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voltage regulators


nick franco
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Hi all, I'm looking to drop voltage from 14.4-12 to 5 via a regulator for my on board record deck.

Switching regulators seem to be much more efficient than the linear type.

Are there any drawbacks to the switching ones? Advantages to the linear? Better options to drop voltage?

Thank you, nick

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Hi Nick, I would go for the switching type, they give less heat off, can have a higher max. output and weight not much.

I use them too for powering an XL1 (~7 volts)and an XL2, or a spy camera at 9 volts. Normally no issues as long as there max. output is high enough. Most of them will switch off anyway when they get too hot or you draw too much.

 

One time I saw a interference in the picture, but that one was a switching unit from Mains (220 V~)

 

Officially your garantee is not valid anymore when you power this equipment with any other then the original supply... but what can you do.....

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Hey Guys,

 

 

I completely agree with what Rob says. But if cost/size is an issue, go with a linear type. a 7805 (5volt reg) will cost you about a buck... and is very tiny (TO-220) in comparison to a comparabe switching regulator that will cost you around twenty for comparable output. The difference in size is due to the complexity of the design of a switching type. Also, a linear is slightly more forgiving with over current, spikes and whatnot...they won't shut off, but will get hot and drop the voltage accordingly.

 

~C

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Charles, I did make my first regulaters like that in the beginning, but found them not so reliable. Most recorders use a bit more than the 1 amp max from an 7805. I know you can have 2 amp regulators now, but the heat coming off them is a lot: they have to get rid of 7 to 10 volts at that amperage, which is between 10 and 20 watts.

You need a big cooling surface for that or a fan too.

 

Another issue, depending on the setup of your rig, but if you have a switchable 12/24 rig, your rigs "ground" is probably not the same as the "ground" of the cooling surface, an if they touch each other you have nice sparks

:D

 

The switched regulaters come many times in a plastic housing, just velcro them anywhere convenient.

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  • 2 weeks later...
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Rob is dead on. The only major drawback to switching regulators is the interference that can be induced in the delicate video signal. Fortunately this is an easy fix with a couple of capacitors. The cost of a switching regulator is negligible relative to everything else in the film/steadicam world. You can get a really nice adjustable 3-amp DC-DC switching regulator (Power Trends) from DigiKey for about $18 USD. Then a couple of bucks for capacitors, wire, a trim pot, a pico fuse (to protect against shorts), heat shrink to cover the board when you are done, epoxy and you're all set. These regulators are very efficient, produce a lot less heat (wasted battery power), don't take up that much space, don't weigh much, all said and done for under 30 bucks.

 

Hope this helps, if you need more info or picts let me know.

Edited by Matt Petrosky
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  • 10 years later...

Apologies for dredging up an old thread, but here's my way of increasing the current out of a 3-terminal voltage regulator to drive an HDMI-SDI converter on my Steadicam Pilot HD rig with the Panasonic GH4. (With different connectors it could be used on pretty much any model of Steadicam, or for multiple other uses.)

 

Basically, you add a pass-transistor, with the output-terminal of the regulator connected to the output (the Collector) of the transistor, and solder a resistor between the Base and Emitter of the transistor, which then goes to the input of the regulator. Here's the circuit-diagram:-

post-17188-0-58415300-1471950512_thumb.jpg

 

The voltage regulator is any of the 78xx series positive 3-pin voltage regulators, the pass-transistor is a Silicon PNP power transistor. I used the very common TIP32 in a TO-220 package, same as the regulator, so they could share a common heat-sink. You need to work out the value of the resistor (easy enough), and the capacitor is a 0.22microFarad cap for stability at the input of the voltage regulator (it's not very clear on the diagram). All this should cost less than $5, which is pretty cheap in the world of Steadicam!

 

Here's how it works: Power in (16.2 volts from your IDX battery, for example) is applied to the Emitter of the transistor and also to the 2.5 Ohm resistor (which I made by putting four 10-Ohm 1/2 Watt resistors in parallel). The other end of the resistor is connected to the Base terminal of the transistor and to the Input terminal of the voltage regulator.

 

As the current flows into the voltage regulator, a voltage is developed across the resistor. You want this voltage to be 0.6 Volts to forward-bias ("turn on") the Base-Emitter junction of the transistor so it conducts and allows current to pass through it. We'll get to the value of the resistor shortly.

 

Now, here's the clever bit. Because the output terminal of the regulator is soldered directly to the Collector (output) of the transistor, the voltage at the Collector must be the same as the output voltage of the regulator. In other words, as the transistor is turned on, the excess voltage will be dissipated across the Emitter-Collector circuit of the power transistor.

 

Okay, how do you work out the value of the resistor? Measure the current drawn by whatever device you intend to drive at the regulated voltage. My HDMI-SDI converter draws 200mA at 9 volts with HDMI in and driving an SDI monitor, so I needed a resistor that developed a voltage of 0.6 volts at 200mA. Ohms law says this is 3 Ohms, but resistors come in a preferred series and the closest value to 3 Ohms is a 2.7 Ohm resistor.

 

Unfortunately I couldn't find a 1W 2.7 Ohm metal-film resistor, so I made a 2.5 Ohm 2 Watt resistor by putting four 10 Ohm 1/2 watt resistors in parallel which becomes a 2.5 Ohm 2Watt resistor...perfect! The wattage is also important because you don't want the resistors to burn out! Power is current squared multiplied by resistance, so 200mA squared multiplied by 2.5 is 0.1 Watts. My 2W resistor should handle it.

 

Now the beauty of this simple but useful circuit is the power transistor can handle far higher current and dissipate far more heat than the regulator on its own. Your device can draw a few amps without any problems, as long as you can get rid of the heat generated. Power transistors are designed to do this all day long, but you have to get rid of the heat, perhaps several watts or more...that's where the "heat-sink" comes in.

 

Both the regulator and transistor are mounted, back-to-back using adhesive heat-transfer tape, to a single TO-220 heat-sink. We just let the entire affair hang out in the air, where natural airflow will allow the heat-sink to do what it does best - get rid of heat. This circuit should work in a 105 deg F day in Abu Dhabi, Arizona (or the Australian outback) as well as it does in a -40 F day in the midst of a Candian winter, or a shoot in the polar regions.

 

So, a few simple, cheap components, a little soldering, some assembly and now you have an adapter lead from your Steadicam Pilot power outlet on the rear of the stage to drive whatever you like. My HDMI-SDI converter was rated 5-12VDC input and I didn't fancy stuffing a raw 16 volts into it. I made a 5-volt lead, a 9-volt lead and a 12-volt lead.

 

The regulator will "drop-out" when the input voltage is about 2 volts above the output voltage, so with the 12-volt lead when the IDX battery drops to 14 volts, the 12-volt regulator shuts down. Just replace it with the 9-volt lead and keep working until the IDX battery itself is discharged. The 5-volt unit runs hotter than the other two, and I prefer to run either 9 or 12 volts into the converter anyway.

 

Keeping this circuit simple is the key to reliability. The power transistor isn't a high-gain device so I haven't bothered adding RF bypassing with ceramic capacitors. If RF energy from handheld radios, base-stations etc causes problems, add a ceramic capacitor between output and earth on the regulator. The capacitor needs to have a low impedance at the RF frequency in use (you use the formula for calculating capacitve reactance to work that out.) Less than 10 Ohms should do.

 

Here are a few photos showing the appearance of the completed unit:-

post-17188-0-23980500-1471952748_thumb.jpg This is the Pass-Transistor side with the resistors visible,

post-17188-0-06182500-1471952811_thumb.jpg and this is the other side with the voltage-regulator and little capacitor visible.

 

I have built 20-Amp variable power supplies using the same basic circuit with an adjustable voltage-regulator so I know this circuit works and works well. Once you have built it, double check you have the polarity of the input and output connectors correct before you go applying any voltage to the input. 78xx voltage regulators HATE reverse polarity!

 

How does the Pilot HD stage look with the GH4 and converter rigged? Like this:-

post-17188-0-03877500-1471953987_thumb.jpg

The stage has plenty of fore-and-aft adjustment, you can see how many weights are needed with the GH4 to properly load up the arm, and the regulator is hangng down behind the rear weights (somewhat out of focus). The HDMI-SDI converter is attached right behind the GH4 with Velcro "sticky-dots" and tilts back a little...a minor issue. The converter is one of the cheap "generics" available on eBay for less than $50. Light, small and well-matched to the Pilot HD, it drives the SWIT monitor nicely. (Photo below)

post-17188-0-86140300-1471954512_thumb.jpg

 

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