0
\$\begingroup\$

I found some articles talking about transformerless power supplies, and I have uploaded the schematic of such a circuit. Does anybody have an idea about the pros and cons of such a power supply? Also how to calculate the value of this capacitor "C1" ?

enter image description here

\$\endgroup\$
3
  • 1
    \$\begingroup\$ This is a non-isolated supply, not hobbiest friendly imho... \$\endgroup\$
    – sstobbe
    Jun 21, 2017 at 2:56
  • \$\begingroup\$ Typical design equations for transformerless supplies can be found in this app note: ww1.microchip.com/downloads/en/AppNotes/00954A.pdf \$\endgroup\$
    – user133493
    Jun 21, 2017 at 3:08
  • \$\begingroup\$ @sstobbe Great thing to consider \$\endgroup\$
    – ahm_zahran
    Jun 21, 2017 at 3:41

2 Answers 2

0
\$\begingroup\$

I've seen these done thusly

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
3
  • 3
    \$\begingroup\$ C1 should be an X1. We've talked about this before. \$\endgroup\$ Jun 21, 2017 at 4:26
  • \$\begingroup\$ Was this answer wrong? @RobertEndl \$\endgroup\$
    – ahm_zahran
    Jun 21, 2017 at 4:49
  • \$\begingroup\$ Sorry, X2. X1 probably overkill. I didn't see the X1 in the schematic cuz I'm getting old and careless. \$\endgroup\$ Jun 22, 2017 at 6:00
-4
\$\begingroup\$

Polypropylene power supplies are a type of capacitive power supplies that supplies a limted current output. The value of the polypropylene capacitor determines the amount of current according to this equation:

X = 1 / (2 π f C)

I = V / X

where

X : capacitor reactance

π : Constant (pi) = 3.14

f : frequency of the main supply (50-60)

C : Capacitance value

I : output current (A)

V : main voltage (110 or 220)

Pros:

  • constant current power supply is better in some applications like LED Lighting
  • wide output voltage range (typically any rated voltage device is able to connect -unless it stands the applied current- )
  • More efficient series connections are possible in some applications like LED lighting

Cons

  • Non-isolated power supply which means rush current can easily destroy your load
  • low output current values (Max ~ 350 mA) due to low available capacitance values. or huge number of parallel connected capacitors (10) to output a current of about 1 Amp.
\$\endgroup\$
14
  • 2
    \$\begingroup\$ Why was this answer accepted within a minute of being posted? This discourages competing answers, which improve the quality of the site. \$\endgroup\$
    – user133493
    Jun 21, 2017 at 3:48
  • 3
    \$\begingroup\$ -1. Please explain why you think the circuit is a constant current supply. The circuit limits current by the reactance of C1 but it is not a constant current supply. Instead, it is a loosely voltage-regulated supply. \$\endgroup\$
    – user133493
    Jun 21, 2017 at 3:54
  • 2
    \$\begingroup\$ The terminology is wrong. A constant current supply responds to varying load impedance by varying its output voltage. This supply does nothing of the sort, it loosely maintans a constant output voltage across C2 and will respond to varying load impedances by sourcing varying currents. \$\endgroup\$
    – user133493
    Jun 21, 2017 at 4:04
  • 1
    \$\begingroup\$ been seeing a lot of these capacitor-based CC drivers recently being incorporated smack dab onto the COB's PCBs, thanks for the rundown on this interesting tech. \$\endgroup\$
    – dandavis
    Jun 21, 2017 at 4:16
  • 2
    \$\begingroup\$ -1 It isn't a constant current supply. It is a power supply with a limited current output. Look closely at the given diagram. It includes a zener diode to regulate the voltage. \$\endgroup\$
    – JRE
    Jun 21, 2017 at 5:34

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