0 - 300V Adjustable Power Supply

0 - 300V Adjustable Power Supply

Introduction

To prevent my high voltage experiments to go up in smoke completely, I designed
a simple circuit which can provide an adjustable voltage source of 0 to 330 Volt..
The supply is short-ciruit proof: the current is limited to about 100mA.

Circuit description

TR1 is a 1:1 mains transformer; it is included for safety.

The mains voltage from TR1 is rectified with bridge D1 (1Amp / 500V) and large elcap C1.

T1 is switched as a source follower: the source of T1 will follow the voltage of the
wiper of R3. D2 is included to protect the gate of T1; although in theory not necessary
I strongly recommend to include it!

T2 and shunt resistor R2 build the current limiter. When the output current becomes too high, T2 will discharge
the gate of T1. This will prevent the current to become too high.
The value of R3 has been determined experimentally; it depends also on the Hfe of T2 so you may need to tune the value of R2.

Note that T1 needs a large heatsink: in worst case T1 will dissipate 330V x 100mA = 33Watt!
Instead of a BUZ 326 (400V/10.5Amp) you can also use an IRF740 (400V/10Amp).
The output impedance of the power supply is determined by the beta of T1, so the larger the MOSFET
the lower the output impedance!

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Simple Negative Adjustable Power supply with 7905

Often we have to adjust the tension of a negative supply and do not have the ideal component hand, this schema in addition to solving this problem, serves up a Power Adjustable Negative. He use the regulator 9v negative, 7905, the envés to use with fixed voltage, we can use it as a variable regulator. The 7905 in this configuration can adjust the output from -5 to-30V with an input of up to-35V. See table below.

Example: Vin = -20 V

Radj	Vout
33	-5,74
100	-6,99
330	-11,03
680	-18,20

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Adjustable Switching Regulator Circuit with LM2576

The Adjustable Switching Regulator Circuit with LM2576 are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving 3A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5V, 12V, 15V, and an adjustable output version.

LM2576 IC Package

Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation and a fixed-frequency oscillator. The Adjustable Switching Regulator Circuit with LM2576 offers a high-efficiency replacement for popular three-terminal linear regulators. It substantially reduces the size of the heat sink, and in some cases no heat sink is required.

IC Switching Regulator Circuit with LM2576

A standard Adjustable Switching Regulator Circuit with LM2576 of inductors optimized for use with the LM2576 are available from several different manufacturers. This feature greatly simplifies the design of switch-mode power supplies.

Other features include a guaranteed ±4% tolerance on output voltage within specified input voltages and output load conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring 50 μA (typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as thermal shutdown for full protection under fault conditions.

Features Adjustable Switching Regulator Circuit with LM2576 :
- 3.3V, 5V, 12V, 15V, and adjustable output versions
- Adjustable version output voltage range,1.23V to 37V
- Guaranteed 3A output current
- Wide input voltage range, 40V up to 60V for HV version
- Requires only 4 external components
- 52 kHz fixed frequency internal oscillator
- TTL shutdown capability, low power standby mode
- High efficiency
- Uses readily available standard inductors
- Thermal shutdown and current limit protection
- P+ Product Enhancement tested

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