The high voltage LM317HV series of ICs will allow to go beyond the traditional voltage limits of an LM317 IC and enable controlling supplies that may be as high as 60V.
0-60V Regulation with a Single IC LM317
Therefore now you can build a universal 0-60V regulated power supply circuit loaded with all the essential features of a work bench test power supply circuit.
Normally a standard LM317 IC power supply is designed to work with inputs not exceeding over 40V, which implies that you cannot enjoy the features of this wonderful linear device for inputs that may be higher than this limit.
Probably the developers noticed this drawback of the device and decided to upgrade the same with its improved version LM317 HV which is specifically designed to handle voltages upto 60V, meaning now you can exploit all the special features of an LM317 IC even with inputs higher than its earlier specifications.
This makes the IC extremely versatile, flexible and a true friend of all electronic hobbyists who are always looking for an easy to build yet rugged and powerful workbench power supply circuit.
Let's learn how this high voltage LM317 HV design is created for the proposed 0-60V variable power supply circuit operations.
Pinout Configuration of LM317HV
The following diagram shows the pinout diagram of the device LM317HV
Image Courtesy: http://www.ti.com/lit/ds/symlink/lm117hv.pdf
LM317HV 0-60V Regulated Adjustable Variable Power Supply The Design
The next diagram shows the standard LM317HV 0-60V variable regulated power supply circuit, in fact this configuration may be universally applicable to all LM317/LM117, LM338, and LM396 IC family.
Referring to the design taken from its datasheet we can see that the variable resistor or the potentiometer is specified as a 5K pot, but actually this should be much higher than this value, may be around 22K for achieving a complete 0 to max adjustable output.
The input shows a 48V but we can go a bit higher than this and use upto 56V DC as the input, but please do not stretch it to full 60V as that would mean operating the device at the verge of its breakdown limit and this could make the IC vulnerable to damage.
In case you operate it with a 60V input or slightly above this, then short circuiting the output terminals accidentally could cause an instant damage to the IC, that's why it is not recommended to force the IC to work at its full throttle. Below this limit, the internal short circuit protection feature could be expected to work normally and safeguard the IC from any possible short circuiting at the output.
C1 may be included only if the shown circuit stage is over 6 inches away from the bridge rectifier and the associated filter capacitor network
C2 is optional and may be included only to improve performance which would help eliminating all possible spikes or transients in the DC line.
For achieving a fixed regulated voltage, R2 could be replaced with a fixed resistor with respect to R1, this may be calculated using the following formula:
Vout = 1.25(1 + R2/R1),
where 1.25 is the fixed reference voltage value generated by the ICs internal circuitry.
You can also use the following software for calculating the same:
Adding Protection Diodes and Bypass Capacitor
The next diagram shows how a couple of diodes may be added to the basic voltage regulator design for reinforcing the circuit with extra protection, although this may not be too crucial.
Here D1 protects the IC from the discharge of C1 due to an accidental short circuit of Vin with the ground line, while D2 does the same against C2 discharge.
The role of C1 is already explained in the previous paragraph, C2 is used as a bypass capacitor. C2 may be included to further improve the output DC regulation as it would help to eliminate all sorts of ripple voltages that might appear across the output.
Adding a Simple Current Limiter Stage
Although the LM317HV is internally restricted to produce not more than 1.5 amps at the output, in case the output current is required to be strictly below this limit or any other desired limit below 1.5 amp, then this feature could be achieved by adding a straightforward BC547 stage as shown below:
The diagram also shows the complete LM317HV high voltage 0-60V variable regulated power supply circuit in a pictorial format.
Here R1 refers to 240 ohm, R2 could be a 22k pot, and Rc may be calculated using the following formula for achieving the required current control feature:
Rc = 0.6/Max current limit value.
For example if the maximum value is selected to be 1 amp, then the above formula could be calculated as:
Rc = 0.6/1 = 0.6 ohms
the wattage of the resistor could be calculated as given under:
0.6 x 1= 0.6 watts
The diode in the bridge rectifier should be preferably 1N5408 diodes for ensuring a smooth rectification with no heating issues.
C1 may be anything above 2200uF/100V, although lower values will also do for lower current loads and for non critical loads which do not mind slight ripple factor in the line.
The transformer could be a 0 - 42V/220V/2amp.
The 0 - 42V is recommended because after rectification and smoothing this final DC could exceed a little over 55V.
The next article we might possibly discuss regarding the various application circuits using the LM317HV high voltage regulator IC.
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