Maker Pro
Maker Pro

How to quickly turn on/off N-FET switching high side of 55V?

F

Fred Bloggs

Jan 1, 1970
0
Michael said:
I don't think that would work for this application - it'll be subject
to 10s of gs of acceleration in all directions. I don't think relays
can handle that, but I guess there could be some special purpose ones
out there. Also, I'm vertically constrained - I have about 2x8x8cm for
this guy - and most relays (of course not all, but most) are pretty
tall.

-Michael

Almost any kind of power relay will maintain its state for practical
purposes at 50g, but the coil power will be a bit hefty compared to a
MOSFET, not too much more, maybe 2x.
You can save yourself a lot of circuit design by going with a P-channel,
then the drive is a simple TTL-> HV current source-> V+ referenced
MOSFET gate. Digikey has these in stock for $5.40:
http://www.vishay.com/docs/73474/sum90p10.pdf
The mounting will be non-trivial.
 
F

Fred Bloggs

Jan 1, 1970
0
John said:
After the first flyback, you could just bang it now and then to keep
the gate charged.

A second transformer could turn on a smaller npn or fet to discharge
the gate, plus a resistor across the zener.

I've combined transformers (for high current) with a wimpy pv isolator
(for dc).

All of that is just so ugly, I think I'm going to get sick...
 
F

Fred Bloggs

Jan 1, 1970
0
Winfield said:
Spoil sport!

Okay how about this, a traditional bootstrap augmented with a SCVM,
simple capacitive voltage multiplier, activated by HV output, to sustain
gate drive. The SCVM could be anything, cheapo logic schmitt
self-oscillating or cheapo CVM IC or anything...
View in a fixed-width font such as Courier.

..
..
..
..
.. HV
.. |
.. .------+-|<|--|-------.
.. | | | |
.. | | | |
.. +----+ | | |
.. | d | | ||- |
.. 12V>-|>|---| r |--------|| |
.. | v | | ||> |
.. | r | === | |
.. | | |Cbst | |
.. +----+ | | |
.. | '------+---------------+---> out
.. | | | |
.. | | ----- -
.. | | | | ^
.. CMOS IN >---' | |SCVM | |
.. Dz -/ | | |
.. ^ ----- ---
.. | | pgnd
.. +-------'
.. |
.. [Rb]
.. |
.. ---
.. sgnd
..
..
 
F

Fred Bloggs

Jan 1, 1970
0
Fred said:
Spoil sport!


Okay how about this, a traditional bootstrap augmented with a SCVM,
simple capacitive voltage multiplier, activated by HV output, to sustain
gate drive. The SCVM could be anything, cheapo logic schmitt
self-oscillating or cheapo CVM IC or anything...
View in a fixed-width font such as Courier.

.
.
.
.
. HV
. |
. .------+-|<|--|-------.
. | | | |
. | | | |
. +----+ | | |
. | d | | ||- |
. 12V>-|>|---| r |--------|| |
. | v | | ||> |
. | r | === | |
. | | |Cbst | |
. +----+ | | |
. | '------+---------------+---> out
. | | | |
. | | ----- -
. | | | | ^
. CMOS IN >---' | |SCVM | |
. Dz -/ | | |
. ^ ----- ---
. | | pgnd
. +-------'
. |
. [Rb]
. |
. ---
. sgnd
.
.

Guess that should look more like this:
View in a fixed-width font such as Courier.


..
..
..
..
.. HV
.. |
.. .------+-|<|--|---------.
.. | | | |
.. | | | |
.. +----+ | | |
.. | d | | ||- |
.. 12V>-|>|---| r |--------|| |
.. | v | | ||> |
.. | r | === | |
.. | | |Cbst | |
.. +----+ | | |
.. | '------+-----+---------+---> out
.. | | | | |
.. | | ----- -
.. | | | | ^
.. CMOS IN >---' | |SCVM | |
.. Dz -/ | | |
.. ^ ----- ---
.. | | pgnd
.. +-------'
.. |
.. [Rb]
.. |
.. ---
.. sgnd
..
..
 
F

Fred Bloggs

Jan 1, 1970
0
A bit more explicit:
View in a fixed-width font such as Courier.

..
..
..
..
.. HV
.. |
.. 12V>-|>|------+------+-|<|--|---------.
.. | | | |
.. | | | |
.. +----+ | | |
.. | d | | ||- |
.. | r |--------|| |
.. | v | | ||> |
.. | r | === | |
.. | | |Cbst | |
.. +----+ | | |
.. | '------+-----+---------+---> out
.. | | | | |
.. | | ----- -
.. | | | | ^
.. CMOS IN >---' | |SCVM | |
.. Dz -/ | | |
.. ^ ----- ---
.. | | pgnd
.. +-------'
.. |
.. [Rb]
.. |
.. ---
.. sgnd
..
..
 
W

Winfield

Jan 1, 1970
0
I didn't answer this, sorry. You can estimate relative
MOSFET dies sizes by comparing power dissipation ratings
and gate capacitance Ciss.
I understand the necessity of needing to be able to quickly sync or
source current into our out of the gate, but it looks like the circuit
has a delay added in between A and B in the form of the inverter. I
mean, couldn't the switching circuit look like below?:

470
+5 --+-----+-/\/\-+
_|_ B | _|_ A
\_/ -> | \_/ ->
TTL | | |
------+----|>o-----+ FOD617D (2)
inverter optoisolator

With the way you have it drawn, it seems to me that there must be some
reason to switch A before B, but I'm not sure what that would be,
especially considering that the delay between switches would be so
small.

The switching time of a cmos gate, typically under 10ns,
is basically zero compared to the several 3 to 5us delay
in the optoisolators, and the 10 to 15us time to charge
the MOSFET gates. So one before the other has no impact.
Generally one likes to draw a circuit including necessary
driving pieces, etc., so as not to make excessive demands
on the signa; source, etc. That's why an inverter would
be customarily shown at the input to start things off.
It's not for a production project - just a research project, so no
fear :)

Well, even so, are you thinking well about the bigger
picture? I mean, is this just a bunch of batteries to
gang up and help run a motor? What's wrong with just
using a diode-OR on each battery? Is it necessary to
isolate the OFF batteries? If so, then you'll need two
MOSFETs back-back (source-to-source) to insure the ON
battery doesn't work to charge the discharged ones.
What about fuses, current-limiting, status indicators,
etc. Does the motor have a PWM modulator or something,
you don't just always give it the full juice, do you?
What about current monitoring, etc.?

All that said, if your batteries are all tied together
and share the ground system, there's a MUCH simpler
approach that can be used. We can dispense with all
the optically-isolated stuff. Like I said, generally
it's more fun on usenet s.e.d. to talk about whatever
interests us most at the time, as conversation goes,
rather than what may actually be best for a project.
Lucky! I'm still stuck.

Took me 2.5 hours to get home! But my Prius was an
ideal car for the task - it's great at stop and go
traffic - the gas engine shuts down so you can inch
forward on batteries. I can get up to 35mph before
the gas engine kicks in, if I'm accelerating slowly.
(And if the battery is well charged, and if the heater
is off, and if it's not so cold the software insists
on protecting the battery. That's a lot of ifs.)
 
W

Winfield

Jan 1, 1970
0
A bit more explicit:
View in a fixed-width font such as Courier.

.
.
.
.
. HV
. |
. 12V>-|>|------+------+-|<|--|---------.
. | | | |
. | | | |
. +----+ | | |
. | d | | ||- |
. | r |--------|| |
. | v | | ||> |
. | r | === | |
. | | |Cbst | |
. +----+ | | |
. | '------+-----+---------+---> out
. | | | | |
. | | ----- -
. | | | | ^
. CMOS IN >---' | |SCVM | |
. Dz -/ | | |
. ^ ----- ---
. | | pgnd
. +-------'
. |
. [Rb]
. |
. ---
. sgnd
.
.

What's SCVM?

I think the "Cbst" capacitor power idea was covered,
"Cbst" would have to hold enough charge to run the
"drvr" for half an hour or more. Maybe if "drvr" is
a micropower circuit, and if "Cbst" is big enough.
 
M

Michael

Jan 1, 1970
0
I didn't answer this, sorry. You can estimate relative
MOSFET dies sizes by comparing power dissipation ratings
and gate capacitance Ciss.

Wouldn't power dissipation ratings also be highly dependent on the
package that the FET was in?
The switching time of a cmos gate, typically under 10ns,
is basically zero compared to the several 3 to 5us delay
in the optoisolators, and the 10 to 15us time to charge
the MOSFET gates. So one before the other has no impact.
Generally one likes to draw a circuit including necessary
driving pieces, etc., so as not to make excessive demands
on the signa; source, etc. That's why an inverter would
be customarily shown at the input to start things off.

Ah - that makes perfect sense.
Well, even so, are you thinking well about the bigger
picture? I mean, is this just a bunch of batteries to
gang up and help run a motor? What's wrong with just
using a diode-OR on each battery? Is it necessary to
isolate the OFF batteries? If so, then you'll need two
MOSFETs back-back (source-to-source) to insure the ON
battery doesn't work to charge the discharged ones.
What about fuses, current-limiting, status indicators,
etc. Does the motor have a PWM modulator or something,
you don't just always give it the full juice, do you?
What about current monitoring, etc.?

So this board is a power distribution board. It carries power to a
number of other boards that run various motors through all sorts of
current loops. It also powers some digital systems that take in the
high voltage and step it down to something more usable.

The reason I want be able to switch on and off the power sources is
that I want to be able to protect them from undervoltage and
overcurrent situations. They are li-polys, so if I drain them too much
or if I pull too much current they die. If I just used diodes I would
lose that protection. I also want it high side switched as we have had
problems due to low side switching - with fun ground loop problems
like through external VGA cables and stuff like that. Also, the hope
was that using FETs would give me a bit more efficiency, though I
suppose that is not a huge gain. Note that there will be 3 power
sources - two batteries and wall power. The wall power input does not
need undervoltage protection, obviously (except for it being too low
to power anything - at about 9VDC).

I don't understand why I would need two mosfets, or even how that
would work... I mean once the FET is off (VGS < VT)current can't flow
through it, or at least that was my understanding. Errr wait -
intrnisic body diode... Argh. It has a 1.3V forward voltage according
to the IRF1407PbF datasheet. I see your point now. What happens to a
FET when it is reverse biased? It looks like the body diode turns on
at about -1.3V and then can handle a ton of current, but what about
between VDS = -1.3V - 0? I'm assuming it's just off. That's not really
relevant, but now I'm really curious as I've never really heard the
properties of N-FETs discussed with regards to VDS < 0. But why put
two FETs source to source? To me it'd make more sense to put a
schottky diode in series with the FET. I'd probably put it on the
drain side of the FET just so as to increase VGS a little. I mean - if
you put two FETs source to source wouldn't you see a 1.3V drop across
one of them?

As for current limiting and indicators and whatnot - I am planning on
putting a 5V buck converter that powers all the logic switching these
FETs, as well as a high side shunt resistor with a high side current
sense amplifier. A comparator will watch the output of the high side
current sense amplifier and drive an OR gate that is driving the FET
driver. I haven't figured out what all indicators are needed - but
that is planned. Probably one to show if a battery has been turned off
for undervoltage, and another to indicate which power source is being
used. Maybe a couple latched LEDs to show if there were any transient
problems (ie a surge in current).
All that said, if your batteries are all tied together
and share the ground system, there's a MUCH simpler
approach that can be used. We can dispense with all
the optically-isolated stuff. Like I said, generally
it's more fun on usenet s.e.d. to talk about whatever
interests us most at the time, as conversation goes,
rather than what may actually be best for a project.

The batteries all share a common ground. What simpler system were you
thinking of? I would really like to keep it high side switched, if
that was your idea.
Took me 2.5 hours to get home! But my Prius was an
ideal car for the task - it's great at stop and go
traffic - the gas engine shuts down so you can inch
forward on batteries. I can get up to 35mph before
the gas engine kicks in, if I'm accelerating slowly.
(And if the battery is well charged, and if the heater
is off, and if it's not so cold the software insists
on protecting the battery. That's a lot of ifs.)

Ah - I did better than you! Took me a mere 1:45 to get home
(typically ~25 minutes). I heard that the highways were completely
backed up so I went back roads the entire way, and it worked out
fairly well. It was clear sailing from Watertown to Cambridge - almost
no cars on the road whatsoever.
 
J

John Larkin

Jan 1, 1970
0
All of that is just so ugly, I think I'm going to get sick...

The general concept is path splitting, using separate, paralleled gain
stages for the DC and AC parts of the signal. We're working on a laser
driver, dc to 15 GHz, that uses split paths. The tricky part here is
the final combining circuit, and getting the step response really flat
in the crossover region. We may just digitize the dc component, run it
through a fir filter, and dac it into the combiner; then all we'll
need is a tuning algorithm, which might finally be a use for my
deconvolution program, which was originally designed to beautify the
step response of a fast-but-ugly TDR.

John
 
J

John Larkin

Jan 1, 1970
0
I understand the necessity of needing to be able to quickly sync or
source current into our out of the gate, but it looks like the circuit
has a delay added in between A and B in the form of the inverter. I
mean, couldn't the switching circuit look like below?:

470
+5 --+-----+-/\/\-+
_|_ B | _|_ A
\_/ -> | \_/ ->
TTL | | |
------+----|>o-----+ FOD617D (2)
inverter optoisolator


I only drew 2 inverters to enforce solid drive to both led's. If the
incoming logic level is known to be sufficiently stiff, a single
inverter will do.

Except that, as drawn, it just doesn't work any more.

With the way you have it drawn, it seems to me that there must be some
reason to switch A before B, but I'm not sure what that would be,
especially considering that the delay between switches would be so
small.

There's no need to consider delays in the led drive; the
phototransistors are orders of magnitude slower than the gate delays
driving the led's.

John
 
M

Michael

Jan 1, 1970
0
I only drew 2 inverters to enforce solid drive to both led's. If the
incoming logic level is known to be sufficiently stiff, a single
inverter will do.

Except that, as drawn, it just doesn't work any more.

Oops - all the snow went straight to my head. :eek: Resistor should be on
other side of B optoisolator.
There's no need to consider delays in the led drive; the
phototransistors are orders of magnitude slower than the gate delays
driving the led's.

John

I had it in my head that phototransistors were fairly slow, hence the
confusion. Thanks for clearing it up!

-Michael
 
F

Fred Bloggs

Jan 1, 1970
0
Winfield said:
A bit more explicit:
View in a fixed-width font such as Courier.

.
.
.
.
. HV
. |
. 12V>-|>|------+------+-|<|--|---------.
. | | | |
. | | | |
. +----+ | | |
. | d | | ||- |
. | r |--------|| |
. | v | | ||> |
. | r | === | |
. | | |Cbst | |
. +----+ | | |
. | '------+-----+---------+---> out
. | | | | |
. | | ----- -
. | | | | ^
. CMOS IN >---' | |SCVM | |
. Dz -/ | | |
. ^ ----- ---
. | | pgnd
. +-------'
. |
. [Rb]
. |
. ---
. sgnd
.
.


What's SCVM?

I think the "Cbst" capacitor power idea was covered,
"Cbst" would have to hold enough charge to run the
"drvr" for half an hour or more. Maybe if "drvr" is
a micropower circuit, and if "Cbst" is big enough.

SCVM is a multiplier used to maintain the gate charge in the big one.
Everything is the same. A simplified drawing assuming minimum HV at 10V
or more would be as shown:
View in a fixed-width font such as Courier.

..
.. HV
.. |
.. 12V>--+-|>|-+--------+-----+-|<|--|---------.
.. | | | | | |
.. | | C | | |
.. | | .--B npn | | |
.. | | | E | |- |
.. | [4.7K] | +-[51]----|| |
.. | | | E | |> |
.. | '----+--B pnp | | |
.. [1K] | C === | |
.. | | | |Cbst | |
.. | | '-----+------+---------------+---> out
.. | | | | | |
.. | |- | +-|>|-----+ -
.. +-------|| SSN1N45BTA| | | ^
.. | |> | | [100] |
.. \| | | | | |
.. 2N7000 ||-------+ -/ | === ---
.. <| | 12VZ ^ ----- | pgnd
.. | | | |C555 |----'
.. --- | | |ASTBL|
.. sgnd | | |10KHz|
.. | | -----
.. | | |
.. CMOS IN >----' +--------'
.. |
.. /}\ 10mA
.. \V/
.. |
.. ---
.. sgnd
..
..
..
reference pg 57, 101 Things a Boy Can Do with a 555...
 
F

Fred Bloggs

Jan 1, 1970
0
John said:
The general concept is path splitting, using separate, paralleled gain
stages for the DC and AC parts of the signal. We're working on a laser
driver, dc to 15 GHz, that uses split paths. The tricky part here is
the final combining circuit, and getting the step response really flat
in the crossover region. We may just digitize the dc component, run it
through a fir filter, and dac it into the combiner; then all we'll
need is a tuning algorithm, which might finally be a use for my
deconvolution program, which was originally designed to beautify the
step response of a fast-but-ugly TDR.

John

I'm not impressed with those numbers or your techniques...very boring stuff.
 
J

John Larkin

Jan 1, 1970
0
I'm not impressed with those numbers or your techniques...very boring stuff.

This stuff keeps me amused, and paid.

What amuses you?

John
 
W

Winfield

Jan 1, 1970
0
Michael said:
Wouldn't power dissipation ratings also be highly dependent on the
package that the FET was in?

No. At least not very much. You'll find that dies mounted
in TO-220 packages have the same thermal resistance as the
same dies mounted in a much larger TO-247 package. And as
the smaller D2-PAK package. It's the die's area footprint
that matters.
So this board is a power distribution board. It carries power to a
number of other boards that run various motors through all sorts of
current loops. It also powers some digital systems that take in the
high voltage and step it down to something more usable.

The reason I want be able to switch on and off the power sources is
that I want to be able to protect them from undervoltage and
overcurrent situations. They are li-polys, so if I drain them too much
or if I pull too much current they die. If I just used diodes I would
lose that protection. I also want it high side switched as we have had
problems due to low side switching - with fun ground loop problems
like through external VGA cables and stuff like that. Also, the hope
was that using FETs would give me a bit more efficiency, though I
suppose that is not a huge gain. Note that there will be 3 power
sources - two batteries and wall power. The wall power input does not
need undervoltage protection, obviously (except for it being too low
to power anything - at about 9VDC).

I don't understand why I would need two mosfets, or even how that
would work... I mean once the FET is off (VGS < VT)current can't flow
through it, or at least that was my understanding. Errr wait -
intrnisic body diode... Argh. It has a 1.3V forward voltage according
to the IRF1407PbF datasheet. I see your point now. What happens to a
FET when it is reverse biased? It looks like the body diode turns on
at about -1.3V and then can handle a ton of current, but what about
between VDS = -1.3V - 0? I'm assuming it's just off. That's not really
relevant, but now I'm really curious as I've never really heard the
properties of N-FETs discussed with regards to VDS < 0.

They conduct current either way if the gate voltage is high
enough over the source. If the reverse-direction current is
high enough the drop across Rds(on) will increase to the
point where the anti-parallel intrinsic diode also conducts.
But why put two FETs source to source?

To make a fully-bidirectional four-quadrant switch, that is
completely OFF in one state and completely ON in the other.
To me it'd make more sense to put a schottky diode in series
with the FET. I'd probably put it on the drain side of the
FET just so as to increase VGS a little. I mean - if you put
two FETs source to source wouldn't you see a 1.3V drop across
one of them?

When the FETs are both ON you get 2*Rds(on), not 1.3 volts.

You may be better off with a diode - assuming you want to
switch from one source to the other without a power break,
you'll need a diode-OR action. An ON/OFF two-MOSFET switch
could conduct huge currents from a high-voltage battery into
a low one.

Before leaving the topic, it's worth noting that MOSFETs
as active rectifiers are better and cheaper than Schottky
diodes. For example, a 60CTQ045 dual 45V Schottky will
drop about 500mV at 30A, whereas an IRF1405 55V MOSFET
will drop only 210mV at 30A (both warmed up to Tj = 100C).
The diode costs $2.78 qty 100, vs $2.64 for the MOSFET.
The batteries all share a common ground. What simpler system were you
thinking of? I would really like to keep it high side switched, if
that was your idea.

I'll answer later. Meanwhile look at Fred's ASCII drawing,
as a start. I'd change a few things, but the basic idea
is to use a capacitor to deliver the MOSFET operating
voltages, and transistor level-shift and driver stages.
 
J

John Fields

Jan 1, 1970
0
No. At least not very much. You'll find that dies mounted
in TO-220 packages have the same thermal resistance as the
same dies mounted in a much larger TO-247 package. And as
the smaller D2-PAK package. It's the die's area footprint
that matters.


They conduct current either way if the gate voltage is high
enough over the source. If the reverse-direction current is
high enough the drop across Rds(on) will increase to the
point where the anti-parallel intrinsic diode also conducts.


To make a fully-bidirectional four-quadrant switch, that is
completely OFF in one state and completely ON in the other.


When the FETs are both ON you get 2*Rds(on), not 1.3 volts.

You may be better off with a diode - assuming you want to
switch from one source to the other without a power break,
you'll need a diode-OR action. An ON/OFF two-MOSFET switch
could conduct huge currents from a high-voltage battery into
a low one.

Before leaving the topic, it's worth noting that MOSFETs
as active rectifiers are better and cheaper than Schottky
diodes. For example, a 60CTQ045 dual 45V Schottky will
drop about 500mV at 30A, whereas an IRF1405 55V MOSFET
will drop only 210mV at 30A (both warmed up to Tj = 100C).
The diode costs $2.78 qty 100, vs $2.64 for the MOSFET.


I'll answer later. Meanwhile look at Fred's ASCII drawing,
as a start. I'd change a few things, but the basic idea
is to use a capacitor to deliver the MOSFET operating
voltages, and transistor level-shift and driver stages.

---
Here's my second cut for the 55V 30A high side driver:

Version 4
SHEET 1 1852 1156
WIRE 800 400 576 400
WIRE 912 400 800 400
WIRE 1168 400 912 400
WIRE 1504 400 1168 400
WIRE 576 480 576 400
WIRE 800 480 800 400
WIRE 912 480 912 400
WIRE 1168 480 1168 400
WIRE 1504 480 1504 400
WIRE 1328 528 1280 528
WIRE 1440 528 1408 528
WIRE 800 624 800 544
WIRE 912 624 912 544
WIRE 912 624 800 624
WIRE 1648 624 912 624
WIRE 576 640 576 544
WIRE 656 640 576 640
WIRE 800 640 800 624
WIRE 800 640 736 640
WIRE 1504 656 1504 576
WIRE 576 704 576 640
WIRE 1648 704 1648 624
WIRE 208 736 96 736
WIRE 368 752 272 752
WIRE 400 752 368 752
WIRE 512 752 480 752
WIRE 1168 784 1168 560
WIRE 1280 784 1280 528
WIRE 1280 784 1168 784
WIRE 1504 784 1504 736
WIRE 1600 784 1504 784
WIRE 96 816 96 736
WIRE 128 816 96 816
WIRE 240 816 192 816
WIRE 368 816 368 752
WIRE 368 816 320 816
WIRE 1168 848 1168 784
WIRE 1504 848 1504 784
WIRE 1648 880 1648 800
WIRE 800 896 800 640
WIRE 800 896 672 896
WIRE 992 896 928 896
WIRE 1104 896 1072 896
WIRE 1280 896 1280 784
WIRE 1328 896 1280 896
WIRE 1440 896 1408 896
WIRE 96 928 96 816
WIRE 128 928 96 928
WIRE 240 928 192 928
WIRE 368 928 368 816
WIRE 368 928 320 928
WIRE 672 944 672 896
WIRE 800 944 800 896
WIRE 928 944 928 896
WIRE 96 960 96 928
WIRE 96 1056 96 1024
WIRE 576 1056 576 800
WIRE 576 1056 96 1056
WIRE 672 1056 672 1024
WIRE 672 1056 576 1056
WIRE 800 1056 800 1024
WIRE 800 1056 672 1056
WIRE 928 1056 928 1024
WIRE 928 1056 800 1056
WIRE 1168 1056 1168 944
WIRE 1168 1056 928 1056
WIRE 1504 1056 1504 944
WIRE 1504 1056 1168 1056
WIRE 1648 1056 1648 960
WIRE 1648 1056 1504 1056
WIRE 96 1104 96 1056
FLAG 96 1104 0
SYMBOL pnp 1440 576 M180
WINDOW 0 75 83 Left 0
WINDOW 3 53 48 Left 0
SYMATTR InstName Q1
SYMATTR Value 2N5401
SYMBOL npn 1104 848 R0
WINDOW 0 71 15 Left 0
WINDOW 3 45 48 Left 0
SYMATTR InstName Q2
SYMATTR Value 2N5550
SYMBOL voltage 800 928 R0
WINDOW 3 40 81 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 0 40 53 Left 0
SYMATTR Value 55
SYMATTR InstName V2
SYMBOL res 1632 864 R0
WINDOW 0 -39 37 Left 0
WINDOW 3 -41 68 Left 0
SYMATTR InstName R4
SYMATTR Value 1.8
SYMBOL voltage 928 928 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 0 39 57 Left 0
SYMATTR Value PULSE(0 5 0.02 1e-6 1e-6 0.05 0.1 1)
SYMATTR InstName V3
SYMBOL res 1088 880 R90
WINDOW 0 -46 56 VBottom 0
WINDOW 3 -38 58 VTop 0
SYMATTR InstName R9
SYMATTR Value 1000
SYMBOL nmos 1600 704 R0
SYMATTR InstName M2
SYMATTR Value SUM75N06-09L
SYMBOL res 1152 464 R0
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL res 1424 512 R90
WINDOW 0 -46 56 VBottom 0
WINDOW 3 -38 58 VTop 0
SYMATTR InstName R1
SYMATTR Value 50k
SYMBOL npn 1440 848 R0
WINDOW 0 72 17 Left 0
WINDOW 3 47 50 Left 0
SYMATTR InstName Q3
SYMATTR Value 2N5550
SYMBOL res 1424 880 R90
WINDOW 0 65 58 VBottom 0
WINDOW 3 73 54 VTop 0
SYMATTR InstName R3
SYMATTR Value 50k
SYMBOL res 1488 640 R0
WINDOW 0 41 43 Left 0
WINDOW 3 34 74 Left 0
SYMATTR InstName R5
SYMATTR Value 1000
SYMBOL ind 640 656 R270
WINDOW 0 45 56 VTop 0
WINDOW 3 -8 54 VBottom 0
SYMATTR InstName L1
SYMATTR Value .005
SYMBOL npn 512 704 R0
SYMATTR InstName Q4
SYMATTR Value 2N5550
SYMBOL res 496 736 R90
WINDOW 0 -11 55 VBottom 0
WINDOW 3 35 55 VTop 0
SYMATTR InstName R6
SYMATTR Value 1000
SYMBOL diode 592 544 R180
WINDOW 0 51 34 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D1
SYMATTR Value MURS120
SYMBOL zener 816 544 R180
WINDOW 0 63 33 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D2
SYMATTR Value BZX84C10L
SYMBOL cap 896 480 R0
WINDOW 0 48 32 Left 0
WINDOW 3 28 61 Left 0
SYMATTR InstName C1
SYMATTR Value 10e-6
SYMBOL Digital\\schmitt 208 672 R0
SYMATTR InstName A1
SYMATTR SpiceLine vhigh 5 vh 1 trise 10e-9 tfall 10e-9
SYMBOL cap 80 960 R0
WINDOW 0 -44 33 Left 0
WINDOW 3 -51 64 Left 0
SYMATTR InstName C3
SYMATTR Value 1e-8
SYMBOL res 336 800 R90
WINDOW 0 -6 58 VBottom 0
WINDOW 3 36 57 VTop 0
SYMATTR InstName R11
SYMATTR Value 910
SYMBOL diode 192 800 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D5
SYMATTR Value 1N4148
SYMBOL diode 128 944 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D6
SYMATTR Value 1N4148
SYMBOL res 336 912 R90
WINDOW 0 -11 56 VBottom 0
WINDOW 3 40 59 VTop 0
SYMATTR InstName R12
SYMATTR Value 8200
SYMBOL res 656 928 R0
WINDOW 0 -36 35 Left 0
WINDOW 3 -57 65 Left 0
SYMATTR InstName R7
SYMATTR Value 5600
TEXT 1672 920 Left 0 ;LOAD
TEXT 104 1072 Left 0 !.tran .1
 
W

Winfield Hill

Jan 1, 1970
0
Note, 0.5V at 30A for a 60CTQ045 dual Schottky is 15W
of heat that has to be dissipated, not a pretty sight!
Two 60CTQ045 (all four sections in parallel) lowers the
voltage drop to about 0.3V at moderate Tj, and lowers
the power dissipation to 9 watts total, and to 4.5W in
each of the TO-220 packages, which is much more sensible.

I'm not sure how useful it is to post Spice analysis
files, it tends to stop or slow down the conversation,
because one can't quickly read it on the spot.

WRT your circuit, John. Whew! A 65-volt gate swing!
That's bold, and assumes the MOSFET's source will follow
fast enough to keep Vgs below the 20-volt limit. Well,
maybe, but I'd at least want a protective gate zener.

I liked Fred's circuit better, but the current sink
+ zener scheme as part of the flying gate-voltage
generator bothered me.

Also, neither circuit addresses Michael's issues,
which involves connecting two batteries and a third
power source, to the 30A output power bus. The sad
power-dissipating 30A diode-OR issue and its wiring,
etc., is still unsettled.
 
J

John Fields

Jan 1, 1970
0
On Dec 15, 12:12 pm, John Fields wrote:
I'm not sure how useful it is to post Spice analysis
files, it tends to stop or slow down the conversation,
because one can't quickly read it on the spot.

---
I like ASCII as much as anyone, but when stuff starts getting
complex to the point where timing is an issue or an ASCII drawing
would just be too busy, I prefer to either run a simulation and post
the schematic list or post a PDF to abse. In any case, how much
bother could it be, if one is interested, to post the thing into
LTSPICE and print out the schematic?
---
WRT your circuit, John. Whew! A 65-volt gate swing!

---
LOL, it's an N channel enhancement mode MOSFET high side driver
switching a 55 volt source into a grounded load!

How else would you propose to do it?
---
That's bold, and assumes the MOSFET's source will follow
fast enough to keep Vgs below the 20-volt limit. Well,
maybe, but I'd at least want a protective gate zener.

---
Easy enough to do. My intent with the "second cut" wasn't to
present a fully fleshed out circuit, but rather to illustrate a way
to use a boost converter to generate the regulated gate drive
voltage and have it ride on the positive supply voltage as it (the
supply voltage) varied.

BTW, did you notice how the current used to drive the Zener and
establish the gate drive voltage is returned to the battery instead
of being wasted? Kinda slick, I thought...
---
I liked Fred's circuit better, but the current sink
+ zener scheme as part of the flying gate-voltage
generator bothered me.

---
Oh, well...
---
Also, neither circuit addresses Michael's issues,
which involves connecting two batteries and a third
power source, to the 30A output power bus. The sad
power-dissipating 30A diode-OR issue and its wiring,
etc., is still unsettled.

---
IMO, getting a good switch is the first order of business and then
getting them to keep from stepping on each others' feet follows.

Since Michael posted:

"The batteries all share a common ground. What simpler system
were you thinking of? I would really like to keep it high side
switched, if that was your idea."

and you replied:

"I'll answer later."

I thought you were going to take that one on. No?
 
W

Winfield

Jan 1, 1970
0
John said:
Winfield said:
John Fields wrote:
Here's my second cut for the 55V 30A high side driver:
Version 4 [ snip ]
I'm not sure how useful it is to post Spice analysis
files, it tends to stop or slow down the conversation,
because one can't quickly read it on the spot.

---
I like ASCII as much as anyone, but when stuff starts getting
complex to the point where timing is an issue or an ASCII drawing
would just be too busy, I prefer to either run a simulation and post
the schematic list or post a PDF to abse. In any case, how much
bother could it be, if one is interested, to post the thing into
LTSPICE and print out the schematic?

Sorry, but it probably limits the conversation to a
few -- you, me, anybody else? And look at the delay.
You may not have had any answer at all.
---
LOL, it's an N channel enhancement mode MOSFET high side
driver switching a 55 volt source into a grounded load!

How else would you propose to do it?

No Sir. Check out the rail-rail current of your
pnp and npn pullup and pulldown transistors, ughh!

The driver's currents should be referenced to the
MOSFET's source. That's where the capacitance is.
BTW, did you notice how the current used to drive the Zener
and establish the gate drive voltage is returned to the
battery instead of being wasted? Kinda slick, I thought...

In the noise level, compared to the mayhem underway.
 
J

John Fields

Jan 1, 1970
0
John said:
Winfield said:
John Fields wrote:
Here's my second cut for the 55V 30A high side driver:
Version 4 [ snip ]
I'm not sure how useful it is to post Spice analysis
files, it tends to stop or slow down the conversation,
because one can't quickly read it on the spot.

---
I like ASCII as much as anyone, but when stuff starts getting
complex to the point where timing is an issue or an ASCII drawing
would just be too busy, I prefer to either run a simulation and post
the schematic list or post a PDF to abse. In any case, how much
bother could it be, if one is interested, to post the thing into
LTSPICE and print out the schematic?

Sorry, but it probably limits the conversation to a
few -- you, me, anybody else? And look at the delay.
You may not have had any answer at all.

---
Well, Win, the design was for the OP so I'd expect that he, at
least, would be willing to accept a format that was convenient for
me to work in and to provide a working model of the circuit.

Whether it's inconvenient for you is really immaterial. Play my way
if you want to, else why don't you ASCII-ize the drawing for
everyone else who you think wants to play your way?
---
No Sir. Check out the rail-rail current of your
pnp and npn pullup and pulldown transistors, ughh!

---
So, since you used the simulator to find that out, It's not _all_
bad, huh? ;)

Anyway, thanks for pointing that error out so politely and, if you
can spare the time, see the file at the end of this post for the
easy fix.
---
The driver's currents should be referenced to the
MOSFET's source. That's where the capacitance is.

---
I prefer to reference the currents to ground for a few reasons:

1. With the load looking like a couple of ohms it won't make any
difference in how long it takes to charge or discharge the gate
capacitance and,

2. The source jumps up to about 50V if the load is disconnected or
opens (whether the switch is on or off) and,

3. With the switch turned off, any current in the driver will have
to return to ground through the load. Not exactly my cup of tea,
but YMMV.
---
In the noise level, compared to the mayhem underway.

---
My, but you're in a bitchy mood.


Maybe this'll cheer you up:

Version 4
SHEET 1 1996 1156
WIRE 752 400 576 400
WIRE 848 400 752 400
WIRE 1104 400 848 400
WIRE 1440 400 1104 400
WIRE 576 480 576 400
WIRE 752 480 752 400
WIRE 848 480 848 400
WIRE 1104 480 1104 400
WIRE 1440 480 1440 400
WIRE 1264 528 1216 528
WIRE 1376 528 1344 528
WIRE 752 608 752 544
WIRE 848 608 848 544
WIRE 848 608 752 608
WIRE 1648 608 848 608
WIRE 1216 624 1216 528
WIRE 1440 640 1440 576
WIRE 576 656 576 544
WIRE 624 656 576 656
WIRE 752 656 752 608
WIRE 752 656 704 656
WIRE 1648 656 1648 608
WIRE 576 704 576 656
WIRE 1104 704 1104 560
WIRE 1216 704 1216 688
WIRE 1216 704 1104 704
WIRE 208 736 96 736
WIRE 1216 736 1216 704
WIRE 1440 736 1440 720
WIRE 1600 736 1440 736
WIRE 368 752 272 752
WIRE 400 752 368 752
WIRE 512 752 480 752
WIRE 1104 768 1104 704
WIRE 1440 800 1440 736
WIRE 1504 800 1440 800
WIRE 1648 800 1648 752
WIRE 1648 800 1568 800
WIRE 96 816 96 736
WIRE 128 816 96 816
WIRE 240 816 192 816
WIRE 368 816 368 752
WIRE 368 816 320 816
WIRE 928 816 880 816
WIRE 1040 816 1008 816
WIRE 1440 848 1440 800
WIRE 1216 896 1216 800
WIRE 1264 896 1216 896
WIRE 1376 896 1344 896
WIRE 1648 912 1648 800
WIRE 96 928 96 816
WIRE 128 928 96 928
WIRE 240 928 192 928
WIRE 368 928 368 816
WIRE 368 928 320 928
WIRE 752 928 752 656
WIRE 880 928 880 816
WIRE 96 960 96 928
WIRE 96 1040 96 1024
WIRE 576 1040 576 800
WIRE 576 1040 96 1040
WIRE 752 1040 752 1008
WIRE 752 1040 576 1040
WIRE 880 1040 880 1008
WIRE 880 1040 752 1040
WIRE 1104 1040 1104 864
WIRE 1104 1040 880 1040
WIRE 1440 1040 1440 944
WIRE 1440 1040 1104 1040
WIRE 1648 1040 1648 992
WIRE 1648 1040 1440 1040
WIRE 96 1088 96 1040
FLAG 96 1088 0
SYMBOL pnp 1376 576 M180
WINDOW 0 75 83 Left 0
WINDOW 3 53 48 Left 0
SYMATTR InstName Q1
SYMATTR Value 2N5401
SYMBOL npn 1040 768 R0
WINDOW 0 71 15 Left 0
WINDOW 3 45 48 Left 0
SYMATTR InstName Q2
SYMATTR Value 2N5550
SYMBOL voltage 752 912 R0
WINDOW 3 40 81 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 0 40 53 Left 0
SYMATTR Value 55
SYMATTR InstName V2
SYMBOL res 1632 896 R0
WINDOW 0 -39 37 Left 0
WINDOW 3 -41 68 Left 0
SYMATTR InstName R4
SYMATTR Value 1.8
SYMBOL voltage 880 912 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 0 39 57 Left 0
SYMATTR Value PULSE(0 5 0.02 1e-6 1e-6 0.05 0.1 1)
SYMATTR InstName V3
SYMBOL res 1024 800 R90
WINDOW 0 -46 56 VBottom 0
WINDOW 3 -38 58 VTop 0
SYMATTR InstName R9
SYMATTR Value 1000
SYMBOL nmos 1600 656 R0
SYMATTR InstName M2
SYMATTR Value SUM75N06-09L
SYMBOL res 1088 464 R0
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL res 1360 512 R90
WINDOW 0 -46 56 VBottom 0
WINDOW 3 -38 58 VTop 0
SYMATTR InstName R1
SYMATTR Value 50k
SYMBOL npn 1376 848 R0
WINDOW 0 72 17 Left 0
WINDOW 3 47 50 Left 0
SYMATTR InstName Q3
SYMATTR Value 2N5550
SYMBOL res 1360 880 R90
WINDOW 0 -25 58 VBottom 0
WINDOW 3 -27 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 50k
SYMBOL res 1424 624 R0
WINDOW 0 41 43 Left 0
WINDOW 3 34 74 Left 0
SYMATTR InstName R5
SYMATTR Value 1000
SYMBOL ind 608 672 R270
WINDOW 0 45 56 VTop 0
WINDOW 3 -8 54 VBottom 0
SYMATTR InstName L1
SYMATTR Value 5e-3
SYMBOL npn 512 704 R0
SYMATTR InstName Q4
SYMATTR Value 2N5550
SYMBOL res 496 736 R90
WINDOW 0 -11 55 VBottom 0
WINDOW 3 35 55 VTop 0
SYMATTR InstName R6
SYMATTR Value 1000
SYMBOL diode 592 544 R180
WINDOW 0 51 34 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D1
SYMATTR Value MURS120
SYMBOL zener 768 544 R180
WINDOW 0 63 33 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D2
SYMATTR Value BZX84C10L
SYMBOL cap 832 480 R0
WINDOW 0 48 32 Left 0
WINDOW 3 28 61 Left 0
SYMATTR InstName C1
SYMATTR Value 10e-6
SYMBOL Digital\\schmitt 208 672 R0
SYMATTR InstName A1
SYMATTR SpiceLine vhigh 5 vh 1 trise 10e-9 tfall 10e-9
SYMBOL cap 80 960 R0
WINDOW 0 -44 33 Left 0
WINDOW 3 -51 64 Left 0
SYMATTR InstName C3
SYMATTR Value 1e-8
SYMBOL res 336 800 R90
WINDOW 0 -6 58 VBottom 0
WINDOW 3 36 57 VTop 0
SYMATTR InstName R11
SYMATTR Value 910
SYMBOL diode 192 800 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D5
SYMATTR Value 1N4148
SYMBOL diode 128 944 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D6
SYMATTR Value 1N4148
SYMBOL res 336 912 R90
WINDOW 0 -11 56 VBottom 0
WINDOW 3 40 59 VTop 0
SYMATTR InstName R12
SYMATTR Value 8200
SYMBOL zener 1568 784 R90
WINDOW 0 -4 32 VBottom 0
WINDOW 3 36 32 VTop 0
SYMATTR InstName D3
SYMATTR Value BZX84C15L
SYMBOL zener 1232 688 R180
WINDOW 0 -41 29 Left 0
WINDOW 3 -77 -2 Left 0
SYMATTR InstName D4
SYMATTR Value DFLZ33
SYMBOL zener 1232 800 R180
WINDOW 0 -37 31 Left 0
WINDOW 3 -70 -4 Left 0
SYMATTR InstName D7
SYMATTR Value DFLZ33
TEXT 1680 944 Left 0 ;LOAD
TEXT 104 1056 Left 0 !.tran .1
 
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