Request: Power Supplies UK700 vs UK1200 Schematic diagrams (and why does my UK1200 sup run much hotter under same load?)

[1024MAK]

Sinclair UK700 PSU for ZX81 schematic

The 10Ω resistor represents the thermal fuse, plus the resistance of the transformer primarily windings.
The 1Ω resistor represents the resistance of the transformer secondary windings.
The 12.9Ω resistor represents the load of a ZX81 plus expansions so as to fully load the PSU.

The voltage source on the left obviously is not in the PSU. Neither is the switch, the voltmeter or the 12.9Ω resistor. The value of the capacitor is normally shown as 4700µF rather than 4.7mF.

If you follow this link it will take you to an approximate circuit simulation. Click on the switch to bring the 12.9Ω resistor into circuit (representing the load / ZX81 etc.).

Mark

[sP1d3r]

Would it be ok to use a UK1400 PSU with a suitable connector for a ZX81, I wonder.

[bola_dor]

Yes
Just double check polarity

[sP1d3r]

Yes
Just double check polarity

Tip positive, I seem to recall.

[1024MAK]

Yes
Just double check polarity

Tip positive, I seem to recall.

Yes, tip is positive, ring is ground/GND/0V. And the correct connector is a mono 3.5mm ‘jack’ plug.

Mark

[bola_dor]

The confusion usually rises on the spectrum barrel plug side.. that is positive in the outside and negative in the inside.

[sP1d3r]

The confusion usually rises on the spectrum barrel plug side.. that is positive in the outside and negative in the inside.

I have a UK1400 psu with a dodgy lead and connector, so I can replace the lead with mains 2-core and a 3.5 mm mono plug.

I know linear PSUs behave differently than SMPS, I'm afraid I need to learn a lot about electrics/electronics.

[1024MAK]

I know linear PSUs…

Got I hate that term when used to describe power supply units/systems. The type of power supply that gets called a ‘linear’ type, is highly non-linear in operation.

If you want to know more, I happy to discuss it. But it would be best to start a new topic rather than cluttering up this topic further.

Mark

[sP1d3r]

The type of power supply that gets called a ‘linear’ type, is highly non-linear in operation.

From what I understand Mark, 'linear' refers to the way the transistors are controlled rather than the supply of power, which would vary dependent upon the application.

[1024MAK]

The type of power supply that gets called a ‘linear’ type, is highly non-linear in operation.

From what I understand Mark, 'linear' refers to the way the transistors are controlled rather than the supply of power, which would vary dependent upon the application.

There are no transistors in any of the Sinclair 9V PSUs as used with the ZX80, ZX81, ZX Spectrum 16K/48K/+, 128K or the +2 (grey). All these computers use a 7805 (or higher current version) series pass voltage regulator (which is also often described as “linear”).

They are described as “linear” to differentiate from switching type power supplies. In a so called “linear” regulator, be it transistor based or IC based, yes, the series pass element is used in its linear part of its gain range. But that is about the only time where you find a straight line / linear characteristic.

Analogue would have been a better word in my humble opinion.

But I will refrain from going continuing into rant mode.

Mark