12V to 9V supply for sounder

[Artimes]

Like many, I have 6 times 1.5V pencil AA batteries to drive my depth sounder. Has anyone a circuit spec to transform boats 12V DC supply to 9VDC. Thanks

 

[halcyon]

You need a LM7805, 4.3 volt zener, 2 caps and a bit of heatsink.
Give you a 9.3 volt short circuit protected supply.

e-mail you a diagram if you need one.


Brian

 

[rogerm]

In fact you can use 'halycons' solution to provide any voltage between 5v and about 10v at 1A for other devices by changing the voltage of the zener ie if you want 7v then 7v -5v = 2v so use a 2v zener. While you can find these (2v zeners) it is easier to use 3 ordinary diodes in series (=2.1v). A 6v supply is quite useful for general portable things like radios. Just fit 1 ordinary diode (app 5.7v).
Roger

 

[johnsomerhausen]

An ordinary diode drops the supply voltage by 0.7 V, so solder 4 of them in series and you'll get a 2.8 voltage drop, from 12 to 9.2 V.
john

 

[halcyon]

The problem with the diode system is that you need a regulated 12 volt supply. If for example you start the engine and the alternater gives you 14.4 volt, less 2.8 volt diode drop would provide 11.6 volt to sounder.
The LM7805 gives you a 9 volt supply independent of input voltage, well from approx 11.0 volt to 32 volt.

Brian

 

[sonarbell]

Why not just use LM 7809. couple of decoupling caps either side, say 10microfarad electrolytics. and all will be well. Most LM series regulators need at least 3volts higher on input to give perfect regulation, but should it drop below, will still work just wont regulate so well.

 

[Artimes]

Thanks to all you honest sailer men/women for information, if you come to Dublin..fee paid will be pint best Guiness

 

[Artimes]

THANK YOU FOR THAT INFO, MOST HELPFULL, IF YOU COULD WITHOUT TROUBLE PROVIDE A DIAGRAM THAT WOULD BE WELL RECIEVED....REGARDS JOHN