Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: James H Harmeyer on February 27, 2016, 12:41:18 pm

Title: Doug's Relay Power Supply and LEDS
Post by: James H Harmeyer on February 27, 2016, 12:41:18 pm

Can anyone tell me if Doug's Relay Power Supply can power 10 or 12 Leds? I believe each Led will have to have a current dropping resistor to bring the 5 vdc down to around 3 volts. But, other than that will the power supply work for 10 Leds?

Title: Re: Doug's Relay Power Supply and LEDS
Post by: sluckey on February 27, 2016, 01:47:31 pm

Doug's relay power supply uses a 7805 regulator chip that can supply 5V at 1.5A if a proper heat sink is used. A typical LED will use .02 amps, so you could theoretically power 75 typical LEDs at that current requirement. 10 or 12 typical LEDs would be no sweat.

Title: Re: Doug's Relay Power Supply and LEDS
Post by: James H Harmeyer on February 28, 2016, 04:36:23 am

Thanks Sluckey for the response and the info, I appreciate your input. But, now I wonder if it would be better to change out the 7805 for a much more efficient switching regulator (LM7805-1A), that doesn't need a heat sink. Or will a good heat sink on the 7805 be good enough to keep this working for a long time? I'm just trying to keep heat from being the cause of a failure.

Title: Re: Doug's Relay Power Supply and LEDS
Post by: sluckey on February 28, 2016, 06:02:54 am

I would stay with the TO-220 case. Just bolt it to the chassis to provide an adequate heat sink. You'll need an insulator.

Title: Re: Doug's Relay Power Supply and LEDS
Post by: PRR on February 28, 2016, 03:53:41 pm

You don't need a regulator. Take your raw 7VDC, use a 270 Ohm resistor for each LED. 19mA per LED, 0.13 Watts per resistor+LED (1/4W Rs are ample), 1.5 Watts total heat for a dozen.

Title: Re: Doug's Relay Power Supply and LEDS
Post by: James H Harmeyer on February 29, 2016, 05:57:06 pm

Sluckey,    what kind of insulator are you talking about for bolting the regulator to the chassis and this will still provide a good enough connection to transfer the heat?

Title: Re: Doug's Relay Power Supply and LEDS
Post by: sluckey on February 29, 2016, 07:11:28 pm

Mica or silicon. Use heat sink grease too.

https://www.google.com/search?sourceid=navclient&aq=&oq=to-220+heatsink+insulator&hl=en-GB&ie=UTF-8&rlz=1T4GZAZ_enUS367US367&q=to-220+heatsink+insulator&gs_l=hp....0.0.0.17337...........0. (https://www.google.com/search?sourceid=navclient&aq=&oq=to-220+heatsink+insulator&hl=en-GB&ie=UTF-8&rlz=1T4GZAZ_enUS367US367&q=to-220+heatsink+insulator&gs_l=hp....0.0.0.17337...........0.)

Title: Re: Doug's Relay Power Supply and LEDS
Post by: Willabe on February 29, 2016, 07:13:53 pm

Quote from: sluckey on February 29, 2016, 07:11:28 pm

Mica or silicon. Use heat sink grease too.

Use heat sink grease on the mica only.