Super low power isolated MOSFET driver

Hi,

I need to slowly drive a high-voltage high-side MOSFET in a 5kV isolated 
setup. This use case reminds an electronic fuse: the MOSFET is expected 
to be almost always ON, but the driver needs to start in an OFF 
condition. Generally the answer would be Si8261, but it
requires ~50mW. So I have devised a much less energy hungry driver based 
on a tiny 1:1 bipolar drive pulse transformer and a 555 (the CMOS 
variant, but I don't have a model for it). It looks fine, switching a 
180nC MOSFET in under 2us; it should be possible to be tweaked to 
consume a milliwatt or two as well. The sim is attached below. My 
concern is with the initial conditions: is this setup guaranteed to 
reset the timer at power-on
provided the transformer is not energized?

Comments warmly welcomed.

	Best regards, Piotr

Version 4
SHEET 1 2408 772
WIRE 464 -928 64 -928
WIRE 176 -832 128 -832
WIRE 304 -832 256 -832
WIRE 544 -832 384 -832
WIRE 128 -704 128 -832
WIRE 176 -704 128 -704
WIRE 544 -704 544 -832
WIRE 544 -704 400 -704
WIRE 128 -688 128 -704
WIRE 64 -640 64 -928
WIRE 176 -640 64 -640
WIRE 1120 -592 880 -592
WIRE 176 -576 -16 -576
WIRE 464 -576 464 -928
WIRE 464 -576 400 -576
WIRE 880 -560 880 -592
WIRE 176 -512 128 -512
WIRE 432 -512 400 -512
WIRE 432 -496 432 -512
WIRE 880 -432 880 -480
WIRE 1120 -432 1120 -592
WIRE 432 -416 432 -432
WIRE -16 -352 -16 -576
WIRE 656 -352 -16 -352
WIRE 832 -352 736 -352
WIRE 880 -320 880 -336
WIRE 1120 -320 1120 -352
WIRE 128 -272 128 -512
WIRE 544 -272 544 -704
WIRE 544 -272 128 -272
WIRE 544 -192 544 -272
WIRE 64 -96 64 -640
WIRE 352 -96 64 -96
WIRE 544 -96 544 -112
WIRE 544 -96 432 -96
WIRE 544 -64 544 -96
WIRE 240 48 144 48
WIRE 352 48 304 48
WIRE 544 48 544 16
WIRE 144 80 144 48
WIRE 352 112 352 48
WIRE 144 192 144 160
WIRE 144 288 144 272
WIRE 352 288 352 192
FLAG 144 288 0
FLAG 352 288 0
FLAG 880 -320 0
FLAG 1120 -320 0
FLAG 128 -688 0
FLAG 432 -416 0
FLAG 544 48 0
SYMBOL voltage 144 64 R0
WINDOW 3 -973 45 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 {Vkey} 100u {Tkey_rise} {Tkey_fall} {Tkey_on} 
{Tkey_period})
SYMBOL cap 304 32 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 10µ
SYMBOL ind2 336 96 R0
WINDOW 3 -12 60 Right 2
SYMATTR InstName L1
SYMATTR Value 400µ
SYMATTR Type ind
SYMBOL ind2 448 -80 M270
WINDOW 0 32 56 VTop 2
WINDOW 3 4 56 VBottom 2
SYMATTR InstName L2
SYMATTR Value 400µ
SYMATTR Type ind
SYMBOL res 752 -368 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 50
SYMBOL nmos 832 -432 R0
SYMATTR InstName M1
SYMATTR Value IXTH88N30P
SYMBOL res 864 -576 R0
SYMATTR InstName R4
SYMATTR Value 300
SYMBOL voltage 1120 -448 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 300
SYMBOL Misc\\NE555 288 -608 R0
SYMATTR InstName U1
SYMBOL voltage 272 -832 R90
WINDOW 0 -32 56 VBottom 2
WINDOW 3 -84 34 VTop 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value PWL(0 0 100u 9.6)
SYMBOL res 400 -848 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 1m
SYMBOL cap 416 -496 R0
SYMATTR InstName C1
SYMATTR Value 1n
SYMBOL res 528 -80 R0
SYMATTR InstName R1
SYMATTR Value 20k
SYMBOL res 528 -208 R0
SYMATTR InstName R6
SYMATTR Value 20k
SYMBOL voltage 144 176 R0
WINDOW 3 -973 45 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 {-Vkey} 550u {Tkey_rise} {Tkey_fall} {Tkey_on} 
{Tkey_period})
TEXT 110 312 Left 2 !.tran 1m
TEXT 328 -8 Left 2 !K L1 L2 0.98
TEXT 32 424 Left 2 !.param Vkey=2.7
TEXT 32 456 Left 2 !.param Tkey_rise=10n Tkey_fall=10n Tkey_on=1u 
Tkey_period=100u

On Sun, 19 Jan 2020 18:41:20 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>Hi,
>
>I need to slowly drive a high-voltage high-side MOSFET in a 5kV isolated 
>setup. This use case reminds an electronic fuse: the MOSFET is expected 
>to be almost always ON, but the driver needs to start in an OFF 
>condition. Generally the answer would be Si8261, but it
>requires ~50mW. So I have devised a much less energy hungry driver based 
>on a tiny 1:1 bipolar drive pulse transformer and a 555 (the CMOS 
>variant, but I don't have a model for it). It looks fine, switching a 
>180nC MOSFET in under 2us; it should be possible to be tweaked to 
>consume a milliwatt or two as well. The sim is attached below. My 
>concern is with the initial conditions: is this setup guaranteed to 
>reset the timer at power-on
>provided the transformer is not energized?
>
>Comments warmly welcomed.

Is PWL a floating power supply, on the high side? Is that available?
Everything is grounded in your sim.

I'd consider going optical, a PV supply and a dual (or maybe single)
optoisolator. No highside power supply, DC drive coupling.



-- 

John Larkin         Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet. 
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

jlarkin@highlandsniptechnology.com wrote:

> Is PWL a floating power supply, on the high side? Is that available?

Yes.

> Everything is grounded in your sim.

Just for the ease of prototyping of the core idea. At the beginning the 
modelling of the bipolar transformer drive was crazy enough. It will be 
fully isolated in the real application.

> I'd consider going optical, a PV supply and a dual (or maybe single)
> optoisolator. No highside power supply, DC drive coupling.

Optical devices have too high FIT value. To be eradicated just after 
electrochemical capacitors.

	Best regards, Piotr

On Sun, 19 Jan 2020 19:50:41 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>
>> Is PWL a floating power supply, on the high side? Is that available?
>
>Yes.
>
>> Everything is grounded in your sim.
>
>Just for the ease of prototyping of the core idea. At the beginning the 
>modelling of the bipolar transformer drive was crazy enough. It will be 
>fully isolated in the real application.
>
>> I'd consider going optical, a PV supply and a dual (or maybe single)
>> optoisolator. No highside power supply, DC drive coupling.
>
>Optical devices have too high FIT value. To be eradicated just after 
>electrochemical capacitors.
>
>	Best regards, Piotr

Tons of parts accumulate FITs too. I haven't found optos to be
unreliable. If PWL is an existing floating power supply, the whole
thing reduces to one optocoupler and no states to have hazards.



-- 

John Larkin         Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet. 
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

On 19/01/2020 5:41 pm, Piotr Wyderski wrote:
> Hi,
> 
> I need to slowly drive a high-voltage high-side MOSFET in a 5kV isolated 
> setup. This use case reminds an electronic fuse: the MOSFET is expected 
> to be almost always ON, but the driver needs to start in an OFF 
> condition. Generally the answer would be Si8261, but it
> requires ~50mW. So I have devised a much less energy hungry driver based 
> on a tiny 1:1 bipolar drive pulse transformer and a 555 (the CMOS 
> variant, but I don't have a model for it). It looks fine, switching a 
> 180nC MOSFET in under 2us; it should be possible to be tweaked to 
> consume a milliwatt or two as well. The sim is attached below. My 
> concern is with the initial conditions: is this setup guaranteed to 
> reset the timer at power-on
> provided the transformer is not energized?
> 
> Comments warmly welcomed.
> 
>      Best regards, Piotr
> 
> Version 4
> SHEET 1 2408 772
> WIRE 464 -928 64 -928
> WIRE 176 -832 128 -832
> WIRE 304 -832 256 -832
> WIRE 544 -832 384 -832
> WIRE 128 -704 128 -832
> WIRE 176 -704 128 -704
> WIRE 544 -704 544 -832
> WIRE 544 -704 400 -704
> WIRE 128 -688 128 -704
> WIRE 64 -640 64 -928
> WIRE 176 -640 64 -640
> WIRE 1120 -592 880 -592
> WIRE 176 -576 -16 -576
> WIRE 464 -576 464 -928
> WIRE 464 -576 400 -576
> WIRE 880 -560 880 -592
> WIRE 176 -512 128 -512
> WIRE 432 -512 400 -512
> WIRE 432 -496 432 -512
> WIRE 880 -432 880 -480
> WIRE 1120 -432 1120 -592
> WIRE 432 -416 432 -432
> WIRE -16 -352 -16 -576
> WIRE 656 -352 -16 -352
> WIRE 832 -352 736 -352
> WIRE 880 -320 880 -336
> WIRE 1120 -320 1120 -352
> WIRE 128 -272 128 -512
> WIRE 544 -272 544 -704
> WIRE 544 -272 128 -272
> WIRE 544 -192 544 -272
> WIRE 64 -96 64 -640
> WIRE 352 -96 64 -96
> WIRE 544 -96 544 -112
> WIRE 544 -96 432 -96
> WIRE 544 -64 544 -96
> WIRE 240 48 144 48
> WIRE 352 48 304 48
> WIRE 544 48 544 16
> WIRE 144 80 144 48
> WIRE 352 112 352 48
> WIRE 144 192 144 160
> WIRE 144 288 144 272
> WIRE 352 288 352 192
> FLAG 144 288 0
> FLAG 352 288 0
> FLAG 880 -320 0
> FLAG 1120 -320 0
> FLAG 128 -688 0
> FLAG 432 -416 0
> FLAG 544 48 0
> SYMBOL voltage 144 64 R0
> WINDOW 3 -973 45 Left 2
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V1
> SYMATTR Value PULSE(0 {Vkey} 100u {Tkey_rise} {Tkey_fall} {Tkey_on} 
> {Tkey_period})
> SYMBOL cap 304 32 R90
> WINDOW 0 0 32 VBottom 2
> WINDOW 3 32 32 VTop 2
> SYMATTR InstName C2
> SYMATTR Value 10µ
> SYMBOL ind2 336 96 R0
> WINDOW 3 -12 60 Right 2
> SYMATTR InstName L1
> SYMATTR Value 400µ
> SYMATTR Type ind
> SYMBOL ind2 448 -80 M270
> WINDOW 0 32 56 VTop 2
> WINDOW 3 4 56 VBottom 2
> SYMATTR InstName L2
> SYMATTR Value 400µ
> SYMATTR Type ind
> SYMBOL res 752 -368 R90
> WINDOW 0 0 56 VBottom 2
> WINDOW 3 32 56 VTop 2
> SYMATTR InstName R3
> SYMATTR Value 50
> SYMBOL nmos 832 -432 R0
> SYMATTR InstName M1
> SYMATTR Value IXTH88N30P
> SYMBOL res 864 -576 R0
> SYMATTR InstName R4
> SYMATTR Value 300
> SYMBOL voltage 1120 -448 R0
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V3
> SYMATTR Value 300
> SYMBOL Misc\\NE555 288 -608 R0
> SYMATTR InstName U1
> SYMBOL voltage 272 -832 R90
> WINDOW 0 -32 56 VBottom 2
> WINDOW 3 -84 34 VTop 2
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V4
> SYMATTR Value PWL(0 0 100u 9.6)
> SYMBOL res 400 -848 R90
> WINDOW 0 0 56 VBottom 2
> WINDOW 3 32 56 VTop 2
> SYMATTR InstName R2
> SYMATTR Value 1m
> SYMBOL cap 416 -496 R0
> SYMATTR InstName C1
> SYMATTR Value 1n
> SYMBOL res 528 -80 R0
> SYMATTR InstName R1
> SYMATTR Value 20k
> SYMBOL res 528 -208 R0
> SYMATTR InstName R6
> SYMATTR Value 20k
> SYMBOL voltage 144 176 R0
> WINDOW 3 -973 45 Left 2
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V2
> SYMATTR Value PULSE(0 {-Vkey} 550u {Tkey_rise} {Tkey_fall} {Tkey_on} 
> {Tkey_period})
> TEXT 110 312 Left 2 !.tran 1m
> TEXT 328 -8 Left 2 !K L1 L2 0.98
> TEXT 32 424 Left 2 !.param Vkey=2.7
> TEXT 32 456 Left 2 !.param Tkey_rise=10n Tkey_fall=10n Tkey_on=1u 
> Tkey_period=100u

Simple answer is no. In the absence of transformer pulses the Trig and 
Thrs pins will power up at 50% Vdd which is midway between their 
comparsion references so neither state can be assured. You need to find 
a way to assert Rst or drive Thrs higher than 2Vdd/3 to get power up in 
the output low state.

piglet



In practice 555's tend to power up

jlarkin@highlandsniptechnology.com wrote:
> On Sun, 19 Jan 2020 19:50:41 +0100, Piotr Wyderski
> <peter.pan@neverland.mil> wrote:
> 
>> jlarkin@highlandsniptechnology.com wrote:
>>
>>> Is PWL a floating power supply, on the high side? Is that available?
>>
>> Yes.
>>
>>> Everything is grounded in your sim.
>>
>> Just for the ease of prototyping of the core idea. At the beginning the
>> modelling of the bipolar transformer drive was crazy enough. It will be
>> fully isolated in the real application.
>>
>>> I'd consider going optical, a PV supply and a dual (or maybe single)
>>> optoisolator. No highside power supply, DC drive coupling.
>>
>> Optical devices have too high FIT value. To be eradicated just after
>> electrochemical capacitors.
>>
>> 	Best regards, Piotr
> 
> Tons of parts accumulate FITs too. I haven't found optos to be
> unreliable. If PWL is an existing floating power supply, the whole
> thing reduces to one optocoupler and no states to have hazards.

MIL-HDBK-217 (which introduced FITs IIRC) is a random-number generator.

You can improve your design's FITs by taking out all the ESD protection, 
current limiters, fuses, supply-reversal protection diodes, self-test 
capability, and other such non-essential functions.

It also assumes that all failures have an Arrhenius temperature 
dependence, which is nuts.

Cheers

Phil Hobbs
-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

The bipolar 555 is piss, obviously you'd use a CMOS model, yeah.

I've done that before (happened to be a discrete circuit).  But have you 
thought about common mode immunity yet?

Consider using something like this,
https://www.digikey.com/product-detail/en/pulse-electronics-power/PH9185.011NLT/553-2052-1-ND/3503429
and don't simply nod at the CT windings: take full advantage of them.  The 
CMRR of this part is surprisingly good, up to surprisingly high frequencies. 
You will have a very hard time doing it unbalanced.

Even an Ethernet transformer will do, if you don't mind the 1kV isoation 
rating (in this case obviously you would mind).  The flux is quite small, 
but more than adequate for little pulses, and the isolation barrier is 
smaller (lower capacitance).  Double balanced design again, and usually 
comes with CMCs included (for even more immunity).

Forget if you can find COTS Ethernet transformers with reinforced kV+ 
isolation, if so that may be handy.  Huh, probably same price as the Pulse 
part anyway...

Another approach that may be of interest, pulse or frequency modulation. 
ASK through one transformer allows you to maintain high-side power, while 
filtering the signal for immunity.

OOK through two transformers, you could do the same while sharpening it with 
a flip-flop (in essence, detect and filter two signal paths, and route them 
to your 555's inputs).

PSK would be... interesting to decode without a clock reference (two 
transformers would be easy, one would be harder), but could be unambiguous 
(in phase = on, etc.; or 90 deg. to the right = on, etc.).

FM, you could use a crude discriminator, like a missing-pulse detector; give 
or take additional filtering before or after, you can clean up most 
interference.

Could all be done at VHF too, in which case planar magnetics are feasible 
(coreless or otherwise), or even at UHF where interference from power 
supplies is unlikely and the resulting bandwidth (which might be say 5-10% 
of Fc) is competitive with monolithic drivers.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"Piotr Wyderski" <peter.pan@neverland.mil> wrote in message 
news:r024bu$4ra$1@gioia.aioe.org...
> Hi,
>
> I need to slowly drive a high-voltage high-side MOSFET in a 5kV isolated 
> setup. This use case reminds an electronic fuse: the MOSFET is expected to 
> be almost always ON, but the driver needs to start in an OFF condition. 
> Generally the answer would be Si8261, but it
> requires ~50mW. So I have devised a much less energy hungry driver based 
> on a tiny 1:1 bipolar drive pulse transformer and a 555 (the CMOS variant, 
> but I don't have a model for it). It looks fine, switching a 180nC MOSFET 
> in under 2us; it should be possible to be tweaked to consume a milliwatt 
> or two as well. The sim is attached below. My concern is with the initial 
> conditions: is this setup guaranteed to reset the timer at power-on
> provided the transformer is not energized?
>
> Comments warmly welcomed.
>
> Best regards, Piotr
>
> Version 4
> SHEET 1 2408 772
> WIRE 464 -928 64 -928
> WIRE 176 -832 128 -832
> WIRE 304 -832 256 -832
> WIRE 544 -832 384 -832
> WIRE 128 -704 128 -832
> WIRE 176 -704 128 -704
> WIRE 544 -704 544 -832
> WIRE 544 -704 400 -704
> WIRE 128 -688 128 -704
> WIRE 64 -640 64 -928
> WIRE 176 -640 64 -640
> WIRE 1120 -592 880 -592
> WIRE 176 -576 -16 -576
> WIRE 464 -576 464 -928
> WIRE 464 -576 400 -576
> WIRE 880 -560 880 -592
> WIRE 176 -512 128 -512
> WIRE 432 -512 400 -512
> WIRE 432 -496 432 -512
> WIRE 880 -432 880 -480
> WIRE 1120 -432 1120 -592
> WIRE 432 -416 432 -432
> WIRE -16 -352 -16 -576
> WIRE 656 -352 -16 -352
> WIRE 832 -352 736 -352
> WIRE 880 -320 880 -336
> WIRE 1120 -320 1120 -352
> WIRE 128 -272 128 -512
> WIRE 544 -272 544 -704
> WIRE 544 -272 128 -272
> WIRE 544 -192 544 -272
> WIRE 64 -96 64 -640
> WIRE 352 -96 64 -96
> WIRE 544 -96 544 -112
> WIRE 544 -96 432 -96
> WIRE 544 -64 544 -96
> WIRE 240 48 144 48
> WIRE 352 48 304 48
> WIRE 544 48 544 16
> WIRE 144 80 144 48
> WIRE 352 112 352 48
> WIRE 144 192 144 160
> WIRE 144 288 144 272
> WIRE 352 288 352 192
> FLAG 144 288 0
> FLAG 352 288 0
> FLAG 880 -320 0
> FLAG 1120 -320 0
> FLAG 128 -688 0
> FLAG 432 -416 0
> FLAG 544 48 0
> SYMBOL voltage 144 64 R0
> WINDOW 3 -973 45 Left 2
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V1
> SYMATTR Value PULSE(0 {Vkey} 100u {Tkey_rise} {Tkey_fall} {Tkey_on} 
> {Tkey_period})
> SYMBOL cap 304 32 R90
> WINDOW 0 0 32 VBottom 2
> WINDOW 3 32 32 VTop 2
> SYMATTR InstName C2
> SYMATTR Value 10&micro;
> SYMBOL ind2 336 96 R0
> WINDOW 3 -12 60 Right 2
> SYMATTR InstName L1
> SYMATTR Value 400&micro;
> SYMATTR Type ind
> SYMBOL ind2 448 -80 M270
> WINDOW 0 32 56 VTop 2
> WINDOW 3 4 56 VBottom 2
> SYMATTR InstName L2
> SYMATTR Value 400&micro;
> SYMATTR Type ind
> SYMBOL res 752 -368 R90
> WINDOW 0 0 56 VBottom 2
> WINDOW 3 32 56 VTop 2
> SYMATTR InstName R3
> SYMATTR Value 50
> SYMBOL nmos 832 -432 R0
> SYMATTR InstName M1
> SYMATTR Value IXTH88N30P
> SYMBOL res 864 -576 R0
> SYMATTR InstName R4
> SYMATTR Value 300
> SYMBOL voltage 1120 -448 R0
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V3
> SYMATTR Value 300
> SYMBOL Misc\\NE555 288 -608 R0
> SYMATTR InstName U1
> SYMBOL voltage 272 -832 R90
> WINDOW 0 -32 56 VBottom 2
> WINDOW 3 -84 34 VTop 2
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V4
> SYMATTR Value PWL(0 0 100u 9.6)
> SYMBOL res 400 -848 R90
> WINDOW 0 0 56 VBottom 2
> WINDOW 3 32 56 VTop 2
> SYMATTR InstName R2
> SYMATTR Value 1m
> SYMBOL cap 416 -496 R0
> SYMATTR InstName C1
> SYMATTR Value 1n
> SYMBOL res 528 -80 R0
> SYMATTR InstName R1
> SYMATTR Value 20k
> SYMBOL res 528 -208 R0
> SYMATTR InstName R6
> SYMATTR Value 20k
> SYMBOL voltage 144 176 R0
> WINDOW 3 -973 45 Left 2
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V2
> SYMATTR Value PULSE(0 {-Vkey} 550u {Tkey_rise} {Tkey_fall} {Tkey_on} 
> {Tkey_period})
> TEXT 110 312 Left 2 !.tran 1m
> TEXT 328 -8 Left 2 !K L1 L2 0.98
> TEXT 32 424 Left 2 !.param Vkey=2.7
> TEXT 32 456 Left 2 !.param Tkey_rise=10n Tkey_fall=10n Tkey_on=1u 
> Tkey_period=100u 

On Sun, 19 Jan 2020 18:26:14 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>> On Sun, 19 Jan 2020 19:50:41 +0100, Piotr Wyderski
>> <peter.pan@neverland.mil> wrote:
>> 
>>> jlarkin@highlandsniptechnology.com wrote:
>>>
>>>> Is PWL a floating power supply, on the high side? Is that available?
>>>
>>> Yes.
>>>
>>>> Everything is grounded in your sim.
>>>
>>> Just for the ease of prototyping of the core idea. At the beginning the
>>> modelling of the bipolar transformer drive was crazy enough. It will be
>>> fully isolated in the real application.
>>>
>>>> I'd consider going optical, a PV supply and a dual (or maybe single)
>>>> optoisolator. No highside power supply, DC drive coupling.
>>>
>>> Optical devices have too high FIT value. To be eradicated just after
>>> electrochemical capacitors.
>>>
>>> 	Best regards, Piotr
>> 
>> Tons of parts accumulate FITs too. I haven't found optos to be
>> unreliable. If PWL is an existing floating power supply, the whole
>> thing reduces to one optocoupler and no states to have hazards.
>
>MIL-HDBK-217 (which introduced FITs IIRC) is a random-number generator.

The handbook doesn't have a table entry for the FITS of "bad design."



-- 

John Larkin         Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet. 
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

On Sun, 19 Jan 2020 17:34:39 -0600, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

>The bipolar 555 is piss, obviously you'd use a CMOS model, yeah.
>
>I've done that before (happened to be a discrete circuit).  But have you 
>thought about common mode immunity yet?
>
>Consider using something like this,
>https://www.digikey.com/product-detail/en/pulse-electronics-power/PH9185.011NLT/553-2052-1-ND/3503429
>and don't simply nod at the CT windings: take full advantage of them.  The 
>CMRR of this part is surprisingly good, up to surprisingly high frequencies. 
>You will have a very hard time doing it unbalanced.
>
>Even an Ethernet transformer will do, if you don't mind the 1kV isoation 
>rating (in this case obviously you would mind).  The flux is quite small, 
>but more than adequate for little pulses, and the isolation barrier is 
>smaller (lower capacitance).  Double balanced design again, and usually 
>comes with CMCs included (for even more immunity).
>
>Forget if you can find COTS Ethernet transformers with reinforced kV+ 
>isolation, if so that may be handy.  Huh, probably same price as the Pulse 
>part anyway...
>
>Another approach that may be of interest, pulse or frequency modulation. 
>ASK through one transformer allows you to maintain high-side power, while 
>filtering the signal for immunity.
>
>OOK through two transformers, you could do the same while sharpening it with 
>a flip-flop (in essence, detect and filter two signal paths, and route them 
>to your 555's inputs).
>
>PSK would be... interesting to decode without a clock reference (two 
>transformers would be easy, one would be harder), but could be unambiguous 
>(in phase = on, etc.; or 90 deg. to the right = on, etc.).
>
>FM, you could use a crude discriminator, like a missing-pulse detector; give 
>or take additional filtering before or after, you can clean up most 
>interference.
>
>Could all be done at VHF too, in which case planar magnetics are feasible 
>(coreless or otherwise), or even at UHF where interference from power 
>supplies is unlikely and the resulting bandwidth (which might be say 5-10% 
>of Fc) is competitive with monolithic drivers.
>
>Tim

How about a retriggerable one-shot? As long as you keep pulsing it,
the mosfet is on.



-- 

John Larkin         Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet. 
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

On Sunday, January 19, 2020 at 9:41:24 AM UTC-8, Piotr Wyderski wrote:

> I need to slowly drive a high-voltage high-side MOSFET in a 5kV isolated 
> setup. This use case reminds an electronic fuse: the MOSFET is expected 
> to be almost always ON, but the driver needs to start in an OFF 
> condition.   ... I have devised a much less energy hungry driver based 
on a tiny 1:1 bipolar drive pulse transformer and a 555 

Not sure about 5kV transformer being 'tiny'.   Why not pulse
a dual optoisolator, and at the  high side have it set/reset a CMOS flipflop.
Even if it takes a couple of milliamps to strobe the opto, if you do that
for a microsecond every tenth of a second, it only takes a tiny
average current at the low side.   If you put some capacitance
on the HV side power, the CMOS drive is quite peppy, even at
trickle-from-a-Li-cell power drain on the high side.