Diy Variable voltage setup

[steelPHASE]

Hi steel pat
Some great info and ideas about the voltage regulators.
Just to clarify if I use a DC-DC buck unit then add the toroidal inductor to the output voltage to reduce any noise that I get on the output voltage. Is that correct. I haven't used these before. If u could draw me a simple sketch of a circuit that would be great.
Let me know
Cheers
Firey,10_0

Heres a quick sketch of what I talked about. You may have to adapt to suit

 

[steelPHASE]

Hey Firey,
Handy with a soldering iron.... does that mean you can design and build your own small circuits?

If so then SP suggestion is not a bad one , but i would add a couple of caps and an inductor to smooth out the output to avoid noise (these do put out noise)
on the other hand , something like an lm317 is low noise already so you may get away with a single cap on the output.

317's are great and would work in this application but do drop more voltage than a DC - DC converter so would need a larger voltage source.
It would require heatsink in this application as well as a few more external parts.

Here's the setup for a LM317 taken from a datasheet I have. I would also add a larger cap on the output in this application.

 

[bicter]

Last post disappeared into the ether :argh:

Food for thought!!!!

As the detector is battery operated, it's unlikely that Minelab will have applied much filtering to the P/S I/P. Using a DC-DC will introduce higher levels of noise into the detector than a linear regulator would. The impact of this is unknown.

Using the LM2596 driven DC-DC, the spec suggests up to 3% ripple on the O/P (Up to 0.5v).

I think the most effective solution would be to change the battery pack to a 12V style, with sufficient AH capacity and regulate to the required voltage using the LDO I suggested earlier.
Using the LDO will minimise the power loss compared to a normal regulator such as the LM317 and therefore provide longer running time for the battery pack.

 

[Rush]

Would this work.

With the component values shown the circuit is designed to have and output voltage range of approximately 1.25 to 13.5 Volts when measured at the output of the regulator. The calculation on the drawing is used to determine the output voltage for given values of R1 and R2.

Because these regulators have a minimum output voltage of 1.25 Volts diodes D3 and D4 will provide a voltage drop of approximately 1.4 Volts so that zero output to the track can be obtained. These diodes need to have at least a 3 amp rating.

The diodes D1 and D2 added to the circuit will prevent damage to the regulator during certain adverse conditions such as the output voltage being higher than the input voltage to the regulator. This can happen if this type of circuit is used as a variable power supply for an electronics test bench and without the added protection of D3 and D4.

A substantial heat sink will be needed for the TTR as quite a bit of heat will be generated when drawing high current with low output voltages. For this reason this circuit is not recommended for use in hand held throttles.

If the less expensive LM 317 regulator is used this circuit makes an excellent test bench power supply just leave out D3 and 4 and add a voltmeter.

 

[Eski]

I would use Low noise LM circuit as per one of SP suggestions (with a couple of diff caps and a toroid inductor of particular value), BUT would use a 3 cell Li-ion/Li-po, I recon you would only need 7AH

 

[Firey10_0]

Thanks to everyone for the info they've supplied. I've decided to give the lm317 a shot and see how it's goes.
Thanks again
Firey10_0