45v to 5v voltage regulation

[chunkitup]

I am adding a 5v relay switch to a peavey amp. The taps I am using are 32Vac which after a bridge rect. will be about 45v. I have a 7805 but I was wondering if dropping 40v would generate too much heat on the 7805? Also what value caps should I use? Should I drop some voltage first then regulate or just use a heatsink?

Here is a pic of what I am going to build.

http://www.eleccircuit.com/wp-conten...y-ic-78s05.gif

[Sowhat]

Yeah! a 7805 being a linear regulator will not cope with that kind of demand, you would have to redefine the meaning of hot with that arrangement for sure! Use a switcher (DC to DC converter) for that type of arrangement like a LM2576. The circuit is a little more complex but will run cool as ice even with loads twice what a linear can handle. Under 1-1/2 amps you will not even need to use a heatsink.

I think the LM2576 can deal with up to a 60 volt drop with ease however I don't really remember the specifics, check it's datasheet.

[Bruce / Mission Amps]

How much current does your relay need to operate?

[R.G.]

How much current does your relay need to operate?

Right **QUESTION** !

[chunkitup]

It is the Omron G5v-2-h1 and it consumes 100mA

[J M Fahey]

And why a 5V relay?
In my 60/100W amps (+/-40V rails) I use 24V relays with a 1K 1/2W resistor in series , and switch them with any general purpose TO92 small transistor.
In the 200/600W ones (+/-65V rails) I use a 48V relay, don't remember the series resistor now, but it also is a relatively small one.
Simple/cheap/safe, and provides least power waste.
Just in case it's not clear, instead of "lowering the rail " I "raise the relay coil voltage".
Remember that higher voltage coils need much lower currents.

[kleuck]

Use a 35 volts 5 watts zener in series with the rail, then a 7805.

[chunkitup]

5v relays are all I have on hand. If I build an amp and need switching I tap into the filament which is 6v in all trannys I use. Peavey uses 32v taps to power the filaments, switching, reverb, tremolo and washing the dishes.

[J M Fahey]

Just checked Mouser:
relay omron g5 v2 h1 Low Signal Relays - PCB | Mouser
In "Low Signal Relays" including "G5 V2 H1" in the name, they display 4.
They "eat" less than you think ... and of course the higher voltage coils are more efficient, since they match the available rails better:
Model-Voltage Current
G5V-2-H1-DC5 30 mA
G5V-2-H1-DC9 16.7 mA
G5V-2-H1-DC12 12.5 mA
G5V-2-H1-DC24 8.33 mA <-- use 1K8 1/2W in series for 40/45V rails
Remember to use a reversed 1N4002 in parallel with the coil.
*Any* small transistor can switch these, or any mechanical footswitch, even those which include a series LED (although it does not shine *that* bright).
In fact, one of my applications is switching a similar relay with a tiny TO92 SCR, as a latching "idiot proof" short circuit protection.

[loudthud]

The link to the 78S05 data sheet isn't working for me. Can that part stand 45V? My old data sheet for the LM7805 says 35V max.

[chunkitup]

Just checked Mouser:
relay omron g5 v2 h1 Low Signal Relays - PCB | Mouser
In "Low Signal Relays" including "G5 V2 H1" in the name, they display 4.
They "eat" less than you think ... and of course the higher voltage coils are more efficient, since they match the available rails better:
Model-Voltage Current
G5V-2-H1-DC5 30 mA
G5V-2-H1-DC9 16.7 mA
G5V-2-H1-DC12 12.5 mA
G5V-2-H1-DC24 8.33 mA <-- use 1K8 1/2W in series for 40/45V rails
Remember to use a reversed 1N4002 in parallel with the coil.
*Any* small transistor can switch these, or any mechanical footswitch, even those which include a series LED (although it does not shine *that* bright).
In fact, one of my applications is switching a similar relay with a tiny TO92 SCR, as a latching "idiot proof" short circuit protection.

You are correct! I was looking at the standard model numbers on the pdf. I think I will go with a DC24 and get rid of the regulator. Even though peavey puts alot of loads on those 32v taps I think the 8.33mA wont tax it too much. Yea I will be using a PV 5150 dual switch for the delta blues amp and I am not really worried if the leds are bright. Much kindness J M Fahey

Note to self: Peavey Delta Blues are no fun to work on.

[Steve Conner]

I agree that the higher the voltage the better. I used 48V relays in my last solid-state amp build.

[Sowhat]

The link to the 78S05 data sheet isn't working for me. Can that part stand 45V? My old data sheet for the LM7805 says 35V max.

The 78XX family has a 35V max but more importantly those things have about a 74 degree C ceiling before they trip out. Dropping that much voltage linerarly develops so much junction temperature that you can't avoid over temping, no matter how much heatsink you pile on it.



Here is a few iterations of my typical auxiliary supply which is partially my main filter, power distrib, star ground and 12VDC effects supply for effects. #1 uses a 7812 for 12VDC and overtemps almost immediately, #2 and #3 show beefier and beefier heatsinks, neither of which did the trick. #4 shows a redesign using an LM2576 which runs cool as can be. The heatsink is there to basically hold the converter sturdy and because I already had one laying around. I don't measure it really dissipating any noticeable heat, but it looks cool!



Here's the actual board under thermal test... 30.6 degrees C... 2.6 over ambient, YEAH! now we're talking!