70V questions

Hi Guys

I need to use 70V to power a solenoid for about 1sec at a time. I
would like to controll it with a PIC microcontroller.

What would be the best to get the 5V of the pic to activate the 70V
circuit of the solenoid? Is there any super transistor or is the only
way to do it by using a relay? Can somebody give me some google
keywords to find the right component to use and the applicable
attributes that I need to look out for?

In addition to that, I don't know how to get 70V from anywhere.
Preferrably, I want to get it from the wall socket. The transformers I
can find is only betwen 3V and 24V. I'm in Europe. Where can I buy
something that I plug into the wall and get 70V out. Again a few
google keywords will be helpful.

Safety: The 24V doesn't seem to shock me at all. Will 70V give you a
shock?

Thanks!

 

[Art]

Without the apparent knowledge of what, and where, you are attempting ot
accomplish, it may be best to refer your specific quest to a qualified
electrician. Even 24 VAC, (and even less) may be lethal if inappropiately
connected to the human body. IHMO!
<coetzee.evert@gmail.com> wrote in message
news:b21e4cd4-9991-4bd4-a10b-54b130aa1bfb@b15g2000hsa.googlegroups.com...

Hi Guys

I need to use 70V to power a solenoid for about 1sec at a time. I
would like to controll it with a PIC microcontroller.

What would be the best to get the 5V of the pic to activate the 70V
circuit of the solenoid? Is there any super transistor or is the only
way to do it by using a relay? Can somebody give me some google
keywords to find the right component to use and the applicable
attributes that I need to look out for?

In addition to that, I don't know how to get 70V from anywhere.
Preferrably, I want to get it from the wall socket. The transformers I
can find is only betwen 3V and 24V. I'm in Europe. Where can I buy
something that I plug into the wall and get 70V out. Again a few
google keywords will be helpful.

Safety: The 24V doesn't seem to shock me at all. Will 70V give you a
shock?

Thanks!

 

Hi , thanks for your feedback.

Here's a diagram of what I more-or-less want to achieve (looks better
in fixed width font like courier):
-------- -----------
| | | |
5V | | 72V
| PIC---BBB |
| | | |
|------| ----SOL----

I have a 5V circuit with an intelligent PIC in it which will send out
a signal when the SOLenoid should be switched on. The solenoid needs
72V. The BBB is a big black box which, I suppose will either be a
transistor grouping thing or a relay of some sort.

The solenoid takes anything between 12 and 72V depending on how long
you have it working and how hard it should work. I have a 24V PSU that
plugs into the wall and converts 220Vac to 24Vdc. I think it's maximum
1A. I need something similar but in a 72V flavour.

And this is where I want to know, is this type of voltage getting
dangerous and which parts I should use for the BBB and the 72V
supplier.

 

[John Fields]

On Wed, 21 Nov 2007 05:11:57 -0800 (PST), coetzee.evert@gmail.com
wrote:

Hi , thanks for your feedback.

Here's a diagram of what I more-or-less want to achieve (looks better
in fixed width font like courier):
-------- -----------
| | | |
5V | | 72V
| PIC---BBB |
| | | |
|------| ----SOL----

I have a 5V circuit with an intelligent PIC in it which will send out
a signal when the SOLenoid should be switched on. The solenoid needs
72V. The BBB is a big black box which, I suppose will either be a
transistor grouping thing or a relay of some sort.

The solenoid takes anything between 12 and 72V depending on how long
you have it working and how hard it should work. I have a 24V PSU that
plugs into the wall and converts 220Vac to 24Vdc. I think it's maximum
1A. I need something similar but in a 72V flavour.

And this is where I want to know, is this type of voltage getting
dangerous

---
Yes.
---

and which parts I should use for the BBB and the 72V
supplier.

---
View in Courier:

Ideally, you could do something like this, but to get 72V into the
solenoid you'll need a transformer with a 51V secondary, which might
be tricky to find.

220AC---[FUSE]--> |
|S1A
O
| +-----+
P||S--|~ +|-------------+
R||E | | |
I||C--|+ -|--+--[BFC+]--+
| +-----+ | |
O FWB GND |
|S1B [SOLENOID]
220AC>----------> | |
|
D
PIC>--------------------------------------G IRL3215
S
|
GND>----------------------------------------+


Transformers with 24V secondaries are very common, though, so here's
what I'd do:



220AC---[FUSE]--> |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+--------+
| R||E | | | |
| +--I||C-+ | | | [SOL]
| | | | | |+ |
| | T2 | | |[4700ľF] D
| | O O | | | | G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|$ -|---+--------+ |
| +-----+ | |
O | |
|S1B | |
220AC>------------> | | |
| |
GND>---------------------------------------------+ |
|
PIC>--------------------------------------------------+

That is, use two transformers with 240V primaries wired in parallel
and 24V secondaries wired in series aiding.

You could also use transformers with 120V primaries by wiring the
primaries in series.

A 4700ľF reservoir capacitor will get you about 2Vpp of ripple
across the energized solenoid, and the transformers' secondaries
should be rated for about 1.8 times the solenoid load current, or
about 2A.

Also, there's nothing magic about the MOSFET, all you really need is
a logic level N channel device capable of handling the solenoid
current when it's turned on and holding off the solenoid voltage
when it's turned off.


--
JF

 

[John Fields]

On Wed, 21 Nov 2007 09:44:18 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Wed, 21 Nov 2007 05:11:57 -0800 (PST), coetzee.evert@gmail.com
wrote:

Hi , thanks for your feedback.

Here's a diagram of what I more-or-less want to achieve (looks better
in fixed width font like courier):
-------- -----------
| | | |
5V | | 72V
| PIC---BBB |
| | | |
|------| ----SOL----

I have a 5V circuit with an intelligent PIC in it which will send out
a signal when the SOLenoid should be switched on. The solenoid needs
72V. The BBB is a big black box which, I suppose will either be a
transistor grouping thing or a relay of some sort.

The solenoid takes anything between 12 and 72V depending on how long
you have it working and how hard it should work. I have a 24V PSU that
plugs into the wall and converts 220Vac to 24Vdc. I think it's maximum
1A. I need something similar but in a 72V flavour.

And this is where I want to know, is this type of voltage getting
dangerous

---
Yes.
---


and which parts I should use for the BBB and the 72V
supplier.

---
View in Courier:

Ideally, you could do something like this, but to get 72V into the
solenoid you'll need a transformer with a 51V secondary, which might
be tricky to find.

220AC---[FUSE]--> |
|S1A
O
| +-----+
P||S--|~ +|-------------+
R||E | | |
I||C--|+ -|--+--[BFC+]--+
| +-----+ | |
O FWB GND |
|S1B [SOLENOID]
220AC>----------> | |
|
D
PIC>--------------------------------------G IRL3215
S
|
GND>----------------------------------------+


Transformers with 24V secondaries are very common, though, so here's
what I'd do:



220AC---[FUSE]--> |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+--------+
| R||E | | | |
| +--I||C-+ | | | [SOL]
| | | | | |+ |
| | T2 | | |[4700ľF] D
| | O O | | | | G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|$ -|---+--------+ |
| +-----+ | |
O | |
|S1B | |
220AC>------------> | | |
| |
GND>---------------------------------------------+ |
|
PIC>--------------------------------------------------+

That is, use two transformers with 240V primaries wired in parallel
and 24V secondaries wired in series aiding.

You could also use transformers with 120V primaries by wiring the
primaries in series.

A 4700ľF reservoir capacitor will get you about 2Vpp of ripple
across the energized solenoid, and the transformers' secondaries
should be rated for about 1.8 times the solenoid load current, or
about 2A.

Also, there's nothing magic about the MOSFET, all you really need is
a logic level N channel device capable of handling the solenoid
current when it's turned on and holding off the solenoid voltage
when it's turned off.

---
Oops...

I assumed that the solenoid will draw about 1A when it's energized
with 72V, so the foregoing may be invalid.

Do you know how much current it will draw? Or what its resistance
is? Also, what will its duty cycle be?


--
JF

 

Hi. thanks for the detiailed response JF.

I'm using the following solenoid: www.radionics.ie : RS Part number
search (top of page): 431-7560
(19mm push, 12V)

I'm looking at about 3.5% duty cycle.
It says on the datasheet( http://docs-europe.electrocomponents.com/webdocs/05c2/0900766b805c2a1f.pdf)
that the wattage increase by the square of the increase in voltage.
12->72 = 6x increase so 36x increase in wattage. (1/36 for the duty
cycle)
7W at 100% duty @ 12V so we're looking at 252W on 72V on a 3.6% duty
cycle.

Unfortunately they don't mention current or resistance in the
documentation but I can go and measure tonight.

 

[John Fields]

On Wed, 21 Nov 2007 08:20:59 -0800 (PST), coetzee.evert@gmail.com
wrote:

Hi. thanks for the detiailed response JF.

I'm using the following solenoid: www.radionics.ie : RS Part number
search (top of page): 431-7560
(19mm push, 12V)

I'm looking at about 3.5% duty cycle.
It says on the datasheet( http://docs-europe.electrocomponents.com/webdocs/05c2/0900766b805c2a1f.pdf)
that the wattage increase by the square of the increase in voltage.
12->72 = 6x increase so 36x increase in wattage. (1/36 for the duty
cycle)
7W at 100% duty @ 12V so we're looking at 252W on 72V on a 3.6% duty
cycle.

Unfortunately they don't mention current or resistance in the
documentation but I can go and measure tonight.

I found this,:

http://docs-europe.electrocomponents.com/webdocs/05b8/0900766b805b88ed.pdf

so if yours is the 12V nominal unit it'll have a coil resistance of
20.7 ohms, so the current with 72V across it will be:

E 72V
I = --- = ------- ~ 3.5 amperes,
R 20.7R

and the power it'll be dissipating will be:


P = IE = 3.5A * 72V = 252 watts,


so the duty cycle must be limited to:


Pnom * 100% 7W * 100%
D = ------------- = ----------- = 2.778%
Pon 252W

or less to keep from overheating the unit.

So now we have enough to look at the power supply again,
but the energy stored in its magnetic field is going to generate a
nasty spike when the thing turns off and the field collapses. I
didn't see any inductance spec's in the data sheets, so can you
measure it or find out what it is?


--
JF

 

On Nov 21, 4:20 pm, coetzee.ev...@gmail.com wrote:

Hi. thanks for the detiailed response JF.

I'm using the following solenoid:www.radionics.ie: RS Part number
search (top of page): 431-7560
(19mm push, 12V)

I'm looking at about 3.5% duty cycle.
It says on the datasheet(http://docs-europe.electrocomponents.com/webdocs/05c2/0900766b805c2a1...)
that the wattage increase by the square of the increase in voltage.
12->72 = 6x increase so 36x increase in wattage. (1/36 for the duty
cycle)
7W at 100% duty @ 12V so we're looking at 252W on 72V on a 3.6% duty
cycle.

I just measured and found the following:

On a 24V system, the current is 1.1A and the resistance of the
solenoid is about 23ohm.
So sounds like I'll need about 3A current on 72V. That sounds like A
LOT!

Now a far as I understand a wallwart power supply will keep on giving
juice until you reach the maximum current that it's designed for. So
clearly I can't get 3A out of a 1A psu. What about batteries? What
happens if I put 8x9V in series? That will give me 72V but what's the
maximum current that I can draw from it?

 

Hi John

This is brilliant to see that your calculations tie up with what I
measured on the 24V.

How do I measure the inductance? What do you mean about the spike?
Some magnetic force or a current? Is it the opposite of capacitance?
Then I guess the falling magnetic field will cause a current and then
probably in opposite direction...

BTW I'm using this to knock a little ball the same way as a pool que
hits a pool ball. I presume that a solenoid is the best electrical
component to do this?? My 72V plan should be able to give me the force
required but maybe there's some magical component that can give more
bang per volt.

I'm also considering a solenoid with a higher resistance, which to me
means it must have more wounds/windings to more work. (Surely this
logic is correct - If it's the same brand, looks more or less the
same, then, if the wattage is higher, it must work harder and maybe I
can get away with lower voltage and current for the same performance)

Anyway.. How do I measure inductance?

 

[John Fields]

On Wed, 21 Nov 2007 12:34:24 -0800 (PST), coetzee.evert@gmail.com
wrote:

Hi John

This is brilliant to see that your calculations tie up with what I
measured on the 24V.

How do I measure the inductance? What do you mean about the spike?
Some magnetic force or a current? Is it the opposite of capacitance?
Then I guess the falling magnetic field will cause a current and then
probably in opposite direction...

BTW I'm using this to knock a little ball the same way as a pool que
hits a pool ball. I presume that a solenoid is the best electrical
component to do this?? My 72V plan should be able to give me the force
required but maybe there's some magical component that can give more
bang per volt.

I'm also considering a solenoid with a higher resistance, which to me
means it must have more wounds/windings to more work. (Surely this
logic is correct - If it's the same brand, looks more or less the
same, then, if the wattage is higher, it must work harder and maybe I
can get away with lower voltage and current for the same performance)

Anyway.. How do I measure inductance?

---
There are several ways.

But first, before we get to the rest of your questions, what kind of
test equipment do you have?


--
JF

 

On Nov 22, 12:58 am, John Fields <jfie...@austininstruments.com>
wrote:

On Wed, 21 Nov 2007 12:34:24 -0800 (PST), coetzee.ev...@gmail.com
wrote:





Hi John

This is brilliant to see that your calculations tie up with what I
measured on the 24V.

How do I measure the inductance? What do you mean about the spike?
Some magnetic force or a current? Is it the opposite of capacitance?
Then I guess the falling magnetic field will cause a current and then
probably in opposite direction...

BTW I'm using this to knock a little ball the same way as a pool que
hits a pool ball. I presume that a solenoid is the best electrical
component to do this?? My 72V plan should be able to give me the force
required but maybe there's some magical component that can give more
bang per volt.

I'm also considering a solenoid with a higher resistance, which to me
means it must have more wounds/windings to more work. (Surely this
logic is correct - If it's the same brand, looks more or less the
same, then, if the wattage is higher, it must work harder and maybe I
can get away with lower voltage and current for the same performance)

Anyway.. How do I measure inductance?

---
There are several ways.

But first, before we get to the rest of your questions, what kind of
test equipment do you have?

--
JF

I have a digital Volt, Current and resistance meter. (Made by El
Cheapo). I see they call it a domestic meter:
http://www.maplin.co.uk/Module.aspx?ModuleNo=37279&C=Maplin&U=SearchTop&T=multi%20meter&doy=22m11
This is the only measuring tool I have. :-s

 

Also, there's nothing magic about the MOSFET, all you really need is
a logic level N channel device capable of handling the solenoid
current when it's turned on and holding off the solenoid voltage
when it's turned off.

Hi John, I would like to get back to the MOSFET comment. This sounds
scary to me. About the current. Do you mean, as we both calucated that
if the 72V will use 3A current, the then mosfet may need 5V 3A, in and
that will allow the 72V 3A out?

So my pic needs to give 3A??? This sounds almost impossible. I'll have
to check the datasheets. Is this how all transistors work re current:
The current in the base needs to be the same as the current you want
in/out on the collector and emitter?

And then of course, my next question will be if you can suggest an
appropriate mosfet from my local shop: www.radionics.ie

Thanks & Regards
Evert

 

[John Fields]

On Sun, 2 Dec 2007 08:03:56 -0800 (PST), coetzee.evert@gmail.com
wrote:

Also, there's nothing magic about the MOSFET, all you really need is
a logic level N channel device capable of handling the solenoid
current when it's turned on and holding off the solenoid voltage
when it's turned off.

Hi John, I would like to get back to the MOSFET comment. This sounds
scary to me. About the current. Do you mean, as we both calucated that
if the 72V will use 3A current, the then mosfet may need 5V 3A, in and
that will allow the 72V 3A out?

---
No. What I meant was that when there's zero volts on the gate, the
MOSFET will be turned OFF and the drain will be required to stand
off the supply voltage. On the other hand, when the gate is at 5V
the MOSFET will be turned ON and the solenoid current will flow
through the MOSFET from drain to source.

There is no current required into or out of the gate except what's
needed to charge and discharge the gate capacitance.
---

So my pic needs to give 3A??? This sounds almost impossible. I'll have
to check the datasheets. Is this how all transistors work re current:
The current in the base needs to be the same as the current you want
in/out on the collector and emitter?

---
No. for bipolar transistors there's a characteristic named 'beta'
(or Hfe) which specifies the current gain of the transistor:

Ic
Hfe = ----
Ib

For example, if a transistor is specified as having a minimum beta
of 100 with 100mA of collector current, then the maximum base
current required to get that 100mA of collector current will be:

Ic 100mA
Ib = ----- = ------- = 1mA
Hfe 100

For MOSFETs, in this type of application, all that's necessary is to
raise the voltage on the gate high enough to lower the resistance of
the drain-to-source channel to the point where its resistance is
negligible with respect to the load.
---

And then of course, my next question will be if you can suggest an
appropriate mosfet from my local shop: www.radionics.ie

---
Which circuit are you planning on using?


--
JF

 

No. for bipolar transistors there's a characteristic named 'beta'
(or Hfe) which specifies the current gain of the transistor:

Ic
Hfe = ----
Ib

For example, if a transistor is specified as having a minimum beta
of 100 with 100mA of collector current, then the maximum base
current required to get that 100mA of collector current will be:

Ic 100mA
Ib = ----- = ------- = 1mA
Hfe 100
Ok, got that.

For MOSFETs, in this type of application, all that's necessary is to
raise the voltage on the gate high enough to lower the resistance of
the drain-to-source channel to the point where its resistance is
negligible with respect to the load.
Why am I talking about Collectors,Bases, Emitters and you talk about

drains and sources. Are these the same? Why the different naming then?

And then of course, my next question will be if you can suggest an
appropriate mosfet from my local shop:www.radionics.ie

---
Which circuit are you planning on using?

This seems the simplest. (stolen from your message above)
220AC---[FUSE]--> |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+--------+
| R||E | | | |
| +--I||C-+ | | | [SOL]
| | | | | |+ |
| | T2 | | |[4700ľF] D
| | O O | | | | G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|$ -|---+--------+ |
| +-----+ | |
O | |
|S1B | |
220AC>------------> | | |
| |
GND>---------------------------------------------+ |
|
PIC>--------------------------------------------------+

Thanks a lot for all your help. I really appreciate it.

 

[John Fields]

On Mon, 3 Dec 2007 02:23:35 -0800 (PST), coetzee.evert@gmail.com
wrote:

No. for bipolar transistors there's a characteristic named 'beta'
(or Hfe) which specifies the current gain of the transistor:

Ic
Hfe = ----
Ib

For example, if a transistor is specified as having a minimum beta
of 100 with 100mA of collector current, then the maximum base
current required to get that 100mA of collector current will be:

Ic 100mA
Ib = ----- = ------- = 1mA
Hfe 100
Ok, got that.

For MOSFETs, in this type of application, all that's necessary is to
raise the voltage on the gate high enough to lower the resistance of
the drain-to-source channel to the point where its resistance is
negligible with respect to the load.

Why am I talking about Collectors,Bases, Emitters and you talk about
drains and sources. Are these the same? Why the different naming then?

---
Bipolar Junction Transistors (BJT) and Metal Oxide Semiconductor
Field Effect Transistors (MOSFET) are two completely different
animals, but they each have three terminals with the bipolar's base
corresponding to the MOSFET's gate, the bipolar collector
corresponding to the MOSFET drain and the bipolar emitter
corresponding to the MOSFET source.

For the BJT:

http://en.wikipedia.org/wiki/Bipolar_junction_transistor

and the MOSFET:

http://en.wikipedia.org/wiki/MOSFET
---

And then of course, my next question will be if you can suggest an
appropriate mosfet from my local shop:www.radionics.ie

---
Which circuit are you planning on using?

This seems the simplest. (stolen from your message above)
220AC---[FUSE]--> |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+--------+
| R||E | | | |
| +--I||C-+ | | |+ [SOL]
| | | | |[4700ľF] |
| | T2 | | | |100V D
| | O O | | | | IRL3215G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|$ -|---+--------+ |
| +-----+ | |
O | |
|S1B | |
220AC>------------> | | |
| |
GND>---------------------------------------------+ |
|
PIC>--------------------------------------------------+

Thanks a lot for all your help. I really appreciate it.

---
You're welcome. Use an IRL3215.

Also, just to be safe,

220AC---[FUSE]--> |
|S1A
O T1 FWB
| O O +-----+
+----P||S---|~ +|---+-------+-----+
| R||E | | | | |A
| +--I||C-+ | | |+ [SOL][1N4003]
| | | | |[4700ľF] | |
| | | | | |100V +-----+
| | T2 | | | | D
| | O O | | | | IRL3215 G--+
+-|--P||S-+ | | | S |
| R||E | | | | |
+--I||C---|~ -|---+-------+ |
| +-----+ | |
O +--[ZENER>]--+
|S1B | 1N4734A |
220AC>------------> | | |
| [10K]
GND>------------------------------------+ |
|
PIC>-------------------------------------------------+


--
JF

 

[John Fields]

On Tue, 4 Dec 2007 09:11:37 -0800 (PST), coetzee.evert@gmail.com
wrote:

Hi John

I thought I had all I needed but now I have one last embarrassing
question to ask...

---
Don't be embarrassed. You knew you didn't know and asked for help.
That's commendable.
---

Should the 5V ground be connected to the 70V ground? I.e should the
5V gnd be connected to the mosfet source?

---
Yes.
---

What is the reason for it to be attached not attached?

---
The source is common to both the 70V supply and the supply providing
the signal the PIC will send to the gate, so their grounds both have
to be connected to the source.


--
JF

 

thanks. Got that bit about the grounds connected to the source.

Was reading art of electronics last night (rocket science to me!) and
then I saw something that you said as well:
"Always use a supression diode when switching an inductive load"

They had the following diagram:
+Vcc --+---COIL----+----C E----- GND
| | B
+---|<------+ |

Ok. So I unleash the 72V through my favourite coil. When I stop the
voltage.... The magnetic field subsides. But according to you and the
book it generates somesort of spike.

So the way I figure it, is that the current must be generated in the
opposite way. So previosly the C of coil in my diagram was the + and
the L was -. Now I think the L will be + and the C -. So can I
'replace' the coil with a battery for the millisecond or two that the
field dissolves?

Anyway... that's the only way I can explain the use of the diode. When
the 72V is running through the coil it has no use. When it is switched
off, it will allow my new 'battery' with a + on the L side to short
circuit itself and that I guess takes care of the current generated...
Is this correct?

So if all this guessing of mine is correct then my question is... So
what? What will happen if the C of the BJT is more - than the E and B?

 

[John Fields]

On Sun, 9 Dec 2007 15:31:13 -0800 (PST), coetzee.evert@gmail.com
wrote:

thanks. Got that bit about the grounds connected to the source.

Was reading art of electronics last night (rocket science to me!) and
then I saw something that you said as well:
"Always use a supression diode when switching an inductive load"

They had the following diagram:
+Vcc --+---COIL----+----C E----- GND
| | B
+---|<------+ |

Ok. So I unleash the 72V through my favourite coil. When I stop the
voltage.... The magnetic field subsides. But according to you and the
book it generates somesort of spike.

---
Yes.

the magnetic field doesn't just subside, it collapses very quickly
and when it does it cuts the turns of the coil and induces a voltage
across the coil opposite in polarity to the voltage impressed upon
it by the battery. That is, with the transistor turned ON the
voltage on the collector side of the coil will be close to ground,
but when the transistor turns OFF The voltage on the collector will
rise as described by:

dI
E = L ----
dt

where E is the voltage appearing across the coil, in volts

L is the inductance of the coil, in henrys and

dI
---- is the time rate of change of current in the coil.
dT

For example, I don't remeber all the details, but let's say your
solenoid has an inductance of 0.1 henry, there's 3 amperes of
current in it when you open the switch, and it takes 1 millisecond
for the current to decay to zero amps from 3 amps.

Then:

dI 0.1H * 3A
E = L ---- = ----------- = 300 volts
dt 0.001S

Which will more than likely punch a hole through the transistor if
the diode isn't there.

BTW, just for grins, take a look at what happens if dT is 100ľS.
---

So the way I figure it, is that the current must be generated in the
opposite way. So previosly the C of coil in my diagram was the + and
the L was -. Now I think the L will be + and the C -. So can I
'replace' the coil with a battery for the millisecond or two that the
field dissolves?

---
Yes, but you've got it backwards. You have to put the + of the
battery on the collector and the - on the supply
---

Anyway... that's the only way I can explain the use of the diode. When
the 72V is running through the coil it has no use. When it is switched
off, it will allow my new 'battery' with a + on the L side to short
circuit itself and that I guess takes care of the current generated...
Is this correct?

---
Kinda, but the + will be connected to the collector. What happens
is that when the coil voltage tries to rise past the supply plus the
drop across the diode, the diode clamps the transistor collector to
the supply plus one diode drop while the coil discharges through the
diode. So that'll be supply plus about 0.7V, which shouldn't bother
the transistor at all.
---

So if all this guessing of mine is correct then my question is... So
what? What will happen if the C of the BJT is more - than the E and B?

---
It won't go negative, it'll go hugely positive and let all of the
magic smoke out of the transistor.


--
JF

 

Hi JF

Again thanks for the info.

I went shopping the other day and they didn't have the parts I was
looking for. So now I'm searching online to try and find them on some
online shops.

I found a pretty good webites to get datasheets. But I have to open
every one to see if it qualifies.

Do you know:
1. It seems like there's an international product numbering system for
electronic components (or does every manufacturer number their own
way?)
2. Is there a place where I can search all MOSFETS (e.g.) and find the
code for the ones that qualify for me. E.g. 5V gate and 200V for the
supply.

Regards & Merry Christmas

 

[John Fields]

On Thu, 20 Dec 2007 05:38:58 -0800 (PST), coetzee.evert@gmail.com
wrote:

Hi JF

Again thanks for the info.

I went shopping the other day and they didn't have the parts I was
looking for. So now I'm searching online to try and find them on some
online shops.

I found a pretty good webites to get datasheets. But I have to open
every one to see if it qualifies.

Do you know:
1. It seems like there's an international product numbering system for
electronic components (or does every manufacturer number their own
way?)

---
AFAIK every manufacturer names their products in their own way.

Notable exceptions are second-sourced parts where the part numbers
from the second source generally mimic the original or, at least,
integrate the original manufacturer's part number into their own.
---

2. Is there a place where I can search all MOSFETS (e.g.) and find the
code for the ones that qualify for me. E.g. 5V gate and 200V for the
supply.

---
Not that I know of.

However, all is not lost.

Many manufacturers provide editable online parametric tables for
their parts which will allow you to define the search criteria and
which will display parts which meet those criteria.

Some distributors do also. Digi-Key is a good example, and their
engine will search across all the lines they carry, so that probably
comes as close to supplying what you describe as there is.
---

Regards & Merry Christmas

---
Thanks. You too.


--
JF