In my device I'm using a "capacitance multiplier" to filter DC-DC output voltage. That's my schematic:

enter image description here

In Multisim simulation I've achieved necessary output parameters, but when I soldered my PCB and measured the output voltage I've got huge mismatch.

According to simulation, when the output load is 10MOhm (approx. multimeter resistance) voltage comes about 4.4 volts. When I measure open output I got 3.7 volts. To estimate loading caracteristics I connected 10 Ohm resistor and got 2.6 volts instead of 3.8 in model. What reasons could cause that mismatch?

  • \$\begingroup\$ We're missing your input voltage. Note that the circuit is a filter, not a regulator. \$\endgroup\$ – Transistor Mar 24 at 12:16
  • \$\begingroup\$ Neither is it an effective capacitance multiplier. \$\endgroup\$ – Andy aka Mar 24 at 12:36
  • \$\begingroup\$ @Transistor, 5 volts input \$\endgroup\$ – Ivan Mar 24 at 12:56
  • \$\begingroup\$ @Andy aka, i'm more RF-engineer than circuit designer, so i dont claim that my solution is absolutely right :) \$\endgroup\$ – Ivan Mar 24 at 13:01
  • \$\begingroup\$ @Transistor, of course i understand that it's a filter. In my schematic i use it to minimize noise from DC-DC before LDO to improve noise supresssion, because that voltage goes to RF board. \$\endgroup\$ – Ivan Mar 24 at 13:11

Zero load current is a problem for many sim programs. If you calculate the voltage across C30, and through the two base-emitter junctions, you will see that the output never should be above 4 V.

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  • \$\begingroup\$ i think it's most belivable version. I've made this scheme at breadboard and got similiar results. Fortunately, i could rise DC-DC output to compensate "additional' drop, if it does not vaying so much with different load consumption. \$\endgroup\$ – Ivan Mar 24 at 13:54

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