How to Add IC Voltage Regulator to Wall Adapter/Battery

Often what you required to run an equipment or device is a well-regulated source of DC power.  To do this, you need to add ic voltage regulator Regulated power supplies gives out stable desired voltage output. You will even need one for your projects. In its simplest form they call it a battery eliminator. For some application the simple battery eliminator is less desirable. Therefore, you need a well-regulated for equipment from batteries and from a wall adapter that outputs a DC voltage

You can construct a well-regulated power supply. To do this, you add a voltage regulator IC to ordinary DC output from wall adapter or a battery. The voltage regulator is either a fixed type positive (+ve) or negative (-ve). Available also are adjustable voltage regulator. The regulated power supply unit finds application where you require stable power output. They are to power device such as indirect ophthalmoscope, portable light source and host of others. It also functions as a small power supply unit for electronics experiments.

Example for add IC Voltage Regulator:

• 78xx typical example: 7812 is a positive 12v fixed voltage regulator IC. For example 7805 voltage regulator IC
• 79xx typical example: 7912 is a negative 12v fixed voltage regulator IC
• LM317 Adjustable positive
• LM337 Adjustable negative

The ic voltage regulator for example LM317 looks like power transistor but is a complete regulator on a chip.

Here is a typical circuit:    It is important to identify the pinouts to add IC voltage regulator and to use it appropriately. Here are pinouts for the most common types:

Note: Various manufacturers may label the pins differently than shown. Best approach is to check the datasheet if you are in doubt.

Design Information to add Variable IC Voltage Regulator

For the LM317 circuit above,

1. R2 = (192 x Vout) – 240, where R2 in ohms, Vout is in volts and from design it’s between 1.2 V and 35 V.
2. Vin is at least 2.5 V greater than Vout. Select a wall adapter with a voltage at least 2.5 V greater than your regulated output at full load. However, note that a typical adapter voltage may vary quite a bit depending on manufacturer and load. You will have to select one that isn’t too much greater than what you really want since this will add unnecessary wasted power in the device and additional heat dissipation. For example: if expected maximum Vout is 15v. Then R2 = (192 x 17) – 240 = 2,784Ω or 2K8. Vin, then is at least Vout + 2.5v = 17 + 2.5 = 19.5v
3. As indicated in its data sheet, maximum output current for LM317 is 1 A. Your adapter or battery must be capable of supplying the maximum current safely and without its voltage drop below Vin + 2.5v minimum as declared in 2 above.

Choice of Capacitor

1. You may add extra filter capacitance (across C1) on the adapter’s output to reduce its ripple and thus the swing of its input. This may allow you to use an adapter with a lower output voltage. This also reduce the power dissipation in the regulator as well. Using 10,000 uF per “amp” of output current will result in less than 1 V p-p ripple on the input to the regulator. As long as the input is always greater than your desired output voltage plus 2.5 V, the regulator will totally remove this ripple resulting in a constant DC output independent of line voltage and load current fluctuations.
2. Select a capacitor with a voltage rating at least 25% greater than the adapter’s “unloaded” peak output voltage and observe the polarity! For example, if the “unloaded” peak output voltage is 19.5v as calculated for the Vin in 2 above, then voltage of the filter capacitor would be 19.5v + 25% which is approximately 45v.

Note:

1. Wall adapters as battery eliminator may not have any filter capacitors so we will need IC regulator with this type. Quick check: If the voltage on the adapter’s output drops to zero as soon as it is pulled from the wall – even with no load – it does not have a filter capacitor.
2. The tab of the LM317 ic voltage regulator is connected to the center pin – keep this in mind because the chip will have to be on a heat sink if it will be dissipating more than a watt or so. P = (Vout – Vin) * Iout.
3. There are other considerations – check the datasheet for the LM317 particularly if you are running near the limits of 35 V and/or 1 A.
4. For a negative output power supply, use the corresponding negative voltage regulator and note that their pin-out is NOT the same as for the positive variety. See above!

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Reference:

Various Schematics and Diagrams

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: This notice is included in its entirety at the beginning. There is no charge except to cover the costs of copying. Introduction High Voltage Power Supplies – Home-built and commercial units.