1.5A LM7805 substitute?

[blueroomelectronics]

I'm looking for an inexpensive linear LM7805 repacement that can supply 1.5A
The LM317 supports 1.5A but I don't need the adjustable features and would prefer a simple regulator. TO-3 case fine too, are they still very common?

 

[justDIY]

the xx7805 is too expensive, or what?

try searching your distributor for just 7805 instead of using National's (original) part number LM7805.

examples KA7805, ST7805, etc

edit oh, i think i see what you're getting at ... the 78xx is typically rated at only 1a not 1.5a - hows about the xx1084 (or 5,6) I think it comes in fixed varieties as well as the adjustable version.

 

[blueroomelectronics]

Thanks justDIY, yes I like the old 7805 and they can even keep you warm. The AP1084 5V & 5A wow. I'll look into it.

 

[k7elp60]

Another possibility is the LD1085V50 by STM, Mouser has stock.

 

[Speakerguy]

Texas Instruments TL780-05

1% Voltage tolerance, otherwise fairly standard.

 

[Krumlink]

Yes I agree with speaker guy, I have used these before (matter of fact one is on my Binary Clock, it can pull 1A+ sometimes) and you can hook it up like a standard 7805. Works great.

 

[picbits]

78S05CV from ST (another great company I buy from) are £0.44 each and will supply up to 2 Amps if adequately heatsinked.

TO220 as well

DESCRIPTION
The L78S00 series of three-terminal positive regulators
is available in TO-220 and TO-3 packages
and with several fixed output voltages, making it
useful in a wide range of applications. These regulators
can provide local on-card regulation, eliminating
the distribution problems associated with single
point regulation. Each type employs internal current
limiting, thermal shut-down and safe area protection,
making it essentially indestructible. If adequate
heat sinking is provided, they can deliver over 2A
output current. Although designed primarily as fixed
voltage regulators, these devices can be used with
external components to obtain adjustable voltages
and currents.

 

[Hero999]

I don't understand why you can't use the LM317, so what you have to add two resistors? Big deal.

The LM7805's peak current is 2.2A but the datasheet doesn't say for how long. You could probably draw 1.5A for longer periods with no trouble.

Have you tried the LM7805 and had problems?

 

[blueroomelectronics]

I thought about splitting the regulators.
The circuit has 10 Omron 5V relays that draw 80ma each 800ma, a PIC, Ethernet & LCD with backlight ~200ma
That's just too close to 1A when everything is running.
I could run the relays from unregulated DC but I'd need either 5V, 9V, 12V or 24V DC, BUT I need a low voltage AC source from the wall for a zero crossing circuit. I've posted an early schematic (Ladybug) on these forums but would repost it in this thread if that would help.
So here's the so far best solution but...
6.3VAC wall adapter (do they exist?)
bridge, (full wave tap for zero crossing), diode (7.5VDC here)
pair of 7805 (one for logic + 2 relays, other for 8 remaining relays)

Problem is I'd like to optionally have the user choose the power source ie battery 13.8V or 12.6VAC so I'd like a range of power input options. Plus I'd like to keep the bridge too so the input power is non polarized.

The LM317 will get just as hot as the 7805 when blowing off that kind of current.
A switchmode supply may be a better solution in the long run.

 

[Hero999]

6.3VAC is a bit low for an LM7805.

You could use 9VAC with 12V relays running from the unregulated DC, higher voltage relays will draw less current.

What about doing away with the relays and using triacs?

I don't understand why you're bothering with zero corssing for relays anyway.

You could use a normal mains adaptor and make your own SMPS on the output, if you want to save yourself the large heat sink.
https://www.romanblack.com/smps/smps.htm

 

[1Steveo]

Just a thought a 34063a will put out 1.5 amps. My cell phone chargers use them.

 

[blueroomelectronics]

The 6.3VAC through a full bridge will produce about 8.3VDC (1.414*6.3-1.4)
12V relays might be an option, I did find an article on switching relays at zero crossing to minimize contact pitting. But I do have the snubbers on there...
2A 5V switch mode wall adapters are cheap and common, cheaper than using a regulator actually, I could use a crowbar circuit (PTC & diode) to keep the end user from wiring it in backwards as it's all screw terminals.
Relays can switch DC.
The wall adapter just might be the way to go.
Hero999 how did your PIC programmer project go, are you getting into PICs?

 

[Hero999]

8.3V is the peak voltage, the vally will be much lower, better stick a huge 10,000:mu:F capacitor on there.

I finished my programmer but haven't got round to buying any PICs.

I've been building up a list of things I need to order and will put them in with it.

 

[jpanhalt]

A DigiKey search returns 69 items with 1.5 to 5 A ratings, including the UA7805 at 1.5 A. Some are pretty expensive. The Sharp PQ050RD is 2A at $1.19 and the LD1085 is 3A at $1.95. John

 

[kchriste]

You could use latching relays to reduce current consumption. I like your 5V regulated wall adapter idea; 1.5A through a linear regulator is just gonna generate too much heat.

 

[blueroomelectronics]

Well I found a cheap source of 2A 5V switchmode wall warts. I'm going to use them in the design. The relays are HLS-4078 5V contact. x10