Types of regulation circuits?

[GarageBoy]

Ok, I've heard of Buck circuits, Boost Circuits, Buck/Boost Circuits, the BadBoy type and the MadMax type. What do they mean and how do they perform? Also, can you guys give examples of how the run time is on each of the circuits?
(e.g. the madmax dims from the start)
Thanks!

 

[idleprocess]

A simple boost converter just boosts the voltage from the source high enough to meet/exceed the Vf of the LED. I think the simplest boost converters can be made with a switching transistor or two, a small handful of resistors and capacitors, and a small coil.

Smarter boost converters boost voltage and regulate output current for consistent brightness.

In effect, boost converters require more current on the supply side to balance watts in and watts out, including converter losses.

Any LED light with a power source that's less than its nominal Vf requires a boost converter.

Buck converters cut the supply voltage to meet the Vf of the LED. I think that most buck converters are really just current supplies set to whatever works best for the given LED. Current supplies automatically adjust their internal resistance to supply constant current to the load up until the output voltage exceeds Vin-Voverhead.

A buck/boost converter is capable of both functions if you want a variety of power supplies, or expect your power source to vary dramatically.

I'm sure others will add more and perhaps even correct me.

 

[evan9162]

Actually, typically a buck circuit refers to a switching type circuit that drops the voltage the same way a boost circuit does - by switching on and off the load through an inductor - the description you provided about a boost still applies, just in reverse.

Regulators that simply drop the voltage and dissipate the extra voltage as heat are Linear regulators.

 

[GarageBoy]

Thanks! So both Mad Max and Bad Boys are boost circuits, but the bad boy regulates current as well?

 

[GarageBoy]

So a Mad Max and a Bad Boy are boosts? So how are they different?

 

[Starlight]

Here is a quote from a post by McGizmo about converters at the Sandwich Shoppe. I hope it helps you.

"I have seen various posts in regards to the wizard converter and of course now the next generation Wiz2. For those unfamiliar with the wiz, I think a little background is advisable. I will relay what I know and recall, to the best of my knowledge. The best of my knowledge may fall short of reality so please chime in and make corrections where needed!

Wayne started his drivers with the max series. These were and are voltage regulated drivers which boost the supplied voltage up to higher outputs to the LED's. His next development was the BadBoy converters which are a boost circuit that provides a set constant current to the LED. For various reasons, the LED manufacturers suggest a constant current drive as the preferred method for driving LED's.

Some time after SureFire came out with the KL1 shich has a buck/boost constant current driver, Wayne came up with the wizard. A buck/boost driver can accept voltage both above and below the voltage required by the LED and it, in the case of a constant current buck/boost driver, can either boost the voltage up or step the voltage down while continuing to provide a constant current to the LED. Unfortunately, the versatility of such drivers comes with a cost which turns out to be efficiency. This loss in efficiency can be considered in terms of reduced runtimes but in the case of these LED lights, I think it is important to consider where this "wasted" energy goes! Yup! Heat!

To my limited knowledge, the KL1 is the only commercially available LED light with a buck/boost driver. It provides a constant current in the mid 300 mA's to the LED. Wayne's Wizard, with an output set at 400 mA is very comperable and can handle an even greater range of input voltages. The inefficiencies wasted in heat, at these drive levels can be handled by reasonable thermal considerations and relief in good flashlight designs. Unfortunately, with the 5W LED's and now the Lux III's there are needs and demands for more current and power than the wizard is capable of. A 611 mA output for a LuxIII or 1 watt LED has been accepted as the maximum output to demand from the wizard."

 

[GarageBoy]

Ahhh thanks!

 

[INRETECH]

The problem with a boost circuit, is that you need to pull more current and then the in-eff of the circuit

For example, to make 3v battery run a 5w part (7.5v @ 750ma), you would need to increase the voltage 2.5x, and thus the current as well - so it would be drawing 1.25a; and since the covertors average about 75% eff - 1.25/.7, actual current on the battery would be approx 1.75A

If you have the room, it would be much MORE eff - to just use more batteries

 

[INRETECH]

Correction, current would be 1.875A before in-eff, and 2.6A after...

 

[idleprocess]

There are some fairly efficient boost converters out there - I think I've seen 90%, but those typically only boost 2-3V to the typical white LED's 3.6V Vf. Single-cell converters seem to be decently efficient so long as they're driving small loads such as a handful of 5mm LEDs being run close to spec.