Superior 7805 Voltage Regulator?

Has anyone tried one of these LM7805 switching regulators in place of the stock 7805, e.g. in a Mega Drive? Apparently they're a drop in replacement and run more efficiently and cool.

LINK: http://www.protostack.com/semicondu...witching-regulator-lm7805-drop-in-replacement

The website states:

• Efficiency up to 96%
• Pin Compatible with LM7805
• No heat-sink needed
• Short circuit and overheating protection
• Low ripple and noise
• Flame retardant to UL94-V0

 

no, but if you need 5v i have used these in nes, snes
works a treat
http://etim.net.au/shop/shop.php?crn=2&rn=547&action=show_detail

 

Oh cool, didn't know about those! I'll look into them, thanks.

 

I've heard some people say these introduce noise on the audio lines. Anyone have thoughts on that? 'cause otherwise I feel like these are probably worth the cost for longevity sake.

 

The various “7805 replacements” out there certainly are more efficient than the linear 7805, because they are switching DC-DC converters. They will outclass the linear 7805 in terms of efficiency and heat output, manufacturers declare it on datasheets (current draw and input to output voltage difference).

However, the linear 7805 will reject low bandwidth noise and ripple; the “7805 replacements” might (probably not so much) reject some noise and ripple, but they will introduce more (higher frequency) noise since it is constantly switching in the range of tens to hundreds of KHz (audio range). In order to clean-up this noise, a lot of capacitance needs to be added to the output. The linear 7805 can respond to voltage changes/drops (transience) rapidly in the nanoseconds range, the “7805 replacements” is rather sluggish in the microseconds range.

 

So what's your verdict on this? Keep the linear regulator or replace with the switching regulator and up the filter cap?

 

Keep the linear regulator.

If the 7805 on my SNES stops working, I'll just spend $3 on Ebay to acquire ten LM7805s. Those "7805 replacements" alone are costly even without the additional filtering components. (http://www.mouser.com/ProductDetail/CUI/V7805-1000/?qs=sGAEpiMZZMt6Q9lZSPl3RUpRpHStGpLQt1aFy4oQuOzuWzCeP6kPoQ==).

 

Thanks for all the info eb1560. That's interesting that the newer replacements aren't as good at rejecting noise and ripple. I reckon I'll stick with the linear 7805's in my Mega Drive so. As you say they can be bought for wayyy cheaper. Only downside I see really is they get hot and require the big heat sink and thermal compound. Not a big deal really though.

If I ever need to buy any, do you think these are suitable: http://ie.rs-online.com/web/p/linear-voltage-regulators/0463054/. They're "ON" brand.

 

I've used these switching replacements, they worked OK in the snes mini I had to use it (someone threw away the heatsink in a poor mod job).

There was no noticeable noise in the picture or audio. But YMMV

 

The linear 7805s can operate up to 125 C (257 F), heat can be reduced by lowering the input voltage (no less than 8V) – but doing this can become complicated (even if it is unregulated). I like additional headroom for current, I'd get the 1.5 amps version:

• MC7805CT (MCC/ON)
• L7805CV (STMicroelectronics)
• UA7805CKCT (Texas Instruments)

I breadboarded one of those “7805 replacements,” but I wouldn’t consider implementing one on my SNES for electrical reasons, unless I was in a similar situation without that heatsink.

 

These need to be tested more. I've experienced issues with some original SNES models and AV Famicoms. It's introducing video noise (diagonal ripples) with some setups. I want to love these new regulators but they are not drop in replacements in all situations.

Haven't tried them in the SNES mini

 

Try adding a 47uF non polar ceramic cap on the output (between out and gnd). That is generally how you filter out SMPS noise.

I still like to use linear regulators and supplies because I don't want to have to deal with SMPS noise. Even if I lose the heatsink, I could just replace it with my own.

 

If these switching replacement regulators are intended for powering only digital circuits, then noise isn’t too much of a concern, and they can quite easily replace a typical linear 7805 regulator. On the other hand, if they are powering analog circuits (very sensitive to power ‘cleanliness’), then things will get a bit more complicated to dampen the noise, especially ringing. A linear 7805 would be better suited for the SNES, since the 5V rail powers both analog and digital circuits. In order to troubleshoot and reduce the noise when implementing a switching regulator, you would need to understand the type of noise (waveform), and whether it originates from the input (parasitics) or from the regulator itself.

 

I know its a drop in replacement but could you add smoothing on the output to reduce noise? I guess then it's no different than going with a small PCB and using flex

 

Capacitors can certainly be added to the output for filtering. I would suspect nothing greater than 10uf or 22uf would be necessary (maybe even far less) to filter the noise generated by these regulators, but optimal values ought to be verified. Unless one wants to gently scrape off the soldermask, the SNES doesn’t really appear to offer many options for adding extra passive components or a combination to form a filter.

Although, noise may come from the regulator's input, and not necessarily the output - switching regulators don't reject as much noise as linear regulators, thus more components are needed. A circuit laxly designed for a linear 7805 may not be well suited for a switching regulator, which requires a more careful layout with regards to parasitics (undesired capacitance and inductance). Oftentimes ringing is an issue on the input, which is passed onto the output, a filter would likely be needed to correct the ringing, there is no 'one solution fixes everything' for this.

 

Thank you. That's what I experimented with last year (slightly different values). The SNES had little improvement with the additional cap. Though I will revisit this again when time permits.

 

I experimented with switching 7805 replacements last year with mixed results. In an SHVC Super Famicom with an OEM PSU, it introduced significant video noise (rolling bands). In a non-TMSS Genesis (which has two 7805s), the video and audio remained perfect. The Genesis runs cool to the touch now, which is an improvement, but I decided to stick with 7805s for everything in the future since they're cheaper and there's no chance of degraded AV quality.

I put a standard 7805 back in the SFC and it was perfect again. I kept the switching 7805s in the Genesis though as a curiosity.

 

It's going to very much depend on anything decoupling etc in the power circuit you are installing it into.

As per any retrofit, it's a cause by cause basis and you may need to make modifications.