Pump up the charge: Getting -5V from a 5V power supply
nicole.express
nicole.express
Because I can't see the datasheet of the audio amplifier, it may be wired in a way that it doesn't use significant current from this supply (for example, in the pre-amp part of the circuit). But then we wouldn't be getting the advantage of 17v supply to make it louder than other games.
When overloaded, simple switching power supplies like this lose their regulation. In this case, the switcher operates at 10kHZ, so it might introduce a high-pitched sound to the output.
You can probably get away with connecting the -5v input to GND to make the circuit run at 12v instead of 17v. Or, look for a more capable negative power supply.
[1] https://www.renesas.com/us/en/document/dst/icl7660-datasheet
Even so, I wouldn't be surprised if the high-pitched sound you can faintly hear in the video at the end is due to the effect you mentioned.
If you need more power, I'd suggest a module like this one: https://www.ti.com/lit/ds/symlink/ptn78000a.pdf Switched capacitors are great for low currents, but inductors work better for higher currents.
[this]: https://www.digikey.com/en/products/detail/mornsun-america-l...
It actually makes a lot of sense once you draw it out. The startup is the truly confusing bit, but fortunately it's only unstable for your brain. These guys are actually pretty robust if you can find a part that withstands the full voltage stress (|Vin| + |Vout|), which isn't too hard these days. Highly recommended for a production-quality negative rail generator. Just don't try and do it with a regular buck; synchronous controllers only need apply.
> So what if we immediately disconnected the capacitor from the rest of the universe, including its power supply and ground? Well, if we did that after the capacitor was charged, we’d find a differential voltage on the power supply. What if we hooked up ground to the side that had -5V before?
Is this a typo - should this say "to the side that had +5V before?" (ie change minus to plus)?
I think I have a handle on the design, which is that it's charging a capacitor with +5V, changing the charging side to ground, discharging the capacitor through what used to be the input (you can tell I'm not an electrical engineer, I suspect these terms are very faulty) and causing a -5V flow that way. If that's true, I think it's a typo (?); if not, and much more likely, my understanding is flawed. Insight here would be much appreciated.
Yes.
> I'm struggling to understand the design, but I think it's charging a capacitor with +5V, changing the charging side to ground, discharging the capacitor through what used to be the input (you can tell I'm not an electrical engineer, I suspect these terms are very faulty) and causing a -5V flow that way.
That's correct enough. It's all a matter of perspective. I'd probably say you discharge it through what used to be ground, though as the article notes technically ground is the source of electrons - but we usually talk about holes and positive (conventional) current.
Imagine measuring the voltage on a AA battery: 1.5V. Then you flip it around and measure again: -1.5V. Voltage is all relative to where you measure, usually ground. It's a tricky concept.
+5v -> +
Cap
0v -> -
+5v ------> +5v
0v -> + --> 0v
Cap
- --> -5v
That's a typo and an embarrassing one; thanks for pointing it out, I've updated the post.
- 12 - -5 = 17, not 18
- 'never non-zero' should be 'always non-zero' or 'never zero'
Is it that obvious I don't proofread very thoroughly?
https://datasheetspdf.com/pdf-file/635283/ETC/M51516L/1
The dual capacitor on the output isn't really needed and it just filters out more bass sounds since essentially there are two capacitors in series. It seems who drawn the circuit adapted it from the stereo version without much thinking. Actually there should be no need for output capacitors at all if the internal amps are well balanced, but that should be checked with a multimeter before removing them. Good thing the Zobel network wasn't omitted, but there should also be some good capacitive decoupling on the chip supply lines to avoid motorboating and other noises.
Anyway, to get the right supply voltage the best approach is to raise +Vcc through a switching step up regulator rather than using a charge pump negative supply as they can't give the necessary current.
I probably have a few of those chips in a drawer, iirc they're used in some HAM radio equipment from the 80s, but if I had to repair a circuit using them, I'd solder a small cheap Class-D module in place of the chip since they're a lot better in pretty much everything. Probably not the preferred solution for restoring old games boards though.
https://www.maximintegrated.com/en/design/technical-document...
In my case, I was looking for a way to get decent analog power from a USB port for a non audio related project, but a LiPo battery would present a similar challenge.
Power = voltage x current = (voltage) squared / resistance.
The little rectangular 9V batteries have very high internal resistance as well as low energy capacity. The nominal 9V can easily fall below 6V with heavy loads.
If you only need 1 watt (times 2 for stereo), loud enough for average rooms with speakers of reasonable efficiency, then one 9V battery would be enough. It wouldn't last long though.
With two in series you can go louder, provided the amplifier is rated for the higher voltage.
Remember to put fuses in your power leads (except the ground return). Good quality batteries can get hot trying to power a short circuit.
Wait, I don't understand. Why not just connect pins 2 and 6 to ground? You'll get less oomph out of the amplifier, but it should still work?
Power supply design is NOT something to leave to the last step or to give short shrift.
When I worked at Hewlett-Packard, there was a story going around that a division decided to give a summer intern the job of designing a new product's power supply. It did NOT end well - the product suffered field failures, cost a ton in warranty costs and delayed the full release of the product by a year. After that, power supply design was something that the top engineer had to be involved with especially in an intern was involved. This pairing actually resulted in both a better product and in having the intern learn more and be more likely to work for HP full time eventually.