P
panfilero
Guest
I was wondering, if I'm using FETs to switch on/off 100V at 10A. Do I need some kind of snubber circuit for my FET? Or do snubbers just apply to relays? my load is just resistive.
thanks
thanks
J
Jim Thompson
Guest
On Mon, 24 Sep 2012 09:14:25 -0700 (PDT), panfilero
<panfilero@gmail.com> wrote:
minimize device dissipation and/or to stay inside of safe operating
limitations.
Back in the early '80's I did an off-line 200W switcher for GenRad
using HV bipolar devices (MJE-something-or-other, TO-220,
half-H-bridge).
I used a current probe and a voltage probe to get V-I load line plots,
and got switching very nearly right along the axes (*)
Ran so cool I took off the heat-sinks.
Then I wondered how "cool"?
Without thinking I grabbed a flag to see... forgetting that there was
340V P-P there... instant entertainment for the technicians ;-)
(*) Snubber was an inductor, resistor, capacitor, diode combination...
so it behaved differently depending on switching direction.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice
480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
<panfilero@gmail.com> wrote:
Snubber design is an art. They can be used to tailor load lines to
minimize device dissipation and/or to stay inside of safe operating
limitations.
Back in the early '80's I did an off-line 200W switcher for GenRad
using HV bipolar devices (MJE-something-or-other, TO-220,
half-H-bridge).
I used a current probe and a voltage probe to get V-I load line plots,
and got switching very nearly right along the axes (*)
Ran so cool I took off the heat-sinks.
Then I wondered how "cool"?
Without thinking I grabbed a flag to see... forgetting that there was
340V P-P there... instant entertainment for the technicians ;-)
(*) Snubber was an inductor, resistor, capacitor, diode combination...
so it behaved differently depending on switching direction.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice
480)460-2350 Fax: Available upon request | Brass Rat || E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
J
Jim Thompson
Guest
On Mon, 24 Sep 2012 20:19:02 +0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
<presence@MUNGEpanix.com> wrote:
Sure can make a non-dancer dance ;-)
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice
480)460-2350 Fax: Available upon request | Brass Rat || E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
C
Cydrome Leader
Guest
Jim Thompson <To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote:
Sounds like using your hand to discharge photoflash capacitors where the
cap is hidden somewhere.
Ha!
Sounds like using your hand to discharge photoflash capacitors where the
cap is hidden somewhere.
T
Tim Wescott
Guest
On Mon, 24 Sep 2012 09:14:25 -0700, panfilero wrote:
current off from an inductive load you need a snubber of some sort.
No, if the load is purely resistive you don't need a snubber. Of course,
if your load is more inductive than you thought you may find out that you
needed a snubber after all. If you're in luck, the FET's intrinsic diode
to the + rail will be all you need.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Yes, FET switches need snubbers, too. Any time you're switching the
current off from an inductive load you need a snubber of some sort.
No, if the load is purely resistive you don't need a snubber. Of course,
if your load is more inductive than you thought you may find out that you
needed a snubber after all. If you're in luck, the FET's intrinsic diode
to the + rail will be all you need.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
J
John Larkin
Guest
On Mon, 24 Sep 2012 20:16:14 -0500, Tim Wescott <tim@seemywebsite.com>
wrote:
clamp diode. Some fets are avalanche rated, but a catch diode or an RC
snubber across the load is a good investment when switching a
kilowatt: there may be some inductance around.
Slowing down the gate drive is good, too, if the situation allows.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
wrote:
Discrete 3-terminal fets will have a substrate diode, but no flyback
clamp diode. Some fets are avalanche rated, but a catch diode or an RC
snubber across the load is a good investment when switching a
kilowatt: there may be some inductance around.
Slowing down the gate drive is good, too, if the situation allows.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
P
panfilero
Guest
On Monday, September 24, 2012 11:14:26 AM UTC-5, panfilero wrote:
thanks for the replies!