SG3525 DC Converter 12V to +35V,-35V

The selected switching topology is called a "push-pull" converter, because the transformer has a double primary (or a "centre-tapped" one, if your prefer). The centre tap is permanently connected to the car battery (via an LC filter to avoid creating peaks in the battery lines, which could affect other electronic equipment in the car). The two ends of the primary are connected to a pair of paralleled MOSFETs each that tie them to ground in each conduction cycle (Vgs of the corresponding MOSFET high).

These MOSFETs should be fast, able to withstand high currents (in excess of 30A each if possible) and have the lowest possible Rds(on). The proposed On-Semiconductor�s MTP75N06 can withstand 75Amp and has a Rds(on) below 10 milliohm. This is important, because the lower this resistance is, the less power they are going to dissipate when switching with a square waveform. Another alternatives are MTP60N06, or the more popular BUZ11 and IRF540.

Although the schematics show a previous bipolar push-pull stage, you can also connect the gate resistor directly to the output of the controlling IC, leaving out the transistors, as the SG3525 is capable to drive up to 500 mA (theoretically), more than enough to switch the MOSFETs fast.

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12V to 16V DC/DC Converter with LM2577

The circuit is a boost step-up regulator based around an LM2577-ADJ voltage regulator chip and a few other discrete components. Resistors R1 and R2 set the regulated output voltage.

A switch inside the voltage regulator closes between pins 4 and 3, causing current to flow through the inductor to ground. When the switch is released a few microseconds later, a back-EMF 'kick' is produced by the inductor, resulting in a positive pulse with respect to the input voltage. This pulse charges the output capacitor via the schottky diode, which tends towards an equilibrium voltage.

The switch continues to oscillate, the diode preventing the switch from shorting the output capacitor during the 'on' phase. The output voltage is monitored via the voltage divider R1/R2, causing the duty cycle of the switch oscillator to be continuously regulated in order to maintain a constant output voltage under varying loads.

12V to +/- 30V DC to DC Converter

This is a DC to DC converter for car power amplifier. 12V input generates +30V and -30V output for preamp or power amplifiers. Circuit uses SG3525 IC, Mosfets and switching power supply.

DC13.8V to DC250V easy circuit

I have done a lot of work with valves in recent years. For me valves have many advantages, least of all the price; since they are now "obsolete" it is quite easy to get hold of them for next to nothing at rally's and junk sales. I recently purchased a couple of hundred battery valves for less than SEK1 (US$ 0.15) each.

The biggest problem with valves is the PSU needed to provide +250 vDC and 6.3 vAC for the fillaments. The transformers are no-longer available at a reasonable price, but a pair of 12v-6v-0v-6v-12v mains transformers will do the job just as well. For portable use only one transformer is required together with a pair of power transistors such as 2N3055 etc.

Above is the circuit of a converter that will generate the required volrages from a 12 volt source.

Above is the circuit of a converter that will generate the required volrages from 220 volt mains.

Just one word of warning: Dont forget to put a "bleeder" 100K - 270K ohm resistor accross the 250vDC output if your equipment doesn't already have one built in. Failure to do this can be fatal because the PSU smoothing capacitors can store a lethal charge for days.

Finally if you think that there is no place for valves in QRP or portable work then think again. An "EL84" will deliver 10 watts on the lower HF bands. It draws 300mA @ 6.3v (2.1 watts) for the heater as well as + 53mA at 250vDC (about 15 watts) for the anode and screen. The DC-PSU.GIF will provide this and draw less than 2 amperes from a car battery. A 48A/H car battery will therefore last over 24 hours NONSTOP TRANSMIT !!! If you also think that valves are difficult to build with then try one. You will be surprised.

6V to 12V Converter

This inverter circuit can provide up to 800mA of 12V power from a 6V supply. For example, you could run 12V car accessories in a 6V (British?) car. The circuit is simple, about 75% efficient and quite useful. By changing just a few components, you can also modify it for different voltages.

Schematic
Parts
R1, R4 ----- 2.2K 1/4W Resistor
R2, R3 ----- 4.7K 1/4W Resistor
R5 ----- 1K 1/4W Resistor
R6 ----- 1.5K 1/4W Resistor
R7 ----- 33K 1/4W Resistor
R8 ----- 10K 1/4W Resistor

C1,C2 ------ 0.1uF Ceramic Disc Capacitor
C3 ----- 470uF 25V Electrolytic Capcitor

D1 ----- 1N914 Diode
D2 ----- 1N4004 Diode
D3 ----- 12V 400mW Zener Diode
Q1, Q2, Q4 BC547 NPN Transistor
Q3 ----- BD679 NPN Transistor

L1 ----- See Notes
MISC ----- Heatsink For Q3, Binding Posts (For Input/Output), Wire, Board

Notes

1. L1 is a custom inductor wound with about 80 turns of 0.5mm magnet wire around a toroidal core with a 40mm outside diameter.

2. Different values of D3 can be used to get different output voltages from about 0.6V to around 30V. Note that at higher voltages the circuit might not perform as well and may not produce as much current. You may also need to use a larger C3 for higher voltages and/or higher currents.

3. You can use a larger value for C3 to provide better filtering.

4. The circuit will require about 2A from the 6V supply to provide the full 800mA at 12V.

33 Volt DC to DC Converter

33 Volt DC To DC Converter

Description: 33 Volt DC To DC Converter

This is the right solution for your MOSFET based low power linear amplifier if you have no AC source in your house and have to rely on battery. Generally IRF MOSFET transistors require DC supply at least 24 to 36 volts for efficient operation and their output power drops drastically when the supply voltage is only about 12 volts. The dc to dc converter described here is very simple and enables you to apply 33 volts to IFR transistors from your 12 volt rechargeable battery. Another advantage is that you can reduce the size of your power transformer if you are working on mains. It will also come handy for field days when you have to depend on battery for operating your rig without mains supply. A pair of 2N3055 , work as an oscillator at high frequency and the higher voltage appearing across the secondary of the oscillator coil rectified and filtered to get 33 volts dc. The oscillator coil is wound on 30 mm diameter toroid, which is available easily anywhere .Two of them are used after fixing them together with quickfix. The primary containing 9+9 turns is wound with 20 awg enameled copper wire and the feedback winding 4+4 turns is wound over it. The secondary is wound using 22 awg wire, about 36 turns. This power supply should be switched off, when receiving as otherwise , it may produce noise in receiver. Four numbers of high speed switching diodes BA 157 and 1000 mF/ 50 volts filter capacitor produces 33 volt DC. The usual rectifiers diodes are not suitable here because, the voltage is at high frequency. The two transistors [T1 and T2 ] are mounted on a heat sink it is found that the transistors get only slight warm during transmission.