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PS3 Voltage Regulator
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Our new PS-3 regulator board is versatile in that it can be used for both vacuum tube power amps and preamplifiers. The PS-3
regulator board is a low cost solid state voltage regulator circuit that provides very good load and line regulation resulting in a ripple output that
is extremely low. In fact, it converts 2 volts of ripple voltage on a stock Dynaco amplifier into less than 0.2 volts of ripple!! The PS-3 regulator is
constructed on a very small 2.8" x 3.75 board. The height of the board, mounted, is approximately 1.5 inches and can therefore fit in many existing
chassis.
As with all regulators, it is limited by the power dissipation in the series pass transistor. However, this circuit is very versatile
and can be used within a range of 40 volts to 480 volts as long as the input-to-output voltage is carefully balanced with the current requirements (see
equation below for calculating the mosfet power dissipation).
The PS-3 is offered as a kit or assembled. If you purchase the complete kit, please specify your input and output voltage
requirements and we will calculate and select the appropriate resistor and zener diode values.
Please be sure to specify your input voltage supplied to the regulator
and your desired regulated output voltage |
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Below is your basic circuit that is commonly referred to as a Pass Regulator. Actually, it is and it isn't a regulator. Most voltage
regulators we are familiar with these days incorporate the use of feedback which monitors the current demand and then feeds this information back to the
regulator that in turn increases or decreases the current.
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The desired output voltage of the regulator is achieved by properly selecting the total voltage
of the zener diode stack Z1, Z2, Z3 & Z4. The pass transistor, Q1 can be thought of as a simple source-follower dc amplifier. It increases the load
resistance seen by the zener diodes by a factor of beta. In this circuit arrangement the diode stack is required to supply only the gate current for Q1.
The net result is that the load regulation and ripple characteristics, of the zener diodes, are improved by a factor of beta. In the case of the PS-3,
the beta is very high due to the use of the mosfet. Additionally, C2 reduces the ripple even more and also provides a slow start capability for the
PS-3.
You can find more elaborate voltage regulator schemes however we feel they are overkill for use with vacuum tube equipment.
Vacuum tubes do not draw high currents and therefore a power supply that is quiet (low ripple) and stiff enough for a few hundred milliamperes of
current will provide reduced distortion and a strong bass response. The PS3 accomplishes this in spades.
Design Notes
Several calculations are required for the design of the PS-3 circuit.
These are the resistance and power dissipation of R1, and the power dissipation of Q1. Additionally, the voltage values of the zener diodes must be
selected and summed to obtain the approximate regulated output voltage. R1 is designed to supply the zener current to the zener diode string. The
resistance value is calculated as follows:
ResistanceR1 = (VB+(min) - VZ)/1.1 IZ
IZ is the approximate current required for the zener diodes to regulate. This value is approximately 8 to 12 mA for the 5 watt zener
diodes in the 50 to 150 volt range. The power dissipation in the resistor can be calculated as follows:
PR1 = [VB+(max) - VZ] x 2 / Resistance R1
The power dissipated in the pass transistor can be calculated with the following equation:
PQ1 = IL(max) x VDS ,where VDS is the input-to-output voltage differential
The power dissipation in the mosfet should be kept to approximately 10 watts or less for reliable operation. If
more heat must be dissipated, Q1 can be located off the circuit board and mounted on a larger heatsink. The regulated output voltage is obtained by
selecting four zener diodes with voltage ratings that sum to the desired output voltage. The final voltage will be the sum of the zener diode string.
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Obviously this circuit has a lot of potential (no pun intended). How else can you squeeze 10,000uf worth of capacitance into a 3" x 4" footprint?
You can add this regulator to any power supply that has 20-30 volts to spare. It
works well with both tube and solid state rectified power supplies. If using with a tube rectifier, the value of C1 should be reduced to 40uf or
less or a pi-filter can be added as shown below.. Below are a few examples.
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| PRICING AND OPTIONS |
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PS3 |
Kit includes all Parts |
$60.00 |
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Please note: When you checkout, be sure to specify the input voltage you'll be supplying to the regulator and your desired regulated output
voltage. We will calculate the necessary values. You can provide this information in the comments box on our checkout page.
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