0
\$\begingroup\$

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?

\$\endgroup\$
  • \$\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
0
\$\begingroup\$

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.

| improve this answer | |
\$\endgroup\$
  • \$\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

Your Answer

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

Not the answer you're looking for? Browse other questions tagged or ask your own question.