In article <> (Justino M. R. Lourenco) writes:

>   Hello !

>	   I would like to know if i can connect directly the primary of a TV  
>   Flyback Transformer to 110 V a.c. to get H.V.

>	   The primary of the TV flyback has several primary Windings , how  
>   to deal with that when connecting to 110 V A.C.

No.  It requires a high frequency waveform to provide any substantial
output.  Furthermore, it WILL melt down if you try 110 VAC 60 Hz without
current limiting.  None of the windings are suitable.

If you want to play around with a flyback to generate high voltage, try
the following or email me for a dual 555 based HV generator.  Both use
low voltage DC for the primary drive power.  This is safer for you
and will be less costly in the long run as you blow up fewer expensive
parts trying to get it to work!

--- sam

Simple High Voltage Generator - 12 V in, 12,000 V out inverter.

   *VCC     Q1   +-----------------C ||
     o           |                 C ||
     |       B |/ C                C ||
     |  +------|    2N3055         C ||
     |  |      |\ E            5T  C || C-------|>|----------o  +HV
     |  |        |                 C || C     HV Diode, usually
     |  |       -_-                C || C        built in
     |  |                          C || C
     +--|--------------------------C || C
     |  |   Q2  _-_                C || C
     |  |        |                 C || C Secondary (HV) winding,
     |  |    B |/ E            5T  C || C intact.
     |  |  ----|    2N3055         C || C
     |  |  |   |\ C                C || C
     |  |  |     |                 C || C
     |  |  |     +-----------------C || C
     |  |  |                         || C
     |  |  ------------------------C || C-------------------o  -HV
     |  |                      2T  C ||
     |  |               +----------C ||
     |  |               |      2T  C || T1 - Flyback transformer from BW
     |  +--------------------------C ||      or color TV or computer monitor.
     |                  |
     |            R1    |    R2
                  110        27    _|_
                  2W         5W     -

Read in Entirety!

1. Obtain flyback transformer with known good HV secondary winding. primary
   may be left intact if it is known to be in good condition - non shorted.
   A flyback removed due to failure may be used if it was the primary that
   failed and the primary turns can be removed without damaging the HV
   secondary or losing the secondary return connection!  Flybacks fail
   in both ways (primary and secondary).

2. Wind 10 turn center tapped drive winding and 4 turn centertapped feedback
   winding using  #16-20 guage insulated wire.  Make sure both halves of
   each coil are wound in same direction.

3. VCC should typically be in the range 12-24 volts at a couple of amps.
   Circuit should start oscillating at around 5 volts VCC or so.  If you do not
   get any HV out, interchange the connections to the transistor bases.  Heat
   sinks are advised for the transistors.  Be aware of the capability of
   your flyback (BW monitors up to 15KV, color up to 30 KV).  You risk
   destroying the secondary windings and/or HV rectifier if you get carried
   away.  Running this on 24 volts will probably cause an internal arc-over
   in a small flyback, at which point you start over with more caution
   and a new flyback.

4. Actual output will depend on turns ratio of the flyback you have.
   For typical monochrome computer monitors or video display terminals,
   you should be able to get around 12,000 volts with 12 volts input.
   I made one from a dead MacPlus flyback from which I removed the (dead)
   primary windings.

5. Frequency of operation will be in the KHz to 10s of KHz range depending
   on VCC, load, and specific flyback characteristics.

6. You can experiment with # turns, resistor values, etc. to optimize
   operation and power output for you needs.

7. CAUTION: contact with output will be painful, though probably not
   particularly dangerous due to low (a few mA) current availability.
   HOWEVER, if you add a high voltage capacitor to store the charge,
   don't even think about going near the HV!

Parts list:

Q1, Q2 - 2N3055 or similar NPN power transistors (reverse polarity of
         VCC if using PNP transistors.)  Maximum stress on transistors
         are about 2-3 times VCC.  Heat sinks will be needed for continuous

R1     - 110 ohms, 2W resistor.   This provides base current to get circuit

R2     - 27 ohms, 5W resistor.  This provides return path for base feedback
         during operation.

T1     - Flyback transformer from/for BW TV, color TV, or computer monitor
         modified according to text above.  Most modern flybacks include
         built-in HV rectifier diode(s) so output without additional components
         will be high voltage positive pulses.  Note: this kind of flyback
         transformer drives the CRT directly and uses its glass envelope
         as the high voltage filter capacitor.  (A foot square piece of
         1/8" Plexiglas with Aluminum foil plates makes an adequate
         filter capacitor.)

Wire   - a couple of feet of #16-#20 hookup wire, magnet wire, or any other
         insulated wire for home made primaries.  Use electrical tape to
         fix windings to core.  Wind feedback winding on top of drive winding.

Date: Tue, 9 Jan 1996 16:43:29 GMT

Original Subject: Re: TV Flyback QUESTION

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