Power Supply
The power supply of the PS1 is an all-in-one provider for the following:
- Power outlet hookup through a non-standard C7 power cord.
- Rectifies, stabilizes and transforms the AC domestic voltage levels to roughly 8v and 3.3v.
- Handles power on and off by a dual pole switch on the 8v and 3.3v lines.
- Handles reset through a momentary switch.
- Delays and monitors the reset logic through a supervisor chip.
- Provides power and reset logic to the motherboard through a 5-pin cable.
The final pinout of the power plug ends to be always the same on most versions of the console:
| 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|
| 8V | GND | 3.3V | GND | !RESET |
Some of the early models have a different 7-pins plug, with the following pinout:
| 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|
| 8V | GND | 3.3V | GND | 3.3V | GND | !RESET |
The motherboard then breakouts the power plug into the following subrails:
- "MOT_+8V", with a 0.8A fuse, a 1uH inductance, and a 47uF 16V polarized capacitor.
- "EXT_+8V", with a 0.8A fuse
- "DIG_+3.3V", with a 2A fuse, a 1k pull up resistor to !RESET, and a 220uF 4V polarized capacitor.
- "CTR_3.3V", with a 0.6A fuse.
The datasheets are claiming that the second power rail is 3.5v, but it magically becomes 3.3v on the motherboard itself, without any component in between. Doing some investigation shows that using a plain 3.3v power line will work fine.
The 8v power rail has two main consumers. The first one is the cd-rom and its motors. The second one is a bit more peculiar: there are two LDO regulators that are chained to each other, behind a 0.8A fuse.
The first regulator is a 5v regulator, that brings power to the audio amplifier and video d/a converter, both behind their individual inductance and capacitors, and provides a "DIG_+5V" power rail, also on its individual inductance, used by the audio dram chip.
Then the second regulator is a 3.5v regulator, breaking out to its own power rails of "AUD_+3.5V", with an inductance and capacitor and "SER_+3.5V", with only a capacitor, both feeding into the analog power rails of the SPU.
As for the 3.3v power rail from the PSU, the CTR_3.3V rail is used exclusively to power on the controllers, while the DIG+3.3V rail powers on every chip of the motherboard. In fact, the SPU uses a total of 3 power lines: DIG_+3.3V, used on many different pins, and also the AUD_3.5V and SER_3.5V rails, used on fewer, dedicated pins.
It seems fairly clear that the 8v power rail from the PSU is used mainly to handle the higher voltage motors, and anything that's analog signal related - with the exception of providing 5v to the SPU DRAM chip - while the 3.3v power rail from the PSU is used exclusively for anything digital and logic-related.
The reset circuitry is mostly handled through the PSU itself, active low as typical for chips, with the exception of a single 1k pull up resistor on the motherboard itself. This means that the motherboard can be powered on with simply the first 4 pins of its power plug, and the reset signal will be naturally asserted high, meaning all of the logic will boot and hopefully work.
The reset controller chip on the PSU will do 3 things:
- Monitor the power levels of the 8v and 3.3v power rails
- Listen for the user button for issuing a reset on the console
- Debounce and ensure a minimum reset delay of 300ms on power up and user reset
During testing, not providing a proper reset signal will sometime result in bootup glitches, up to complete system freeze.
Importantly, the reset monitor chip is an open-drain output, which is important since devices connected to the reset line can pull the reset line low to issue a reset during gameplay. If replacing the chip, care must be taken to avoid using a push-pull mechanism, and use an open-drain too, otherwise this would create a short with any in-game reset device. The MCP120-315 is a good candidate to monitor the 3.3v line while keeping an open-drain output, and a 300ms minimum reset delay.
Preliminary tests shows that the console is consuming about one amp with no accessories connected. Further analysis is required.
There's a total of 5 SMD fuses located on the motherboard, which are all the same throughout all versions of the console, save it for the very last version of the psone, that changed them for more available versions of parts. The SMD footprint of the original fuses is 3x2.5mm j-lead, whereas the footprint of the latest psone model is 0603.
- PS601 is a 0.8a fuse on the 8v line going to the drive's motors.
- PS602 is a 0.8a fuse on the 8v line going to any of the external 8v lines, such as memory cards, controllers, or PIO.
- PS603 is a 0.8a fuse on the 8v line going to the 5v and 3.3v LDOs on the motherboard, that are described above.
- PS604 is a 2.3a fuse on the 3v line going to any of the digital equipment on the motherboard, such as CPU, GPU, SPU, etc.
- PS605 is a 0.6a fuse on the 3v line going to any external 3.3v line, such as memory cards, controllers, or PIO.
There are several reasons why one would want to replace the original PSU with something different.
- The power on switch is AFTER is transformer, meaning that the AC domestic voltage section of the PSU is always energized and flowing through the transformer's coil. This has two consequences:
- The PS1 will always consume electricity, even its main button is powered off, which is a waste of power.
- When working on the system with the plastic shell removed means there is an exposed AC domestic voltage lingering around, even when the console is turned off, which can prove dangerous.
- One may want to remotely turn the console on or off, or reset it remotely, for automation purposes. Note that asserting the reset line low means that the various memory chips aren't erased, which can be useful in some debugging scenarios. Also, the PIO port won't lose power during a reset.
- One may want to replace a defective power supply board.
- Using DC 12v as a power input can sometimes be more accessible than AC domestic.
While the console shouldn't require too high of a power supply, a strong 5A 12v power supply is considered, such as https://www.amazon.com/gp/product/B01461MOGQ/
In order to build a compact, versatile and flexible replacement PSU, it is best to simply use two holes on the PCB to provide power. Then, one can simply use the power connection of their choice. Still, a typical 5.5x2.1mm connector, as a pigtail wire is probably a wise choice: https://www.amazon.com/dp/B0768V9V5Q
The soft power on sequence will be handled through a solid state relay, such as the KF0602D. This provides the added feature of having several built-in diodes, protecting against backward currents, in case the power supply is wired wrong.
The LM7808 in TO-220 package is considered, but any 8v LDO regulator should do the trick nicely. The typical pinout is going to be
| 1 | 2 | 3 |
|---|---|---|
| Input | GND | Output |
There are several competing standards when it comes to 3.3v regulation, with regards to pinouts. Some are available with the same pinout as the LM7800 series as described above, such as the AZ2940-3.3. But the most common, the LM1117-3.3 (or its cousin, the AMS1117-3.3) is unfortunately different from other sorts of regulators:
| 1 | 2 | 3 |
|---|---|---|
| GND | Output | Input |
Since the 3.3v regulator will soak 8.7v worth of power, it may emit a non-trivial amount of heat, and also consume more power than needed. It might be worth investigating buck regulators for the 3.3v power rail. The TIDA-00947 demonstration board from Texas Instruments, centered around a TPS54202 buck regulator could be worth such investigation, given its low EMI, and TO-220-style package.
Heat sinks should be considered, such as https://www.amazon.com/gp/product/B07G5ZV2J7/
It is worth to note that if the LM1117-style pinout is used, the central pad is going to be energized with 3.3v, instead of being grounded like with the other pinout. Care needs to be taken.
While the original PSU monitors both the 8v and 3.3v circuits, it might be worth simply monitoring the 3.3v power rail. This results in easier logic to put in place. The MCP120-315 is a good candidate.
Here is a digikey-only shopping cart for all the components, minus the PCB and the heatsinks: https://www.digikey.com/short/pv452t
Most if not all of the components might be available for less in other locations, such as Amazon or eBay, as per links throughout this page.
The goal for a first version of a replacement power supply is to be simple, cheap and versatile. The proposed design allows for several simple ways to power on and reset the machine. Being a full drop in replacement board isn't the goal however, so the buttons of the plastic shell won't activate anything, and the led won't light up.
There are two variants of the proposed design, one for each pinout of the 3.3v regulator. Variant 1 uses the LM1117 pinout, and is available on OSH Park, and in the repository as EAGLE and Gerber files. Variant 2 uses the L7800 pinout for both the 8v and 3.3v regulators, and is available on OSH Park, and in the repository as EAGLE and Gerber files.
Both variants have exactly the same assembly layout.
This is the header for connecting to the motherboard. The connector should be keyed the same was as the 5-pins connector for the PSU. It should be fairly easy to extend this to the 7-pins connector used by the PU-8 version of the motherboard.
This is an optional power on led indicator. The right footprint is for a resistor, that connects to the 3.3v rail. Just use the appropriate resistor value for the LED you'd be adding.
Each regulator uses this pattern. The arrows indicate the flow of current. An arrow from the capacitor to the regulator indicates this is the input capacitor. An arrow from the regulator to the capacitor indicates this is the output capacitor. The following capacitors are recommended:
- 8v regulator in: 0.47uF
- 8v regulator out: 0.1uF
- 3.3v regulator in: 0.1uF
- 3.3v regulator out: 10uF
The pinout is described on the side, to distinguish between Variant 1 and 2. I for Input, O for Output, and G for Ground.
The voltage input goes to this header on the left. Please note the polarity, and you probably need at least 12v to accommodate the dropout of the 8v regulator.
This is the location for the MCP100-315DI/TO reset controller chip. The layout is using the "D" bondout layout.
This is where the solid state relay goes. The footprint is tuned for the KF0602D, but it should accommodate other similar relays.
And finally, this is the main controlling header. The "VIN" pin is a direct line from the voltage in. The "PON" pin is the activation pin of the relay. The "GND" pin goes to ground. The "RST" pin is the !RESET signal line. And the 3V3 pin is the output of the 3.3v regulator.
This arrangement enables using either plain switches, or some more advanced logic. When using switches, an on/off switch needs to be placed between pins "VIN" and "PON", or a simple jumper for continuous operation. This will activate the relay using the 12v input, which should be more than enough for the purpose of the operation. And if desired, a momentary switch can be placed between pins "GND" and "RST".
And when using logic, one can simply provide a 3.3v signal to PON to activate the relay, and sink RST to ground in order to issue a reset. VIN can potentially be used with its own circuitry to power on said advanced logic, and 3V3 may be used to monitor the status of the power output. It is important to realize that if using external logic to reset the motherboard, it'll need to sink up to 4mA of current, due to the 1k pullup on the motherboard. Also, it shouldn't try to assert that signal high, but rather, leave it to be high impedance instead.
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When using the LM1117-3.3 pinout, as well as a heat sink, that heat sink will be energized at 3.3v, and will also be physically close to the 8v regulator's heat sink, which will be grounded. Care needs to be taken to avoid these two to touch, which can be done by using kapton tape on the side of the heat sinks, to insulate them from each other.
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This module hasn't been extensively tested. There might be issue that'd arise in certain peak usage, caused for example by a brown out of one of the regulators, noise from the lack of proper filtering, or glitches from the lack of the 8v rail monitoring.
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Given the work to be done by the module, it might be wise to fabricate the pcb using 2oz copper.
Version 2 of this PCB might add the following:
- Full board replacement. This would require measuring the official board, and finding appropriate buttons for reset and power on.
- Advanced reset and power on logic. This could leverage for example the ESP-01 board, to toggle power on and reset through Wi-Fi, or using an FT232, to do this via USB and its GPIO.
- Better and more advanced noise filtering.