Linear regs above 35v

[Matt_Edwards]

I have have caused a problem for myself. All be LED lights run on 24volts DC. This means I can use a 7805 regulator for the uController - no sweet. It was all part of the design.

However recently I have had to do some 36volt light strings. the trusty little 7805 has a max Vin of 35v. I have measure my +36v supply ( simple linear) at +40 with little load.
I have thought of a series element (AKA 12v stud zener). or measuring the current and putting in a dropping resistor.
These will only be used where I need a DMX controller with the light.

Has any one got a sweet solution?
Cheers
Matt

[mrpackethead]

I have have caused a problem for myself. All be LED lights run on 24volts DC. This means I can use a 7805 regulator for the uController - no sweet. It was all part of the design.

However recently I have had to do some 36volt light strings. the trusty little 7805 has a max Vin of 35v. I have measure my +36v supply ( simple linear) at +40 with little load.
I have thought of a series element (AKA 12v stud zener). or measuring the current and putting in a dropping resistor.
These will only be used where I need a DMX controller with the light.

Has any one got a sweet solution?
Cheers
Matt

How much current are you talking?? Generally speaking if its small current requirements that you can use a zener..

However if its higher current, then you're possibly looking at having to use a switching supply.. ( better efficency, but at some cost ). Im using these to provide 12V to strings of RGB pixels, when i need to have *Long* runs of power.. I'm feeding in 48V

Simple alternative, you coudl look at using a LM317HV which is a adj linear regulator good for up to 60V input. (http://www.national.com/mpf/LM/LM317HV.html)

[P. Short]

Are you sure that the voltage is as low as 40V? I would expect that you would end up with more than 50V if you are using a full-wave rectifier on the output of a 36VAC transformer. MPH's question is important as well.

[Matt_Edwards]

Phil,
Absolutely sure. I measured.
I did not use a 36Vac transformer, a just added a 12Vdc plug pack in series with my normal 24Vdcsupply to test the kit.
Plug pack have poor regulation and as a result.

My final linear supply will be a 24Vac tranny with full wave rectification and 10000uF caps. the should give me 34Vdc.

Cheers
Matt

[P. Short]

It may be a bit higher under light load. The voltage rating of a transformer applies when it is under the specified load, it will be higher under no load or low load. I would expect it to come out around 36 or 37V.

[wjohn]

how about a DC-DC controller?

there are isolated and non - isolated versions. Depending on the controller you need to power, and the version of Code (PWM/non-PWM). I have only read up on them, not used them todate.

John.

[Matt_Edwards]

Guys thanx for your input.
I built my final Linear tonight. works as expected ~37 volts no load, so things are sweet on that front. I don't think I mentioned I borrowed 3x 12v SMPSs from work for the testing whilst I decided to go 36V SMPS ( Mean Well brand out of China) or Linear Tranny from my local comic electronics store (Jaycar is more interested in farting ashtrays than supporting hobbist). Well I blew them up. so I was stuffing around getting what ever I could late on sunday night so the testing would go on.

John, many moon ago I designed fly back and push-pull SMPSs. it was great fun. But not enough time to do this now.

I am thinking of a Pre regulator.
Advantages:
I keep the boards identical to all the others that operate on 24V
the uController load is pretty small
I will still keep the 7805

Disadvantages:
regulation can be crap. but that doesn't concern me too much as I still have a 7805.
it is such a waste of Power!!
cheers
matt

[ErnieHorning]

7824, max input is 40 volts. Regulation good.