar to a darlington, but different. In the Sziklai,  the small
> transistor and the big one are different sexes.

http://www.phys.ualberta.ca/~gingrich/phys395/notes/node97.html

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2001\09\22@200546 by David VanHorn

flavicon
face
At 10:11 AM 9/23/01 +1200, Jinx wrote:
> > > What's a Sziklai?
>
> > > B.  A wild boar native to New Zealand
>
>True. It's big and it's flightless so it's here
>
> > Its similar to a darlington, but different. In the Sziklai,  the small
> > transistor and the big one are different sexes.
>
>http://www.phys.ualberta.ca/~gingrich/phys395/notes/node97.html


Are we doing the fossil messages again?

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