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sturgessb
Joined: 25 Apr 2008
Posts: 246
Location: Norwich, UK
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Posted: 18 May 2010, 14:01 PM Post subject: |
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righto, ill be disconnecting that when i get home then 
would a switching regulator do the job safely?
Ben |
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twesthoff
Joined: 17 Mar 2006
Posts: 199
Location: Fredericksburg, VA
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Posted: 18 May 2010, 14:05 PM Post subject: |
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| FFMan wrote: | | max current draw is 200ma, mostly down to the ultra bright leds i need to use for outdoor use. |
If you connect a 10-12 ohm 1W resistor in series between the fuse and D1 it may make the circuit more reliable by limiting the current D2 will receive when spikes occur. The most common failure mode of zener diodes is to short, and in this circuit it will then blow the fuse. If you don't use the fuse, then the zener gets hot and makes smoke.
I would also recommend using a smaller voltage value for zener D2 such as 20-25V. Some 7805 regulators are rated for a maximum voltage of 30V so it should be lower than that. |
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twesthoff
Joined: 17 Mar 2006
Posts: 199
Location: Fredericksburg, VA
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Posted: 18 May 2010, 14:16 PM Post subject: |
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| sturgessb wrote: | righto, ill be disconnecting that when i get home then
would a switching regulator do the job safely?
Ben |
It all depends on the circuit used or the ratings on the regulator used. High voltage spikes must be kept away from the regulator in some way. If you simply add a 20V zener diode and fuse on the input to the regulator, (like it is in the circuit mentioned previously), you will do a lot toward making it reliable with the 7805.
The special automotive type regulators have high input voltage ratings meant to withstand a typical car's voltages. |
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