Actions
Forum Thread Details
  • State Not Answered
  • Replies 10 replies
  • Subscribers 303 subscribers
  • Views 2428 views
  • Users 0 members are here
Related
See a helpful answer?

Be sure to click 'more' and select 'suggest as answer'!

If you're the thread creator, be sure to click 'more' then 'Verify as Answer'!

Reverse protection of Multicomp pro DC/DC converters MP-K78xx?

DavidOB

Hi,

I'm unable to find rating and description of MP-K78xx DC/DC converters in respect to reverse current/voltage protection. I have some questions:

1. What happens if another voltage source is connected to the output if this converter is not powered and used with typical application circuitry with input/output 10/22uF ceramics capacitors?

2. Same question as 1. but what if the converter is powered?

3. Same question as 1. but what if the converter input is shorted to ground?

3. What would happen if that another source voltage is higher than the converter nominal output? E.g. MP-K7803-500R3 is used for a battery powered device and USB + is connected to the output power rail while connected with a PC. If USB cable is connected, its 5V would then go into this 3.3V K7803 output.

Parents
  • 0

    Good questions and you're right to research them.  LM78xx (and LM79xx) don't like reverse current so I always provide diode protection in case there is any over voltage/current problem downstream.  I've used these types of parts quite a lot and it's good to know that Multicomp are now doing them as they look significantly cheaper.  When using them, I've always followed the same principles in terms of protection as I have with a typical LM78 component.

    These are footprint compatible with LM78XX devices so you could get a good idea of what is/isn't allowed from other data sheets for an actual LM78xx (Texas Instruments data sheets are usually comprehensive in my experience).  Also, this device is a re-branded LM alternative so find an equivalent from TracoPower or Recom and check out their data sheets (I'd bet someone else's bottom dollar that it's actually manufactured by TracoPower or Recom!!.)  

    For example, here's a datasheet for a Recom LM78XX replacement.  It shows how to handle reverse current if it's powered down.    I think this answers your Q1 and, in fact, Q3 as if there is no input to it, there's no output which is pretty much the same as powered down I think??

    Q4 (your second Q3) and Q2 should be covered by the diode protection circuit with the Schottky diode - as Shabaz mentioned in his response.  

  • 0 in reply to Andrew J

    Interesting, they are a really good price. I've added a few of the in-stock options into the shopping basket since they are so useful.

Reply Children
No Data