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High Voltage DC-DC Converter Single Transistor Oscillator Circuit

OddMix.com - Technology Note - TN1206 - Karl Nagy

Warning! - Higher voltages are dangerous! - Never use both hands at the same time while working on high voltage circuits! - Disconnect power from a circuit when work on it! Think carefully when around high voltages!

Figure 1. High Voltage DC to DC Converter Oscillator Schematic [4 KB]
Figure 1. High Voltage DC to DC Converter Oscillator Schematic

Occasionally high voltage is necessary for experimenting with traditional vacuum tubes, cold cathode displays or other circuits that require high voltage (B+) power supplies.There is a way to avoid high voltage for tube circuits by using space charge tubes but those tubes are difficult to find.

Oscillator circuits can be used to provide high voltage with modest power as a simple DC to DC converter. This HV [High Voltage] oscillator circuit uses a single round ferrite piece for a transformer core. The diameter of this ferrite core is 8 [MM], and it is 19 [MM] long, but these dimensions are NOT critical. Almost any ferrite piece will do nicely.

Standard transformer laminations are not very useable for this project because of their heavy iron magnetizing losses due to the high oscillator frequency. If a long ferrite antenna rod is available - from an old radio - a small piece can be broken off to serve the purpose. Even an old threaded ferrite tuning screw from an RF coil will be fine, or a small size toroid coil - if it is ferrite and not powdered iron - will be even better.

Picture 1. HV DC to DC Converter Circuit Two 1 M Resistors on right is the load [21 KB]
Picture 1. HV DC to DC Converter Circuit Two 1 M Resistors on right is the load

It is onto this ferrite core the L3 coil is wound first. L3 is 400 turns using 0.1-0.2 [MM] enameled, solid copper wire. Almost any size wire is useable but it has to fit onto the core. Nothing fancy required with this winding, it is just done by free hand.

Once this high voltage coil is made the rest of the HV transformer is easy. Using heavier gage enameled wire, or even regular general purpose hook-up wire, whatever is available, L1 - 15 Turns and L2 - 5 Turns coils are made.

The wire gage and the number of turns can be varied around bit. With more turns the secondary voltage available will decrease - along with the frequency - in accordance with the turn ratio. Winding less turns is not advised as the present frequency of the oscillation is already in the Megahertz range and this high frequency results in more magnetizing losses.

The dimension of the Vector board is 70 x 50 [MM] or 7 x 5 [cm] - about 3 x 5 [inches], also not critical. Any size vector board can be used. The oscillator design uses many common, readily available parts and it is easy to build or change as required. The output of this converter is in the 400 - 600 volt range - see Table 1 - depending on the type of the output transformer and the load. Loaded with a NE1 Neon Bulb, it is a stabilized at 165 VDC.

                      Table 1. Input Output Voltage for HV Oscillator:
                      ---------------------------------------
                      Input      Input      Output     Output
                      Voltage    Current    Voltage    Load		 
                      Voltage    Current    No Load    NE1		 
                      ---------------------------------------
                      6 V         80 mA      400 V     165 V
                      9 V        120 mA      600 V     165 V
                      ---------------------------------------

Because the NPN transistor Q1 operates in a saturated mode as a switch that operates safe and cool even while switches significant power. D1 diode is important to protect the transistor form the high voltage inductive kicks. The output power can be more with a larger ferrite core - especially with a toroid - and a slower operating frequency. The C2 filter capacitor removes most of the ripple. A voltage regulator can also be added if needed. It can be as simple as a neon bulb with a serious pass transistor.

                      Parts list for High Voltage DC to DC Converter:
                      B1 - Battery, 5 - 9 Volt 
                      C1 - Capacitor 180 pF - 0.01 uF, 200 VDC, Mica or Disc
                      C2 - Capacitor, 0.1 uF, 200 VDC, Disc or Film
                      D1, D2 - Diode 1N914
                      NE1 - Neon Bulb , 165 VDC
                      Q1 - Transistor, 2N2102, NPN, HS Switch
                      R1 - Resistor 2 K, 5%, 1/4W, CC
                      TR1 - Transformer L1=15T - L2=5T - L3=400 Turns on Ferrite 

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