So grateful for your knowledge. I happen to have plenty 4N25 optos around and plenty others. I have been having a lot of cranky MOSFET failures lately.
Glad to be introduced to these devices, but they do not seem to be commonly sold. Currently, I use a dickson charge pump to make a reservoir, and a pair of PC817's as a push-pull gate drivers. This is quite a lot to solder up for a single MOSFET though. There must be some other chip that professionals use when they need to control dozens for MOSFETS from an isolated source.
Many useful videos lately, Lewis -- well done. Just a few comments: At 1:28, since the MOSFET gate draws essentially no current, low power Zener/resistor pairs can be used to protect both Vce and Vgs for use at higher Vcc levels. This might be cheaper than sourcing high V rated optocouplers and MOSFETs. // At 7:35, for inductive loads, the back EMF diode should be located at the load (e.g. across a motor's terminals), not in the control circuit. A MOSFET's intrinsic body diode should not be substituted for the back EMF diode. // At 8:24, depletion mode N-channel MOSFETs are available, but options are fairly limited in the wild; Digi-Key lists only ~70 examples. Also, since they're actually P-type devices, they have substantially higher on-resistance [Rds(on)] than enhancement mode devices. This results in lower drain current ratings and higher power dissipation in the same package.
Thank you for your video. You say that the only drawback of the Photovoltaic MOSFET Drivers is cost. How about current consumption? Reading the hotovoltaic driver datasheets it seems like they provide data with the assumption of 10mA LED current. Isn't that a lot compared to most traditional gate drivers? Have you tried how low LED current can we go and still make sure a N-channel MOSFET is fully turned on in a high-side switch scenario? Thank in advance.
@@LewisLoflin thank you for your reply. I'm considering using a photovoltaic mosfet driver IC in a bidirectional mosfet switch module I'm building. It will consist of two back to back n-mosfets and carry up towards 100A. How low led current in the driver is realistic to go, and still have the mosfets fully on? I'm asking because sometimes the module will be used to pass charge current from a small solar panal which could be really low. Then 10mA just to keep the mosfets gates on is a considerable amount of current lost. Thank you in advance.
They are no longer available. Look for a VOM1271 that works better. See the following video: czcams.com/video/azJo4h-ei6I/video.html And this webpage: www.bristolwatch.com/ele3/1g.htm
Thanks for putting this together. I have setup the same exact circuits as you show for either N channel or P channel and i'm driving it from an Arduino using PWM. If my PWM frequency is low say 1000 hz or less, the MOSFET's run cool (12 volt, 1 amp load), but the circuit has a nasty buzzing sound. If i turn the PWM frequency up to say 15K or 30K, the MOSFET's get extremely hot after a few seconds. For my N-channel config I'm using these, CSD18536KCS and a 4N25 opto isolator. My Vgs is 12 volts. I have no clue why the mosfets get burning hot at a 1 amp load--but only when the pwm frequency is high. Thoughts?
Thanks a lot, you do properly make the best videos about optocouplers! :-) May I please ask you, if you disregard the LCR's is it possible to regulate the resistance of the internal p / n junction by changing the amount of light the LED is emitting?
i was under the understanding that due to the physical construction of a working mosfet... body diode is always present. which is why u need two to switch dc, not just a digikey search for diodeless mosfet. as far as gate not related to voltage u r switching.. couldnt the same thing be achieved by powering a the gate driver ic from a floating/isolated point of load converter? does output voltage required vary at all with switched voltage in your config or do you just aim for something significantly above data sheet threshold v but below max and it works ?
Cool!! Thank you for the Information. One question: As the photo diods act like a power source wouldn't it thus be even possible to drive an N-Channel Mosfet as a high side switch? The 7-8V of the photo diods should add up to the source voltage and thus ensure the Vgs threshold voltage with respect to source pins voltage just fine, even though source pin in a high side switch configuration is not connected to Minus but to the positive side of the Load.
Yes, that is clear. Are you familiar with n-channel high side switch boost capacitor drivers? The capacitor is a energy source for the gate voltage as its voltage adds up to the source voltage in high side switch configuration. I wonder whether the photovoltaic drivers render bost capacitor configurations obsolet as the photovoltaic is a power source itself.
yes, you can do that. G must be >vGS(th) above S, whatever S is. I find 4 flat red LEDs in series hit by a bright white LED (driven @3.3v) outputs 4-7v @20-50ua.
Went to your web page. Agree with most everything except your anti-Christian BS. Why ruin an otherwise good website with polemic nonsense? Keep it to yourself. By the way, I'm from Kingsport.
Actually, I'm more pro-Christian. See the Christmas graphic on my mainpage. I came to the conclusion I was wrong, but still have theological differences.
Perfect video for beginners as well as professionals.
So grateful for your knowledge. I happen to have plenty 4N25 optos around and plenty others. I have been having a lot of cranky MOSFET failures lately.
Glad to be introduced to these devices, but they do not seem to be commonly sold. Currently, I use a dickson charge pump to make a reservoir, and a pair of PC817's as a push-pull gate drivers. This is quite a lot to solder up for a single MOSFET though. There must be some other chip that professionals use when they need to control dozens for MOSFETS from an isolated source.
This compenent saved my phd
Many useful videos lately, Lewis -- well done. Just a few comments: At 1:28, since the MOSFET gate draws essentially no current, low power Zener/resistor pairs can be used to protect both Vce and Vgs for use at higher Vcc levels. This might be cheaper than sourcing high V rated optocouplers and MOSFETs. // At 7:35, for inductive loads, the back EMF diode should be located at the load (e.g. across a motor's terminals), not in the control circuit. A MOSFET's intrinsic body diode should not be substituted for the back EMF diode. // At 8:24, depletion mode N-channel MOSFETs are available, but options are fairly limited in the wild; Digi-Key lists only ~70 examples. Also, since they're actually P-type devices, they have substantially higher on-resistance [Rds(on)] than enhancement mode devices. This results in lower drain current ratings and higher power dissipation in the same package.
I used these parts in this newer project: www.bristolwatch.com/ele4/index.htm
Those Crydom SSRs are a neat package but quite expensive. Are there any less costly solutions when using low voltage (14VDC) at 1 amp?
You are a real good teacher!
many SSRs don't have current limiting on the LED emitter. check the datasheet to make sure or you'll destroy your expensive SSR. i'm a fan of cpc1706.
The examples don't include current limiting on the LEDs but the working schematics do.
Thank you for your video. You say that the only drawback of the Photovoltaic MOSFET Drivers is cost. How about current consumption? Reading the hotovoltaic driver datasheets it seems like they provide data with the assumption of 10mA LED current. Isn't that a lot compared to most traditional gate drivers? Have you tried how low LED current can we go and still make sure a N-channel MOSFET is fully turned on in a high-side switch scenario?
Thank in advance.
I meant that in regard to the photovoltaic section output that is very low current.
@@LewisLoflin thank you for your reply. I'm considering using a photovoltaic mosfet driver IC in a bidirectional mosfet switch module I'm building. It will consist of two back to back n-mosfets and carry up towards 100A. How low led current in the driver is realistic to go, and still have the mosfets fully on? I'm asking because sometimes the module will be used to pass charge current from a small solar panal which could be really low. Then 10mA just to keep the mosfets gates on is a considerable amount of current lost. Thank you in advance.
Hi Lewis, Where can I find the PIV5050N? I did a search for them with no results. Do they have a different model number possibly? Thanks, Ken
They are no longer available. Look for a VOM1271 that works better.
See the following video: czcams.com/video/azJo4h-ei6I/video.html
And this webpage: www.bristolwatch.com/ele3/1g.htm
Thanks for putting this together. I have setup the same exact circuits as you show for either N channel or P channel and i'm driving it from an Arduino using PWM. If my PWM frequency is low say 1000 hz or less, the MOSFET's run cool (12 volt, 1 amp load), but the circuit has a nasty buzzing sound. If i turn the PWM frequency up to say 15K or 30K, the MOSFET's get extremely hot after a few seconds. For my N-channel config I'm using these, CSD18536KCS and a 4N25 opto isolator. My Vgs is 12 volts. I have no clue why the mosfets get burning hot at a 1 amp load--but only when the pwm frequency is high. Thoughts?
That is due to low duty cycle in addition if a magnetic load the diode suppression is likely to produce heat.
Thanks a lot, you do properly make the best videos about optocouplers! :-)
May I please ask you, if you disregard the LCR's is it possible to regulate the resistance of the internal p / n junction by changing the amount of light the LED is emitting?
i was under the understanding that due to the physical construction of a working mosfet... body diode is always present. which is why u need two to switch dc, not just a digikey search for diodeless mosfet.
as far as gate not related to voltage u r switching.. couldnt the same thing be achieved by powering a the gate driver ic from a floating/isolated point of load converter? does output voltage required vary at all with switched voltage in your config or do you just aim for something significantly above data sheet threshold v but below max and it works ?
thanks sir am wery happy to waching this video
sooper your seeche ant afditing calasing sooper
am steding this video
am happy to sir
Can you do a video to explain the PVN012PbF photovoltaic relay by International Rectifier?
If you send me 1 or 2 yeas I will.
New stuff for me. Thanks
Thanks for the excellent video. How would you keep the Crydom package cool. There doesn’t appear to be a provision for attachment to a heat sink?
If it is getting hot there's too much current.
Thanks
Cool!! Thank you for the Information.
One question:
As the photo diods act like a power source wouldn't it thus be even possible to drive an N-Channel Mosfet as a high side switch?
The 7-8V of the photo diods should add up to the source voltage and thus ensure the Vgs threshold voltage with respect to source pins voltage just fine, even though source pin in a high side switch configuration is not connected to Minus but to the positive side of the Load.
No the photodiode current is very low and is used to turn on the MOSFET only.
Yes, that is clear. Are you familiar with n-channel high side switch boost capacitor drivers? The capacitor is a energy source for the gate voltage as its voltage adds up to the source voltage in high side switch configuration.
I wonder whether the photovoltaic drivers render bost capacitor configurations obsolet as the photovoltaic is a power source itself.
No I'm not.
yes, you can do that. G must be >vGS(th) above S, whatever S is. I find 4 flat red LEDs in series hit by a bright white LED (driven @3.3v) outputs 4-7v @20-50ua.
Very informative and useful . Thank you for highlighting an easier method for switching a Mosfet Transistor.
I wish to transmit audio (line level) through an optoisolator to control a charge of 9V AC. Do you have a suggestion?
I would not recommend transmitting audio through an optoisolator. They are not intended for this. You will get distortion.
Went to your web page. Agree with most everything except your anti-Christian BS. Why ruin an otherwise good website with polemic nonsense? Keep it to yourself. By the way, I'm from Kingsport.
Actually, I'm more pro-Christian. See the Christmas graphic on my mainpage. I came to the conclusion I was wrong, but still have theological differences.
This one is boring.
You can increase video speed in the settings panel. That helped me. This is actually a good, informative video.
That's because you're boring, lol.