This project is a Voltage Regulator Module for the Socket 7 mainboards as defined by Intel in it's Pentium® Processor Flexible Motherboard Design Guidelines. You can upgrade VRM capable Socket 7 mainboards with this module to be able to use dual-voltage CPUs like Intel Pentium MMX, AMD K6, AMD K6-2 etc.
WARNING: inserting the module the wrong way around would put +12V on all critical lanes. It would destroy the mainboard, the CPU, the memory and all expansion cards. This can't happen on mainboards with VRM socket, because there it is not possible to insert it in reverse. On free standing VRM pinheader, it is may be a good idea to cut +12V pin 5 and the unused pin 22 to use them as a key.
Youtube Videos:
- Part 1: https://youtu.be/CMiGVQbMC5U
- Part 2: https://youtu.be/J0NLGfocviU
- Part 3: https://youtu.be/kBPp9EAIC8I
- Part 4: https://youtu.be/XV0b5Tvf5gY
Various voltages can be set using the SW1 switch on the module (0=off, 1=on):
| Voltage | Switches | CPU Examples |
|---|---|---|
| 3.2V | 0000 | AMD K6 (only 233 MHz) |
| 2.9V | 1000 | AMD K6, IBM 6x86MX |
| 2.8V | 0100 | Intel Pentium MMX, IBM 6x86L, Rise MP6 |
| 2.6V | 1100 | ??? |
| 2.4V | 0010 | AMD K6-2 |
| 2.3V | 1010 | AMD K6-2 |
| 2.2V | 0110 | AMD K6 / K6-2(+) / K6-3(+) (and mobile) |
| 2.1V | 1110 | AMD Mobile K6 / K6-2 |
| 2.0V | 0001 | AMD Mobile K6 / K6-2(+) / K6-3(+) |
| 1.9V | 1001 | AMD K6-2E+ |
| 1.8V | 1101 | AMD Mobile K6-2(+) |
| 1.7V | 0111 | AMD K6-2E+ / K6-3E+ |
| 1.6V | 1111 | AMD K6-2E+ / K6-3E+ |
The transistor Q1 with integrated pull-up resistor is optional. It is used for enable/disable signal and is unused on most mainbards.
The PCB is made for a through hole inductor, but if you have only SMD it is also possible to solder that instead. Keep in mind that the inductor has to stand the required current. Also slightly different inductors are allowed, everything between 2µH and 4,7µH should work as well. With the higher inductance you get less current ripple, also voltage ripple can look better, but the maximum possible current will decrease. Playing with different inductors will also influence the compensation network.
Capacitors C7 and C8 are used in so called compensation network and are responsible for DC-DC converter activation and stability. Those parts are very delecate and dependent on the ESR and values of the output capacitors C9-C12, and the inductor L1. If your regulator shows stability issues or not starting at all, try to remove the capacitor C8. If you change any other parts C7, C8 and R1 have to be adapted accordingly.
| Part | Count | LCSC# | Comment |
|---|---|---|---|
| C1, C15 | 2 | C13585 | 10u capacitor SMD 1206 |
| C2, C14 | 2 | C51205 | 4.7u capacitor SMD 1206 |
| C3, C6, C13 | 3 | C696845 | 0.1u capacitor SMD 1206 |
| C4, C5 | 2 | C407963 | 2200u capacitor TH Radial D10.0mm, P5.00mm |
| C7 | 1 | C107186 | 220n capacitor SMD 1206 |
| C8 | 1 | C541493 | 39p capacitor SND 1206 |
| C9-C12 | 4 | C407858 | 1000u capacitor TH Radial D8.0mm, P3.5mm |
| D1 | 1 | C109000 | Switching diode |
| J1 | 1 | C2897435 | Connector angled 02x15 pins 2.54mm |
| L1 | 1 | N/A | 3.3µH inductor |
| Q1 | 1 | C13871 | NPN-Transistor with pull-up BEC |
| Q2, Q3 | 2 | C496603 | N-MOSFET GDS at least 15A |
| R1, R2, R6 | 3 | C144515 | 15K resistor SMD 1206 |
| R3, R10 | 2 | C144508 | 1K resistor SMD 1206 |
| R4, R8 | 2 | C229609 | 3K resistor SMD 1206 |
| R5 | 1 | C3000607 | 21K resistor SMD 1206 |
| R7 | 1 | C229767 | 6,3K resistor SMD 1206 |
| R9 | 1 | C352163 | 0K resistor SMD 1206 |
| SW1 | 1 | C15781 | DIP6 Switch THT 4 buttons 2.54mm |
| U1 | 1 | C235991 | NCP1579 DC-DC Controller |
The inductor doesn't need to be very exact, anything between 2.5µH and 4.7µH should work, but the sweet point is at around 3.3µH. The inductor can be self made by using a T50 ferrite toroid. For example T50-26 with permeability 75µ wrapped in 10 loops of 1.3 mm coper.
If the NCP1579 is not available, probably ISL6545, NCP1587 or L6726 will work as well, but they haven't been tested yet. If you go with ISL6545, it has a different reference voltage of 0.6V instead of 0.8V as for NCP1579, so you need to use different resistors on the feedback:
| Part | LCSC# | Comment |
|---|---|---|
| U1 | C2657973 | ISL6545 DC-DC Controller |
| R4 | C3000626 | 4,32K resistor SMD 1206 |
| R5 | C137309 | 33K resistor SMD 1206 |
| R6 | C137348 | 25K resistor SMD 1206 |
| R7 | C132649 | 10K resistor SMD 1206 |
| R8 | C870818 | 5K resistor SMD 1206 |
This module should run with all mainboards, which provide the VRM module header as specified in Intel Pentium Mainboard Design Guidelines. Most of such boards were based on Intel Triton (i430FX) and VIA Apolo Master (MV series) chipsets, but there were also quite a lot of later boards with newer chipsets (f.e. i430VX), which supported such an external VRM as well. So far this VRM was tested using various CPUs and voltages on following mainboards:
| Manufacturer | Model |
|---|---|
| Asus | P/I-P55TP4XE(G) |
| Gigabyte | GA-586-ATE/P |
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