Powersupply FAQ

From IndividualComputers
Jump to: navigation, search
This page is work in progress. Please check back later.

This page has been created because of the amount of questions being asked regarding power supplies for various retro platforms.

Contents


why don't you offer a power supply for C64/Amiga/etc?

We did not offer them *yet* due to the high cost for safety regulation checks. A power supply connects to the mains grid, and therefore must comply with numerous international and local regulations that we can't possibly all cover for a retro-product with relatively small expected sales quantities. We therefore decided to provide DC-DC converter solutions, so the safety regulations part can be covered by companies that have the required experience and quantities for grid-connected power supplies. Our product liability insurance has already approved of this approach. Prototypes are working, and we expect to ship the first units before the end of Q2/2020.

can you recommend a power supply for C64/Amiga/etc?

Unfortunately, the answer to this is no. We are not aware of any "proper" replacement power supplies on the market. Most of what we've seen lately is just putting together PSU chassis with the cables and connectors, violating practically all the rules in the book. Safety regulations are violated, flammable materials are being used as cases, and we've even seen mains switches being operated outside rated specifications. If you do not have the means to judge if a power supply is safe, then ask the vendor if it's covered by a product liability insurance. If the answer is "no" or there is no answer, then avoid the product by all means.

If you have the education and skill, we recommend servicing the original power supplies instead. DON'T DO THIS if you are not qualified for the job.

so what are the problems with available solutions?

While generally power supplies on the market are not bad per se, so far all we have seen fail to meet one or more simple requirements to make them suitable for retro computers - most often compensation for the voltage loss on the cable that connects the power supply with the computer. Note that all of the following are generally solved standard problems - a proper power supply can and should deal with them.

undervoltage

Commodore PSUs are usually far from the power sink, so you have to look at a chain of losses between source and sink: The cable, the connector, the switch (in case of the C64), the fuse (if applicable) and the common mode choke.

  1. You can pre-compensate by raising the output voltage by a fixed value - that's what most Commodore PSUs do.
  2. You can measure the voltage by feeding it back to the PSU using a so called "sense wire". This will improve the situation, but won't compensate for all losses, as part of the losses are happening inside the computer, where the sense line can't be applied from the outside.
  3. You can measure the current that's being drawn and adjust the output voltage dynamically by a value that will compensate for all losses, so the voltage at the sink (the actual chips) is constant within very strict limits. While this is the most expensive approach, it's also the best one that will provide best protection your hard-to-find (and even harder to replace!) gear.

To find out if a particular PSU does any kind of compensation for the voltage loss on the cable, measure the voltage(s) inside the computer, when the computer is running. Ideally, change the load while doing measurements, such as spinning up a CD-drive, inserting floppies or park/unpark harddisks.

A PSU that simply does nothing in terms of compensating for these losses is not suitable.

why undervoltage is a problem

While the original NMOS/HMOS hardware can live with up to 10% under-voltage, CMOS chips have taken over and have been dominating the computer chips market since the late 1980s. With 5V types having phased out since the 1990s, it has become common practise to use 3.3V-chips that are 5V-tolerant. Practically all commercial and hobby projects released in the last 20 years have been using 3.3V parts, which requires a small voltage regulator to generate these 3.3V. However, these regulators need a certain "headroom" for regulation, which implies stricter limits than the +/- 5% load regulation that most power supplies guarantee: A standard low-drop 3.3V voltage regulator requires at least 4.85V input, but 5% off 5V results in 4.75V. While this works in most cases, it will make the so-called SCR-latchup more likely, especially if the power supply is not fast enough regulating load changes (technical term: transient response).

ripple

Simply said, "ripple" is the amount of "noise" leftover on the output voltage. For stable power supplies, less ripple is generally a sign of better quality, as is the fact that you can actually find the amount of ripple being specified in its documentation. You should be able to find a PSU with less than 100mV ripple easily, but you should keep in the back of your head that the original Commodore specification requires 50mV ripple maximum. This is quite challenging to achieve, as even high-quality PSU chassis often specify 80mV ripple.

A PSU that has more than the required maximum amount of ripple is not suitable.

why ripple is a problem

Digital components work with direct current and can only tolerate a very small amount of leftover alternating voltage. Thats why on the motherboards you will usually see all those capacitors near most ICs, their only purpose is to block unwanted alternating current from the ICs. Now, this can only work up to a certain amount of ripple on the input voltage - and when this limit is exceeded things start to act funny. This is even more of a problem when using a modern "switched" power supply, as in this case the ripple frequency is totally different (usually higher) than what it would be with a classic linear power supply.

Further, ripple will add to the undervoltage problem: If you measure the voltage with a multimeter, you will only see the average voltage and you have no information about ripple. However, if your power supply has a ripple of 100mV and you are using a modern piece of equipment with a 3.3V regulator, you need to take the lowest-possible momentary voltage into account. This means that the requirement of 4.85V may be fulfilled, but at 100mV ripple, the voltage will swing between 4.80V and 4.90V, causing either malfunction or permanent damage in case if an SCR-latchup.


regulation reference

ATX power supplies often regulate both the 5V and 12V output based on the load on the 12V rail. That means if there is no sufficient load on the 12V rail, the 5V output will become unstable and the power supply is not sufficient. For this reason most ATX power supplies are not working properly for Amigas or C64s.

galvanic insulation of AC voltage

In the original C64 and VIC20 power supplies the AC voltage comes from a seperate winding of the transformer, which makes it perfectly floating against any potential, including the 5V rail which is generated from another winding of the transformer. Some commercially-available power supplies therefore heavily violate international safety regulations by adding an extra transformer to provide galvanically-isolated 9V AC to the C64 or C128. This is merely a demonstration of the lack of knowledge of these vendors. A quick look at the schematics of the C128/C64 reveals that there's a bridge rectifier in these computers that will settle any difference in the potential of the two transformer windings to a maximum of a diode, which is usually around 0.7V. Therefore, the galvanic isolation of the two voltages is not a technical requirement. In fact, the heat generated by the bridge rectifier will be lower if the potential difference between the two voltages is kept at a minimum, and getting heat out of your classic computers is generally a good thing.

There is, however, a reason for galvanic isolation of the AC voltage, and that's the switch of the computer: It will only separate one of the two AC wires, and leave the GND connection to the power supply in place. This would mean that even when the C64/C128 is switched off, current could flow between the still-conducted AC line and GND. A properly-designed power supply will sense the load on 5V and switch off AC generation in case the computer is switched off. We currently see this as the only viable method to comply with standby-consumption requirements: A separate transformer will consume up to 2W even when it's not loaded, whereas EU legislation requires standby-consumption to be no higher than 0.3W. The USA even have more strict regulations in place, called the "DoE Level VI" which requires standby consumption of external power supplies with multiple output voltages to be under 0.3W. This is practically impossible to achieve with a classic transformer that's capable of supplying 10W on it's output. Further, it is not legally clear if this transformer must be seen as a single supply with a single AC output voltage; if this interpretation is applied, then the maximum no-load consumption must be below 0.21W, and that figure is impossible to achieve with a classic transformer - this is where modern voltage conversion circuits come into play.

OK, i understand. Can you still give me the data i need to find a suitable power supply?

While we can not recommend a specific product, we will try to provide the data you need to select/verify a suitable power supply. Note that generally the more of the above listed information you can find in the documentation for a certain power supply (or chassis), the higher quality it likely is. With our specialized DC-DC converter solutions in the works, our general recommendation is of course to wait for our solution to be available :-)

Please notice the following is provided without warranty of any kind and doing whatever with your power supplies is entirely your own risk.

Chameleon

The power connector of the Chameleon is a standard USB connector. Use a USB port or -power supply that can deliver 5V DC at at least 500mA. This will make the Chameleon work, but have hardly any extra power for the SD-card, keyboard, mouse and Docking Station, if that's connected. You should therefore choose a USB power supply with a little higher rating 1A (or 1000mA) will be sufficient. While ripple is mostly not specified on USB power supplies, it should be below 100mV. Some USB power supplies are rated 5.2V instead of 5.0V. If you experience problems, for example when hot-inserting an SD card, such a slightly-increased voltage rating is worth a try.

C64 Reloaded

The power connector of the C64 reloaded is a standard 12V DC plug, outer diameter 5.5mm, inner diameter 2.5mm, The power connector of the C64 reloaded mk2 is a standard 12V DC plug, outer diameter 5.5mm, inner diameter 2.5mm or 2.1mm.

The power supply should be able to provide at least 1 amp of current. 2 amps is recommended if you want to operate the Commodore 64 Reloaded MK2 with power-hungry devices like the Commodore 1750 or a SuperCPU. For best picture- and sound quality, the power supply should have less than 100mV ripple on 12V.

Commodore 64

The power supply connector is a 7 pin DIN connector (DIN 45329).

WARNING: The power supply connector of the VIC20 and C64 are physically compatible, and generally the power supplies are interchangeable. However, some VIC20 power supplies are rated for less current than what is needed for the C64, which makes them fail and as a consequence may also damage the C64.

Pinout at the solder side in the computer is equivalent to the pinout at the outside of the plug at the cable, pinout at the solder side of the plug at the cable is equivalent to the pinout at the outside of the computer.

Pin Voltage Current Comment
902503-06
1 GND may not be connected or not exist in the plug
2 GND DC Ground
3 GND may not be connected or not exist in the plug
4 - 5V or Not connected
5 + 5V DC 1.5 A
6 9V AC1 1.0 A phase 1
7 9V AC2 1.0 A phase 2

While most C64s have been shipped with a 1.5A power supply, these wedge-shaped PSUs are prone to failure these days. We generally recommend to go for the white brick-shaped 1.7A-rated power supplies. These will have enough headroom to power a few extra devices.


Commodore VIC20

On early models the power supply connector is a simple "two prong" connector. The power supply for these machines is a bare transformer that outputs 9V AC, the entire PSU itself is in the VIC20.

On later models the power supply connector is a 7 pin DIN connector (DIN 45329).

WARNING: The power supply connector of the VIC20 and C64 are physically compatible, and generally the power supplies are interchangeable. However, some VIC20 power supplies are rated for less current than what is needed for the C64, which makes them fail and as a consequence may also damage the C64.

Pinout at the solder side in the computer is equivalent to the pinout at the outside of the plug at the cable, pinout at the solder side of the plug at the cable is equivalent to the pinout at the outside of the computer.

Pin Voltage Current Comment
251052-02 (*) 251053-02 251053-04 251053-06
1 GND may not be connected or not exist in the plug
2 GND DC Ground
3 GND may not be connected or not exist in the plug
4 - +5V DC or not connected, may not exist in the plug
5 + 5V DC 1.5A 1.7A 1.7A 1.5A
6 9V AC1 0.3A 1.0A 1.0A 1.0A phase 1
7 9V AC2 0.3A 1.0A 1.0A 1.0A phase 2

(*) This specific model is famous for destroying C64s


TODO: recommended rating

TODO: recommended max ripple

Commodore 128

The original C128 power supplies are quite sufficient and reasonably powerful, which makes them attractive to rework for use with a C64 or VIC20.

WARNING: The C128 power supply input is identical in shape to that of the Amiga 500/600/1200, but they are *not* compatible. Using the C128's PSU on an Amiga or vice versa will potentially damage your hardware!

Pinout at the solder side in the computer is equivalent to the pinout at the outside of the plug at the cable, pinout at the solder side of the plug at the cable is equivalent to the pinout at the outside of the computer.

Pin Voltage Current Comment
310416-03
1 +5V DC 2.5A
2 GND Shield?
3 9V AC 1.0A
4 GND DC Ground
5 9V AC 1.0A

TODO: recommended rating

TODO: recommended max ripple

Amiga

WARNING: The C128 power supply input is identical in shape to that of the Amiga 500/600/1200, but they are *not* compatible. Using the C128's PSU on an Amiga or vice versa will potentially damage your hardware!

Pinout at the solder side in the computer is equivalent to the pinout at the outside of the plug at the cable, pinout at the solder side of the plug at the cable is equivalent to the pinout at the outside of the computer.

Pin Voltage Current Comment
312503-02 312503-03 391029-02 391029-03
1 +5V DC 2.5A 4.5A 3.0A 3.0A
2 GND Shield
3 +12V DC 1.0A 1.0A 0.5A 0.5A
4 GND DC Ground
5 -12V DC 0.1A 0.1A 0.1A 0.1A
  • the main load is on the 5V rail
  • the 12V rail is specified to have 10% load regulation, and will vary from a few mA to over 1A load if a CD drive and/or 3.5-inch hard disks are connected.
  • the 12V rail is also directly used for the audio filter, so ripple should be low and ripple frequency should be outside audible frequencies
  • load on -12V is negligible with -29mA typical.
  • the -12V rail is also directly used for the audio filter, so ripple should be low and ripple frequency should be outside audible frequencies

A plain Amiga 500, 600 or 1200 requires a bit over 2A on the 5V rail to operate. Even with Indivision AGA MK2 and a 68030 accelerator, this is hardly going beyond 2.6A, so a 3A power supply is mostly sufficient. However, with ripple and insufficient voltage regulation (see above), you should give it some regulation head room and go for a higher rating.


Links

Personal tools
Namespaces

Variants
Actions
Navigation
Icomp
Tools
Print/export