19V laptop adapter as TI power?

[Kchula-Rrit]

I've been mulling this idea for a while to power a TI.

 

I have several 19V power bricks, including some 12V car adapters, from deceased laptops.  If I could set a ground at +6V relative to the negative lead, I could use a LM7905 to generate the -5V.  The +6V "ground" would give me 13V to feed a LM7812 to give me +12V, and a LM7805, maybe through a dropping resistor, to get +5V.  A diode bridge would drop the voltage, hopefully without generating so much heat.

 

Do power bricks have floating outputs?

 

K-R.

[+OLD CS1]

Is 13V enough headroom for the 7812?

[Kchula-Rrit]

Good point.  I think the 78XX/79XX requires a couple of volts difference between input and output to work.  Sigh.  If I could find a +12V to -5V converter, that would take care of the headroom problem.  I'm poking around the Digi-Key site anyway, so I can take a look...

 

K-R.

 

[wierd_w]

https://www.mouser.com/datasheet/2/405/slts037a-206022.pdf
 

Looks like it would have more than enough oomph, and do exactly what you need. Just a bit bulky/pricey.  However, proof that such things do exist.

[jens-eike]

The QI power supply (with 2 wires in) works from 18V DC.

 

[+FarmerPotato]

13 hours ago, Kchula-Rrit said:

I've been mulling this idea for a while to power a TI.

 

I have several 19V power bricks, including some 12V car adapters, from deceased laptops.  If I could set a ground at +6V relative to the negative lead, I could use a LM7905 to generate the -5V.  The +6V "ground" would give me 13V to feed a LM7812 to give me +12V, and a LM7805, maybe through a dropping resistor, to get +5V.  A diode bridge would drop the voltage, hopefully without generating so much heat.

 

Do power bricks have floating outputs?

 

K-R.

Take a look at TI’s line of LDO voltage regulators. They come in a wide variety of capacities and features like low ripple. 
 

Use an op amp in inverting configuration. This gives you a virtual ground and Vout = -Vin 

[Kchula-Rrit]

On 7/20/2020 at 10:15 AM, FarmerPotato said:

Take a look at TI’s line of LDO voltage regulators. They come in a wide variety of capacities and features like low ripple. 
 

Use an op amp in inverting configuration. This gives you a virtual ground and Vout = -Vin 

I found a LM675 power op-amp on the Digi-Key Web site.  It puts out 3 amps.  Have to order a few for experiments.

 

They also stock regulators that have a 0.75V drop-out.

 

K-R.

 

[Kchula-Rrit]

An update on the power-supply--

 

Here is a picture of my battery-powered TI99, affectionately known as Tortoise.

 

Not exactly a car battery; I used a 5A-Hr lithium-ion battery to run the CPU, and a 2.6A-Hr lithium-ion battery to run the monitor.  The black box contains the battery and DC converters to run the CPU and monitor.  The other picture is a close-up of the battery box.  The two connectors are billed as speaker connectors for high-powered audio amps.  I figured, if it's good enough for the Who, it should handle my little computer.  A 19V power brick recharges the batteries, but the charger will handle 5V to 24V.

 

K-R.