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'[EE] Repost: PV OptoIsolator / MOS Driver Info'
2007\12\14@101542 by Bob Axtell

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My post of yesterday never showed up. Here it is again:

The MOS Drivers are made of opto-isolated PV cells
internally wired in series. These allow you to DIRECTLY
turn on and off any power MOSFET through an isolated
I/O.

My favorite is Toshiba's TLP191B. With 2500v RMS of
isolation, the device, 1/4 the size of a 4N26, can deliver
over 20VDC with 5V applied tio the input thru a 330 ohm
resistor. While its spec says "min 7VDC" of output, it actually
delivers quite a bit more; I needed a 220K load resistor to
speed up on/off times and to prevent overdriving my power
FETs.

--Bob Axtell

2007\12\14@104600 by Alan B. Pearce

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>My post of yesterday never showed up. Here it is again:

It showed in my mail, 'cause I went looking for the device you quoted.

>While its spec says "min 7VDC" of output, it actually
>delivers quite a bit more; I needed a 220K load resistor to
>speed up on/off times and to prevent overdriving my power
>FETs.

What speed do you actually achieve, because the app-notes I found by them
regarding these seemed to figure on quite long switching times, and they
didn't seem to quote a different time for the ones with internal resistor.

2007\12\14@144133 by Thomas Lehmann n/a

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face
I used the PVI1050N from International Rectifier a lot.
The PVI Series Photovoltaic isolators employ fast turn-off circuitry, so
there is not gate-to-source-resistor needed and the switching times are
improved.
The device contains to photovoltaic sources, nominally 5 volts per channel.
Usually the series connection of two channels are used for the gate drive of
one power mosfet.

Regs.
Thomas

/*
What speed do you actually achieve, because the app-notes I found by them
regarding these seemed to figure on quite long switching times, and they
didn't seem to quote a different time for the ones with internal resistor.
*/

2007\12\14@164803 by Bob Axtell

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Alan B. Pearce wrote:
>> My post of yesterday never showed up. Here it is again:
>>    
>
> It showed in my mail, 'cause I went looking for the device you quoted.
>
>  
>> While its spec says "min 7VDC" of output, it actually
>> delivers quite a bit more; I needed a 220K load resistor to
>> speed up on/off times and to prevent overdriving my power
>> FETs.
>>    
>
> What speed do you actually achieve, because the app-notes I found by them
> regarding these seemed to figure on quite long switching times, and they
> didn't seem to quote a different time for the ones with internal resistor.
>
>  
And I was never able to make it go faster than about 100Hz as a result;
my 220K sped it up only a little.
But what I plan to do is to simply use this as a power supply; I will
beef up the supply with a low-leak
capacitor, then switch it at high speed with a fast optoisolator. HP
makes some fast components like
this.

--Bob

2007\12\17@042148 by Alan B. Pearce

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>I used the PVI1050N from International Rectifier a lot.
>The PVI Series Photovoltaic isolators employ fast turn-off
>circuitry, so there is not gate-to-source-resistor needed
>and the switching times are improved.

OK, thanks for the pointer.

2007\12\17@084827 by Martin Klingensmith

face
flavicon
face
Bob Axtell wrote:
> And I was never able to make it go faster than about 100Hz as a result;
> my 220K sped it up only a little.
> But what I plan to do is to simply use this as a power supply; I will
> beef up the supply with a low-leak
> capacitor, then switch it at high speed with a fast optoisolator. HP
> makes some fast components like
> this.
>
> --Bob
>  


Are you going to get enough current from this device? It says it
provides a typical 40uA current.
-
Martin

2007\12\17@105529 by Bob Axtell

face picon face
Martin Klingensmith wrote:
> Bob Axtell wrote:
>  
>> And I was never able to make it go faster than about 100Hz as a result;
>> my 220K sped it up only a little.
>> But what I plan to do is to simply use this as a power supply; I will
>> beef up the supply with a low-leak
>> capacitor, then switch it at high speed with a fast optoisolator. HP
>> makes some fast components like
>> this.
>>
>> --Bob
>>  
>>    
>
>
> Are you going to get enough current from this device? It says it
> provides a typical 40uA current.
> -
> Martin
>  
Its in a commercial design, drives 50A MOSFET directly without anything.
But is is MORE
than 40uA according to my Fluke.

--Bob

2007\12\17@144605 by Martin Klingensmith

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Bob Axtell wrote:
{Quote hidden}

You're using this as an isolated power supply, and it switches at what
speed? Sorry, it seems like a novel use and I'm trying to see exactly
what you're doing.
-
Martin

2007\12\17@152122 by Bob Axtell

face picon face
Martin Klingensmith wrote:
{Quote hidden}

The way the thread began was that someone asked how to drive a MOSFET
directly with an optoisolator.
Of course, you can't really do so unless you have an isolated power
supply floating up there that can be
used to switch the MOSFET input. MOSFET power switches usually need
10-15V at 50uA to turn on a
power MOSFET.

I then told him about the TLP191B, which is a photvoltaic module; its
input is an IR diode junction, and the
output is a pack of PV cells wired in series. The IR excites the PV
cells, thus generating 10-20V or so, dependent
on the input current on the IR diode. My useage is simply ON or OFF, and
the TLP191B does that reliably
directly.  But how would you drive a MOSFET at PWM speeds?

It turns out that the PV cells switch very slowly. I am planning to
simply excite the TLP191B constantly, then use
the 20V "power supply" as the power to switch a FAST standard
optoisloator, such as one of HP's units. Then
a PWM signal can indirectly drive the MOSFET at a reasonable speed (such
as 16Khz).


--Bob

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