Electronics > Beginners
what is for "CURRENT REGULATOR DIODE"?
Benta:
--- Quote from: exe on April 07, 2019, 08:48:38 pm ---
--- Quote from: Benta on April 06, 2019, 07:51:30 pm ---1N5303 is available from several suppliers:
Central Semiconductor, Digitron, Microsemi...
--- End quote ---
I'm not sure if it's easy to buy from them and it's worth it.They are manufacturers, I don't think they even deal with individual customers.
--- End quote ---
The standard way to solve this is to got to their web site and check their sales channels for distributors. No semiconductor manufacturer I know of sell to SMBs or individuals.
exe:
--- Quote from: Benta on April 08, 2019, 07:15:25 pm ---The standard way to solve this is to got to their web site and check their sales channels for distributors.
--- End quote ---
You're right. I said they are unobtanium because most big distributors I know don't have CRD in their inventory (digikey, mouser, tme, etc), or they cost a fortune. However, less popular distributors do have them. Like here: https://www.futureelectronics.com/search/?text=Microsemi&q=Microsemi:relevance%3AmanufacturerName%3AMicrosemi:category:current-limiting-diodes&selectedTab=products&selectedSubCategory=current-limiting-diodes&selectedParentCategory=diodes . The price is not very attractive to say the least. It can be anywhere between $2 and $200 per device.
I ended up with buying jfet from onsemi for ~$0.3, I do manual characterization and have a trim-pot for fine adjustment :). Not sure if it's worth it. Probably, depends on required characteristics. The thermal stability and output impedance are not as great as I hoped. But they can have quite a small drop-out voltage. Anyway, I'm no expert, just played a bit on a breadboard.
Calvin:
Hi,
--- Quote ---But they can have quite a small drop-out voltage
--- End quote ---
Typically not, because to function as a proper CCS the Vds should be >2x Vgs.
Also, high-Idss/high-Vgs types degenerated by a larger source resistor are way better than types with just the desired Idss and Gate and Source shorted.
Useable standard types like the 4393 to 4391 are relatively cheap and easy to source active devices.
The 4391 is also fine as cascode for a 4392 or 4393, raising the output impedance very high .... drawback is the required high Vds voltage of > 5-10V.
regards
Calvin
David Hess:
--- Quote from: Calvin on April 09, 2019, 11:43:22 am ---
--- Quote ---But they can have quite a small drop-out voltage
--- End quote ---
Typically not, because to function as a proper CCS the Vds should be >2x Vgs.
--- End quote ---
The most common discrete JFET based constant current diodes operate with a Vgs of 0 volts (the gate is tied to the source) so they do indeed have a very low dropout voltage which is limited by their Vds saturation voltage. This is reflected by their specifications where low current diodes have a low dropout voltage (below 1 volt) and high current diodes have a high dropout voltage because the dropout voltage is the product of the current and channel resistance.
Calvin:
Hi,
yes You´re right about Vgs=0 .... but that´s also the reason why those ´constant current diodes´are rather quick´ndirty ccs that by far don´t exploit t he potential of a proper degenerated JFET based ccs.
regards
Calvin
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