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Copyright © 1994-2007
Reproduction of this document in whole or in part is permitted if both of the
following conditions are satisfied:
1.This notice is included in its entirety at the beginning.
These designs are similar to circuits found in: "Build your own working
Fiberoptic, Infrared, and Laser Space-Age Projects", Robert E. Iannini,
TAB books, 1987, ISBN 0-8306-2724-3 and many other places.
For larger (e.g., color TV or monitor) flybacks, or use with more than 12 VDC
in, transistors with higher power ratings may be needed for sustained operation
in addition to a good heat sink. An alternative is to parallel more than
one power transistor along with small (e.g., .05 ohm, 2 W) current balancing
resistors in series with their emitters.
I built one from a dead Mac-Plus flyback from which I removed the (dead)
primary windings.
HOWEVER, if you add a high voltage capacitor to store the charge,
don't even think about going near the HV!
Some experimenting with different value resistors and even the number of turns
on each winding may improve performance for your particular flyback.
Most modern flybacks include built-in HV rectifier diode(s) and/or
voltage multiplier (tripler) so output without additional components
will be high voltage positive or somewhat smoothed HV DC.
Note: this kind of flyback transformer drives the CRT directly and
uses its glass envelope as the main high voltage filter capacitor.
(A foot square piece of 1/8 inch Plexiglas with Aluminum foil plates
makes an filter capacitor.)
(From: Robert (rrtcj@hotmail.com).)
Measurements: With an input voltage of 16 VDC, the output voltage is
about 12 kV. Without the filter choke, the input current with no load is
5 A; with the filter choke it is only 3.2 A. With the output shorted
(arcing), the current is about 9 A in both cases.
In fact I don't need big heatsinks. With the 2N3773, I can drive this circuit
continuously with one medium-size heatsink and the transistors get only
warm!!!
During initial testing at least, a Variac on the input (or variable voltage
power supply) is highly desirable to avoid blowing anything should your wiring
or parts not be quite right and to gain a feel for the capabilities of your
circuit before it is too late! In neither of these is available, use a 10 ohm
25 W power resistor or 100 W light bulb in series with the load (inverter) to
limit current to a safe value - one that won't fry too many things too quickly.
A typical circuit is shown below:
All of these parts should be readily available:
The high voltage section on the right may actually be constructed as a
voltage multiplier rather than a single winding with multiple HV diodes.
The rectifiers or multiplier, and/or focus/screen divider may be external
to the flyback transformer in some models.
Flyback transformers used in black-and-white TVs and monochrome computer
monitors do not have a focus and screen divider network.
The ferrite core of a flyback transformer is constructed with a precision
gap usually formed by some plastic spacers or pieces of tape. Don't lose
them if you need to disassemble the core. The ferrite core is also
relatively fragile, so take care.
The focus and screen divider network uses potentiometers and resistors
(not shown) with values in the 10s to 100s of M ohms so they may not
register at all on your multimeter. The high voltage rectifiers (CR1
to CR3 on this diagram) are composed of many silicon diodes in series
and will read open on a typical VOM or DMM.
Note that there is no standardization to the color code. However, the fat
wire to the CRT is most often red but could also be black. Of course, you
cannot miss it with the suction cup-like insulator at the CRT anode end.
-- end V1.25a --
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DISCLAIMER
We will not be responsible for damage to equipment, your ego, blown parts,
county wide power outages, spontaneously generated mini (or larger) black
holes, planetary disruptions, or personal injury that may result from the use
of this material.
Introduction
Simple High Voltage Generator
The basic circuit described in this document is capable of generating up to
30 kilovolts or more from a low voltage DC source using the flyback (LOPT)
transformer salvaged from a B/W or color TV or computer monitor. Typical
output with a 12 VDC 2 A power supply or battery will be 12,000 V. Maximum
output current at full voltage is typically around 1 to 2 mA. Higher currents
are available but the output voltage will drop. At 2 kV, more than 10 mA may
be possible depending on your particular flyback transformer input voltage
and current.
Safety Considerations
Before thinking about experimenting with anything using or producing high
voltages, see the document: Safety Guidelines for High
Voltage and/or Line Powered Equipment. While the circuit described below
isn't likely to be lethal using the suggested input voltage and components,
who knows how you might 'enhance' it! :-)
High Voltage Inverter
HV Inverter Circuit Diagram
As you can see from the schematic below, it doesn't get much simpler than this!
+Vcc Q1 +----------------+
o | )::
| B |/ C )::
| +------| 2N3055 )::
| | |\ E 5 T ):: +------|>|----------o +HV
| | | )::( HV Diode, usually
| | -_- )::( built in.
| | )::(
+--|-------------------------+ ::(
| | Q2 _-_ )::(
| | | )::( Secondary (HV) winding,
| | B |/ E 5 T )::( intact.
| | ----| 2N3055 )::(
| | | |\ C )::(
| | | | )::(
| | | +----------------+ ::(
| | | ::(
| | -----------------------+ :: +------------------o -HV
| | 2 T )::
| | +---------+ ::
| | | 2 T ):: T1 - Flyback transformer from B/W or
| +-------------------------+ color TV or computer monitor.
| |
| R1 | R2
+----------/\/\/\--+--/\/\/\--+
110 27 _|_
5 W 5 W -
Pinout for TO3 metal can transistor:
_
/ O \ View from bottom (pin side).
/ o o \
( B E ) B = Base, E = Emitter, C = Collector.
\ /
\ O / C The metal case is the Collector.
Pinout for the TO220 or TOP3 plastic case transistor:
TO3Pn
TO220 _____
_____ / \
| o | | O | View from front (label side).
|-----| |-------|
|Label| | | B = Base, E = Emitter, C = Collector.
|_____| | Label |
| | | |_______| If there is an exposed metal tab, that is
| | | | | | the Collector as well.
B C E | | |
B C E
A slightly modified version of this basic circuit which I use as an RF source
to excite a glow discharge in helium-neon laser and other gas discharge tubes
is shown in: Flyback Based RF Source. This one uses
a flyback transformer without a high voltage rectifier (or with the rectifier
removed). The inductor, L1, is an addition that should reduce the stress on
the transistors and power supply by limiting current at the time each of the
transistors go into saturation just before the base drive switches to the
opposite side. I have not specifically tested this circuit with the inductor
but have used it with similar inverters.
HV Inverter Assembly
Read the following in its entirety! This assumes the basic circuit using
a small flyback and input voltage of 12 VDC or less. Some modifications
may be needed when using larger flybacks and higher input voltages.
HV Inverter Parts List
None of the component values are critical. It is quite likely that everything
needed is already patiently waiting in your junkbox. If not, except for the
flyback, most if not all of the parts should be available from Radio Shack.
See the section: "Low voltage power supply" for a simple design to use with
this inverter.
Suggested Enhancements
Here are some minor changes that should improve the efficiency of this circuit.
Low Voltage Power Supply
LV Power Supply Description
The power supply (12 to 24 V) doesn't need to be anything fancy. Regulation
is not needed so a simple power transformer-bridge rectifier-filter capacitor
design will be fine. The circuit described below will provide about 15 VDC at
up to 3 A. Unless you are going for maximum output, this should be adequate.
_ T1
H o-----o/ o---- _------+ 5 A diodes
S1 Power F1 Fuse )|| or bridge
1 A )|| +---------+----|>|-------+-------+-----o +Vcc
)||( ~| D1 |+ |
)||( +----|<|----+ | +_|_ C1
115 VAC )||( 12 VAC D2 | | ___ 20,000 uF
)||( +----|>|----|--+ - | 25 V
)||( | D3 | |
)|| +---------+----|<|----+----------+--+--o Gnd
)|| ~ D4 - _|_
N o---------------------+ -
LV Power Supply Parts List
Typical Flyback Schematic
This diagram shows a typical flyback that might be found in a direct
view color television or computer monitor. Resistances are included for
illustrative purposes only and may be quite different on your flyback!
+--|>|-----------o HV to CRT
_ 1 ::( CR1 (25 to 30 kV,
| B+ o-------------+ ::( suction cup on
Drive | )::( fat red wire)
winding < ):: +-------+
| 1.32 ):: |
| 2 ):: +--|>|--+
|_ HOT o-------------+ ::( CR2
_ 3 ::(
| 50 o-------------+ ::(
| ):: +-------+
| .11 4 ):: |
| 35 o-------------+ :: +--|>|--+
Various | )::( CR3 |
auxiliary < .28 )::( /
windings | 5 )::( \<-------o Focus
| 16 o-------------+ ::( / (3 to 10 kV,
| )::( \ orange wire)
| .12 6 )::( |
|_ 0 o----------+--+ ::( 9 |
_ | 7 :: +--+ /
| H1 o----------)--+ :: | \<-------o Screen
CRT Heater < .08 | 8 ):: | / (200 to 800 V,
|_ H2 o----------+--+ | \ brown wire)
| | |
| +----|--------o To CRT DAG
| | ground
+---------------+
