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I have a small, dead power supply for a camera battery charger (cheap replacement, no brand name). I opened it up and discovered that one of the MOSFETs is burned out. The datasheet (in chinese) is at http://pdf.peidan.cn/BCB/cs1n60f.pdf . I'd like to try and replace it, perhaps with something with a better heatsink. What are the key specs that I need to look out for, and which specs is it ok to improve?

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Look for improvements of the following parameters:

  • Id = 1 A (more is better)
  • Rds(on) = 10.5 Ohm (less is better)
  • Idm = 4 Amps - (More is better)

The following parameters should remain similar:

  • Vgs(th) = 2-4 Volts - Less than 2 Volt minimum is good, but not necessary
  • Vdss = 600 Volts - More is not needed, could perhaps go down to 400 Volts
  • td(on), trise, tfall, td(off) should remain similar or slightly lower than in the existing part's datasheet.

Of these parameters, lowering the Rds will benefit you the most, resulting in less heat generated.

Based on the above suggestions, locating a suitable power MOSFET on a vendor's parametric search (such as on Digikey) should be easy.


Update: Reasoning behind key recommendations above:

  • Id, more is better: The existing MOSFET may have blown due to excessive current, beyond the specifications. Having more margin for error will reduce the likelihood.
  • Rds(on), less is better: The higher the on resistance, the more power (as heat) the MOSFET would need to while passing current - Power P = I^2 * R. Really hot = grilled MOSFET, medium-rare to well done.
  • Idm, more is better: Similar to Id above, other than in some circuit designs, the constraining factor is not sustained current, but current spikes going beyond the Id value but staying within the maximum intermittent current permissible. If this maximum was exceeded at some point during operation, such as due to a main power line voltage surge, that may have been responsible for the component failure.
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  • \$\begingroup\$ Thanks, that's the kind of thing I'm looking for. Are changes to some of those values (thinking voltage or resistance) likely to change the output of the charger, and could I replace the appropriate resistors with higher/lower valued ones to fix that? \$\endgroup\$ – naught101 Jan 31 '13 at 5:38
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    \$\begingroup\$ @naught101 The reduction if Rds(on) is extremely unlikely to adversely impact operation: Power MOSFETs used for switching typically run in the plateau part of the graph, so there's no careful voltage / current tuning needed. The only other factor to watch out for is switching speed - I'll edit that into the answer. \$\endgroup\$ – Anindo Ghosh Jan 31 '13 at 5:42
  • \$\begingroup\$ It'd be great, if you (or someone) has time, to add reasons why those higher/lower values are better. \$\endgroup\$ – naught101 Jan 31 '13 at 6:49

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