Obsolete Darlington Replacement  - Page 1
Forum section: electronics / beginners

author: b9creations
author_rank: Contributor
timestamp: July 03, 2015, 01:48:05 pm
content: Hello,Looking to possibly replace obsolete MJE5742 Darlington Transistor with something more modern that is also available in SMD configuration. Is it possible to replace with Power mosfet instead? If so where to begin?When I looked for Darlington's with the same specs there were no viable matches, but not really sure which of the specs are crucial and which of the specs are not important...This is another 555 ignition coil driver circuit. Unfortunately I am unable to post the circuit to public domain...Thanks very much for any help suggestions, Jeff

author: electrophiliate
author_rank: Regular Contributor
timestamp: July 03, 2015, 02:08:07 pm
content: A power MOSFET would be preferable over a darlington transistor, but modern ignition coil drivers usually use IGBTs designed for the task.Something like the IRGB14C40L* or ISL9V5036P3 may suit your needs.[edit: is in a TO-220 package but also comes in a TO-263AB package as IRGS14C40L for SMD]

author: Deathwish
author_rank: Unknown
timestamp: July 03, 2015, 02:10:51 pm
content: this help ?http://www.digikey.co.uk/product-detail/en/MJE5742G/MJE5742GOS-ND/919522

author: b9creations
author_rank: Contributor
timestamp: July 03, 2015, 02:34:06 pm
content: Thanks guys, I did not know about IGBT's so I appreciate that. Yes even though it's more less obsolete it's still available in to220 package, but there is no SMD equivalent as far as I can tell, so rules out modernization plan. Maybe I should rephrase question to how to go about finding SMD equivalent, if it's even possible?Perhaps the entire circuit would need to be re-designed which is beyond my capabilities.. I may need to end up hiring someone I guess, but thought maybe there was a small chance I could learn how to go about this myself?Greatly appreciated.. Jeff

author: Tandy
author_rank: Frequent Contributor
timestamp: July 03, 2015, 02:56:13 pm
content: Assuming the darlington is being used as a switch rather than amplifier then you could probably use a BUB323Z in a D2PAK for Surface Mount.

author: electrophiliate
author_rank: Regular Contributor
timestamp: July 03, 2015, 03:04:02 pm
content: Here is the SMD version (TO-263AB package) of the original darlington BJT:http://www.digikey.com.au/product-detail/en/MJB5742T4G/MJB5742T4GOSCT-ND/2699500

author: HighVoltage
author_rank: Super Contributor
timestamp: July 03, 2015, 03:11:40 pm
content: Quote from: b9creations on July 03, 2015, 02:34:06 pmIt seems you want to drive an ignition coil with a 555 timer for setting the duty cycle and frequency.The IGBT was already pointed out and will most likely be the easiest way for implementation.I would suggest the Fairchild ignition IGBT in SMD housing.Essentially you can drive the IGBT directly with the output of the 555, making your circuit very simple.But then, it depends all on what you want to achieve with the circuit.If you don't want to post the details in public domain, you can send me a PM.

author: b9creations
author_rank: Contributor
timestamp: July 03, 2015, 03:26:15 pm
content: Excellent! Thanks everyone, this is exciting. : )Perhaps it would help to post at least a portion of the circuit...(This basically shows only the output of pin 3 of the 555)The 555 is set up for variable voltage/frequency output control.I have it set up on a breadboard and it's working very well.And Kat I will definitely take you up on that, give me a minute I will send you PM..Best, Jeff