what switching power regulator Ben uses to replace the 7805

[mindstein]

Hi,
Does anyone know what the switching power regulator that Ben has used occasionaly to replace the 7805 voltage regulator is?

I know he has mentioned using a switching power regulator instead of the 7805 and saved about 100 milli amp and that it generates much less heat than the 7805. But he never mentioned which switching regulator he uses.

My portable is kind of tight inside and eliminating the heatsink that I have on the 7805 would help a lot.

My batteries are 9.6v so a lot of extra heat is beeing generated.

[JackFrost22]

an ldo chip

[A.J. Franzman]

Hi,
Does anyone know what the switching power regulator that Ben has used occasionaly to replace the 7805 voltage regulator is?

I know he has mentioned using a switching power regulator instead of the 7805 and saved about 100 milli amp and that it generates much less heat than the 7805. But he never mentioned which switching regulator he uses.

My portable is kind of tight inside and eliminating the heatsink that I have on the 7805 would help a lot.

My batteries are 9.6v so a lot of extra heat is beeing generated.

an ldo chip

"LDO" = Low DropOut, this refers to the minimum difference between input volts and output volts. For a 7805 with a "dropout" rating of about 2 volts, the regulator will quit working when the input drops to about 2 volts MORE than the output voltage. There are LDO regulators (of several types - see below) that have dropout ratings as low as tenths or hundredths of a volt. So while a 7805 would barely work at all with a 6-cell rechargeable NiMH or NiCd (7.2 volt) supply, an LDO regulator might actually give useable runtime in this situation.

But just saying "an ldo chip" doesn't mean anything because there are linear LDO regulators, and switching LDO regulators, and switching LDO controllers by the hundreds out there. Linear is definitely not what you want in high-power battery operated situations like this, whether a normal linear type like the 7805 or a low dropout type of linear regulator will only make a little difference with higher battery voltages.

Unfortunately, switching regulators and controllers are not stand-alone devices like a 7805 or LDO linear regulator - they need more components to make them work, and are VERY picky about the exact specs of those parts, and how they are positioned relative to one another, and how they are connected. Not something recommended for an electronics novice, and probably not going to save you any space anyway.

Here's some more stuff copied from the topic "Atari plastic":

I found that there are DC-DC switching regulator ICs of a type called "Buck/Boost", that can take in (for example) anything between 4 - 12 volts and output rock-steady 5VDC. Using one of these will be more efficient than a 7805 and allow one to get FULL use of the batteries' available capacity, using say 6 x NiMH AA cells for 7.2 volts initially.

A chip I found that may be just the ticket for this application, is National Semiconductor's LM2591. Using a circuit topology called "inverting buck/boost" (not to be confused with "step-up/step-down buck/boost" - see 2 paragraphs down), this chip can take anything from 4.5 to 20 volts in, and convert it to 5.0 volts out at better than 80% efficiency.

In this configuration the batteries' (-) connects to the output (+) and this intermediate level is called "ground". So, the regulated output (-) is "below" ground - that's why it's called "inverting". The Atari won't care what the regulator thinks "ground" is, just connect the output (-) to the Atari (-) and output ("ground"/+) to Atari (+). This is useful for one other quirky thing that the VCS needs - the color adjustment pot "high" input voltage. The high input here will be higher than it was (5.0V plus the battery voltage), so using this method will require slight color pot readjustment. Also, as the batteries die, the color of the unit will drift a little - this could be considered a good thing, letting you know when you're running out of playtime.

If you can find one, a "step-up/step-down buck/boost" regulator might be even better - but they're rather new and quite hard to find with the kind of input/output ratings we need.

As for powering the unit, yes a DC-DC converter is more effective than a 7805 regulator but the regulator is free. Also it about 20mA power lost (according to Ladyada's comment about the 7808 on the hip screen). The atari also only consumes about 350 (maybe less) mA an hour, something that takes that little power is hardly a conser about being really effective you get a decent run for the batteries.

Ladyada's comment is really not applicable here - she was talking about disconnecting the 7808 (8 volt) regulator in the "Hip Gear" screen. That regulator only powers its audio amplifier, and she made her current comparison (before disconnection) while the unit was not playing any sound.

I did some calculations last night, and figured that if your battery supply is nominally 7.2 volts, and your switching regulator only 80% efficient (most are higher), you should get nearly 30% more runtime compared to an LDO linear regulator. With higher battery voltage, the difference becomes even greater - using a 9.6V battery supply, runtime will be almost double using a switching regulator vs. LDO linear - and possibly even better than double when comparing switching against the 7805. Is that worth the extra cost and effort? You decide...

[HK-47]

and probably not going to save you any space anyway.

But were trying to save battery life, not space.

[A.J. Franzman]

and probably not going to save you any space anyway.

But were trying to save battery life, not space.

My portable is kind of tight inside and eliminating the heatsink that I have on the 7805 would help a lot.

My batteries are 9.6v so a lot of extra heat is beeing generated.

[SNESguy]

I personally have National Semiconductor's LM2575 switching regulator, and I must say it is a wonderful little device. It has only four other components besides the IC and generates NO HEAT AT FULL LOAD. It outputs 5v @ 600mA. I am currently using one in my second SNESp. I got it from a friend, but I believe National Semiconductor is giving free kits if you request them.

[SNESguy]

Pardon me, that was the LM2574, not the LM2575.

It operates with an input voltage as low as 6.1v.

[A.J. Franzman]

Are you sure it's a '74? Those are only rated to 500mA, you're lucky to get 600mA out in your system. An LM2595 might be a better choice in your case. Just to be on the safe side, I'm looking for a minimum 1000mA capability. Even if it's major overkill for a ~2.5 - 3 inch screen, it will be able to handle the load if I later upgrade to a larger screen.

[SNESguy]

OK then, you are looking for the LM1575-5.0. It is rated at just over 1000mA, or 1 amp. I wouldnt mind having one myself. Does that suit your tastes? I'm just trying to help out.

[SNESguy]

I'm pretty sure of those numbers because I have the product manual right here with me.

[A.J. Franzman]

The 1575 or 2575 can work but there are better choices. In standard buck configuration, these will need a fairly large 150 uH inductor. They also have about a 2 volt dropout, so you'll need an 8-cell supply.