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CACD Group
updated 2000.03.30
Author Janez Puhan

Transformerless DC Voltage Converter

The circuit

Generation of high DC voltages leads to corona and isolation effects in wire windings when transformers are used. A transformerless voltage multiplier can be more suitable for conversion of low DC voltages to higher ones. It can be accomplished with a network of diodes and capacitors which rectifies a chopped DC input voltage and additively charges capacitors to the desired high voltage level.

In the following example, the input voltages, v1 and v2, are chopped by an astable multivibrator composed mainly of an operational amplifier, e1, and two MOSFETs, m1 and m2. The multiplier capacitors are charged up to the peak to peak amplitude of the square wave voltage at node (1). The resulting DC output voltage, therefore, depends on the number of cascaded capacitors.



The input file

transformerless dc voltage converter

.control
  tran 0.25ms 100ms
  plot v(1) v(2) v(13) v(14) xlabel t[s] ylabel 'v(1) v(2) output [V]'
    + title 'TRAN analysis'
.endc

v1 5 0 dc 0 pwl 0 0 1ms 15V
v3 6 0 dc 0 pwl 0 0 1ms -15V

r1 2 1 10k
r2 3 1 10k
r3 0 3 1k

c1 2 0 1uF
c2 3 0 0.1uF
c3 7 1 1uF
c4 1 8 1uF
c5 5 9 1uF
c6 6 10 1uF
c7 7 11 1uF
c8 8 12 1uF
c9 9 13 1uF
c10 10 14 1uF

d1 5 7 dio
d2 8 6 dio
d4 7 9 dio
d5 10 8 dio
d6 9 11 dio
d7 12 10 dio
d8 11 13 dio
d9 14 12 dio

m2 1 4 6 6 noname2 w=1.2mm l=6um
m9 1 4 5 5 noname1 w=1.2mm l=6um

x1 2 3 4 5 6 ua741

.model dio d cjo=3pF
.model noname1 pmos rd=1 cbd=1uF
.model noname2 nmos rd=1 cbd=1uF

.subckt ua741 11 7 5 23 2
  r1  13 2  1k
  r2  12 2  50k
  r3  14 2  1k
  r4  15 2  5k
  r5  21 2  50k
  r6  22 2  100
  r7  17 16 39k
  r8  18 19 4.5k
  r9  19 20 7.5k
  r10 24 5  50
  r11 5  8  25

  c1 18 10 30pF

  q1  26 11 25 qnl
  q2  26 7  1  qnl
  q3  9  6  25 qpl
  q4  10 6  1  qpl
  q5  9  12 13 qnl
  q6  10 12 14 qnl
  q7  23 9  12 qnl
  q8  26 26 23 qpl
  q9  6  26 23 qpl
  q10 6  16 15 qnl
  q11 16 16 2  qnl
  q12 17 17 23 qpl
  q13 18 17 23 qpl
  q14 18 19 20 qnl
  q15 20 10 21 qnl
  q16 20 21 22 qnl
  q17 10 4  2  qnl
  q18 18 24 5  qnl
  q19 4  8  5  qpl
  q20 4  4  2  qnl
  q21 23 18 24 qnl
  q22 2  20 18 qpl

  .model qnl npn bf=150 rb=100 va=200 ccs=2pF cje=3pF cjc=2pF tf=0.3ns tr=6ns
  .model qpl pnp bf=80  rb=20  va=200         cje=6pF cjc=4pF tf=1ns   tr=20ns
.ends

.end

The results

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