From time to time I want to integrate a 12V Eurorack module in my 15V banana setup. So I needed a 15V to 12V adaptor. Nothing spectacular. Just from the datasheet.
The documentation and the Gerber files for download can be found in my website.
Just the standard configuration from the datasheets.
For a standalone project with a small case I was in need of an small dual voltage PSU. I can’t find a dual voltage wall wart, but I had an external AC Power Adapter from Yamaha the PA-30. The PA-30 has a 2x18V AC output with a three pole connector. So I decided to build a small PSU with the LM317L and LM337L. The design is straight forward. It is easy to expand for more current and other voltages if you need to. If you don’t want to use a external AC Power Adapter you can use a center tapped transformer.
The documentation and the Gerber files for download can be found in my website.
Nothing special here. Just refer to the data sheet of the LM317L/LM337L. Calculate R1/R2 and R3/R4 to your needs. The given values here are for +/-15V. Input is from a center tapped transformer or external AC Power Adapter like the Yamaha PA-30. For more current replace the LM317L/LM337L Version with the TO220 version. You’ll need to redesign the PCB then
Basic PSU with 78xx voltage regulator
In many cases it is useful to have a easy to build fixed voltage PSU at hand. For this case I have made a PCB which works with the 78xx series voltage regulators in TO220 housing. The implementation follows closely a straight forward design as in the data sheet. I have tested this design with a current load of 1A for some hours. No problems whatsoever.
Specs and features
• Input: Select transformer according to your needs
• Output: Voltage depends on the regulator used / 1A DC
The documentation for download can be found in my website.
Basic PSU with 78xx voltage regulator schematic
Nothing special here. Just refer to the data sheet of the 78xx. Calculate R1 to keep the current through the LED within the specs.
Basic PSU with 78xx voltage regulator
For my Next Generation Formant project i needed a replacement for the obsolete uA726, because i wanted to stay as close as possible to the original Elektor Formant VCO with my NGF VCO Core 2. This means a heated exponential matched transistor pair. There are a variety of possibilities to achieve this goal. Most of those solutions uses now obsolete parts or are hard to build. But there is still on well known solution with with the 3046 transistor array. And best, it is still available. At least the SMD Version is still in production. The DIL version can be found as well, but is no longer in production.
The circuitry I found on the net did only use one transistor for the heating. This leaves one transistor unused. My thought is using two transistors makes for a faster heating up and more stability against environmental change. To my surprise I can not find a solution which uses two transistors instead of one. Here is my take on the circuitry.
3046 heater schematic
This circuitry is part of my NGF VCO Core 2. It make use of two transistors to heat the 3046. It works with the SMD and DIL Version as well. The given resistor values keep the current values and the power dissipation below the maximum ratings. T3 is used to measure the actual temperature. The voltage drop over T3 is direct proportional to the chip temperature. It is compared to the voltage at pin 2 of the 3046 which is derived from TR6. The temperature is easily adjusted with TR6. Between heating off and maximum temperature. The testing bridge is driven with a stabilized 10V voltage source. T4 and T5 are used as heaters. R41 and R43 limit the maximum current. The different values are selected with purpose to keep pin 13 of the 3046 (the substrate) the lowest negative point at the chip.
The below picture shows the graph temperature in deg. Celsius vs. Voltage in mV at pin2. It is quite linear. You can easily derive the needed voltage for your preferred temperature from the graph. The data were taken from a LM3046 SMD mounted on a PCB. The figures for the DIL Version are slightly different. They will show up on my website as well as some more details ASAP. Temperature was measured with Fluke 63 IR thermometer.
3046 heater: temperature vs. voltage plot
Basic PSU with LM350
In most cases it is not necessary to use an ultra low ripple PSU for driving a synthesizer. A normal basic PSU with low ripple is sufficient in most cases. Those basic PSU has the advantage off better thermal and power efficiency. My implementation here is the same as my ultra low ripple PSU without the input low pass filter. Leaving this filter out lowers the power consumption at about 50%. And avoids the additional internal heating of the housing. It is possible to use a lower rated transformer with 15V/50VA (75VA for two PSU). The output current is increased. Those changes lowers the overall parts count and cuts the cost down as well. The PSU is build around the well known LM350 and follows mostly a straight forward design as in the data sheet. I have tested this design with a current load of 2.5A for some hours. No problems whatsoever. For a +/- 15V PSU you need two of those. You have to daisy chain them and use the connection as ground
Basic PSU with LM350 – schematic
This design is straight forward like in the data sheet of the LM350. After the rectifier diodes C6 and C7 are the reservoir capacitors. LED1 indicates the presence of the unregulated voltage before the LM350. R1 limits the current for the LED. The LED is a low current 2mA type D5 serves as protection diode against reverse biasing the voltage regulator. R6, R7 and TR1 serves as voltage divider to adjust the output voltage to 15V. The 1.2V reference voltage between ADJ and out is amplified about 12-times to make a 15V output. So is the noise and ripple. C11 between ADJ pin and GND reduces noise and ripple considerably. Protective diode D6 is needed to safely discharge C11 if the output is short-circuited. D8 protects against short-circuited when you daisy chain two PSU for a +/- PSU if the other output is short circuited. With the above measures the ripple is quite low. With a 15V/75VA transformer (for two PSU) this PSU is good for output current of about 2.5A (both). Above this value the voltage drop over the regulator drops under the necessary 3V. To stay on the save side the recommended fuse is rated for 2.5A/slow-blow.
Basic PSU with LM350 – front left view
Basic PSU with LM350 – front view
Basic PSU with LM350 – left view
Basic PSU with LM350 – right view
Basic PSU with LM317
In most cases it is not necessary to use an ultra low ripple PSU for driving a synthesizer. A normal basic PSU with low ripple is sufficient in most cases. Those basic PSU has the advantage off better thermal and power efficiency. My implementation here is the same as my ultra low ripple PSU without the input low pass filter. Leaving this filter out lowers the power consumption at about 50%. And avoids the additional internal heating of the housing. It is possible to use a lower rated transformer with 15V/50VA. The output current is increased. One more benefit is more room on the PCB which is used to integrate a fuse on the PCB. Those changes lowers the overall parts count and cuts the cost down as well.
The PSU is build around the well known LM317 and follows mostly a straight forward design as in the data sheet. I have tested this design with a current load of 1.25A for some hours. No problems whatsoever. For a +/- 15V PSU you need two of those. You have to daisy chain them and use the connection as ground
Basic PSU with LM317 schematic
This design is straight forward like in the data sheet of the LM317. After the rectifier diodes C5 and C6 are the reservoir capacitors. LED1 indicates the presence of the unregulated voltage before the LM317. R1 limits the current for the LED. The LED is a low current 2mA type D1 serves as protection diode against reverse biasing the voltage regulator. R3, R4, TR2 serves as voltage divider to adjust the output voltage to15V. The 1.2V reference voltage between ADJ and out is amplified about 12-times to make a 15V output. So is the noise and ripple. C7 between ADJ pin and GND reduces noise and ripple considerably. Protective diode D5 is needed to safely discharge C7 if the output is short-circuited. D3 protects against short-circuited when you daisy chain two PSU for a +/- PSU if the other output is short circuited. With the above measures the ripple is quite low. With a 15V/50VA transformer (for two PSU) this PSU is good for output current of about 1.3A (both). Above this value the voltage drop over the regulator drops under the necessary 3V. To stay on the save side the recommended fuse is rated for 1.25A/slow-blow.
Basic PSU LM317 top left view
Basic PSU LM317 left view
Basic PSU with LM317 front view
Ultra low ripple PSU with LM350 stuffed PCB
Sometimes you need a PSU with very low ripple. With a common voltage regulator this can be achieved by some additional filtering. Here I use a LM350 with an additional RC filter before the smoothing capacitors and a capacitor in the regulation path of the LM350. After the rectifier diodes C6 and C7 are the reservoir capacitors followed by the RC filter build of R2; R3, R4, R8 and C8, C9. D5 serves as protection diode for reverse biasing the voltage regulator. R6, R7, TR1 serves as voltage divider to adjust the output voltage to15V. The 1.2V reference voltage between ADJ and out is amplified about 12times to make a 15V output. So is the noise and ripple. C11 between ADJ pin and GND reduces noise and ripple considerably. Protective diode D6 is needed to safely discharge C11 if the output is short-circuited. D7 protects against short-circuited when you daisy chain two PSU for a +/- PSU if one of the outputs is short circuited. With the above measures the ripple is down in the noise floor. The drawback of this schematic is increased power consumption. The resistors in the RC input filter get rather hot under heavy load Use 2W (minimum) or higher rated resistors and mount them with some distance to the PCB. You should keep the load under 2A. You can drive heavier loads, but watch for the temperature of the resistors. You can find more details in “Small signal audio design” second edition from Douglas Self in chapter 25 p713ff.
Ultra low ripple PSU with LM350 schematic
Ultra low ripple PSU with LM350 front view
Small PSU with LM317 / LM337
Lately I used my small variable PSU with LM317 / LM337 as fixed PSU build in a Module. In an earlier post I wrote: “Because it is small the heatsinks are not that big and close together. Don’t drive it to hard”. This only applies when you want the output to be variable. If used for fixed voltages you can drive it harder when you choose an appropriate AC input voltage. The AC input voltage should match the DC output voltage in this case. This lowers the voltage drop at the voltage regulators LM317 / LM337. It is about 4V then. With 1A load the power dissipation is down to 4W. I have tested the small PSU for several hours loaded with 1A at 15V without any problem getting to hot. The test was done on the bench in free air. If you use an enclosure check for the air flow.
Small PSU with LM317 / LM337 as module
Low ripple PSU with LM317
This PSU is build around the well known LM317 and follows mostly a straight forward design as in the data sheet. To mention is an additional filter before the LM317 to lower the ripple. With this filter the ripple is down in the noise floor. I have tested this design with a current load of 1.2A for some hours. No problems whatsoever. Because the heat sink is not that big I recommend keeping the load below 1A. It is getting quite hot though. For a +/- PSU you need two of those. You can daisy chain them and use the connection as ground.
Low ripple PSU with LM317 schematic
The design is straight forward like in the data sheet of the LM317. The led indicates the presence of the unregulated voltage before the LM317. R2, R5 and C5 builds a RC input filter between the reservoir capacitor and the regulator. The resistors should kept low and the capacitance high. The filter sinks the ripple below the noise level of the regulator. You have some loss of efficiency due to the voltage drop across the series resistor. All protection features of the LM317 regulator are preserved.
Low ripple PSU with LM317
Low ripple PSU with LM317
Small variable PSU with LM317 / LM337
It comes in handy to have a small PSU with variable output voltages around to test modules with different voltages or drive small projects. The emphasis is on driving small projects. Tests are better done with a lab PSU. I just made a small PCB for a +/- 12..17V with LM317 and LM337. There is nothing special about it. Straight forward design. Because it is small the heatsinks are not that big and close together. Don’t drive it to hard.
Small variable PSU with LM317 / LM337 schematic
Small variable PSU with LM317 / LM337
Small variable PSU with LM317 / LM337