I have been working on a Schroff/Cherokee Europe PE1947/23B SMPS (circa 2004?) and have had trouble identifying a component within the circuit.

This SMPS features the following outputs:

  • +12v DC @ 8A
  • -12v DC @ 4A
  • +5v DC @ 36A

All of the outputs appear to be generated from a central transformer with a winding for each output. From the way it is structured, it appears that each output is electrically isolated from all other outputs.

Across the output windings of the transformer are a small brown component, shown below, that I cannot identify. The component has six leads (three per side) and a metal cover along the top of the component, under which appears to be ferrite material. Top view Side view 1 Side view 2

In the circuit, the two larger leads (which pass through to the top of the device) are connected across the transformer winding for the applicable rail to a rather esoteric control circuit. Note that these winding voltages are much higher the final output voltage (around 55v and 120v AC for the 5 and 12v rails, respectively). These then look like they are fed through a rectifier and then a buck circuit.

Within the circuit, the smaller leads are bridged to the adjacent lead (as shown in the image below), and each of these feeds to a rather esoteric control circuit the output transformer secondary winding for the associated output.connections

I have removed one of these components from the circuit, and found that the two smaller leads on one side are not connected to each other, but they are connected to the corresponding lead on the opposite side of the device. Resistance between the two larger leads is approximately one ohm, and looks like it feeds a coil inside the device.

The resistance seems too low to be a relay. I note that the +12v and -12v rails have this (component), but the +5v rail does not (possibly due to its higher current rating).

This leaves me with the following questions:

  • Where can I find a datasheet for this device?
  • What is the likely purpose of this device in the circuit (I'm thinking some kind of current sensing)?

Update 1 (clarification):

In the image below, the black circles are the terminals of the device. The yellow text shows the resistances between various terminals (measured at DC with a digital multimeter). The green areas show how the terminals are connected on the PCB.


Update 2 (more clarification):

Below is the control daughterboard mentioned in the comments. This appears to be shared between a few different Cherokee Europe power supplies. These supplies were also made by or for Phillips, and appear in various telecommunications oriented power supplies, as well as the Phillips Allura nuclear gamma camera. control pcb daughter

This is the control PCB in circuit. The ribbon cable at the bottom of the image is connected to each of the three output rails. Under the heatsink near the top left corner is an LM340T15, which is fed from a 20v transformer tap via a half-wave rectifier. The two power transistors near the centre right of the image are both BD132 PNP transistors. control pcb in circuit

  • \$\begingroup\$ May be a noise filter. Could be coupled L's or L's and C's. \$\endgroup\$ – Russell McMahon Oct 11 at 5:34
  • 1
    \$\begingroup\$ @BruceAbbott I have updated my original post with an extra diagram that should hopefully clarify this. \$\endgroup\$ – toxicantidote Oct 11 at 13:48
  • 1
    \$\begingroup\$ From the appearance alone it looks like it might be a current transformer or some other sort of current transducer, but if that's the case the the way it's being used in the circuit makes no sense whatsoever, so I have to conclude that it isn't being used for that. Bruce's idea that it might be to power the control circuit seems reasonable, or it could be a transformer plus signal conditioning to provide an input signal to the control board as part of the feedback. \$\endgroup\$ – Hearth Oct 14 at 21:45
  • 1
    \$\begingroup\$ When the PSU is powered on, what sort of signal do you get across the smaller leads? If it's a transformer I would assume some kind of sinusoid at a low (relative to the big leads) voltage. Knowing exactly what that voltage is would help to determine if it's being used to measure something or to power something. \$\endgroup\$ – Hearth Oct 14 at 21:49
  • 1
    \$\begingroup\$ @toxicantidote A current transformer would typically have the lower-resistance winding carry the sensed current, with the higher-resistance (i.e. more turns) winding being the output. They don't coil around each other; a current transformer is just an ordinary transformer, really, with an extremely high turns ratio. \$\endgroup\$ – Hearth Oct 16 at 2:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.